40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  Cryo Lab eLog, Page 56 of 58  Not logged in ELOG logo
ID Date Author Type Category Subject
  119   Wed Mar 30 02:02:34 2011 DmassNotesCavityQ vs thickness of substrates

It seems we may want to say something quantitative about how cavity mirror thickness effects the bottom line performance of the reference cavity before we get mirrors for said cavity.

So far, we have used the equations from Kenji Numata's 2004 PRL paper on thermal noise in cavities to understand how thermal noise of the various cavity components couples in to cavity length noise.

equation (3) gives a single sided PSD (in m^2/Hz) of cavity length noise from mirror substrate thermal noise (under certain assumptions*):

G(f) = 4 k T (1-sigma^2) / (omega sqrt(pi) E w0) Phi_substrate

where sigma is Poisson's ratio, omega is the (optical) angular frequency, E is the Young's modulus, w0 is the spot size on the mirror, Phi_substrate is the loss of the mirror substrate.

 

The dependence on mirror substrate thickness is contained in Phi_substrate. I talked to Alastair, since he seems to know some things about loss. For fused silica, it seems that the accepted way of thinking about how the bulk loss and surface loss contribute to the total loss is:

Phi_total = Phi_bulk x E_bulk / E_total + Phi_surf x E_surf / E_total

Where the bulk and surface losses are weighted by the fraction of total energy in each respective "zone". I don't see any reason why this equation should hold for an amorphous material but not a crystalline one.

In a paper about Silicon cantilever Q-measurements there is some relevant info.

Figure 11 shows various results silicon oscillator Q vs thickness at 4K. Figure 10 shows the temperature dependence of one of the oscillators (7 um thick cantilever). Applying envelope physics to this, it seems we can guess the following about silicon Q's for a mirror (making some assumptions about thickness >> diameter - only semi valid here):

Q(3mm,4K) ~ 10^8

Q(120K) ~ Q(4K)/5

Q(300K) ~ Q(4K)/2.5

And from looking at the graph and doing some rough interpolation, we get:

0.74 log(thickness in um) + 5 = log(Q-factor), or

10^5 x (thickness [um])^0.74 = Q-factor

for curiosity of scaling: dQ/dthickness(3mm,4K) ~ 10^5 x 0.74 x (thickness [um])^-0.26

so we have:

Q(3mm,120K) ~ 10^8/5

 

Q(6mm,120) ~ 10^8/5 x 2^0.74

I plugged these numbers into the formulas given for both spacer thermal noise, and substrate thermal noise for 3mm and 6mm substrates. I used a biggish spot (250 um), and a loss of 3e4 for the coating.

In reality the question of thermal noise is more complicated than just using these equations blindly...

As a first pass, my inclination is to say that if we can't get 6mm mirrors without a big PITA, 3mm would be *fine* for cavity version 1, and following some more detailed understanding of the thermal noise couplings, cavity version 2 could be made with bigger mirrors.

 

TL;DR Bigger mirror substrates are better up to a point, but in a simple analysis of noise couplings, choosing 3mm mirrors doesn't totally screw us.

 

Attachment 1: SubstrateNoise.pdf
SubstrateNoise.pdf
  118   Tue Mar 29 21:48:35 2011 FrankNotesNoise Budgetsome more resources for thermal noise calculation

collection of data and references for noise calculations for ET, including Silicon data from large mirror substrates down to thin cantilever blades.
Two pictures as an overview:

1.jpg

2.jpg

entire document see link here: Mirror thermal noise calculation for ET

  117   Mon Mar 28 15:53:22 2011 FrankCryostatSensorsTemperature sensors and temp controllers to start with

again i've compared the performance of various temp sensors and temp controllers to see which one would be good to start with.
I've assumed that we might wanna start with a commercial solution as we have tons of other problems to solve in the beginning and don't wanna care about designing and building a super low-noise temp sensor readout and control unit. So i've checked what's available and basically found two multi-channel cryo temp controllers which are sold under different names from different companies:

  1. Lakeshore 336   ~$3,610    datasheet         manual
  2. SRS CTC100c    ~$2,600    datasheet

both are 4-sensor input, analog output units with 2 integrated variable DC current sources (up to 100W).
Interfaces to the outside world are analog, USB, Ethernet, serial etc.

I've used the comparison for the control stability from Lakeshore which can be found on page 5 in the manual of the 4-channel cryo temp controller.
The accuracy and noise for both controllers is almost identical. The SRS is slightly better in some things, the Lakeshore in others, so it's good enough for a start.

Here the table with highlighted values for the ELECTRONICS ONLY.

sensor-comparison.jpg

From that we see that using a commercial unit gives us something about +/-1.6mK to +/-4.8mK for super long-term stability (not noise at higher frequencies!).
This is good enough for what i've estimated here some time ago what we can get for the long-term stability.  While Germanium is good for low temperatures (e.g. 18K) , platinum RTDs, silicon diodes and Cernox are good for higher temperatures (300K-77K).

Cernox sensors require calibration. On the other hand platinum RTDs offer high uniform sensitivity with excellent reproducibility. They follow a standard curve above 70 K and are easily interchangeable and cheap. We can also get dual sensors in one unit for in- and out-of-loop measurements at the same point (if we want).

Both controllers support any kind of diode or RTD/thermistor as the sensor so we are totally flexible and can also compare different sensors e.g. mounted to a huge block in vacuum to measure the noise/stability of them and then switch to something we like more later on.

So i would go for platinum RTDs in the beginning and the SRS CTC100c which offers everything we need including data-logging (unlimited on a usb stick, until full) and a graphical display showing graphs for everything we want, so we don't need a data acquisition system at the beginning. That's all for $2600. They also have 4 sensors, so in and out-of-loop for both cavities and two independent heater units. Perfect for our system.

  116   Mon Mar 28 12:58:28 2011 FrankNotesCavityQ vs thickness of substrates

i've checked the change in Q vs thickness for the mirrors. I think we want to go for thicker ones to be on the save side.
The Q for the measured 6mm is still high enough but we don't know how it changes from 6 to 3mm and changing the diameter from 3" to 1".

Here the plot from one of Ronny's publications "High mechanical Q-factor measurements on silicon bulk samples":

Q_vs_thickness.jpg

  115   Mon Mar 28 12:38:15 2011 FrankUpdateCavityupdated refcav drawings

made some slight changes to the spacer drawing. updated files below:

cavity_spacer_2inx4in_-_Sheet1.pdf

cavity_spacer_2inx4in.SLDDRW

cavity_spacer_2inx4in.SLDPRT

  114   Sun Mar 27 12:19:55 2011 FrankThings to BuyCavityStatus update - Quotes on silicon mirrors and spacer - updated march 28

Current status of companies/quotes for silicon mirrors and spacer i've asked.

Company Mirrors Spacer
McCarter Technology Inc will quote Monday will quote Monday
Coastline Optics Inc
quote available won't do
Gooch & Housego can't do can't do
Almaz Optics, Inc. pending pending
ELECTRO OPTICAL COMPONENTS, Inc pending pending
Umicore Laser Optics USA can't do can't do
Rocky Mountain Instrument Co quote available will quote next week
Mindrum Precision, Inc will quote next week will quote next week
Perkins Precision Developments, LLC pending pending
Lightmachinery ? (didn't ask) Pending (Dmass)
     

Any other companies we should ask?

  113   Sat Mar 26 18:20:24 2011 FrankThings to BuyCavityQuotes on silicon mirrors and spacer - updated march 26

Current status of companies/quotes for silicon mirrors and spacer i've asked.

Company Mirrors Spacer
McCarter Technology Inc will quote Monday will quote Monday
Coastline Optics Inc
quote available won't do
Gooch & Housego can't do can't do
Almaz Optics, Inc. pending pending
ELECTRO OPTICAL COMPONENTS, Inc pending pending
Umicore Laser Optics USA can't do can't do
Rocky Mountain Instrument Co quote available will quote next week
Mindrum Precision, Inc will quote next week will quote next week
Perkins Precision Developments, LLC pending pending
Lightmachinery ? (didn't ask) Pending (Dmass)
     

Any other companies we should ask?


More details see below:

McCarter Technology Inc
- QUOTE REQUESTED
http://www.mccarteret.com

  • military/ NASA contractor
  • can superpolish silicon

http://optics.nasa.gov/tech_days/tech_days_2005/docs/21%20McCarter%20Single%20Crystal%20Silicon%20Mirrors.pdf

 

Coastline Optics Inc - QUOTE AVAILABLE
http://www.coastlineoptics.com/

  • can provide a 1 Å RMS microroughness finish on a 1"Ø, 1M concave ROC, silicon substrate,
    but this would be a custom build item
    .
  • Also provides coatings: The coating would be a low scatter Ion Beam Sputtered, TiO2/SiO2 multilayer dielectric, tailored to our requirements.
  • A rough order of magnitude for this work would be $6500 with a lead time of 3 to 4 months.
  • 10-20 pieces is the minimum lot size for the substrates and the cost is roughly $3,500 less the coating. 

 

Gooch & Housego - CAN'T DO IT, ONLY FLAT/FLAT
www.goochandhousego.com

  • Better than 1 Å surface roughness
  • Laser quality 1/10 wave flatness, 10/5 scratch dig

Reply from them:
"We offer 1"Ø 1M ROC Fused Silica Substrates, which are usually in stock. Or we
could manufacture 1"Ø 1M BK-7 Substrates, which would be a custom job. I understood
your e-mail to be 1"Ø 1M Silicon Substrates, which we are not able to manufacture."

 

Almaz Optics, Inc. - - QUOTE REQUESTED
www.almazoptics.com

 


ELECTRO OPTICAL COMPONENTS, Inc - QUOTE REQUESTED
www.eoc-inc.com

  • do silicon mirrors all the time for CO2 lasers, surface only >3nm rms, but could buy pre-polished substrates and let them repolish somewhere else

 

Umicore Laser Optics USA - CAN't DO GOOD SURFACE QUALITY
also known as http://www.ulooptics.com, manufacturer of CO2 laser optics and beam delivery systems

  • standard quality silicon mirrors (concave) are stock parts, e.g. 10SIS3-05
  • http://www.ulooptics.com/docs/pdf/silicon_laser_mirrors_lenses.pdf
  • http://www.ulooptics.com/docs/pdf/silicon_co2_supermax_laser_mirrors.pdf
  • Surface Accuracy only  L/40 @ 10.6µm
  • contact see here : http://www.ulooptics.com/docs/pdf/ulo_Si_supermax.pdf

 

Rocky Mountain Instrument Co.- UPDATED QUOTE RECEIVED, CAN DO SPACER TOO
http://rmico.com/specifications/mirrors

  • Silicon (monocrystaline- any crystal orientation) PO/CC mirror (uncoated)
  • Diameter= 25.4mm +0/-0.25mm
  • Edge thickness= 3mm +/-0.1mm
  • ROC= 1m
  • Surface figure= l/10 @1.5um
  • Surface quality= 20/10
  • Surface roughness < 1nm

10 pcs : $150 ea
20 pcs : $120  ea    

Expected Delivery: 4 WEEKS ARO
       

Mindrum Precision, Inc. - QUOTE REQUESTED 
www.mindrum.com

 

Perkins Precision Developments, LLC - QUOTE REQUESTED
www.perkinsprecision.com

  112   Fri Mar 25 12:59:34 2011 FrankThings to BuyGeneralSources for silicon mirrors - updated march 25

 

Updated collection of companies/quotes for silicon mirrors :


McCarter Technology Inc
- QUOTE REQUESTED
http://www.mccarteret.com

  • military/ NASA contractor
  • can superpolish silicon

http://optics.nasa.gov/tech_days/tech_days_2005/docs/21%20McCarter%20Single%20Crystal%20Silicon%20Mirrors.pdf

 

Coastline Optics Inc - QUOTE AVAILABLE
http://www.coastlineoptics.com/

  • can provide a 1 Å RMS microroughness finish on a 1"Ø, 1M concave ROC, silicon substrate,
    but this would be a custom build item
    .
  • Also provides coatings: The coating would be a low scatter Ion Beam Sputtered, TiO2/SiO2 multilayer dielectric, tailored to our requirements.
  • A rough order of magnitude for this work would be $6500 with a lead time of 3 to 4 months.
  • 10-20 pieces is the minimum lot size for the substrates and the cost is roughly $3,500 less the coating. 

 

Gooch & Housego - CAN'T DO IT, ONLY FLAT/FLAT
www.goochandhousego.com

  • Better than 1 Å surface roughness
  • Laser quality 1/10 wave flatness, 10/5 scratch dig

Reply from them:
"We offer 1"Ø 1M ROC Fused Silica Substrates, which are usually in stock. Or we
could manufacture 1"Ø 1M BK-7 Substrates, which would be a custom job. I understood
your e-mail to be 1"Ø 1M Silicon Substrates, which we are not able to manufacture."

 

Almaz Optics, Inc. - - QUOTE REQUESTED
www.almazoptics.com

 


ELECTRO OPTICAL COMPONENTS, Inc - QUOTE REQUESTED
www.eoc-inc.com

  • do silicon mirrors all the time for CO2 lasers, surface only >3nm rms, but could buy pre-polished substrates and let them repolish somewhere else

 

Umicore Laser Optics USA - CAN't DO GOOD SURFACE QUALITY
also known as http://www.ulooptics.com, manufacturer of CO2 laser optics and beam delivery systems

  • standard quality silicon mirrors (concave) are stock parts, e.g. 10SIS3-05
  • http://www.ulooptics.com/docs/pdf/silicon_laser_mirrors_lenses.pdf
  • http://www.ulooptics.com/docs/pdf/silicon_co2_supermax_laser_mirrors.pdf
  • Surface Accuracy only  L/40 @ 10.6µm
  • contact see here : http://www.ulooptics.com/docs/pdf/ulo_Si_supermax.pdf

 

Rocky Mountain Instrument Co.- UPDATED QUOTE RECEIVED, CAN DO SPACER TOO
http://rmico.com/specifications/mirrors

  • Silicon (monocrystaline- any crystal orientation) PO/CC mirror (uncoated)
  • Diameter= 25.4mm +0/-0.25mm
  • Edge thickness= 3mm +/-0.1mm
  • ROC= 1m
  • Surface figure= l/10 @1.5um
  • Surface quality= 20/10
  • Surface roughness < 1nm

10 pcs : $150 ea
20 pcs : $120  ea    

Expected Delivery: 4 WEEKS ARO
       

Mindrum Precision, Inc. - QUOTE REQUESTED 
www.mindrum.com

 

Perkins Precision Developments, LLC - QUOTE REQUESTED
www.perkinsprecision.com

 

 

 

  111   Fri Mar 25 01:23:48 2011 FrankThings to BuyCavityRefCav spacer cad drawings

Diameter still pending. Question is which tolerances for raw material are available, e.g. can we buy a 2" crystal and still get a 2" cavity out of it or do we have to buy 3" crystals which are much more expensive.
If we have to go for the larger one we then could go for larger diameter without increasing the cost. Or we go slightly under 2" for the cavity when starting with 2".

cavity_spacer_2inx4in.SLDPRT

cavity_spacer_2inx4in.SLDDRW

cavity_spacer_2inx4in_sheet1.pdf

  110   Thu Mar 24 17:50:52 2011 DmassDailyProgressCavityPMC

Quote:

I am getting a quote for metal PMCs made from:

Al

Stainless

NVar

 

More details to follow

 Before the happy metal pmc gets finalized, here is some information to stimulate some controversy, and maybe constructive Socratic dialogue...

First image:

  • Since my hand is still broken, I made a doodle of the algebra involved in the PMC.
  • I set the total length to 6.3", which seemed to give some OK HOM filtering (elog:96)

Second Image:

  • This is what I have in solidworks so far
  • We still need:
    • O-ring choice for the outside of the mirror - the recession in the clamp is a 1.05" clearance
    • Mounting bracket / contacts for the spacer (balls a la 40m PMC seem bad, use pins for precise placement?)
    • PZT - do we need to shrink the back hole to use a reasonable one?

The eventual (aka imminent) plan is to send drawings to local shops...I talked to Ken Mailand, he liked ASCO Engineering
in north hollywood. I also talked to Rich Abbott, and he liked Futrell's in West Covina.

 

Attachment 1: pmc_geometry.png
pmc_geometry.png
Attachment 2: pmc_screenshots.png
pmc_screenshots.png
  109   Thu Mar 24 00:41:42 2011 FrankHowToNoise Budgethow to determine required mirror specs

Try to summarize how to estimate the contribution from surface figure, quality (scratch dig) and roughness to the performance of the cavity including a short description of the individual parameter:
This is required to estimate the minimum requirements for the mirror surface for a high finesse silicon cavity.
The problem is that standard values we ask for FS mirrors all the time are hard, almost close to impossible to get for silicon substrates.

e.g. standard surface figure for a silicon mirror at 1um is lambda (!), a good one L/2. Even cheap Thorlabs mirrors usually have L/10 at 633nm for comparison. Same for the other two parameters.

 

1) surface roughness

surface roughness is typically given as a single rms value without any information about the boundaries for the integrated spatial frequencies.
What i got from talking to Hiro is that without having this particular information the number is kind of useless, it could mean anything without further information how they measured it (same situation as for the linewidth for lasers)

So we have two options: ask the company for the PSD vs spatial frequency or for some rms numbers measured for different lower spatial frequency, e.g. approx our beam size on the mirrors

As this might be difficult or might take too long i prefer a third option:

  • We assume that a very good polished mirror has a similar PSD shape as the ones we have for several optics from LIGO/VIRGO
  • the region of interest for small optics can be fitted by a simple linear equation (see T070052)
  • the ones which are worse have higher noise levels for high frequencies and are about the same for low frequencies (simply changing the slope of the fit)
  • we then can calculate the loss with the given formula

2) surface quality

surface quality (scratch dig) is described by two numbers, one for scratches, one for digs/bubbles. Description copied from google search:

Purpose:
This document defines surface quality on optical components per MIL-O-13830.

Definitions:

  • SCRATCH: Any marking or tearing of the part surface.
  • DIG: A small rough spot on the part surface similar to a pit in appearance. A bubble is considered a dig.
  • SLEEK SCRATCH: A hairline scratch.
  • CRUSH or RUB SCRATCH: A surface scratch or a series of small scratches.

Method:
The size of a defect is to be measured through the use of an optical comparator:
Surface quality is to be specified by a number such as 60/40. The first digits relate to the maximum width allowance of a scratch as measured in microns. The next digits indicate to maximum diameter allowance for a dig in hundredths of a millimeter. Thus, as can be seen from the table below, a surface quality callout of 60/40 would permit a scratch width of .06 mm (60 micron -or- 0.0024") and a dig diameter of .40 mm (400 micron -or- 0.0158").


Scratch or
Dig Number
Maximum
Scratch Width
Maximum Dig
or Bubble Diameter
Dig or Bubble
Separation Distance
# mm inch mm inch mm inch
120 0.12 0.0047 1.20 0.0473 20 0.787
80 0.08 0.0031 0.80 0.0315 20 0.787
60 0.06 0.0024 0.60 0.0236 20 0.787
50 0.05 0.0020 0.50 0.0196 20 0.787
40 0.04 0.0016 0.40 0.0158 20 0.787
30 0.03 0.0012 0.30 0.0118 20 0.787
20 0.02 0.0008 0.20 0.0079 20 0.787
15 0.015 0.0006 0.15 0.0059 20 0.787
10 0.010 0.0004 0.10 0.0039 1.0 0.040
5 0.005 0.0002 0.05 0.0020 1.0 0.040
3 0.003 0.00012 0.03 0.0012 1.0 0.040

The formula for calculating the loss from such surface errors is given in one of Hiros talks, e.g. G1000484. The two missing parameter needed is the depth of the defect and the length, but we could use some average/typical number for a start.

3) surface figure

will come next

  108   Tue Mar 22 17:58:23 2011 FrankMiscCavityturning mirror transmission

i've polished the back of one of our turning mirrors (Newport 10D20DM.8) which originally come with a frosted back surface.
Used one of the "bad" mirrors which has some slight scratches at the outer area. Used first contact to protect the HR coating while polishing.
Now i was able to measure the transmission of those mirrors.

laser power 44.63 mW, transmission @0 degree ~251.8uW  > ~5600ppm transmission

laser power 44.67mW, s-pol, transmission @45 degrees ~5.11uW > ~114ppm transmission

laser power 37.05mW, p-pol, transmission @45 degrees ~158uW > ~3500ppm transmission

reflectivity too high for the PMC cavity, not taking the additional problem of having a frosted back surface into account

  107   Mon Mar 21 22:26:38 2011 FrankThings to BuyGeneralSources for silicon mirrors - updated march 23

started a collection of companies/quotes for silicon mirrors :


McCarter Technology Inc
http://www.mccarteret.com

  • military/ NASA contractor
  • can superpolish silicon

http://optics.nasa.gov/tech_days/tech_days_2005/docs/21%20McCarter%20Single%20Crystal%20Silicon%20Mirrors.pdf

 

Coastline Optics Inc - QUOTE AVAILABLE
http://www.coastlineoptics.com/

  • can provide a 1 Å RMS microroughness finish on a 1"Ø, 1M concave ROC, silicon substrate,
    but this would be a custom build item
    .
  • Also provides coatings: The coating would be a low scatter Ion Beam Sputtered, TiO2/SiO2 multilayer dielectric, tailored to our requirements.
  • A rough order of magnitude for this work would be $6500 with a lead time of 3 to 4 months.
  • 10-20 pieces is the minimum lot size for the substrates and the cost is roughly $3,500 less the coating. 

 

Gooch & Housego - CAN'T DO IT
www.goochandhousego.com

  • Better than 1 Å surface roughness
  • Laser quality 1/10 wave flatness, 10/5 scratch dig

Reply from them:
"We offer 1"Ø 1M ROC Fused Silica Substrates, which are usually in stock. Or we
could manufacture 1"Ø 1M BK-7 Substrates, which would be a custom job. I understood
your e-mail to be 1"Ø 1M Silicon Substrates, which we are not able to manufacture."

 

Almaz Optics, Inc. - CAN ONLY SUPPLY BLANKS, MAYBE GOOD FOR SPACER
www.almazoptics.com

 


ELECTRO OPTICAL COMPONENTS, Inc - QUOTE REQUESTED
www.eoc-inc.com

  • do silicon mirrors all the time for CO2 lasers, surface only >3nm rms, but could buy pre-polished substrates and let them repolish somewhere else

 

Umicore Laser Optics USA
also known as http://www.ulooptics.com, manufacturer of CO2 laser optics and beam delivery systems

  • standard quality silicon mirrors (concave) are stock parts, e.g. 10SIS3-05
  • http://www.ulooptics.com/docs/pdf/silicon_laser_mirrors_lenses.pdf
  • http://www.ulooptics.com/docs/pdf/silicon_co2_supermax_laser_mirrors.pdf
  • Surface Accuracy only  L/40 @ 10.6µm
  • contact see here : http://www.ulooptics.com/docs/pdf/ulo_Si_supermax.pdf

 

Rocky Mountain Instrument Co.- QUOTE RECEIVED, CAN DO SPACER TOO
http://rmico.com/specifications/mirrors

  • Silicon (monocrystaline- any crystal orientation) PO/CC mirror (uncoated)
  • Diameter= 25.4mm +0/-0.25mm
  • Edge thickness= 3mm +/-0.1mm
  • ROC= 1m
  • Surface figure= l/20 @10.6mm
  • Surface quality= 40/20
  • Surface roughness < 1nm

10 pcs : $125 ea
15 pcs : $115 ea
20 pcs : $100  ea    

Expected Delivery: 4 WEEKS ARO

Asked again what they can do in terms of surface figure and quality  if we pay more money
       

     

  106   Mon Mar 21 21:11:32 2011 FrankCryostatCavitySilicon Type

the Q-measurements were done with doped Cz-grown silicon (see thesis) so i don't see why we should go for the super-expensive, super-pure FZ-grown stuff.

According to literature the linear thermal expansion coefficient is identical for all crystal orientations [100], [110] and [111] as the structure is cubic (e.g. see here).
So regarding the zero CTE point we can use any orientation. However, the Q is different for different orientations, but i think high enough in all cases (but should recalculate noise model for worst case values).

Quote:

I was giving the cryo poster at the LV meeting, and one of our references wandered up (Ronny Norwaldt). He asked me what type ofsilicon we were going to use, and I had no idea, so I turned to wikipedia. It seems there are potentially 3 types of Silicon (different fab processes) we might use for the cavity spacer.

Two are monocrystalline:

One is monocrstalline:

Siemens process Silicon has ~10^-9 purity. Frank says that the Q is bad for this stuff. Ronny agreed. Reference?

I asked light machinery for quotes for a 4x2 reference cavity out of the Czochralski and the Float-Zone stuff, so we'll see what they say they can do.

 

 

 

  105   Mon Mar 21 15:32:47 2011 DmassDailyProgressCavityPMC

I am getting a quote for metal PMCs made from:

Al

Stainless

NVar

 

More details to follow

  104   Mon Mar 21 15:20:08 2011 DmassLaserLaserBeat Found

Using the df/dI and dP/dI measurements (elog:47 and elog:46), these are the AM/FM ratios of the diodes:

Covega: 6x10^-11 RIN/Hz

Emcore: 3.8x10^-12 RIN/Hz

 

  103   Tue Mar 15 14:59:12 2011 DmassCryostatCavitySilicon Type

I was giving the cryo poster at the LV meeting, and one of our references wandered up (Ronny Norwaldt). He asked me what type ofsilicon we were going to use, and I had no idea, so I turned to wikipedia. It seems there are potentially 3 types of Silicon (different fab processes) we might use for the cavity spacer.

Two are monocrystalline:

One is monocrstalline:

Siemens process Silicon has ~10^-9 purity. Frank says that the Q is bad for this stuff. Ronny agreed. Reference?

I asked light machinery for quotes for a 4x2 reference cavity out of the Czochralski and the Float-Zone stuff, so we'll see what they say they can do.

 

 

  102   Tue Mar 8 11:34:51 2011 FrankCryostatCryoRadiative Pole

i think it has to be (T1 + T2 )( T12 - T22 ) and then whatever i said below is right. Not temp difference, no net heat exchange, infinity resistance

hmm, the sign seems to be right

 

Quote:

i didn't read it carefully but my guess is that you are using a formula which doesn't work in that special case.
The reason is that this formula might be derived from the simple Boltzmann equation with two surfaces for different (!!) temperatures.

If you start using the formula with the view factor to calculate the amount of heat transferred between both surfaces
q1-2=sigma(T14-T24) divided by the rest like epsilon, view factor etc, same as in your formula you see that the heat transfer is zero.
So if you do it for both directions, q1-2, q2-1 both are zero ! So where does the formula come from is the question. But no temp difference no radiative heat transfer (at least that's what i learned years ago)
I guess the only reason why you get anything is that epsilon and the surface is not identical for both sides.
I think you can't use that simplified formula as this might be based on sigma(T14-T24) in the fist place assuming both temperatures are not identical.

But that's just a guess

Quote:

I did a couple calculations today to figure out the radiative pole for the proposed cryostat design.

The first REALLY simple one was just radiative heat transfer ignoring radiosity. This was pretty clearly a poor approximation, as it yielded an answer for tau which is independent of the emissivity of the radiative shield.

Next, I tried to use the equivalent thermal resistance to find the pole. I have attached that calculation, and suspect some glaring typo I carried through, since its answer was 3 months for the time constant.

 

1$ to anyone who finds the typo(s) / bad assumption(s) which make the answer no longer wrong or comes up with evidence that this is correct.

 

 

  101   Tue Mar 8 02:34:52 2011 dmassCryostatCryoRadiative Pole

Here is the calculation which gave me a semi reasonable answer for the radiative time constant.

I left out the view factor (for now), and pretended they were radiatively coupled via two close big planar surfaces.

Surface 1 is the can, surface 2 is the cryo cavity.


I suspect less than 20% change from the view factor if we try not to make it big.

Attachment 1: IMG_0430.JPG
IMG_0430.JPG
Attachment 2: IMG_0431.JPG
IMG_0431.JPG
  100   Tue Mar 8 02:15:44 2011 FrankCryostatCryoRadiative Pole

i didn't read it carefully but my guess is that you are using a formula which doesn't work in that special case.
The reason is that this formula might be derived from the simple Boltzmann equation with two surfaces for different (!!) temperatures.

If you start using the formula with the view factor to calculate the amount of heat transferred between both surfaces
q1-2=sigma(T14-T24) divided by the rest like epsilon, view factor etc, same as in your formula you see that the heat transfer is zero.
So if you do it for both directions, q1-2, q2-1 both are zero ! So where does the formula come from is the question. But no temp difference no radiative heat transfer (at least that's what i learned years ago)
I guess the only reason why you get anything is that epsilon and the surface is not identical for both sides.
I think you can't use that simplified formula as this might be based on sigma(T14-T24) in the fist place assuming both temperatures are not identical.

But that's just a guess

Quote:

I did a couple calculations today to figure out the radiative pole for the proposed cryostat design.

The first REALLY simple one was just radiative heat transfer ignoring radiosity. This was pretty clearly a poor approximation, as it yielded an answer for tau which is independent of the emissivity of the radiative shield.

Next, I tried to use the equivalent thermal resistance to find the pole. I have attached that calculation, and suspect some glaring typo I carried through, since its answer was 3 months for the time constant.

 

1$ to anyone who finds the typo(s) / bad assumption(s) which make the answer no longer wrong or comes up with evidence that this is correct.

 

  99   Tue Mar 8 01:24:12 2011 dmassCryostatCryoRadiative Pole

I did a couple calculations today to figure out the radiative pole for the proposed cryostat design.

The first REALLY simple one was just radiative heat transfer ignoring radiosity. This was pretty clearly a poor approximation, as it yielded an answer for tau which is independent of the emissivity of the radiative shield.

Next, I tried to use the equivalent thermal resistance to find the pole. I have attached that calculation, and suspect some glaring typo I carried through, since its answer was 3 months for the time constant.

 Finally, I realized how easy the "real" calculation was and plugged in radiosity, coming up with a 5.5*10^5 second pole for 120 K. THIS SEEMS REASONABLE

1$ to anyone who finds the typo(s) / bad assumption(s) which make the answer no longer wrong or comes up with evidence that this is correct.

Attachment 1: HeatTransferPole.pdf
HeatTransferPole.pdf HeatTransferPole.pdf
  98   Fri Mar 4 14:46:02 2011 DmassComputingGeneralUpdated Cryowiki

I had to edit the CryoWiki  conf/mime.conf file by adding the following line

stp     !application/solidworks

so that it would not forbid solidworks uploads.

The file in question lives on nodus, under the CryoWiki directory in /users/public_html

  97   Fri Mar 4 13:59:57 2011 DmassCryostatDrawingsCryostat update

Dick Gummer sent me a solidworks model (I will put i on the wiki instead of here since I think it's their int. property).

He asked what layout we wanted for the bolt holes on the cold plate, both for the downward facing part (where we will attach the reference cavities) and the upward facing part below the access port where we will try to attach a copper braid as an alternative to filling the dewar

  • For the bottom of the cold plate I said 3/8" deep 1/4-20 tapped holes,1" spacing, with a half inch offset from dead center of the coldpate
  • For the upwards facing holes on the top of the coldplate just outside the LN2 chamber, I told him to make some 3/8-16, helicoil reinforced holes (as Warren suggested very aggressive bolts here so we can get a lot of force between the two eventual Cu contacts). These would be 1"x1.5" on center.

I also had him rotate the access port so that it was 90 degrees from the optic axis

  96   Wed Mar 2 16:03:34 2011 DmassMiscDrawingsPMC for 1550nm - HOM spacing

At Frank's request, I ran the MATLAB script for cavities (which is on the svn) to check out different length for the PMC ands HOM spacing.

Here are a few different lengths with a Finesse of 100. To get roughly the right parameters for a triangular PMC, I used a curved-flat Fabry-Perot with L=length of the PMC (not perimeter).

 

The lengths are round metric numbers. Feel free to run the code before you submit drawings.

The call is like:

%% Call  the script "cavityinfo.m" with various arguments
% arguments are R1,R2,Finesse,Length in cm
figure(1)
clf
cavityinfo(100,1e20,100,17)
%orient landscape
%print -dpdf /Users/dmass/Documents/MATLAB/Cryo/refcav/PMC170mm %Change this (obviously)

The script, cavityinfo.m, is in mDV/extra on the svn.
 

Attachment 1: PMCall.pdf
PMCall.pdf PMCall.pdf PMCall.pdf PMCall.pdf PMCall.pdf PMCall.pdf
  95   Tue Mar 1 14:38:46 2011 FrankMiscDrawingsPMC for 1550nm

i will add two drawings from two metal PMC spacers here ASAP a made some time ago. have to make graphs and convert it to Solidworks first, but don't have the files on my Laptop.

One is a single-piece spacer which we used for almost any PMC made in the past years at AEI.
The second one is a special design where the mirrors can be clamped. It was initially designed for an experiment measuring power fluctuations by placing an absorbing crystal or Kerr material in a cavity and measure the length change.

Design1: standard spacer, not converted into imperial units. Will make changes in Solidworks after we know the required length for proper HOM spacing at 1550nm. Mirrors are glued to spacer, curved mirror glues on piezo stack (1" dia, 1/4" thick, 1/2" hole) which is glued on spacer. We also built several modified versions with piezos longer than 1" to allow large range ultra-low-noise driving using single opamps (no noisy HV amplifier required, only differential LT1028 stage)

pmc-spacer.ipt

pmc-spacer.idw

pmc-spacer.pdf

Design2: spacer with clamped mirrors. Original design has curved mirror glued to PZT and glued to spacer is it (almost) never changes. The other mirrors were clamped to allow impedance matching of PMC with high intravcavity losses, e.g. due to absorptive media placed in waist. Modified version (not shown here) has a large threaded hole from the top to place medium in waist between flat mirrors. Medium was glued to treaded piece inserted. Treah was super-fine to allow good adjustment to match brewster angle for inserted crystal.

pmc_spacer_clamp.ipt

pmc_spacer_clamp.idw

pmc_spacer_clamp.pdf

PMC.jpg

  94   Tue Mar 1 14:34:52 2011 Frank the Funkasaurus RexDailyProgressCavityLocking the Diode Lasers to the Cavity

I tried locking the diode lazers to the ULE-mirror cavity but the noise was too big and I didn't get no error signulz.

  93   Mon Feb 28 14:57:24 2011 warrenCryostatDrawingscavity support version 2

Quote:

I think that gold heat shield and the radiative heater should go in-between the cavity and this holder. Otherwise, there will be a thermal short between the cold plate and the cavity.

So Rana,

Not shown in the drawing are sets of nylon screws and G-10 washers that hold the three distinct thermal masses together without touching.

The three separate masses are 1) cold plate, 2) heater plate, 3) mounting frame, rails, and cavity.

So am I right that you want the surrounding box to attach to the heater plate instead of the mounting frame?  Sounds ok to me. 

Also not shown is the weak thermal link (so set the thermal time constant between the heater plate and the cavity).  So we need to mount the cavity heater and thermometer to the frame ( assuming there is enough thermal conductivity through the knife edge).  Haven't figured out why we need a radiative heater too.     

  92   Sun Feb 27 14:45:49 2011 ranaCryostatDrawingscavity support version 2

I think that gold heat shield and the radiative heater should go in-between the cavity and this holder. Otherwise, there will be a thermal short between the cold plate and the cavity.

  91   Sat Feb 26 14:04:15 2011 FrankCryostatDrawingscavity support version 2

will make a CAD drawing over the weekend. The distance for the knife edges should be enough. Will see when i have the 3d-model.

Quote:

Here is version 2.    Complete in all mechanical parts, if you can use a little imagination and read my mind on a few of the details.  Only part left out, that I know of, is the thermometers and heaters, but they are quite easy to add, probably on outside.

As drawn, maximum distance between knife edges is 2.5".   Enough?

 

 

  90   Fri Feb 25 11:42:46 2011 WarrenCryostatDrawingscavity support version 2

Here is version 2.    Complete in all mechanical parts, if you can use a little imagination and read my mind on a few of the details.  Only part left out, that I know of, is the thermometers and heaters, but they are quite easy to add, probably on outside.

As drawn, maximum distance between knife edges is 2.5".   Enough?

 

Attachment 1: cavity_mount_v2_pg1.png
cavity_mount_v2_pg1.png
Attachment 2: cavity_mount_v2_pg2.png
cavity_mount_v2_pg2.png
  89   Wed Feb 23 03:12:34 2011 ranaCryostatDrawingscryostat support

The holder looks good to me. Like Warren says, we need to make it easy to tune the support points to minimize the seismic coupling. It would be nice to see how the radiative shields fit in around this. Can we get a drawing that has a cavity and shields too?

  88   Mon Feb 21 10:10:29 2011 WarrenCryostatDrawingscryostat support

Frank,

I like the idea of interchangable fins!  Thinking about good ways to do this.   And the CAD drawing looks great!  I am envious; maybe I need to learn how to do that.

There is at least one major mistake in the design shown: the two support frames need to be slide on the rails, and the rails need separate support brackets to attach to a rigid mounting plate above. 

 

Do Rana and David have comments?

How about we skype some further conferring today.   Let's set it up by email.

Warren

 

  87   Sat Feb 19 22:17:36 2011 FrankCryostatDrawingsCryo cavity support proposal

i made a quick CAD model to see how it looks like. Used all numbers from Warrens drawing but 2.25" height for optical axis instead.
Positions and size of threaded holes are for illustration purposes only. (Made through holes everywhere to make it vacuum compatible and easier to clean)

cavity-frame2.jpg

Quote:

i had a closer look into some details of the drawing and i realized that something is wrong with some of the numbers:

The total height of the thing is labeled as 3.875". The optical axis is 2.5" from the top, the radius of the cavity is 1.5" (3" dia).
So the cavity would stick out of the bottom of the frame
(2.5" + 1.5" = 4" > 3.875")

So i had a closer look and i think you used 0.25 per square of the paper.
So then the optical axis is 2.25" from the top according to the drawing, not 2.5". Then the cavity would fit inside, but would rest on 1/8" thick bottom only, which is very thin for a 4.5" wide structure and a almost 5lb cavity.

I have to look closer into the Cryo drawings to understand which constraints we have.

Quote:

Attached below is the version 1 of a support for the cryo cavity. 

The basic idea is to mimic the lens-mounts that slip through a set of round "rails", actually shafts.

Not shown is a 1/8" copper plate "wrapped" around three sides, and a pressed against the frames by six large screws.

The only detail to be worked out is the precise way to shape and size the two "fins" that actually touch the silicon cylinder.

Now need feedback from y'all.

 

 

  86   Sat Feb 19 21:39:01 2011 FrankCryostatDrawingsCryo cavity support proposal

i had a closer look into some details of the drawing and i realized that something is wrong with some of the numbers:

The total height of the thing is labeled as 3.875". The optical axis is 2.5" from the top, the radius of the cavity is 1.5" (3" dia).
So the cavity would stick out of the bottom of the frame
(2.5" + 1.5" = 4" > 3.875")

So i had a closer look and i think you used 0.25 per square of the paper.
So then the optical axis is 2.25" from the top according to the drawing, not 2.5". Then the cavity would fit inside, but would rest on 1/8" thick bottom only, which is very thin for a 4.5" wide structure and a almost 5lb cavity.

I have to look closer into the Cryo drawings to understand which constraints we have.

Quote:

Attached below is the version 1 of a support for the cryo cavity. 

The basic idea is to mimic the lens-mounts that slip through a set of round "rails", actually shafts.

Not shown is a 1/8" copper plate "wrapped" around three sides, and a pressed against the frames by six large screws.

The only detail to be worked out is the precise way to shape and size the two "fins" that actually touch the silicon cylinder.

Now need feedback from y'all.

 

  85   Sat Feb 19 17:23:05 2011 FrankCryostatDrawingsCryo cavity support proposal

nice idea, i really like it!

You have easy access to the entire cavity from all sides and we are flexible in choosing the point of suspension.

I don't know how much contact for the fins we need to get the heat out of the spacer in a descent amount of time.
What i really like is that we can easily make the bottom inner part (where the fins are) flat, so that we can make the "fin part" exchangeable.
This gives us the freedom to change the design or material we want to use to support the cavity and design/change the amount of direct heat flow if required.
So e.g. we could make the "fins" out of G10 to reduce the direct coupling to the outer part and use more of the radiative heat exchange. By choosing the material we can easily shift it around by a lot.
By that we can optimize the pole frequency and by that the temp noise filtering in that stage. It also gives us the flexibility to easily (and cheap) change the shape of the support structure.

Also using an additional taped whole on the top we can use a Teflon screw or so as kind of a caging mechanism (stopper) so that the cavity can only move in the horizontal direction (where we need something too)

Quote:

Attached below is the version 1 of a support for the cryo cavity. 

The basic idea is to mimic the lens-mounts that slip through a set of round "rails", actually shafts.

Not shown is a 1/8" copper plate "wrapped" around three sides, and a pressed against the frames by six large screws.

The only detail to be worked out is the precise way to shape and size the two "fins" that actually touch the silicon cylinder.

Now need feedback from y'all.

 

  84   Sat Feb 19 11:46:49 2011 WarrenCryostatDrawingsCryo cavity support proposal

Attached below is the version 1 of a support for the cryo cavity. 

The basic idea is to mimic the lens-mounts that slip through a set of round "rails", actually shafts.

Not shown is a 1/8" copper plate "wrapped" around three sides, and a pressed against the frames by six large screws.

The only detail to be worked out is the precise way to shape and size the two "fins" that actually touch the silicon cylinder.

Now need feedback from y'all.

Attachment 1: cavity_mount_v1.png
cavity_mount_v1.png
  83   Fri Feb 18 12:43:13 2011 FrankComputingGeneraljava problem fixed

installed java on the centos machine in the Cryo lab to have remote access to the scopes and download data.

It's a bit tricky as the instructions given on the java webpages are WRONG. I found my old entry about that in the ATF elog  link

  82   Fri Feb 18 12:13:20 2011 FrankThings to BuyCavityCavity Questions for the Quote
  • no hydroxy catalysis bonding of mirrors on cavities. makes everything really bad! LISA people have tried it and lost one order of magnitude in stability! (see documentation on wiki posted last year)
  • i think also no metal brazing as Rana mentioned before as we don't know how this affects the stability.
  • There is nor reason for those crazy techniques as optical contacting is very simple with standard surface figures (L/10, probably less, SD 60/40 or so) and if this doesn't work properly we can always fix them from the side with glue (NO glue between spacer and mirror)
  • mounting has to be on knife-edge (not really sharp like a wire, but like a small o-ring) type posts or so at specififc location within 1/20 inch or better if we don't want to be limited by seismic very soon.
    This is probably not required for the very first one but we should make the design so that we can have it like that  easily without redesigning everithing. Defninetely no huge clamping block like we have right now for the FS spacer cavity on the cryo table. Documentation on how to mount a cavity right is also on the wiki

current specs i'm asking for is L/10 , SD 20/10 or better for the inner 1.5 inch for the end surfaces where the mirrors will be attached, rest of the surface polished with SD 40/20 or better, outer cylinder surface ground or polished to see the difference in price (silicon is hard to polish with good surface figures, especially for non-flat surfaces)

Quote:

Some things from talking to Warren:

  • What is the surface figure on the radius of the cavity, and are we asking companies to grind this as precisely as they can reasonably do (which is what fraction of lambda)?
  • How are the various surfaces of the Si spacer polished?
  • Instead of optically contacting the mirrors to the cavity, would we consider metallizing the polished surfaces then vacuum brazing them (hopefully Warren will say more on this)
    • Maybe something like the following would be a good thing to metallize a surface with:
    • Al + 5% Mg
    • Cu + 2% Be
    • Gold-Silver Alloy
  • The above question gives us another question: does anyone do this already, maybe the x-ray telescope people know something (Caltech or MIT?)
  • Do we want to do Hydroxy Catalysis Bonding (this might be too permanent...)

Warren also had an idea about how to mount the cavity which could be high Q and adjustable, he called it a translator. He had a rough sketch on a napkin, maybe something to consider either for the first or second generation of cavity mounting schemes. We should say something quantitative about the various mounting schemes if we can.

 

  81   Thu Feb 17 23:47:06 2011 ranaThings to BuyCavityCavity Questions for the Quote

I think that we would get an optical polish for the spacer all over and a good optical polish on the surfaces on which we would optically contact (let's just assume that we contact until we have a quantitative reason to do so or not).

I don't want to do any brazing since we don't understand the thermal noise we would get from that.

  80   Thu Feb 17 22:52:42 2011 Dmass/WarrenThings to BuyCavityCavity Questions for the Quote

Some things from talking to Warren:

  • What is the surface figure on the radius of the cavity, and are we asking companies to grind this as precisely as they can reasonably do (which is what fraction of lambda)?
  • How are the various surfaces of the Si spacer polished?
  • Instead of optically contacting the mirrors to the cavity, would we consider metallizing the polished surfaces then vacuum brazing them (hopefully Warren will say more on this)
    • Maybe something like the following would be a good thing to metallize a surface with:
    • Al + 5% Mg
    • Cu + 2% Be
    • Gold-Silver Alloy
  • The above question gives us another question: does anyone do this already, maybe the x-ray telescope people know something (Caltech or MIT?)
  • Do we want to do Hydroxy Catalysis Bonding (this might be too permanent...)

Warren also had an idea about how to mount the cavity which could be high Q and adjustable, he called it a translator. He had a rough sketch on a napkin, maybe something to consider either for the first or second generation of cavity mounting schemes. We should say something quantitative about the various mounting schemes if we can.

  79   Thu Feb 17 12:35:25 2011 Dmass, FrankUpdateLasermore laser characterization work going on

PK borrowed two nice Scopes for evaluation (Agilent MSO7104B and Tek MSO4101, both 1GHz and 4 or 5MSP/s). They look more like small TV's with a lot of knobs (nice large screens).

So we have two ~$20K scopes to have a closer and probably more detailed look into what's going on when beating the laser diodes and measuring the linewidth / frequency jitter.
We started last night and got a little more familiar with the Agilent scope and how to sample the beat signal, do an FFT and some statistics. It's really nice !

We will continue today and the next days and post the results as soon as we know we think to measure

 

 

  78   Wed Feb 16 16:24:19 2011 DmassUpdateGeneralRoad Map for Cryo Lab

I want to generate a more coherent (recorded) roadmap for the cryolab so that we can better prioritize our course of action. Before I put together some visual diagram representing this information (which I think will be useful for us), I am going to write down a list of the stuff we know we want to do, as well as the more far fetched things we might one day want to do. Here is the list by category, PLEASE ADD THINGS IF YOU WANT - if you reply to this post with suggestions, I will try to incorporate them into edits of this post. In no particular order, we have:

CRYOSTAT

  • Heat load analysis (DC) - compare to LN2 volume
    • G10, radiation, aluminum  
  • Thermal pole estimation from the above materials / joints
  • Thermal equivalent circuit analysis (and possible LISO model - uber LOW priority)
  • Windows - choose the substrates we want -
    • We can get 100$ lambda/10 sapphire 1" substrates from CVI
    • MDC brazes covar to the sapphire substrates, (after this is our first opportunity to coat them), then ships them to Dick who will weld the brazed sapphire to his flange. We have a few choices:
      • We can get MDC to have their coating company (American Photonics) do a v-coating run on them (I will call them to see if they seem good or not - quantitatively) before shipping them to Dick
      • We can get MDC to ship them to CVI then ship them to Dick
      • We can let Dick weld them into complete flanges (~2-3 inches in diameter), then have ATF coat them
      • We can use them uncoated to start (this might even be OK because we have such a large angle of incidence and can dump the ghost beams), then we can coat them later if we want by sending the flange-window assemblies to ATF (or someone else) - though we would be without an operational cryostat while we did this.
  • We need to decide on what vacuum pump(s) we want - for the inner chamber we will probably copy the cart setup in the ATF that Alastair is using (with a Turbo). For the outer vacuum chamber we dont need a very hard vacuum, which opens up different pump technologies
  • Check out what the state of the indium recycling loop is for Caltech so that we don't pay 100-200$ per seal / pumpdown (maybe some paperwork to fill out?)
  • Verify that we can keep a LN2 dewar down in the lab (or at least in the hallway), possibly paperwork affiliated with this as well.

CAVITY

  • Finish mocking up one of the temperature control ideas by putting in material properties and seeing what poles we can make easily
  • Make a noisebudget for the temperature noise of the cavity + temperature control loop
  • Think about / make a seismic noisebudget once we have a preliminary suspension scheme
  • Get a spacer! (Frank is in negotiations with companies - status = ?)
  • Mirror choice for the cavity
    • Choose a g-factor (see this elog for HOM spacing)
    • Choose a Finesse
    • Think a bit about how how Finesse(T) goes, and make sure that a 10^5 Finesse at room temperature can't turn into a 10^6 Finesse at 123K or 18K
      • Just model it as a basic stack of whatever materials we are using, then see about the signs of thermorefractive and thermoelastic derivaties
  • Optically contacting vs glue - Is this debate closed? Do we know the downsides of each?
    • Frank was looking into yield strains of glue vs contacting, and since Si isn't amorphous, we may have to worry about differential contraction even with Si mirrors and a Si spacer if we can't identify the relative directions of the crystal axes

 

LASERS

  • Diode vs Fiber laser
  • We can't lock the diode to the cavity as built with ULE mirrors and Fused Silica spacer
    • We think this means we need a filter cavity (a PMC with a PZT)
    • We need to think a tad about choosing the Finesse in a quantitative way for this cavity...
    • This means we need to understand WHY we can't lock the laser to the cavity right now in a quantitative way
    • To this end we need to:
  • Get a real frequency noise measurement of the laser diodes
    • Lock it to a cavity and get a bound on the error signal between the two (didn't work!)
    • Sweep a cavity and check that we are actually single mode (Frank played around with sweeping, results?)
    • Use a PLL and calibrate the error signal to the VCO to determine frequency noise of the beat (bad idea - overly complicated and a VCO with the right range might not exist)
    • Use a PFD (Phase Frequency Discriminator) like they did at the 40m to measure the frequency noise directly - probably easy with such high noise
      • THIS is the measurement of choice of the above options.

META (LAB, ETC)

  • Get PMA to install a longer corkboard by the CryoLab / Greg's lab so that we can post more results on the fly
  • Use compressed air to blow the remaining dust off the fixtures / continue to mop frequently until we truly decimate the particle count...we have gotten it down another order of magnitude to 2K/ft3 (from 30K/ft3) from our cleaning efforts if we are not present in the lab, so the main source is stirring up all the dust from the surfaces

 

 

  77   Fri Feb 11 19:57:44 2011 Dmass, FrankLab InfrastructureGeneralextensive lab cleaning

we cleaned the lab this afternoon. This time also the top of the pipes, lamps, cable trays, HVAC system etc, short: all horizontal surfaces.

Here some pictures of how dirty it was:

100_1215.JPG

HVAC system - we actually removed some pounds of dirt

 

100_1223.JPG

HVAC system - before and after using the vacuum cleaner

 

100_1219.JPG

some of the pipes - they are actually white, not grey/brown as on the picture

 

100_1224.JPG

cleaning tool - to scrub the surface and vaccum.

  76   Tue Feb 1 19:06:23 2011 DmassLaserLaserBeat Found

I updated this elog entry (RIN plots)

  75   Tue Feb 1 10:53:38 2011 FrankNotesCavityFS cavity parameters

 Jep, right. Using the right units for the calculation helps Fixed the two bugs in the code. Here the updated plot:

FS_203mm_fl-cc50cm.png

Quote:

I think this g might be wrong - (all I know I get from page 746 of Siegmann)

When someone says "g-factor" of an asymmetric cavity,  they either mean g1*g2, or sqrt(g1*g2),

In either case, what I get is:

  • g1 = 1-Lcav/R1 = 1-8*2.54/50 = 0.59
  • g2 = 1
  • sqrt(g1*g2) = 0.77 / g1*g2 = 0.59
  • Either way, I get something very different from 0.035

(The units of Lcav have an extra m in them too.)

  74   Tue Feb 1 01:30:08 2011 DmassNotesCavityFS cavity parameters

Quote:

calculated for flat/cc (50cm) ULE mirror set and FS resonantor (8" long)

FS_203mm_fl-cc50cm.png

 

 

 I think this g might be wrong - (all I know I get from page 746 of Siegmann)

When someone says "g-factor" of an asymmetric cavity,  they either mean g1*g2, or sqrt(g1*g2),

In either case, what I get is:

  • g1 = 1-Lcav/R1 = 1-8*2.54/50 = 0.59
  • g2 = 1
  • sqrt(g1*g2) = 0.77 / g1*g2 = 0.59
  • Either way, I get something very different from 0.035

(The units of Lcav have an extra m in them too.)

  73   Tue Feb 1 01:16:20 2011 DmassDailyProgressPlotsCavity HOM vs g-factors

I made some code in MATLAB to generate plots of the cavity HOM spacing (as well as some other information) and spit it out. The code is available on the 40 svn under mDV/extras/cavityinfo.m (see 40m elog for info on using the svn)

  • Input: both mirror radii, finesse, cavity length
  • Output: Plot with HOM spacing, and details about waist size and g-factors

Attached is a set of plots with the following mirror combinations (in cm):

50 - 50

100 - 100

200 - 200

50 - 100

50 - flat

100 - flat

For all the plots I assumed a (reasonable) 10k Finesse.
The first set is with a 4 inch cavity.

The second set of plots is for 7 inches (the longest possible length we could fit in the cryostat we're thinking of getting from Dick Gummer)

Attachment 1: RefCav4inchesAll.pdf
RefCav4inchesAll.pdf RefCav4inchesAll.pdf RefCav4inchesAll.pdf RefCav4inchesAll.pdf RefCav4inchesAll.pdf RefCav4inchesAll.pdf
Attachment 2: RefCav7inchesAll.pdf
RefCav7inchesAll.pdf RefCav7inchesAll.pdf RefCav7inchesAll.pdf RefCav7inchesAll.pdf RefCav7inchesAll.pdf RefCav7inchesAll.pdf
  72   Mon Jan 31 22:00:33 2011 FrankLab InfrastructureGenerallatest particle counts

peak around afternoon 1/28 due to lab cleaning

CryoLab_data_plot3.png

  71   Mon Jan 31 21:21:33 2011 FrankNotesCavityFS cavity parameters

calculated for flat/cc (50cm) ULE mirror set and FS resonantor (8" long)

FS_203mm_fl-cc50cm.png

 

 

  70   Sat Jan 29 01:14:15 2011 FrankMiscPlotsSilicon - absorption plots

yep, sorry 

Quote:

Is the X-axis of the third figure wavelength in nm?

 

ELOG V3.1.3-