I liked to know quantitatively where the spot is on a mirror.
With an interferometer and A2L scripts, one can make the balance of the coil actuators
so that the angle actuation does not couple to the longitudinal motion.
i.e. node of the rotation is on the spot
Suppose you have actuator balancing (1+α) f and (1-α) f.
=> d = 0.016 x α [m]
Full Imbalance α = 1 -> d = 15 [mm]
10% Imbalance α = 0.1 -> d = 1.5 [mm]
1% Imbalance α = 0.01 -> d = 0.15 [mm]
Eq of Motion:
I ω2 θ = 2 R f
(correction) - I ω2 θ = D f cos(arctan(L/2/D))
(re-correction on Sep 26, 2017) - I ω2 θ = D f
m ω2 x = 2 α f ,
(correction) - m ω2 x = 2 α f ,
where R is the radius of the mirror, and D is the distance of the magnets. (kinda D=sqrt(2) R)
d, position of the node distant from the center, is given by
d = x/θ = α I / (m R) = 2 α β / D,
where β is the ratio of I and m. Putting R=37.5 [mm], L=25 [mm], β = 4.04 10-4 [m2], D~R Sqrt(2)
i.e. d = 0.015 α [m]
Kiwamu and Koji
- Checked the SRM/PRM balancing after the gluing.
- The mirrors were removed from the suspensions for baking.
- Bob is going to bake them next week.
I've added a diagram in the wiki under IFO Upgrade 2009-2010->New CDS->Diagram section Joe_CDS_Plan.pdf (the .svg file I used to create it is also there). This was mostly an exercise in me learning inkscape as well as putting out a diagram with which lists control and model names and where they're running.
A direct link is: CDS_Plan.pdf
Awhile back we had requested a feature for the RCG code where a single file would define a memory location's name as well as its explicit hex address. Alex told me it had been implemented in the latest code in SVN. After being unable to find said file, I went back and talked to him and Rolf. Rolf said it existed, but had not been checked into the SVN yet.
I now have a copy of that file, called G1.ipc. It is supposed to live in /cvs/cds/caltech/chans/ipc/ , so I created the ipc directory there. The G1.ipc file is actually for a geo install, so we'll eventually make a C1.ipc file.
The first couple lines look like:
There are also section using ipcType IPC:
Effectively the ipcNum tells it which memory location to use, starting with 0x2000 (at least thats how I'm interpreting it. Every entry of a given ipcType has a different ipcNum which seems to be correlated to its description (at least early on - later in the file many desc= lines repeat, which I think means people were copy/pasting and got tired of editing the file. Once I get a C1.ipc file going, it should make our .mdl files much more understandable, at least for communicating between models. It also looks like it somehow interacts with the ADCs/DACs with ipcType PCI, although I'm hoping to get a full intro how to use the file tomorrow from Rolf and Alex.
Koji, Steve, and Kevin looked into calibrating the Wilcoxon accelerometers. Once calibrated, the accelerometers will be used to monitor the motion of the PSL table.
We want to use the shaker to shake each accelerometer and monitor the motion with an OSEM. We will make a plate to attach an accelerometer to the shaker. A flag will also be mounted on this plate.The OSEM will be mounted on the table next to the shaker and positioned so that the flag can block the LED light as the plate moves up and down. We will then measure the motion of the accelerometer as it is shaken from the OSEM signal. The OSEM signal will be calibrated by keeping the plate and the flag still and moving the OSEM down along the flag a known distance with a micrometer.
Sure. I figured I would put up a How-To if it works.
Would it be possible to write about the technique on a wiki page as you get measurements and results?
I used the Mathematica CurveFit package that we use in Ph6/7 to make the fits for the beam profile data. I wrote two functions that use CurveFit shown in the attachment to make the fits to the error function and square root.
I have worked out the first set of adjustments to make on the MC mirrors (all angle figures are in units of the increments on the control screen)
Using the method described in the previous post, I obtained the following matrix relating the angle-to-length coupling and the angular deviations. In the following matrix, Mij corresponds to the contribution of the jth degree of freedom to the ith A-to-L coupling, with the state vector defined as xi = (MC1P, MC2P, MC3P, MC1Y, MC2Y, MC3Y), where each element is understood as the angular deviation of the specific mirror in the specific direction from the ideal position, such that x = 0 when the cavity eigenmode is the correct one and the beams are centered on the mirrors (thus giving no A-to-L coupling regardless of the components of M).
-0.2843 -0.4279 -0.1254 0 0 0
-0.8903 -0.4820 -0.6623 0 0 0
0.5024 0.0484 -0.0099 0 0 0
0 0 0 0.1145 -0.1941 -0.3407
0 0 0 0.0265 1.5601 0.2115
0 0 0 0.1015 0.1805 -0.0103,
giving an inverse
0.0003 -0.0001 0.0020 0 0 0
-0.0031 0.0006 -0.0007 0 0 0
0.0018 -0.0018 -0.0022 0 0 0
0 0 0 -0.0013 -0.0015 0.0117
0 0 0 0.0005 0.0008 -0.0008
0 0 0 -0.0037 -0.0010 0.0044
The initial coupling vector is then acted on with this inverse matrix to give an approximate state vector x containing the angular misalignments of each mirror in pitch and yaw. The results are below:
Restarted the elog with the script as it was down.
Beginning last week, I have been helping Koji with some of the IO work that must be done for the 40m upgrade. The first thing he asked me to do is to help with the alignment of the MC.
As I understand, it became apparent that the IFO beam was not centered on all (or any) of the MC mirrors, which is disadvantageous for obvious reasons. We are trying to correct this, using the following strategy:
Using the results of these measurements, it is possible to evaluate the components of a block-diagonal matrix M which relates the tilt-to-displacement coupling of each DOF to each mirror's misalignment in that degree, i.e.,
a = M x
with a a 6-dimensional vector containing the coupling of each degree of freedom to the length of the cavity and x a 6-dimensional vector containing the angular misalignments of each. Due to orthogonality of pitch and yaw, M will take the form of a 6x6 matrix with two non-zero 3x3 blocks along the diagonal and zero matrices on the off-diagonal blocks.
The idea is to isolate components of M by moving one mirror at a time, solve for them, then find the inverse M-1 that should give us the required angular adjustments to obtain the beam-centered ideal cavity mode.
In theory, this need only be done once; in practice, our measurement error will compound and M will not be accurate enough to get the beams exactly centered, so we will have to iterate.
NOTE: The fact that we are adjusting the three cavity mirrors to obtain the ideal mode means that we will necessarily tarnish our coupling into the cavity. Once we have adjusted the mirrors once, we will need to re-steer the input beam and center it on the REFL diode.
Status: This process has been completed once through step 5. I am in the process of trying to construct the matrix for the first adjustment.
I thought that the micrometer I was using to move the razor through the laser beam was metric; however, it is actually english.
After discovering this mistake, I converted my previous measurements to centimeters and fit the data to
w = sqrt(w0^2+lambda^2*(z-z0)^2/(pi*w0)^2) with the following results:
reduced chi squared = 14.94
z0 = (-4.2 ± 1.9) cm
w0 = (0.013 ± 0.001) cm
The mode profile of Gaussian beams in our PPKTP crystals was calculated.
I confirmed that the Rayleigh range of the incoming beam (1064 nm) and that of the outgoing beam (532 nm) is the same.
And it turned out that the waist postion for the incoming beam and the outgoing beam should be different by 13.4 mm toward the direction of propagation.
These facts will help us making optical layouts precisely for our green locking.
The result is shown in the attached figure, which is essentially the same as the previous one (see the entry).
The horizontal axis is the length of the propagation direction, the vertical axis is the waist size of Gaussian beams.
Here I put x=0 as the entering surface of the crystal, and x=30 mm as the other surface.
The red and green solid curve represent the incoming beam and the outgoing beam respectively. They are supposed to propagate in free space.
And the dashed curve represents the beams inside the crystal.
A trick in this calculation is that: we can assume that the waist size of 532 nm is equal to that of 1064 nm divided by sqrt(2) .
If you want to know about this treatment in detail, you can find some descriptions in this paper;
"Third-harmonic generation by use of focused Gaussian beams in an optical super lattice" J.Opt.Soc.Am.B 20,360 (2003)"
I've added a new page in the wiki which describes the current naming scheme for the .mdl model files used for the real time code generator. Note, that these model names do not necessarily have to be the names of the channels contained within. Its still possible to make all suspension related channels start with C1:SUS- for example. I'm also allocating 1024 8 byte channels for shared memory address space for each controller and each simulated plant.
The wiki page is here
Name suggestions, other front end models that are needed long term (HEPI is listed for example, even though we don't have it here, since in the long run we'd like to port the simulated plant work to the sites) are all welcome.
The PRM/SRM were balanced with the standoffs. We glued them to the mirror.
This was the last gluing so far until we get new PRM/ETMs.
Give me the plot of the fit, otherwise I am not convinced.
I tried Koji's suggestions for improving the fit to the vertical beam profile; however, I could not improve the uncertainties in the fit parameters.
I started retaking the data today with the same laser settings used last time and noticed that the photodiode was saturating. We were using an ND 4.0 neutral density filter on the photodiode. Koji and I noticed that the coating on the filter was reduced in the center and added an additional ND 0.6 filter to the photodiode. This seemed to fix the photodiode saturation.
I think that the photodiode was also saturating to a lesser extent when I took the last set of data. I will take another vertical beam profile tomorrow.
[Edit by KA: Metallic coating started being evaporated and the ND filters reduced their attenuation. We decided to use absorptive one as the first incident filter, and put a thinner one behind. This looked fine.]
Talked with Jay briefly this morning.
We are due another 1-U 4 core (8 CPU) machine, which is one of the ones currently in the test stand. I'm hoping sometime this week I can convince Alex to help me remove it from said test stand.
The megatron machine we have is definitely going to be used in the 40m upgrade (to answer a question of Rana's from last Wednesday's meeting). Thats apparently the only machine of that class we get, so moving it to the vertex for use as the LSC or SUS vertex machine may make sense. Overall we'll have the ASS, OMC, Megatron (SUS?), along with the new 4 1-U machines, for LSC, IO, End Y and End X. We are getting 4 more IO chassis, for a total 5. ASS and OMC machine will be going without full new chassis.
Speaking of IO chassis, they are still being worked on. Still need a few cards put in and some wiring work done. I also didn't see any other adapter boards finished either.
To fix a problem one of the models was having, I checked the CVS version of the Bitwise.pm file into the SVN (located in /home/controls/cds/advLigoRTS/src/epics/util/lib), which adds left and right bit shifting funtionality. The yec model now builds with the SVN checkout.
Also while trying to get things to work, I discovered the cdsRfmIO piece (used to read and write to the RFM card) now only accepts 8 bit offsets. This means we're going to have to change virtually all of the RFM memory locations for the various channels, rather than using the values from its previous incarnation, since most were 4 bit numbers. It also means it going to eat up roughly twice as much space, as far as I can tell.
Turns out the problem we were having getting to compile was nicely answered by Koji's elog post. The shmem_daq value was not set to be equal to 1. This caused it to look for myrimnet header files which did not exist, and caused compile time errors. The model now compiles on megatron.
[Edit by KA: 4 bit and 8 bit would mean "bytes". I don't recall which e-log of mine Joe is referring.]
I scanned the temperature of the crystal oven on Friday night in order that we can find the optimal temperature of the crystal for SHG.
The optimal temperature for this crystal was found to be 36.2 deg.
The crystal is on the PSL table. The incident beam on the crystal is 27.0mW with the Newport power-meter configured for 1064nm.
The outgoing beam had 26.5mW.
The outgoing beam was filtered by Y1-45S to eliminate 1064nm. According to Mott's measurements, Y1-45S has 0.5% transmission for 1064nm, while 90% transmission for 532nm. This means I still had ~100uW after the Y1-45S. This is somewhat consistent with the offset seen in the power-meter reading.
First, I scanned the temperature from 28deg to 40deg with 1deg interval.The temperature was scaned by changing the set point on the temperature controller TC-200.The measurements were done with the temperature were running. So, the crystal may have been thermally non-equilibrium.
Later, I cut the heater output so that the temperature could be falling down slowly for the finer scan. The measurement was done from 38deg to 34deg with interval of 0.1deg with the temperature running.
I clearly see the brightness of the green increase at around 36 deg. The data also shows the peak centered at 36.2deg. We also find two lobes at 30deg and 42deg. I am not sure how significant they are.
Koji and I wanted to turn off the IFO-room AC so the wind would not blow on MC1-3. We could not. The switches were probably bypassed when the power transformer was replaced at the last scheduled power outage.
There is one three position manual/off/auto switch next to the filter for each unit at CES. They have to be in AUTO position when we want to turn AC on/off from the lab.
Joe and I started working on the new LSC FE control today. We made a diagram of the system in Simulink, but were unable to compile it.
Joe checked out the latest CDS software out of their new SVN and put it somewhere (perhaps his home directory).
The SVN checkout was done on megatron. It is located under /home/controls/cds/advLigoRTS
So, to compile (or at least try to) you need to copy the .mdl file from /cvs/cds/caltech/cds/advLigo/src/epics/simLink to /home/controls/cds/advLigoRTS/src/epics/simLink on megatron, then run make SYS in the advLigoRTS directory on megatron.
The old checkout from CVS exists on megatron under /home/controls/cds/advLigo.
Once you made a CDS model, please update the following wiki page. This will eventually help you.
LSC Plant Model. That is all.
LSC Plant Model. That is all.
1. The vertical axis should start from zero. The horizontal axis should be extended so that it includes the waist. See Zach's plot http://nodus.ligo.caltech.edu:8080/40m/2818
2. Even if you are measuring only the linear region, you can guess w0 and z0, in principle. w0 is determined by the divergence angle (pi w0/lambda) and z0 is determined by the linear profile and w0. Indeed your data have some fluctuation from the linear line. That could cause the fitting prescision to be worse.
3. Probably the biggest reason of the bad fitting would be that you are fitting with three parameters (w0, z0, zR) instead of two (w0, z0). Use the relation ship zR= pi w0^2/lambda.
The vertical beam profile of the Innolight 2W laser was measured at eight points along the axis of the laser.
These measurements were made with the laser crystal temperature at 25.04°C and the injection current at 2.091A. z is the distance from the razor blade to the flat black face of the front of the laser.
The voltage from a photodiode was measured for the razor at a number of heights. Except for the first two points, one scan was made with the razor moving down and a second scan was made with the razor moving up. This data was fit to
y = a*erf(sqrt(2)*(x-x0)/w) + b with the following results:
The values for w and its uncertainty were estimated with a weighted average between the two scans for the last six points and all eight points were fit to
w = w0*sqrt(1+(z-z0)2/zR2) with the following results:
chi^2/ndf = 17.88
w0 = (0.07 ± 0.13) mm
z0 = (-27 ± 121) mm
zR = (65 ± 93) mm
It looks like all of the data points were made in the linear region so it is hard to estimate these parameters with reasonable uncertainty.
We then copied the directory with the .mdl files and the CDS parts library into our real Simulink Model Directory:
Use this and not someplace in Alex or Rob's home directory !
Joe will put in more details on Monday once he figures out how to build the new stuff. Basically, we decided not to support multiple versions of the CDS real time code here. We'll just stay synced to the latest stable ~versions.
I exported the current version of the LSC FE into our public_html/FE/ area on nodus where we will put all of the self-documenting FE diagrams:
To make a web setup like this, you just use the "Export to Web" feature from the top-level Simulink diagram (e.g. lsc.mdl). Choose the following options:
Note: in order to get the web page to work, I had to change the apache httpd.conf file to allow AddType file overriding. Here's the term cap of the diff:
nodus:etc>diff httpd.conf httpd.conf~
< ServerAdmin firstname.lastname@example.org
> ServerAdmin email@example.com
< AllowOverride FileInfo
Jenne, Koji and I assembled the Covesion Oven today, inserted a PPKTP crystal from Raicol, aligned the crystal to a 50mW focus and
got some green beam coming out.
Covesion Oven assembly
The oven contains a brass clip that can clamp a crystal up to 10mm wide x 0.5mm high x 40mm long (according to the instructions). According to the correspondence from Covesion the clip can accomodate a crystal up to 1.5mm high. Our crystal is 1mm x 1mm x 30mm.
Alignment of the crystal to the focus
The oven was mounted on a 4-axis Newport translation stage. We plonked the assembly onto the table, removed the lid and adjusted the rough position so that a focus of the 1064nm beam, from a 100mm lens, was positioned near the center of the crystal - then it was clamped down to the table. From here we adjusted the alignment of the stage, using an IR card and a viewer to guide us, until we eventually saw some green beam coming out. We were all very excited by this! We optimized the alignment as best we could using the IR card and then we replaced the lid on the oven. At this point the temperature of the PPKTP was around 26.5C and the green beam coming out look quite dim. We turned the oven up to around 36 degC and observed the beam getting much brighter and we approached the optimum phase-matching condition.
We haven't done anyway quantitative measurements yet but we were pleased with how easy this first stage was.
[Edit by Koji] More photos are on Picasa album
What kind of fit did you use? How are the uncertainties in the parameters obtained?
The attached plot shows the spectra of the 3 Z axes of the 3 seismometers we have (this data is from ~20Aug2009, when the Ranger was in the Z orientation) in Magenta, Cyan and Green, and the noise of each of the sensors in Red, Blue and Black. The noise curves were extracted from the spectra using the Huddle Test / 3 Corner Hat method. The Blue and Black traces which are just a few points are estimates of the noise from other spectra. The Blue points come from the Guralp Spec Sheet, and the Black comes from the noise test that Rana and I did the other day with the Ranger (elog 2223).
I'm not really happy with the black spectra - it looks way too high. I'm still investigating to see if this is a problem with my calibration/method....
So, as it turns out (surprise), I'm a spaz and forgot a 2*pi when calibrating the Guralp noise spectra from the spec sheet. I noticed this when redoing the Huddle Test, and comparing my Spec Sheet Guralp noise with Rana's, which he shows in elog 2689. When going from m/s^2, the units in the spec sheet, I just tilted the line by a factor of frequency. Koji pointed out that I needed a factor of 2*pi*f. That moves the Guralp spec line in the plot in elog 2237 (to which this entry is a reply) down by ~6, so that my measured noise is not, in fact, below the spec. This makes things much more right with the world.
In other news, I redid the Huddle analysis of the 2 Guralp seismometers, ala Rana's elog 2689. The difference is now we are on the granite slab, with soft rubber feet between the floor and the granite. We have not yet cut holes in the linoleum (which we'll do so that we're sitting directly on the 40m's slab).
Rana> this seems horrible. Its like there's a monster in there at 6-7 Hz! Either the seismos are not centered or the rubber balls are bad or Steve is dancing on the granite slab again.
I updated the default FILTER.adl file located in /home/controls/cds/advLigo/src/epics/util/ on megatron. I moved the yellow ! button up slightly, and fixed the time string in the upper right.
Good fit. I assumed sqrt(x) is a typo of sqrt(2).
Koji and Kevin measured the vertical beam profile of the Innolight 2W laser at one point.
This data was taken with the laser crystal temperature at 25.04°C and the injection current at 2.092A.
The distance from the razor blade to the flat black face on the front of the laser was 13.2cm.
The data was fit to the function y(x)=a*erf(sqrt(x)*(x-x0)/w)+b with the following results.
Reduced chi squared = 14.07
x0 = (1.964 +- 0.002) mm
w = (0.216 +- 0.004) mm
a = (3.39 +- 0.03) V
b = (3.46 +- 0.03) V
Back in Gainesville in 1997, I learned how to do this using the chopper wheel. We had to make the assumption that the wheel's blade was moving horizontally during the time of the chop.
One advantage is that the repetitive slices reduces the random errors by a lot - you can trigger the scope and average. Another advantage is that you can download the average scope trace using USB, floppy, or ethernet instead of pencil and paper.
But, I never analyzed it in enough detail to see if there was some kind of nasty systematic error.
x0 = (1.964 +- 0.002) mm
w = (0.216 +- 0.004) mm
a = (3.39 +- 0.03) V
b = (3.46 +- 0.03) V
razor height (mm) Voltage (V)
Zach and Koji
We measured uncalibrated angle-to-length coupling using tdssine and tdsdmd.
We made a simple shell script to measure the a2l coupling.
- Opened the IMC/OMC light door.
- Saw the large misalignment mostly in pitch. Aligned using MC2 and MC3.
- Locked the MC in the low power mode. (script/MC/mcloopson AND MC length gain 0.3->1.0)
- Further aligned MC2/3. We got the transmission of 0.16, reflection of 0.2
- Tried to detect angle-to-length coupling so that we get the diagnosis of the spot positions.
- Tried to use ezcademod. Failed. They seems excite the mirror but returned NaN.
- We used tdssine and tdsdmd instead. Succeeded.
- We made simple shell script to measure the a2l coupling. It is so far located users/koji/100421/MCspot
- We blocked the beam on the PSL table. We closed the chamber and left.
Alberto and myself went to downs and acquired the 3rd 4x processor (Dual core, so 8x cores total) computer. We also retrieved 6 BIO interface boards (blue front thin boxes), 4 DAC interface boards, and 1 ADC interface boards. The tops have not been put on yet, but we have the tops and a set of screws for them. For the moment, these things have been placed behind the 1Y6 rack and under the table behind the 1Y5 rack
The 6 BIO boards have LIGO travelers associated with them: SN LIGO-S1000217 through SN LIGO-S1000222.
The 3 seismometers are now on the granite slab. The Ranger is now aligned with the Xarm (perpendicular to the Mode Cleaner) since that's the only way all 3 would fit on the slab.
This is mostly a reminder to myself about what I discussed with Jay and Alex this morning.
The big black IO chassis are "almost" done. Except for the missing parts. We have 2 Dolphin, 1 Large and 1 Small I/O Chassis due to us. One Dolphin is effectively done and is sitting in the test stand. However, 2 are missing timing boards, and 3 are missing the boards necessary for the connection to the computer. The parts were ordered a long time ago, but its possible they were "sucked to one of the sites" by Rolf (remember this is according to Jay). They need to either track them down in Downs (possibly they're floating around and were just confused by the recent move), get them sent back from the sites, or order new ones (I was told by one person that the place they order from them notoriously takes a long time, sometimes up to 6 weeks. I don't know if this is exaggeration or not...). Other than the missing parts, they still need to wire up the fans and install new momentary power switches (apparently the Dolphin boards want momentary on/off buttons). Otherwise, they're done.
We are due another CPU, just need to figure out which one it was in the test stand.
6 more BIO boards are done. When I went over the plans with Jay, we realized we needed 7 more, not 6, so they're putting another one together. Some ADC/DAC interface boards are done. I promised to do another count here, to determine how many we have, how many we need, and then report that back to Jay before I steal the ones which are complete. Unfortunately, he did not have a new drawing for the ASC/vertex wiring, so we don't have a solid count of stuff needed for them. I'll be taking a look at the old drawings and also looking at what we physically have.
I did get Jay to place the new LSC wiring diagram into the DCC (which apparently the old one never was put in or we simply couldn't find it). Its located at: https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=10985
I talked briefly with Alex, reminded him of feature requests and added a new one:
1) Single part representing a matrix of filter banks
2) Automatic generation of Simulated shared memory locations and an overall on/off switch for ADC/DACs
3) Individual excitation and test point pieces (as opposed to having to use a full filter bank). He says these already exist, so when I do the CVS checkout, I'll see if they work.
I also asked where the adl default files lived, and he pointed me at ~/cds/advLigo/src/epics/util/
In that directory are FILTER.adl, GDS_TP.adl, MONITOR.adl. Those are the templates. We also discovered the timing signal at some point was changed from something like SYS-DCU_ID to FEC-DCU_ID, so I basically just need to modify the .adl files to fix the time stamp channel as well. I basically need to do a CVS checkout, put the fixes in, then commit back to the CVS. Hopefully I can do that sometime today.
I also brought over 9 Contec DO-32L-PE boards, which are PCIe isolated digital output boards which do into the IO chassis. These have been placed above the 2 new computers, behind the 1Y6 rack.
Theoretically the waist position of a Gaussian beam (1064) in our PPKTP crystal differs by ~6.7 mm from that of the incident Gaussian beam.
So far I have neglected such position change of the beam waist in optical layouts because it is tiny compared with the entire optical path.
But from the point of view of practical experiments, it is better to think about it.
In fact the result suggests the rough positioning of our PPKTP crystals;
we should put our PPKTP crystal so that the center of the crystal is 6.7 mm far from the waist of a Gaussian beam in free space.
The calculation is very very simple.
The waist position of a Gaussian beam propagating in a dielectric material should change by a factor of n, where n is the refractive index of the material.
In our case, PPKTP has n=1.8, so that the waist position from the surface of the crystal becomes longer by n.
Now remember the fact that the maximum conversion efficiency can be achieved if the waist locates at exact center of a crystal.
Therefore the waist position in the crystal should be satisfied this relation; z*n=15 mm, where z is the waist position of the incident beam from the surface and 15 mm is half length of our crystal.
Then we can find z must be ~8.3 mm, which is 6.7 mm shorter than the position in crystal.
The attached figure shows the relation clearly. Note that the waist radius doesn't change.
Koji and Kevin measured the output power vs injection current for the Innolight 2W laser.
The threshold current is 0.75 A.
The following data was taken with the laser crystal temperature at 25.04ºC (dial setting: 0.12).
EDIT: I used an IFIT (inverse fast idiot transform) to change the x-axis of the plot from Hz to m. I think xlabel('Frequency [Hz]') is in my muscle memory now..
I have redone the beam fit, this time omitting the M2, which I believe was superfluous. I have made the requested changes to the plot, save for the error analysis, which I am still trying to work out (the function I used for the least squares fit does not work out standard error in fit parameters). I will figure out a way to do this and amend the plot to have error bars.
We removed the old SRM and PRM from their cages, and are temporarily storing them in the rings which we use to hold the optics while baking. Steve will work on a way to store them more permanently.
We then hung the new SRM (SRMU03) and new PRM (SRMU04) in the cages. We were careful not to break the wires, so the heights will not have changed from the old heights.
The optics have not been balanced yet. That will hopefully happen later this week.
Are you sure about your x-axis label?
I restarted the elog with the restart script as it was down.
Here is Crystal 724 polished side 2 with all photos along the length stitched together
The 40m's new undergrad Kevin Kuns was introduced to 40m safety hazards. He is new and needs guidance as specially with 2W laser work.
Peter King will train him on Friday to LIGO-laser standard.