I was asked to calculate the lenses that we need in order to obtained a Gouy phase close to 90 degrees between the two mirrors that are in the Xend green. Yesterday, I measured the distances between the mirrors, and the distance between the mirror relative to the cavity as illustrate in the image attached below. I looked in to the 40m elog and Manasa did the last update on the length of the cavity. She measured 37.7 + 0.05m. The waist size of the beam that was measured by Annalisa in ID 8637 after the Faraday was w0=2.943e-5m @ -0.039m. I calculated the waist size inside the cavity, and I found a waist of w0=2.2 mm. My plan this week is to keep working in the calculation and finish all the calculation this week so that next week I can go inside and place the lenses. 

I had been working on the Xend table optical layout update. Since the two steering mirrors in the Xend green are too close to each, there is a very small Gouy Phase different between these two mirrors. It was suggested to place two lenses so that we can increase the Gouy Phase. I have been working with Nick on this problem, and we had found a solution by using a la mode. We had written an a la mode code that optimize the Gouy Phase and the Mode Matching at the same time. After trying different lenses, we found the following results: a mode matching of 0.9939 as it is show in the first attachment below, and we found a Gouy Phase different between the two mirrors of about 60 degrees. I took photos of the Xend Table. The first photo is the Xend table as we had it right now. In the second photo, I moved the 2nd lens, and I placed the two more lenses that we need it, with more or lenses the correct position where they will be placed. The three old lenses will be replaced by three lenses of different focal length as it can be seen in the first attachment below. The first lens and third lens will stay in the same position where the old first lens and old third lens are, and the second lens will be moved by about half of an inch. We might have one or two of the lenses that we need, but we will have to order the rest of the lenses that need. My plan is to verify the lenses that we already have. Then, I need to let Nick know with lenses we need to order. Hopefully, we will be able to update the table by the end of this week if everything turn out fine.

 Current Mode Matching and Gouy Phase Between Steering Mirrors

We found in 40m elog ID 3330 ( http://nodus.ligo.caltech.edu:8080/40m/3330) a documentation done by Kiwamu, where he measured the waist of the green. The waist of the green is about 35µm. Using a la mode, I was able to calculate the current mode matching, and the Gouy phase between the steering mirrors. In a la mode, I used the optical distances,which is just the distance measured times its index of refraction. I contacted someone from ThorLabs (which is the company that bought Optics For Research), and that person told that the Faraday IO-5-532-LP has a Terbium Gallium Garnet crystal of a length of 7mm and its index of refraction is 1.95. The current mode matching is 0.9343, and the current Gouy phase between steering mirrors is 0.2023 degrees. On Monday, Nick and I are planning to measure the actual mode matching. The attached below is the current X-arm optical layout. 

Calculation For the New Optical Layout

Since the current Gouy phase between the steering mirror is essentially zero, we need to find a way how to increase the Gouy Phase. We tried to add two more lenses after the second steering mirror, and we found that increasing the Gouy phase result in a dramatically decrease in mode matching. For instance, a Gouy phase of about 50 degrees results in a mode matching of about .2, which is awful. We removed the first lens after the faraday, and we added two more mirrors and two more lenses after the second steering mirror. I modified the photo that I took and I place where the new lenses and new mirrors should go as shown in the second pictures attached below. Using a la mode, we found the following solution:

 label                         z (m)            type                       parameters         

 -----                          -----              ----                        ----------         

 lens 1                       0.0800          lens                      focalLength: 0.1000

 First mirror              0.1550          flat mirror            none:            

 Second mirror         0.2800          flat mirror            none:            

 lens 2                      0.4275           lens                      focalLength: Inf   

 lens 3                     0.6549            lens                      focalLength: 0.3000

lens 4                      0.8968            lens                      focalLength: -0.250

Third mirror           1.0675            flat mirror            none:            

Fourth mirror         1.4183            flat mirror            none:            

lens 5                      1.6384            lens                     focalLength: -0.100

Fifth mirror            1.7351            flat mirror           none:            

Sixth mirror           2.0859            flat mirror           none:            

lens 6                     2.1621            lens                     focalLength: 0.6000

ETM                      2.7407            lens                    focalLength: -129.7

ITM                       40.5307          flat mirror          none:             

The mode matching is 0.9786. The different Gouy phase different between Third Mirror and Fourth Mirror is 69.59 degrees, Gouy Phase between Fourth and Fifth 18.80 degrees, Gouy phase between Fifth and Sixth mirrors is 1.28 degrees, Gouy phase between Third and Fifth 88.38 degrees, and the Gouy phase between Fourth and Sixth is 20.08 degrees. Bellow attached the a la Mode code and the Plots.

Plan for this week

I don't  think we have the lenses that we need for this new setup. Mostly, we will need to order the lenses on Monday. As I mention, Nick and I are going to measure the actual mode matching on Monday. If everything look good, then we will move on and do the Upgrade.

 Nick and I measured the reflected power of the green light in locked and unlocked. I'm working on the calculation of the mode matching. Tonight, I'll be posted my calculation I'm still working on it.

JCD:  Andres forgot to mention that they closed the PSL shutter, so that they could look at the green light that is reflected off the harmonic separator toward the IR trans path.  Also, the Xarm (and the Yarm) were aligned to IR using the ASS, and then ASX was used to align the green beam to the cavity.

 Nick and I with the help of Jenne scan the green light when the cavity is unlocked. Nick placed a Beam dump on the IR so that we can just scan the green, but it was removed as soon as we finished with the measurement. I'm working on the calculation, and i'll be posted solution tonight.

Data and Calculation for the Xarm Current Mode Matching

Two days ago, Nick, Jenne, and I took a measurement for the Green Transmission for the X-arm. I took the data and I analyzed it. The first figure attached below is the raw data plotted. I used the function findpeaks in Matlab, and I found all the peaks. Then, by taking close look at the plot, I chose two peaks as shown in the second figure attached below. I took the ratio of the TEM00 and the High order mode, and I average them. This gave me a Mode Matching of 0.9215, which this value is pretty close to the value that I predicted by using a la Mode in http://nodus.ligo.caltech.edu:8080/40m/10191, which is 0.9343. Nick and I measured the reflected power when the cavity is unlocked and when the cavity is locked, so we measured the P_reflUnLocked=52+1µW and P_reflOnLocked=16+2µW and the backgroundNoise=0.761µW. Using this information we calculated  P_refl/P_in=0.297. Now, since P_refl/P_in=|E_ref/E_in|², we looked at the electric fields component by using the reflectivity of the mirror we calculated 0.67. The number doesn't agree, but this is because we didn't take into account the losses when making this calculation. I'm working in the calculation that will include the losses.

Today, Nick and I ordered the lenses and the mirrors. I'm working in putting together a representation of how much improvement the new design will give us in comparison to the current setup.

We want to be able to graphically see how much better it is the new optical table setup in comparison to the current optical table setup. In other words, we want to be able to see how displacement of the beam and how much angle change can be obtained at the ETM from changing the mirrors angles independently. Depending on the spread of the mirrors' vectors we can observe whether the Gouy phase is good. In the plot below, the dotted lines correspond to the current set up, and we can see that the lines are not spread from each other, which essentially mean that changing the angles of the two mirrors just contribute to small change in angle and in the displacement of the beam at the ETM, and therefore the Gouy phase is not good. Now on the other hand. The other solid lines correspond to the new setup mirrors. We can observe that the spread of the line of mirror 1 and mirror 4 is almost 90 degrees, which just implies that there is a good Gouy phase different between these two mirrors. For the angles chosen in the plot, I looked at how much the PZT yaw the mirrors from the elog http://nodus.ligo.caltech.edu:8080/40m/8912. In this elog, they give a plot in mrad/v for the pitch and yaw, so I took the range that the PZT can yaw the mirrors, and I converted into mdegrees/v and then I plotted as shown below. I plot for the current setup and for the new setup in the same plot. The matlab code is also attached below.

 Xarm Green Steering Mirror Upgrade

Nick and I did the upgrade for the green steering mirror today. We locked in the TEM00 mode.
We placed the shutter and everything. We move the OL, but we placed it back. Tonight, I'll be doing a more complete elog with more details.

Green Steering Mirror Update

Yesterday, Nick and I completed the green steering mirrors upgrade. I attached the file that contained the procedure that we plan before we did the upgrade. We placed an iris at the input of the OL and we place another iris before the harmonic separator. We did not use the beam scanner because someone was using it, so what we did was to assume that the cavity is well align and place the iris so that we can recover the alignment. We used the measuring tape to approximate as close as we could the position where the lenses were supposed to go. I did a measurement of the derivative of the waist size in terms of the position of the lens and the derivative of the waist Position in terms of the lenses position at the optimum solution that a la mode give us. Because of this plot, we decide to mount lens 3 and lens 5 into translational stages. After mounting each lenses and mirrors we worked on the alignment of the beam into the cavity. We were able to align the green into the cavity and we were able to locked the cavity to the TEM00 mode. We started to work on the optimization of the mode matching. However, the maximum mode matching that we got was around 0.6, which we need to work a little bit more on the tuning of the mode matching. We leave the iris mounted on the table. I took a picture of the table, and I attached below. For the OL, we just make sure that the output where somehow hitting the QPD, but we didn't really I aligned it. We need to work a little bit more on the alignment of the OL and the tuning of the mirror to maximize the green mode matching.

  Calculation for the input mode cleaner

I have been working on the calculation for the input mode cleaner. I have come out with a new optical setup that will allow us increase the Gouy phase different between the WFS to 90 degrees. I use a la mode to calculate it. The a la mode solution :

   label            z (m)      type             parameters         
    -----            -----      ----             ----------         
    MC1                    0    flat mirror      none:            
    MC3               0.1753    flat mirror      none:            
    MC2              13.4587    curved mirror    ROC: 17.8700       
    Lens1            29.6300    lens             focalLength: 1.7183
    BS2              29.9475    flat mirror      none:            
    First Mirror     30.0237    flat mirror      none:            
    WFS1             30.2269    flat mirror      none:            
    Second Mirror    30.2650    flat mirror      none:            
    Third Mirror     30.5698    flat mirror      none:            
    Lens2            30.9885    lens             focalLength: 1     
    Fourth Mirror    31.0778    flat mirror      none:            
    Lens3            31.4604    lens             focalLength: 0.1000
    Fifth Mirror     31.5350    flat mirror      none:            
    Sixth Mirror     31.9414    flat mirror      none:            
    WFS2             31.9922    flat mirror      none:      

I attached a pictures how the new setup is supposed to look like. 

 I did the calculation, and I reduced the beam Path. In my calculation, I restricted the waist size at the WFSs to be between 1mm-2mm also the other parameter is that the Gouy Phase different between the WFSs have to be 90 degrees. I also try to minimize the amount of mirrors used. I found the Gouy phase to be 89.0622 degrees between the WFSs and the following table shows the solution that I got from a la mode:

  label                         z (m)                   type               parameters         
    -----                         -----                    ----                  ----------         
    MC1                    0                        flat mirror           none:            
    MC3                    0.1753               flat mirror           none:            
    MC2                   13.4587              curved mirror    ROC: 17.8700 (m)       
    Lens1                 28.8172              lens                   focalLength: 1.7183(m)
    BS2                    29.9475              flat mirror           none:            
    First Mirror         30.0237              flat mirror           none:            
    Lens3                 30.1253              lens                  focalLength: -0.100 (m)
    Lens2                 30.1635              lens                 focalLength: 0.1250(m)
    WFS1                 30.2269              flat mirror         none:            
    Second Mirror    30.2650              flat mirror         none:            
    Third Mirror       30.5698              flat mirror         none:            
    Lens4                30.8113              lens                  focalLength: -0.075 (m)
    WFS2                31.0778              flat mirror         none:            

In the first image attached below is the a la mode solution that show the waist size in the first WFS, and I used that solution to calculate the solution of the waist size for the second WFS, which is shown in figure 2. I photoshop a picture to illustrate how the new setup it supposed to look like. 

IMC Calculation and Setup

I have been working in the calculation for improving the Gouy Phase separation between the WFSs. I tried different possible setup, but the three big constrains in choosing a good optical table setup are to have a Waist size that range from 1mm-2mm, the Gouy Phase  between the WFSs have to be greater than 75 degrees and there has to be a steering mirror before each WFS. I will be showing the best calculation because that calculation complies with Rana request of having both WFSs facing west and having the shortest beam path. I approximate the distances by measuring with a tape the distance where the current optics are located and by looking at the picture that I took I approximated the distance where the lenses will be placed. I'm using a la mode for calculating the gouy phase different. I attached a picture of the current optical table setup that we have. Using a la mode, I found that the current gouy phase that we have is 49.6750 degrees.

Now, for the new setup, a run a la mode and found a Gouy phase of 89.3728 degrees. I have to create a two independent beam path: one for the WFS1 and another one for WFS2. The reason for this is that a la mode place everything in one dimension so and since the WFS1 will have a divergence lens in order to increase the waist size, and since that lens should not be interacting with the waist size in the WFS2. We need two beam path for each WFS.  A la mode give us the following solution:

For the beam path of the WFS1

    label                z (m)           type             parameters        
    -----                  -----              ----             ----------        
    MC1                   0              flat mirror          none:           
    MC3                   0.1753     flat mirror          none:           
    MC2                   13.4587   curved mirror    ROC: 17.8700 (m)     
    Lens1                 29.3705   lens                  focalLength: 1.0201 (m)
    BS2                    29.9475   flat mirror          none:           
    First Mirror         30.0237   flat mirror          none:           
    Lens3                30.2000    lens                  focalLength: -0.100 (m)
    WFS1                30.4809    flat mirror         none: 

For the beam path of the WFS2

    label                   z (m)             type             parameters        
    -----                    -----                 ----             ----------        
    MC1                    0               flat mirror          none:           
    MC3                    0.1753      flat mirror          none:           
    MC2                    13.4587    curved mirror    ROC: 17.8700 (m)     
    Lens1                  29.3705    lens                   focalLength: 1.0201 (m)
    BS2                     29.9475    flat mirror          none:           
    Second Mirror    30.2650     flat mirror          none:           
    Lens2                 30.4809     lens                  focalLength: -0.075 (m)
    Third Mirror        30.5698     flat mirror          none:           
    WFS2                30.6968      flat mirror          none:  

I attached bellow how the new setup should look like in the second picture and also I include and attachment of the a la mode code.

 I used Mist to be able to see the read out that we get in the WFSs that take the Mode Cleaner Reflection and the QPD that take the transmitted from MC2. In the following, plots I'm misaligned the each mirrors: MC1, MC2 and MC3. The misalignment are in Yaw and Pitch. I'm dividing the WFSs reading by the total power reflect power, and I'm dividing the QPD for the MC2 transmission by the total transmitted power. In my Mist model, I have a laser of 1W and my EOM is modulated at 30MHz instead of 29.5MHz and the modulation depth was calculating by measuring the applied voltage using and Spectrum analyzer. I using Kiwamu measurement of modulation depth efficiency vs the applied voltage, https://dcc.ligo.org/DocDB/0010/G1000297/001/G1000297-v1.pdf,  I got a modulation depth of 0.6 mrad. I put this modulation depth and I got the following plots: The fourth and fifth attachment are for the current optical setup that we have. The sixth and seventh attachment is for the new optical setup. The eighth attachment is showing the mode cleaner cavity resonating. The last attachment contains the plots of WFS1 vs WFS2, MC2_QPD vs WFS1, MC2_QPD vs WFS3 for each mirror misaligned. The last two attachment are the MIST code for the calculation.

We have all the lenses that we need. I checked it last Friday and if everything is good we will be ready to do the new upgrade this coming Friday. For increasing the power, I check and we have different BS so we can just switch from the current setup the BS. Can you let me know if this setup look good or if I need to chance the setup? I would really love to do this upgrade before I leave.

 Upgrade of IMC Reflection Optical Setup

Nick and I upgrade the IMC. We move both WFSs and placed them facing west. When aligning the beam into the WFS, we make sure that the beam were hitting the center of the mirrors and then we placed the lenses in their corresponding position. We used the beam scanner to measure the waist and the waist in the second WFS was bigger than 1mm, and the second WFS was a little bit below than 1mm. We center the beam in the WFSs and in the PD. We did haven't measure whether we have a good Gouy Phase. Below I attached the picture of how the new setup look like.   

[andrei, advait]

I have analyzed the temperature data that we have collected for the past 10 days or so from the X-end temperature sensor that is accessible via Acromag.

The average temperature was 20.74 Celsius, noticeably cooler than the average 24 Celsius in the control room. The day-night temperature variations are clearly visible.

And here is the power spectrum density of these variations:

The red line indicates the frequency of the day-night cycle (1/24hrs), while the green line indicates twice the frequency of the day-night cycle. We can see that the two lines align fairly well with the peaks, which is to be expected. Here I used n_avg=3 in Paco's spec_dens() function, but I am not sure this is the right value to use. Please let me know if you have suggestions in this regard.

As for the noise estimates of the detector used to collected these data, I am not sure how to get those. The above temperature data was collected using a detector that no one knows where exactly it is in the lab, and I don't even know what type of sensor it is. Perhaps there is a way to get a noise estimate from the data that I collected? Again, please let me know.

However, we have a rough estimate for the noise of the AD590 sensor made by Kira that we calibrated and used for the step response test. We estimated this by calculating the standard deviation of the signal measured from the 0 C ice bath. This translates to 0.0134 C. We will probably repeat this measurement in a better way (once we build our own version of the sensor) because the duration of the actual 0 C measurement was just around 2 minutes.

I found the sensor that we used to measure the tmeperature in the lab. It is a SensorGateway (BASE-WIRED) and according to its datasheet it has a temperature resolution of 0.1 Celsius and an accuracy of 1 Celsius. Regardless, I also let it collect some data overnight to get a better grasp of the noise.

I put the sensor in a box, wrapped around two towels. I tried closing the box as much as possible, but the cables connecting to the sensor prevented me from closing the box all the way. I put the box in the same spot where the sensor sat when the environment data was collected. Here is the picture of the device:

I started the data collection yesterday at around 5pm. Here is the raw temperature data collected by the sensor:

The temperature first increased due to the heat put out by the sensor unit itself (this is a server temp sensor, which has its network server for easy access among other features). We can see that the temperature peaked around 4 hours after the experiment started, which is to be expected, around that time (9pm) the temperature in the lab starts to decrease dramatically. The sensor reached a fairly stable equilibrium around hour 10 which would translate to around 3am, which is again to be expected considering our environment temperature measurements. I used the stable region between hours 10 and 13 for noise estimates:

We can see here that the sensor kept "jumping" between two values: 30.9592 Celsius and 30.8967 Celsius. The difference between these readings is 0.0625 Celsius, and it can be seen that there are no intermediary values between these 2 values. I also performed a spectrum analysis just to see what happens:

The dip at around 0.9 Hz is also visbile in the environment temperature spectrum.

I connected

On Wednesday, Rana showed me that there are two AD590 sensors in the PSL/FSS refcav. It seems that one of the sensors is inside a box which is insulated with foam, while the other sensor is just outside the foam. It is likely that even the sensor outside the foam is not reading the environment temperature, but the difference between the two sensors gives us a good idea of the effects of the foam. Here are the plots:

As you can see, RCTEMP seems to have higher variations than RMTEMP. There is also an offset, probably due to the heat disippated by the hardware inside the box. In the freuquency domain:

where we can clearly see that there is a big difference in intensity at frequencies higher than 0.01 Hz. Moreover, RMTEMP (which is indside the box) has the lower intensity, thus showing that the foam is a low-pass filter. The same story can be seen in the coherence plot:

I have since wanted to hopefully use RCTEMP's readings to make a frequency spectrum like the one I made before using the server temperature sensor. However, I am still struggling to download the data from the channel for periods larger than a few hours. I would need data for at least 5 days in order to capture the very low end like 1/24hr.

We found Mon7 in control room dead today afternoon. It's front power on green light is not lighting up. All other monitors are working as normal.

This monitor was used for looking at IMC camera analog feed. It is one of the most important monitors for us, so we should replace it with a different monitor.

Yehonathan and Paco disconnected the monitor and brought it down. We put it under the back table if anyone wants to fix it. Paco has ordered a BNC to VGA/HDMI converter to put in any normal monitor up there. It will happen this Wednesday. Meanwhile, I have changed the MON4 assignment from POP to Quad2 to be used for IMC.

Rana came and helped us figure us where to inject the noise. Following are the characteristics of the test we did:

• Inject normal noise at C1:IOO-MC1_PIT_EXC using AWGGUI.
• Excitation amplitude of 54321 in band 12-37Hz with Cheby1 8th order bandpass filter with same limits.
• Look at power spectrum of C1:IOO-MC_F_DQ, C1:IOO-WFS1-PIT_OUT_DQ and the C1:IOO-MC1_PIT_EXC itself.
• Increased the gain of the noise excitation until we see some effect in MC_F.
• Diaggui also showed coherence plot in the bottom, which let's us have an estimate of how much we need to go further.

Attachment 1 shows a screenshot with awggui and diaggui screens displaying the signal in both angular and longitudinal channels.

Attachment 2 shows the analogous screenshot for MC2.