40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  PSL  Not logged in ELOG logo
Entry  Tue Jul 2 11:21:24 2013, Erica, DailyProgress, fiber optic, mode matching snip_of_beam_profiling_6_27.JPGP1020518.JPG
    Reply  Wed Jul 3 09:46:48 2013, Erica, DailyProgress, fiber optic, mode matching 130703-095332.jpg
       Reply  Thu Jul 11 01:40:19 2013, Erica, DailyProgress, fiber optic, mode matching P1020690.JPGP1020692.JPG
          Reply  Fri Jul 12 00:51:39 2013, Erica, Notes, fiber optic, mode matching P1020705.JPGP1020703.JPG7_11_13_beam_profile.PNG7_11_13_beam_from_fixed_lens.PNG
             Reply  Tue Jul 16 10:27:47 2013, Erica, Notes, fiber optic, mode matching, beam recombination 
                Reply  Tue Jul 16 11:02:47 2013, Erica, Notes, fiber optic, mode matching, beam recombination 130805-120628.jpg
                   Reply  Wed Jul 17 11:58:47 2013, Erica, Notes, fiber optic, mode matching, beam recombination 7_16_13_determining_polarization_axis.PNGTEK0000.PNG
                      Reply  Wed Jul 17 18:29:37 2013, Erica, DailyProgress, fiber optic, reducing drift in the recombined beam 
                         Reply  Sat Jul 20 23:39:09 2013, Erica, DailyProgress, fiber optic, reducing drift in the recombined beam 
                            Reply  Tue Jul 23 10:29:12 2013, Erica, DailyProgress, fiber optic, reducing drift in the recombined beam shielded_10s_TEK0005.PNGunshielded_10s_TEK0027.PNG
                               Reply  Tue Jul 23 11:43:00 2013, Evan, DailyProgress, Electronics Equipment, Zach's op-amp recommendations 
                               Reply  Fri Jul 26 11:07:44 2013, Erica, DailyProgress, BEAT, circuit for measuring temperature fluctations on CTN table P1030056.JPGP1030057.JPGP1030059.JPGP1030056.JPG
                                  Reply  Fri Jul 26 11:22:45 2013, Erica, DailyProgress, BEAT, circuit for measuring temperature fluctations on CTN table 
                                     Reply  Fri Jul 26 11:45:28 2013, Erica, DailyProgress, BEAT, circuit for measuring temperature fluctations on CTN table 
                                        Reply  Mon Jul 29 13:30:26 2013, Erica, DailyProgress, BEAT, adding resistor, capacitor, and sockets w_o_capacitor_7_26_13.JPGcapacitor_7_26_13.JPGP1030066.JPGP1030070.JPG
                                           Reply  Tue Jul 30 12:23:41 2013, Erica, DailyProgress, BEAT, addressed noise problem, DC signal 
                                              Reply  Thu Aug 1 00:25:02 2013, Erica, DailyProgress, fiber optic, insulating foam 731_7graph.PNG731_11graph.PNGP1030318.JPG
                                                 Reply  Fri Aug 2 12:38:41 2013, tara, DailyProgress, fiber optic, insulating foam chmbrtmp.JPGfringe.JPG
                                                    Reply  Tue Aug 6 12:31:24 2013, Erica, DailyProgress, fiber optic, insulating foam P1030403.JPG
                                                       Reply  Wed Aug 7 13:27:00 2013, Erica, DailyProgress, fiber optic, more foam, calculations for convertion from voltage to frequency P1030409.JPGP1030417.JPGP1030420.JPG
                                                          Reply  Wed Aug 7 18:53:20 2013, Erica, DailyProgress, fiber optic, noise budget, Matlab notes. noise_budget.PNGP1030427.JPG
                                                             Reply  Tue Aug 13 12:39:36 2013, Erica, DailyProgress, fiber optic, rewrote calculations for converting from voltage noise to frequency noise P1030458.JPGP1030459.JPGP1030460.JPG
                                                       Reply  Tue Aug 13 12:28:20 2013, Erica, Notes, Electronics Equipment, new AD 590 circuit and its noise calculation, beam alignment P1030461.JPGP1030454.JPGP1030456.JPGP1030457.JPGAD590circuit2.PNG
                                                          Reply  Fri Aug 16 10:35:44 2013, Erica, Notes, Electronics Equipment, AD590 msrmt, conversion to freq noise 
                   Reply  Tue Jul 30 16:19:32 2013, Erica, Notes, fiber optic, setup for beam recombination new_setup.PNGbeam_recombination2.PNG
                   Reply  Mon Aug 5 12:21:00 2013, Erica, Notes, fiber optic, calculation: phase change for fiber 130805-121449.jpg
    Reply  Tue Jul 30 15:48:47 2013, Erica, DailyProgress, fiber optic, noise for GYRO 
Message ID: 1237     Entry time: Fri Jul 12 00:51:39 2013     In reply to: 1235     Reply to this: 1240
Author: Erica 
Type: Notes 
Category: fiber optic 
Subject: mode matching 
I finally got MatLab installed on my computer from Caltech.
You can get programs installed by being a Caltech student/faculty, through IMSS. Here is the website:
http://www.imss.caltech.edu/software
https://idp.caltech.edu/idp/Authn/UserPassword


One of the things, I was unsure about and talked to Evan about mode matching where should the output waist be and how does one calculate it. Previously, I took the mode field diameter from the fiber, the focal length of the lens in the collimator, and then calculated the waist q parameters (from Kogelnik 1966), like I did calculating from the PMC. However, that leaves some questions - once the waist from the fiber is determined, when mode matching, should the incoming waist from the PMC be placed at the lens, or at the distance we calculated the waist to be from the lens in the collimator?

Other potential problems is possible change in the distance from the lens to the fiber in the collimator if one accidentally rotates it while attaching the collimator to the stand.

This can be resolved by looking the Gaussian profile and measuring the radii at various distances, to calculate the waist (see http://nodus.ligo.caltech.edu:8080/PSL_Lab/1222). Then when mode matching, one would try to place the waist at the lens in the collimator. I measured the Gaussian profile from the input side by switching the output and input sides of the beam so the laser was directed into the output end of the fiber, without altering the input end (distance from fiber to collimator, without removing fiber from stand and collimator, etc).

Then I measured the waist after the two fixed lenses from the PMC, to ensure the theoretical calculations for the waist were correct.







When checking the waist coming after the PMC, our calculations from the Gaussian profile did not agree with the location of the waist we observed with our eyes. Evan discovered that the lens we were using was not fused silica (UV) as most lenses are but BK7 (C), which for a given radius of curvature, has a different focal length than fused silica. So the lens we thought was f = 143.2mm had a focal length of f = 127.1 mm. Once this change had been made in the calculations, it agreed with our observations.
This means I'll have to redo the inventory because some of the lenses are fused silica, others are BK7.

Here is the final determination of the location of the waist coming from the PMC and the setup I used to determine it.









This is the new mode matching setup.





After setting it up, I obtained an output of 15%. 1.24mW out of 8.4mW.
ELOG V3.1.3-