Terry and I quickly set up a 1811 on the CLF beam to check for seeding, and we see that our level of 3MHz sidebands on the CLF (which will be at the interferomter carrier frequency) is similar to what was seen at LLO 37945

Details:

We put the 1811 (AC coupled version) in place of the CLF rejected diode.  We used the half wave plate in front of the PBS to reduce the power here.  Once the diode was in we set the waveplate so that we saw 495 +/- 5mV of DC output (transimpedance 10V/mA) and measured the RF (+/- 1dBm for all):

-75dBm at 3.127 MHz
-75dBm at 200 MHz
-75.8 dBm 203.128 MHz  

Comparing this to LLO, we are getting 4 times more DC power, and about 6dBm more 3MHz signal, so that means that relative to the carrier our seeding power level is similar to LLO.  We haven't moved the RF amplifiers, feedthroughs, or attentuators as was done at LLO, which is consistent with the LLO results.  

While we were doing this measurement, I must have bumped the PBS in the CLF path which is very loose in it's mount, misalinging the fiber input  Terry tightened the mount, and we were able to find the beam in reflection off the OPO by carefully adjusting the PBS mount.  Then we used the two steering mirrors in front of the fiber coupler to maximize the transmission.  We found while doing this that the CLF launch diode was misaligned, and it looks like this has been misaligned for more than 20 days.  The beam is now aligned onto the diode.  Terry measured 4mW going towards the fiber, and the fiber launch diode reports 3.75mW towards the fiber.  The CLF Trigger diode reports 1 mW coming out of the chamber.  

I debugged the ISS_AC_COUPLED state with the IMC only. It seems to be doing what it promises now, but we haven't tried it in full lock. It required quite the dance for making sure the two AC coupling loops don't fight each other.

It is in SVN. Below is source code.

class ISS_AC_COUPLED(GuardState):
    index=58
    request =True

    @ISC_library.assert_dof_locked_gen(['IMC'])
    @ISC_library.gen_check_WFS_DC(['IMC'])
    @ISC_library.iss_checker
    def main(self):
        ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_SERVO_TRAMP'] = 0
        # make sure 3rd loop is off
        ezca['PSL-ISS_THIRDLOOP_SERVO_GAIN'] = 0
        # turn off boosts
        ezca.write('PSL-ISS_SECONDLOOP_BOOST_2',0)
        time.sleep(0.1)
        ezca.write('PSL-ISS_SECONDLOOP_BOOST_1',0)
        time.sleep(0.1)
        # set the AC coupling gain to 0
        ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_SERVO_GAIN'] = 0
        ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_INT_OFFSET'] = 0
        # turn on 1Hz AC couplinf of AC coupling to deal with offset
        ezca.switch('PSL-ISS_SECONDLOOP_AC_COUPLING_SERVO', 'FM6', 'ON')
        # smoothly relief the Reference Integrator
        ezca['PSL-ISS_SECONDLOOP_REFERENCE_SERVO_OFFSET'] = 0
        ezca.switch('PSL-ISS_SECONDLOOP_REFERENCE_SERVO', 'INPUT', 'OFF')
        self.timer['pause'] = 15
        self.counter = 0

    @ISC_library.assert_dof_locked_gen(['IMC'])
    @ISC_library.gen_check_WFS_DC(['IMC'])
    @ISC_library.iss_checker
    def run(self):
        # run the fault check function, which prints fault
        # notificaitons, but don't do anything since we don't want to
        # break lock unnecessarily.
        ISC_library.PSL_ready()

        if self.counter == 0 and self.timer['pause']:
            # set up TRAMP for AC coupling
            ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_SERVO_TRAMP'] = 3
            # turn on INPUT coupling to initialize the AC coupling FM6
            ezca.switch('PSL-ISS_SECONDLOOP_AC_COUPLING_SERVO', 'INPUT', 'ON')
            # and start the servo for the OFFSET and reference integrator
            ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_INT_OFSEN'] = 1
            ezca.switch('PSL-ISS_SECONDLOOP_REFERENCE_SERVO', 'OFFSET', 'ON')
            self.timer['pause'] = 10
            self.counter += 1
        if self.counter == 1:
            ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_INT_OFFSET']=(ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_DRIVE_OUT16'] - ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_OUTPUT'])/5000.0
            ezca['PSL-ISS_SECONDLOOP_REFERENCE_SERVO_OFFSET']=(ezca['PSL-ISS_SECONDLOOP_REFERENCE_SERVO_OUTPUT'] )/100000.0
            if abs(ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_DRIVE_OUT16'] - ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_DRIVE_INMON']) < 1.0:
                if abs(ezca['PSL-ISS_SECONDLOOP_REFERENCE_SERVO_OUTPUT']) < 1e-3:
                    ezca.switch('PSL-ISS_SECONDLOOP_AC_COUPLING_DRIVE', 'HOLD', 'OFF')
                    ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_INT_OFSEN'] = 0
                    ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_INT_OFFSET'] = 0
                    ezca.switch('PSL-ISS_SECONDLOOP_REFERENCE_SERVO', 'OFFSET', 'OFF')
                    ezca['PSL-ISS_SECONDLOOP_REFERENCE_SERVO_OFFSET'] = 0
                    self.counter += 1
        if self.counter == 2 and self.timer['pause']:           
            ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_SERVO_GAIN'] = -0.3
            self.timer['pause'] = ezca['PSL-ISS_SECONDLOOP_AC_COUPLING_SERVO_TRAMP'] + 3
            self.counter += 1
        if self.counter == 3 and self.timer['pause']: 
            ezca.switch('PSL-ISS_SECONDLOOP_AC_COUPLING_SERVO', 'FM6', 'OFF')
            self.timer['pause'] = 20
            self.counter += 1
        if self.counter == 4 and self.timer['pause']:
            ezca.switch('PSL-ISS_SECONDLOOP_REFERENCE_SERVO', 'INPUT', 'ON')
            self.counter += 1
        if self.counter == 5: 
                return True
 

Since everybody went to the holiday party tonight, I left the interferometer in low noise. After guardian was done, I punched up the input power to 25W (without reducing the DARM offset, i.e. letting the OMC current grow to 25mA), and then increased the DARM offset by another 9% (~30mA). Finally, I blindly increased the SRCLFF by 9% (punching in 1.09 in the gain), and left it there.

Looks like the machine sat there stably at 90Mpc for the whole holiday party... Merry Christmas!

Normally (assuming a failed component), we would fix this on a Tuesday maintenance day.  Although, this week, we might be too pre-occupied with the Pfeiffer pump systems installation/demonstration at Y-mid to get to it(?) 

Stefan, TVo, Hang

We were able to power up to 28 W and stay there stably for about 15 mins or so. However, after that we still had two kinds of locklosses.

=======================================

In the first time we lost lock when POP18 dropped to 50 and then a fast lock loss. Since we had re-distributed the gains in the common mode board (as powering up, in stead of dropping gains at the very end using IMC-REFL_SERVO_FASTGAIN, we decreased the gain upstream in LSC-REFL_SUM_A_IN2GAIN), this thus ruled out that saturation inside the common mode board was the cause for the fast lock losses. More investigation needed.

Also we noticed that at 20 W the LSC-REFL_A_RF9_Q was very close to zero, meaning a good balance of the upper and lower sidebands, while as we powering up, the REFL_9_Q increased by a lot.

=======================================

In the second time, still after about 15 mins at 28 W, an oscillation at 0.4 Hz grew in CHARD YAW ASC. This might be related to the CHARD blending (for yaw, DC part from REFL 9 and AC part from TR QPD combo) which was designed to happen at 0.4 Hz. As we kept losing optical response in the REFL9 signal, this might then lead to an instability in the signal blending. This hypothesis is also consistent with the fact that we did not see similar behavior in CHARD PITCH, as we changed the input matrix for CHARD PIT DC path to REFL45 (LHO:43633) which decayed much less then the RF9 signal and therefor the pitch stayed stable. The solution might thus be either changing the CHARD YAW to using REFL 45 like we did for pitch, or monitoring the signal strength in both REFL9 and QPD combo to keep their ratio constant, or (for a single lock) servo CHARD YAW only to QPD combos as a quick test.

Hang, TVo, Stefan,

Worrying abut high frequency saturation in the CARM servo (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=45768), we updated the IMC_power_adjust_func() in ISC_library.py to start scaling down the input sliders instead of the output sliders.

Specifically, if IMC-REFL_SERVO_FASTGAIN drops below a certain threshold (FG_THRESH), instead of adjusting IMC-REFL_SERVO_FASTGAIN and LSC-MCL_GAIN, we switch to adjusting IMC-REFL_SERVO_IN1GAIN and LSC-REFL_SUM_A_IN2GAIN.

Since we start off with IMC-REFL_SERVO_FASTGAIN = 0 dB at 2W, FG_THRESH=-20 corresponds to 20W, and would leave everything the same up to 20W.

For now we left FG_THRESH at -10dB (6.3W) to give us an extre factor of 3 saturation headroom.

Below is the source code (in ISC_library.py), which is checked into SVN.

We tested the script for functionality and went to 28W for 15min (92Mpc), but then still lost lock. More work to be done.

#################################################
# check input power
#################################################
def IMC_power_adjust_func():
    # at 2.0 Watts input power the nominal gain on IMC Fast Gain should be 0 dB
    calc_gain = 20.0*math.log10(2.0/ezca['IMC-PWR_IN_OUTMON']) 
    calc_gain = min(calc_gain, 31)

    # it only changes the power if there is a difference of 1 dB.  
    # This is intended to prevent repeated 1 dB gain changes
    #  if we are on the edge between two gain settings with the input power. 
    FG_THRESH=-10    # was -20
    IMC_NOM  = 28
    CMB_NOM  =  8
    PWR_MIN  =  4.0

    if ezca['IMC-PWR_IN_OUTMON'] < PWR_MIN:
        # use old logic - ignore the input sliders
        # this is to avoid interfering with the common mode engage sequence
        diff_gain = calc_gain - ezca['IMC-REFL_SERVO_FASTGAIN']

        if abs(diff_gain) >= 1:
            R_diff_gain=round(diff_gain)
            log('power_adjust is changing IMC Common Mode Board IN1 gain by a bit...' )
            ezca['IMC-REFL_SERVO_FASTGAIN'] += R_diff_gain

            time.sleep(0.2)
            if abs(ezca['LSC-MCL_GAIN']) > 1e-9:
                ezca['LSC-MCL_GAIN'] *= 10**(R_diff_gain/20.0)

            elif abs(ezca['IMC-MCL_GAIN']) > 1e-9:
                ezca['IMC-MCL_GAIN'] *= 10**(R_diff_gain/20.0)
    else:
        # use new logic - incorporate input sliders, start lowering input sliders once IMC-REFL_SERVO_FASTGAIN falls below FG_THRESH
        diff_gain_old = calc_gain - ezca['IMC-REFL_SERVO_FASTGAIN']
        diff_gain = calc_gain - ezca['IMC-REFL_SERVO_FASTGAIN'] + CMB_NOM - ezca['LSC-REFL_SUM_A_IN2GAIN']

        if abs(diff_gain) >= 1:
            R_diff_gain_old=round(diff_gain_old)
            
            if ezca['IMC-REFL_SERVO_FASTGAIN'] + R_diff_gain_old >= FG_THRESH:            
                log('power_adjust is changing IMC Common Mode Board IN1 gain by a bit...' )
                ezca['IMC-REFL_SERVO_FASTGAIN'] += R_diff_gain_old
                if abs(ezca['LSC-MCL_GAIN']) > 1e-9:
                    ezca['LSC-MCL_GAIN'] *= 10**(R_diff_gain_old/20.0)
                elif abs(ezca['IMC-MCL_GAIN']) > 1e-9:
                    ezca['IMC-MCL_GAIN'] *= 10**(R_diff_gain_old/20.0)
                # and set back the input gains where they need to be
                ezca['IMC-REFL_SERVO_IN1GAIN'] = IMC_NOM
                ezca['LSC-REFL_SUM_A_IN2GAIN'] = CMB_NOM
            else:
                # set the output gains where they need to be
                R_diff_gain = FG_THRESH - ezca['IMC-REFL_SERVO_FASTGAIN']
                if abs(ezca['LSC-MCL_GAIN']) > 1e-9:
                    ezca['LSC-MCL_GAIN'] *= 10**(R_diff_gain/20.0)
                elif abs(ezca['IMC-MCL_GAIN']) > 1e-9:
                    ezca['IMC-MCL_GAIN'] *= 10**(R_diff_gain/20.0)            
                ezca['IMC-REFL_SERVO_FASTGAIN'] =FG_THRESH
                # set the output gains
                diff_gain_new = calc_gain - (FG_THRESH) +CMB_NOM - ezca['LSC-REFL_SUM_A_IN2GAIN']
                R_diff_gain_new = round(diff_gain_new)
                ezca['IMC-REFL_SERVO_IN1GAIN'] += R_diff_gain_new
                ezca['LSC-REFL_SUM_A_IN2GAIN'] += R_diff_gain_new
 

Daniel, Nutsinee

Attached a RIN plot of various detectors on ISCT6 table. The blue plot is the intensity noise measured off the laser monitor diode. By the time we get to SHG trans PD the noise is worsen by a factor of 10 at ~2-3kHz. The factor of two difference between SHG trans (red) and the green PDs is due to red->green conversion. Question is, this is what we saw in the IFO squeezing attempt in alog45767 ?   To be sure that switching scheme helps we need the same intensity noise data from LLO to compare. If LLO intensity noise is not as bad as ours switching scheme may not solve the problem. 

The 1TB SSD raid for the /opt/rtcds file system is at 90% full. 513G of this is in the target_archive area. I'm currently creating compressed tar images of these directories (and then deleting the source). This will take several hours to complete. (these directories compress by a factor of roughly an order of magnitude).

New problem?  This is showing that it has shut off.  This is very recent and will show up as a pressure increase soon if it is real -> I will monitor and make comment to this entry when data confirms or refutes.

Tonight we power up to 20 watts and were locked for 5 hours.

I measured the CARM OLG (UGF ~ 15kHz) and error spectrum from 0.5 Hz to 5 MHz in response to Stefan and Hang looking for CARM saturations. (PDFs 1 and 2)
They may have been correct to worry: the noise is worst at 100 kHz, a full factor of 10 above where it is at 8 kHz, with peaks a factor of 10 above that.  I'll run some RMS calculations later, but high frequency definitely dominates this spectrum.  We'll need to think about the saturation limits of the common mode board, and the kind of signals we are sending through it to control the laser.

I also ran some bandlimited frequency noise injections with different DARM offsets.  I found that as I reduced the DARM offset, the frequency noise coupling to DARM got worse.  (PNG 1)
This result was counterintuitive to me.  It makes sense for the high frequency noise around 4.1 kHz which masks the OMC dither to cause the low frequency DARM noise to increase with reduced DARM offset, since there is less light in the OMC. But I would have expected the linear Freq to DARM coupling to decrease with reduced DARM offset.  
This prompted me to run a suite of injections which will be analyzed at a later date.

Summary:

We were able to lock the squeezing angle using the 3MHz signal from the OMC DCPD's, and we have caused a few lockloses.  We have found that our locking scheme is introducing a lot of noise, so our next step is to lock the OPO length to the laser frequency.  

Locklosses:

In our first attempt we used the interferometer locked at 2W DC readout to look for the LO error signal.  We caused a lockloss then, and so we then changed to working with the interferometer locked on RF and the OMC locked.  We caused a couple of other locklosses this afternoon, one when the interferometer was locked on RF and the OPO became unlocked with the beam diverter open.  After this we added closing the beam diverter to the OPO guardian DOWN state, and the state CHECK_EOM (which we enter when the TTFSS EOM is railed).  

After successfully locking the squeezer angle, we transitioned to DC readout.  When we attempted to close the beam diverter we lost lock, which we also don't understand.  

We have been injecting ~10uW of CLF (measured on SQZT6), which gives us about 10 dBm of RF on the 3MHz demod.  We are wondering if this is too much and might be part of our lockloss problems.  We tried reducing it by a factor of 2.  

Locking:

Nutsinee will post details of the squeezing angle lock configuration that we used tonight, even though we don't plan to keep using this scheme. 

The basic steps:

• allow the laser temperature servo to bring the beatnote close to the correct frequency. (OPO guardian in down state)
• Lock the squeezer laser to the OPO using the TTFSS (OPO guardian to OPO_LOCKED_CLF)
• Lock the CLF using it's guardian.  
• We then could see that the frequency of the 3 MHz sidebands were not quite right.  We wrote an epics servo, which zeros the difference between the squeezer vs PSL sample (ref cavity) beatnote and twice the IMC VCO frequency, using the timing system frequency readbacks (which update once per second).  This is currently in the guardian called SQZ_PLL in a state called CHECK_BEATNOTE_2, but it will be moved somewhere else and given a more descriptive name.  This can hold us within 100kHz of the correct frequency.  
• We sent the 3MHz signal to both the OPO PZT and the additive offset of the TTFSS.  The additive offset was needed because of a large peak in the noise at around 1 kHz, which is similar to what was seen with the homodyne locking.  Because our locking scheme where the laser follows the OPO (rather than the other way around) introduces a lot of noise, especially at high frequencies, we have a lot of phase noise which means that we need a bandwidth higher than we can get with the PZT only to lock the squeezing angle.  For this reason we introduce an offset in the OPO PDH locking, which allowed us to lock but is obviously terrible. 
• Injecting squeezing in the IFO with this situation resulted in adding a lot of noise.  (See first attachment)

Uncontrolled squeezing:

• The interesting thing is that when we left the beam diverter open but blocked the CLF field and let the squeezing angle rotate, it actually rotates slowly and the large added noise is gone. The second attachment shows the same reference as the first, but with two traces captured with 4 exponential averages at 1Hz, 75% overlap, one showing close to the highest noise that we saw and one showing close to the lowest noise that we saw.  This seems like squeezing and anti-squeezing based on how flat the noise is, but there are two things that are surprising.  While it might be possible that this isn't anti-squeezing at all, it continued for more than 10 minutes without drifting away.  (We were sitting with CLF blocked and the beam diverter open from 4:45 to 4:55, with the OPO locked and the slow servo keeping it's frequency approximately correct.)
  • The level of anti-squeezing seems too high.  Looking between 1100Hz and 11400 Hz, this is almost 17dB of anti-squeezing.  Nutsinee measured the non linear gain to be 3.6, so with our expected total efficiency of 80%, we would expect at most 8dB of anti-squeezing.  (I know, this sounds like I am making a factor of 2 mistake, but I don't think I am.  I'm attaching the dtt file and my script in case anyone wants to double check.)  You might think that the extra noise we see is just some additional noise that we are adding with the squeezer other than anti-squeezing, but at times the noise level drifts down to just a few dB above shot noise. 
  • This squeezing angle is rotating slowly.  With a nonlinear gain of 3.7 and the efficiency of 80%, this would mean that over the 2 seconds of the low noise measurement the squeezing angle only rotated by about 610 mrad, which would be about 100nm of path length change.   We should compare this with the calibrated squeezing angle error signal which Nutsinee will post, but it seems strange that we needed 10's of kHz bandwidth to lock the squeezing angle with  such a slowly drifting system.  

I believe I have found a relevant bug report and a work around for various issues using the 'Terminator' terminal emulator program, including:

1. New terminals were placed behind existing terminals.
2. Opening a new terminal on a workspace that did not already have a terminal open on it would move an already existing terminal from another workspace to the workspace that the new terminal was opened on.

The bug report is here: https://bugs.launchpad.net/terminator/+bug/1508531

The work around is mentioned in one of the comments. Edit your ~/.config/terminator/config file and add 'dbus=False' under [global_config]. For example:

[global_config]
	dbus=False
[keybindings]
[profiles]
  [[default]]
    scrollback_infinite = True
[layouts]
  [[default]]
    [[[child1]]]
      type = Terminal
      parent = window0
    [[[window0]]]
      type = Window
      parent = ""
[plugins]


This seems to have resolved the issues mentioned above for me.