Sheila, Camilla, Keita

E path (inspection path)

Yesterday we started to set up the inspection path (the path labeled E in D2000021).  We measured that when we move ZM1 from one edge of the DAC range to the other in yaw, we are able to move the beam by 13mm at ZM2.  There is roughly 2 meters from ZM1 to ZM2, so this corresponds to a peak to peak yaw range of ZM1 of (13e-3m/2m)*1/2 = 3.5mrad (the factor of two accounts for reflecting off the surface of ZM1, and is left out of the slider calibration for now).  Lee emailed us that the design (which shows roughly an inch displacement of the beam from it's nominal position at ZM2) was based on E1900343 which says the ZMs will have a range of 25mrad. Our measurements of the range of ZM4 seem to agree that the full range is more like 3.5mrad (60447)

Since we want to have the nominal operating point of be near the middle of the suspension range, this means we really only have about 6mm between the nominal beam position and the misaligned beam position, so we can't place the pick off mirror for the E path without some clipping. Keita has photos illustrating this that he or I will attach soon.

PZT scans

We scanned both PZTs and took photos of the green transmission (Georgia described the PZT drive Friday: 61241, we are using 0-118V).  For PZT1 we see the lack of response at low voltages that was described in the optics lab, 59582.  We get two FSRs in green by scanning PZT2. 

We switched the cable on the interface chassis (U8 of SQZ R2) from PZT1 to PZT2, so that we could use the same driver set up to drive PZT2 (PZT2 is actually not connected to the PZT driver).  For PZT2 we are able to scan 10 FSRs, with a PZT response that is closer to linear throughout the 0-118V range than PZT1.  However, the cavity appears to be misalinged when we drive this PZT, which I believe is the one on the curved mirror.  We see both that the cavity alignment seems to change as the voltage is scanned, which we can understand, and that even at low applied voltages on PZT2 the alignment seems to be poor, which doesn't make sense to me.   We readjusted the input pointing of the green beam to improve the aligment while scanning PZT2.  It seems that we will want to use PZT2, since the response is better.  Photos that we will attach show PZT1 scan, PZT2 scan after realingment, and PZT1 scan again after realingment for PZT2 scan.

OPO locking difficulties, pump fiber input seems misaligned

Before moving on to beam profile measurements and fixing our ZM1/2/3 aligments, we decided to try to look into why our OPO lock seemed so noisey.  We noticed that the PDH error signal pp was only about 300mV, compared to the 1Vpp described in 60166 and comments.  We found that there was less light than expected on the refl diode, and checked powers at various points which can be compared to similar measurements in 60166:

We plan to take some time to realign the beam into the fiber port on SQZT0 this afternoon to increase that coupling.