Yuhang and Michael

After discussion in the TAMA filter cavity meeting on the 29th of September, we realigned the OPO, noting the following points:

• The OPO assembly position with respect to the rotation stage has been set up so that rotating one of the upper screws results in OPO yaw rotation, and rotating both upper screws results in X translation (horizontal direction perpendicular to propagation axis). Likewise, rotating one of the lower screws results in OPO pitch rotation, and rotating both lower screws results in Y translation. See figure 1.
• We confirm that the first stage of the OPO alignment starts with the beam entering the curved HR side (figure 2). This was noted with the black dot in figure 4 of 2682, which is closer to the flat faced side of the plastic holder (i.e. the incoupling mirror is mounted on the opposite side of the assembly from the periscope). The rationale is described in Matteo's thesis with respect to the SHG. We do it this way to ensure that the optical axis and OPO central axis are coincident before placement of the incoupling mirror. After placing the incoupling mirror, the cavity can be scanned for removal of higher order modes. Then, when the alignment of OPO/incoupler is confirmed, the assembly can be turned around for the finesse measurement.
• The beam size of the CC/p-pol beam entering from the HR surface of the OPO in the TAMA experiment is nominally 36 um (Marc 936)
• The distance of the beam from the f = 75 mm lens to the beam waist is measured to be 125 mm (2515). It is estimated that the OPO should be about 57 mm from the top of the periscope (figure 3). Note that there is a mistake in the figures of that elog entry - the predicted waist size of 20 um is with the lensing action of the meniscus (incoupler). Without the incoupler, the beam waist should be 25 um, as measured. However, as noted above, this beam size is setup for the OPO cavity finesse measurement, which is performed after the alignment of the incoupler.

The OPO has been aligned by using the camera to make a reference point (figure 4), placing the OPO, then ensuring that the incident and reflected beams overlap. We confirmed reflection/incidence overlap at the AOM exit port and Faraday Isolator. The beam is also centered on the target as indicated by the camera. In the future, we should take note to have the modulators and FI be further away from the OPO cavity for easier alignment of the reflected beam.

One of the wires detached from the DSub unit (figure 5). It appears to be the positive end coming from the OPO thermistor.