11/19 Participants: Chien-Ming, Shu-Rong, and Yuhang

Today, we finished the telescope of the bright alignment beam, the focal length of L3 is 100 mm and L4 is 150 mm (see Fig.1).
Comparing to the results on 11/14, the beam shape now becomes elliptical after using the Faraday Isolator 2 as shown in Fig. 2 (remove the M4 mirror in this case).
Fig 3. shows the beam shape of the Aux laser 1 coherent control beam (CC beam for short)

Fig 4. shows the transmission spectrum of the OPO cavity by injecting the CC beam. Here we use the Thorlabs InGaAs photodetector to measure the spectrum.

We use the M4 mirror placed on the translation stage to swap the CC beam or the bright alignment beam sending into the OPO.
Fig 5. shows the transmission spectrum of the OPO by injecting the bright alignment beam at the same optical power (60.3 mW) as the CC beam using in Fig. 4
The peak height of TEM00 in Fig.5 bright alignment beam is 8.1 V higher than in Fig.4 CC beam (7.6 V). However, when scaling up the vertical axis, we can see the peaks of other high order modes in the spectrum of bright alignment beam (see Fig. 6) is a little bit worse than in CC beam (see Fig. 7).

Fig. 1 The schematic of the telescope for the bright alignment beam.
Fig. 2 Beam measurement of bright alignment beam on 11/15.
Fig. 3 Beam measurement of CC beam on 11/14.
Fig. 4 The transmission spectrum of injecting the CC beam into OPO.
Fig. 5 The transmission spectrum of injecting the bright alignment beam into OPO.
Fig. 6 Scaling up the transmission spectrum of the bright alignment beam to see the high order modes.
Fig. 7 Scaling up the transmission spectrum of the CC beam to see the high order modes.