This elog covers the testing of Liquid crystal(from here on referred to as LC) (LC1111T-C). In continuation to ongoing work in elog.

1. Observing changes in the linearly polarized laser passing through LC with change in voltage of the LC controller. 

2. Testing stability of measurements for long-term measurement (6 hours in this study)

Details:

1. The setup is shown in Fig 1. The HWP and QWP placed were rotated such that the laser was linearly polarized. This was made sure with the use of the polarization camera. Then the LC was placed after them and the fast axis was rotated manually to make the laser linearly polarized again(see Fig 2, the white line on LC shows the slow axis). The LC was connected to the LC voltage controller and temperature controller. The LC expected characteristics from the datasheet are shown in Fig 3 and 4.  

a. The LC voltage controller's voltage was varied from 0 to 25 V and was swept with a step size of 0.1V and step duration of 2s. 

b. The temperature was observed to be fairly constant at 22.58±0.02ºC 

c. The Normalized Stokes Parameter was observed as shown in Fig.5

d. The Ellipiticty and Azimuth varying with varying voltage were observed as shown in Fig.5 and Fig 7 respectively. 

e. The laser power observed using the camera is shown in Fig. 8. 

2. Since mirror characterization takes long hours we had to check if the LC would be durable for long operational hours. To study this, another measurement was taken for 6 hrs. In this case, no parameters were varied. 

a. The LC voltage controller's voltage was set constant at 0V. 

b. The temperature of the LC during the operation was 22.58ºC±0.3 and was fairly stable for 6hrs (varied from 22.58ºC(at the start), 22.83ºC( at 2.5hrs) to 22.49ºC(at the end))

c. The Normalized Stokes Parameter was observed as shown in Fig.9

d. The Ellipiticty and Azimuth varying with varying voltage were observed as shown in Fig.12 and Fig 13 respectively. 

e. The laser power observed using the camera is shown in Fig. 14. 

Although the parametres are seen to be constant enough during LTM, we will do this measurement again to investigate the peak observed in the ellipticity and azimuth since they appear at the same time. The same peak was also observed in stokes parameters S2 and S3(Fig 10,11). Interestingly, no such peak was observed in the laser power. It would be worth keeping an eye on the LC temperature for this.  

Next Step:

1. 6hrs operation test with LC controller's voltage set at >0V. 

2. Observe the temperature variation of the LC