11/12 Participation: Chien-Ming, Shu-Rong, and Yuhang

Following the SHG telescope set up last Friday, we try to improve its mode matching by adjusting the position of Lens 1 (that is the distance to the input waist which is located at the output end of the EOM). The focal length of Lens1 (L1) =200 mm and L2 = 125 mm (see Fig. 1)

First, we change the position of M1's clamping fork to increase the moving space of L1. However, this cause the alignment of M1 slightly deviated. We spend a lot of time recovering the alignment, but it is worse until we find a 3-Adjuster mirror mount to replace the original M1 mount (2-Adjuster).

Then we install the L1 on the optical rail to optimize the mode matching. Last Friday's L1 position was about 138 mm from the EOM output port, and L2 was about 675 mm from EOM output port. After optimization today, the new position of L1 from EOM is 115 mm and L2 is 674 mm. The SHG scanning spectrum is attached in Figure 3. You can see the mode matching is improved to 95.8%.Although the TEM03 mode shown on the scope is almost disappeared after optimization, and the peak of TEM02 mode also drops compared to last Friday. However, the conversion efficiency of SHG output power is still the same as the result of last Friday.

We also slightly change the temperature of the SHG crystal, but can't find a better result. So we decide to stop here and start to set up another telescope of the light leading to the OPO(bright alignment beam).

We also tested with a LASER current of 1.34A. We can have maximum green power of 237+/- 6 mW.

Problem: Now the green production has a power fluctuation from 137~147mW when SHG's incident IR power is 420mW.

Fig. 1: The modified position of the SHG telescope.

Fig. 2: The pattern of the remained TEM02 mode obtained by the CCD camera, even its peak of transmitted signal showing on the Scope is lower than that of last Friday.

Fig. 3: SHG scanning spectrum

Fig. 4: The simulation of SHG telescope in the update position(now the waist zise of this simulation agrees with Chienming's calculation result)