Theoretically, the linewidth of the SHG laser is two times of the fundamental laser, so the frequency stability of the laser remain unchanged. For the ultra-stable laser researcher, the theoretical conclusion is far from enough. Here are some good references of the experimental results on that conclusion. The linewidth equals to 2 times in an order of 10-20. 

When the active power stability function becomes a fixture

Precilasers’ frequency converted laser products consists of the SHG, SFG and DFG of the fundamental laser. The output power of the converted laser is proportionally to power squared. So the output power stability will decay due to the input power stability, polarization stability and also the temperature accuracy of the nonlinear crystals.

To solve the problem, all Precilasers’ frequency converted laser products will equip the active power stability function to keep the output power stability of <1% peak to peak for over 4h at room temperature and <3% peak to peak for over 4h under high-low temperature environment.