Phase Offset Locking of 689 nm Laser for the Cold Sr Atoms

Phase offset locking between two 689 nm diode lasers is performed. The frequency variation of the beat note is suppressed within 0.2 Hz when it's offset locked, which is approximately 8 orders of magnitude smaller than that of free running case. The phase noise within 400 kHz has been reduced with a maximum value of 30 dB at 100 Hz. The locked laser has been successfully applied for the red MOT of Sr.