Pure Photonics’ tunable lasers offer great stability and performance. The whispermode, with the reduced frequency noise allows users to fully utilize the narrow intrinsic linewidth. However, in this unlocked state, the laser does wander around by 10-20MHz  over time periods of 10 seconds and may drift over longer time periods (hours) due to influences of temperature and other ambient conditions.

The general operation of the locked laser is to activate the laser close to the resonance of the locking element. Within the module the light is split with the majority going to the output of the module and a small part routed to the locking element. The resonance is then found by scanning the frequency and the laser is aligned with a spot half-way down the resonance (where the slope of response versus frequency is largest).

Once the lock-point has been reached the module enters the whispermode and the FM modulation input is used to constantly correct the frequency based on the measurement. Thanks to the internal design of the locking circuit and stability of the electronics we can maximize the number of photodiode counts per MHz, which results in the most accurate locking performance.

For the locking, we can use an H2C2 (Acetylene) gas cell or a high-finesse etalon. The pro’s and con’s of both approached are shown below. 

With an external frequency reference the laser can be actively stabilized to a frequency and realize much better short and long term stability.

We currently offer several versions:

PPCL590: Integrated H2C2 (Acetylene) gas cell

PPCL595: Integrated 50GHz etalon

PPCL597: Integrated 50GHz etalon with back-reflector