The ALS-1 is a highly flexible lock-in amplifier and stabiliser system. It is designed to stabilise a laser in a number of different ways.
The model PL6 laser has an extremely flat PZT signature due to the long cavity length, and applied dither stabilisation techniques are therefore not suitable. With this laser the zero order beam from the diffraction grating is monitored with a thermopile detector. The DC signal from this detector is input to the ALS-1 and compared with a preset value to obtain on error signal. The pzt voltage is then automatically adjusted to bring the error signal to zero, effectively locking the laser output power.
With the FIRL100 or 295 FIR lasers, a small modulation voltage is applied to the piezo ceramic of the CO2 laser and the resultant effect on the FIR output is monitored via a beam splitter and pyro electric detector. This signal is detected using phase sensitive detection and is used to lock the CO2 pump laser output and hence the FIR output. A range of stabilisation systems based on the ALS-1 is available for the 395 FIR laser. These range from simple power stabilisation systems to a sophisticated IF locking system depending on requirements.