Digital Control of Stabilized HeNe Lasers?
These types of lasers have been designed using simple analog techniques for over 35 years. So why change? A few op-amps, a monostable or two, and a handful of discrete parts is sufficient for any conceivable level of performance in a mode-stabilised HeNe laser. There are at most two signals that need to be monitored (the polarization modes) with the objective of maintaining them equal or in a fixed ratio. Yet, I’ve seen at least 3 examples of dual polarization mode stabilized HeNe lasers that have gone from a simple analog approach to a much more complex digital approach, apparently with no obvious technical justification: • HP/Agilent 5517: Xylinx or similar FPGA. • Zygo 7702: Motorola 68HC11 microprocessor. • Teletrac/Axsys: Microchip PIC16C73A-20/SP PIC. All are basic mode stabilized HeNe lasers. The 5517 is a Zeeman-split laser but the stabilization is mode-based. The redesign in each case must have cost a fortune. Since none of these lasers had many adjustments in their analog des