Digital control of diode laser for atmospheric spectroscopy

摘要

A system for remote absorption spectroscopy of trace species using a diode laser (14) tunable over a useful spectral region of 50 to 200 cm-1 by control of diode laser temperature over range from 15 DEG K. to 100 DEG K., and tunable over a smaller region of typically 0.1 to 10 cm-1 by control of the diode laser current over a range from 0 to 2 amps. Diode laser temperature and current set points are transmitted to the instrument in digital form and stored in memory (32) for retrieval under control of a microprocessor (28) during measurements. The laser diode current is determined by a digital-to-analog converter (62) through a field-effect transistor (Q1) for a high degree of ambient temperature stability, while the laser diode temperature is determined by set points entered into a digital-to-analog converter (64) under control of the microprocessor. Temperature of the laser diode is sensed by a sensor diode (18) to provide negative feedback to the temperature control circuit that responds to the temperature control digital-to-analog converter (64).