The United States of America As Represented by the Administrator of the

Robert T Menzies

Michael J Kavaya

Charles W Rutledge

Brendan T McGuckin

A conversion efficiency of 42% and slope efficiency of 60% relative to absorbed pump power are obtained from a continuous wave diode-pumped Tm, Ho:YLiF.sub.4 laser at 2 .mu.m with output power of 84 mW at a crystal temperature of 275 K. The emission spectrum is etalon tunable over a range of 7 nm (16.3 cm.sup.-l) centered on 2.067 .mu.m with fine tuning capability of the transition frequency with crystal temperature at a measured rate of -0.03 cm.sup.-1 .K.sup.-1. The effective emission cross-section is measured to be 5.times.10.sup.-21 cm.sup.2. These and other aspects of the laser performance are disclosed in the context of calculated atmospheric absorption characteristics in this spectral region and potential use in remote sensing applications. Single frequency output and frequency stabilization are achieved using an intracavity etalon in conjunction with an external reference etalon.

Tunable CW diode-pumped Tm,Ho:YLiF.sub.4 laser operating at or near room

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.sup.-1 by control of diode laser temperature over range from 15.degree. K. to 100.degree. K., and tunable over a smaller region of typically 0.1 to 10 cm.sup.-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 (Q.sub.1) 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).

Digital control of diode laser for atmospheric spectroscopy

Continuous offset tuning of a frequency stabilized cw gas laser (10) is achieved by using a spectrophone (14) filled with the same gas as the laser for sensing a dither modulation, detecting a first or second derivative of the spectrophone output with a lock-in amplifier (28), the detected output of which is integrated (36), and applying the integrator output as a correction signal through a circuit (24) which adds to the dither signal from an oscillator (22) a dc offset (B1) that is adjusted with a potentiometer (26) to a frequency offset from the absorption line center of the gas, but within the spectral linewidth of the gas. Tuning about that offset frequency is achieved by adding a dc value (B2) to the detected output of the dither modulation before integration using a potentiometer (30). Tuning may also be achieved by changing the amplitude of dither modulation, or changing the pressure of the spectrophone gas, or any combination of these three tuning parameters which affect the amount of offset of the stabilized frequency from line center.

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Pasadena, CA, United States of America

Robert T Menzies