Far-infrared laser power measurements

Abstract

MARCHThe reason for the dif€erence is obvious as the diode impedance varies periodically from a low to a high value. In the first case, this impedance is in series with the resonant circuit and the change results in strong FM and AM signal components. In the second case, the loop-coupled diode appears as a shunt impedance and the main effect of its time-varying impedance is to produce small changes in the cavity Q, and hence slight amplitude modulation at the signal.Using the arrangement in Fig. l(b), reasonably pure waveforms could be obtained for harmonics from the eighth to the sixteenth. Measurements with a receiver for the eleventh harmonic, for instance, indicated that unwanted harmonics were over 33 dB below the level of the required signal.No s i d c a n t steps were taken to optimize the input matching, and the coupling loop was adjusted to be a reasonable match only for the twelfth h o n i c . Even so, the e5ciency was about 9 percent for the eighth harmonic, dropping to 5 percent for the fifteenth.Unless elaborate filter circuits are to be used, it is obvious from the above simple experiments that the diode circuit must be carefully arranged so as to minimize the effects of the diode impedance changes. (watt) (wan) 2.030 38.5 x 1.462 21.6 x Detector responsitivity 170 V,W with black polyethylene 6ltcr. -C E S [I I S. M. Krakauer, "Harmonic generation, rcftification, and lifetime evaluation with the [2] K. L. Kotzebue, "A circuit model of the S t e p m v c r y diode," Proc. IEEE (Come-step mzovery diode," RM. Abstract-Measmme& of the peak a d average ouQmt powof a 337damncyamidekser.rergorted.Tktestsservedtoiadicatetbe.sef.l-~a t~B i g B~P q . e a c y a * o v~w a v~~ . *l i ona-av-wer--,atiquidb codedIpSb--IUiX-ud ¶-8thlUtOr.This letter reports measurements of the peak and average output power of a recently developed submillimeter far-infrared cyanide laser' oscillating at 337 microns (890 GHz).The cyanide laser, l o c a t e d at the M.I.T. National Magnet Laboratory, Cambridge, Mass.' and manufactured by G . and E. Bradley and Co., is similar to that of Gebbie et al.' It uses a continuous flow of butyronitrile in a 2-meter-long discharge tube. Power is coupled out by a hole in one of the reflectors into l-cm-diarneter light pipe (oversize cylindrical waveguide). Pulsed output power at a 1-100 pps repetition rate is optimized using a Golay cell.Pulse characteristics were determined using a hetiumcooled indium antimonide detector-mixer having a time constant near lo-' second^.^ Pulse shape was found to vary from pulse to pulse, possibly due to multifrequency operation. A scope photograph of a representative pulse is shown in Fig. 1. The InSb detector response was not increased at this frequency by the application of a magnetic field to the detector. Average power was measured using a recently developed room-temperature thermal detector,' useful from 50 GHz to 10 microns. A black