Contains reports on one research project.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U. S. Air Force) under Contract DAAB07-71-C-0300U. S. Air Force Cambridge Research Laboratories Contract F19628-70-C-006

Haus, Hermann A.

Holcomb, T.

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IV. ELECTRODYNAMICS OF MEDIAAcademic Research StaffProf. W. P. Allis Prof. H. A. Haus Prof. J. A. KongProf. L. J. Chu Prof. P. W. Hoff Prof. P. Penfield, Jr.Graduate StudentsE. L. Frohring D. L. Lyon W. A. StiehlT. Holcomb A. H. M. Ross L. TsangE. E. Stark, Jr.A. EXPERIMENTS ON ROOM-TEMPERATURE TEA CO LASERExperiments have been performed on a sealed-off, room-temperature TEA CO laser,with the objective of studying the excitation process in the laser. One startling discoveryis that this laser is superradiant.The discharge length was 76 cm, with 151 1-k2 resistors, one in series with eachpin. A single rod running the length of the tube forms the cathode. The cavity lengthwas 1. 4 m, the reflectivity of the curved output mirror was 98%, the radius of the curvedmirror was 3 m, and the flat mirror was perfectly reflecting.Maximum output power was obtained with a mixture of 144 Torr He, 2. 2 Torr Xe,and 4. 1 Torr CO. Most measurements were performed with this mixture. The additionof xenon was essential to obtain laser operation. It was found that operation withoutxenon did not produce lasing action, and in fact produced an irreversible change in thegas mixture; later addition of xenon did not lead to lasing.A typical output pulse and the accompanying current pulse are shown in Fig. IV-1.The peak power was 100 W. Note that the laser pulse occurred unusually early withinthe current pulse, and that lasing ceased before the current pulse had reached maximum.When the stationary flat mirror was replaced by a rotating flat mirror, in order to checkwhether the occurrence of the lasing pulse could be shifted by delayed Q-switching, itwas found that no such influence was possible.The lasing pulse was passed through a quarter-meter spectrometer to determine thewavelength of operation. The resolution of the spectrometer did not permit us to pin-point the frequencies to better than the following CO lines:Wavelength (FL) Line5. 067652 P6-5 (10)5. 066051 P4-3 (22)5. 064895 P5-4 (16)5. 064805 P 7 -6 (3)This work was supported by the Joint Services Electronics Programs (U. S. Army,U. S. Navy, and U. S. Air Force) under Contract DAAB07-71-C -0300, and by U. S. AirForce Cambridge Research Laboratories Contract F19628-70-C-0064.QPR No. 107(IV. ELECTRODYNAMICS OF MEDIA)Note that all four lines occur between adjacent vibrational levels. It is likely that thepulse has three or four such vibrational transitions in succession. First of all, the pulseusually shows 3 or 4 peaks (see Fig. IV-1). Further evidence in this direction comesfrom an experiment in which the flat mirror was replaced by a grating. The pulse shape200 ns/div. 50 ns/div.Fig. IV-1. Fig. IV-2.Laser and current pulses. Pulses Spontaneous emission pulse. Super-recorded on subsequent shots, esti- position of 5 pulses.mated timing jitter, 30 ns.changed with the grating, and instead of the successive peaks characteristic of laseroperation with the mirror, either 2 peaks or one single peak occurred, depending uponthe grating orientation. These findings suggest that the three or four peaks noted inoperation with a plane mirror represent the occurrence of 3 or 4 successive vibrationallines. 1 The grating strongly selects one of these lines; occurrence of another line pre-supposes initial operation in the strong line.A surprising feature of this laser is the very early occurrence of the laser pulse.The delay of the pulse with respect to the leading edge of the current pulse is of theorder of 20 ns or less. Such early occurrence of lasing can be explained only if thesystem has a very high gain; on the basis of this observation, the supposition was thatthe system might exhibit superradiance. In order to test this hypothesis, we removedthe output mirror and looked for detectable radiation. Figure IV-2 shows the radiationpulse observed under these circumstances. The detected peak power was of the orderof 100 mW. Such behavior of the system can be explained if the gain of the system isof the order of 60 dB/m.T. Holcomb, H. A. HausReferences1. C. K. N. Patel, ,"Vibrational-Rotational Laser Action in CO," Phys. Rev. 141,71-81 (1966).QPR No. 107I --

Electrodynamics of Media

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Electrodynamics of Media

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