High Power 13 C 1602 Laser with Three-Mirror Cavity

A tunable, high power13C16O 2 laser with a three-mirror cavity consisting of two dielectric mirrors and a grating is investigated. The combination of a dielectric mirror and the grating reduces the cavity optical loss and, in this way, an output power of over 25 W is obtained in a single line for a 100 cm long sealed-off discharge tube.


Quantum Electronics Letters
High Power 13C1602 Laser with Three-Mirror Cavity

H. S H I W A T A AND c. S. FOX
Abstract-A tunable, high power 13C1602 laser with a three-mirror cavity consisting of two dielectric mirrors and a grating is investigated.The combination of a dielectric mirror and the gratingreduces the cavity optical loss and, in this way, an output power of over 25 W is obtained in a single line for a 100 cm long sealed-off discharge tube.R ECENTLY a tunable 13C1602 laser was employed for the pumping of an FIR laser to achieve suitable wavelength concidence, but the output power of this laser was only 12 W [ 11 .This is the highest value of output power which has been published.We wish to report a tunable high power 13C1602 laser which has a three-mirror cavity consisting of two dielectric coated mirrors and a grating.The combination of the grating and a mirror internal to the cavity from the grating is able to reduce optical loss by decreasing the optical flux which impinges on the grating.In this way, we obtained approximately twice as high an output power as has been seen previously, while maintaining high electrical efficiency.
Almost all tunable lasers have a grating as a dispersion element, and the output power of these lasers is lower than that of nontunable lasers having no dispersion element.This lower output is attributable to higher optical loss caused by scattering and absorption at the surface of the grating.According to theoretical analysis of the output power of a laser oscillator [2], the output power degradation due to an increased internal optical loss is very significant at low optical gain.
The optical loss is considered to be the product of incident optical flux and the loss coefficient.Thus, if we can reduce the optical flux on the grating, total optical loss will be decreased.
Fig. 1 shows the experimental arrangement.The active length of the sealed-off discharge tube is 100 cm and the internal diameter is 12 mm.Two ZnSe Brewster windows are cemented at each end.The discharge tube is cooled by tap water.The output coupler is a dielectric coated ZnSe flat mirror having a reflectance of 86 percent at 11 .I5 pm.The internal mirror in front of the grating is also a dielectric coated ZnSe flat mirror  having a reflectance of 60 percent at 11.15 pm.We used a flat aluminum evaporated replica grating whose substrate material is glass.This grating is grooved at 150 lines/mm and blazed at 8 pm.The spacing between the output mirror and the internal mirror is 147 cm, and the gap between the internal mirror and grating is 9 cm.In order to avoid damage to the grating due to high power optical flux in the cavity, the grating surface is cooled by forced air convection from a miniature fan.The oscillation wavelength and output power were measured with a spectrum analyzer (Optical Engheering, Model 16-A) and a power meter (Coherent Model CR-205), respectively.The purity of the 13C'a02 gas was 90 percent (molecular) with the remainder being l2Cl60 2.
Fig. 2 shows the output power of individual lines of the P branch of the (00'1) to (10'0) transition.For this 13C160 2 laser operation we used a mixture of 28 percent l3CI6O2, 17 percent 14N2, 47 percent He, and 8 percent Xe at a total pressure of 17 torr.'The transverse mode was recognized as TEMoo by observing the burn pattern, and the beam spot size was approximately 7 mm at the output mirror.At a discharge current of 20 mA, the applied voltage was 9.5 kV, resulting in an electrical efficiency of 13 percent.Since this Iaser has a three-mirror cavity with no automatic cavity length control, the output power was unstable.Data were taken after adjusting the three mirrors manually in the axial direction for maximum output power.Additionally, since the combination of the internal mirror and the grating is a Fabry-Perot etalon, we observed much variation in output power when we changed the incidence angle of the grating slightly while remaining on one spectral line.resulting in an electrical efficiency of 19 percent.For these trials, the reflectances of the flat output mirror and internal mirror were 80 percent and 70 percent, respectively.The reflectances of the output and internal mirrors were not optimized for either the 12C1602 or the 13C1602 lasers.
In summary, we have described a tunable, high output power laser which has an internal mirror before the grating.This internal mirror reduces total optical loss by decreasing the optical flux impinging on the grating, which is a high loss optical element.This method can be applied to other laser systems which incorporate high loss optical components.Abstruct-The physical mechanisms which give rise to conversion gain mance of SIS quasi-particle mixers, the photon-assisted tunneling theory in SIS quasi-particle mixers are studied.It is shown that the S-shape used by Tucker to describe quasi-particle mixing is extended here to tunneling structure at the gap voltage of the I-V curve is essential in include pair current contribution.Based on this complete quantum achieving conversion gain.In the development of SIS quasi-particle theory, the effects of the Josephson noise on SIS quasi-particle mixing mixers, a new approach is used to analyze the embedding network of is discussed and an upper frequency limit of SIS quasi-particle mixing the mixing experiment.The method described in this paper has the is estimated.
advantage over conventional methods that no separate measurements are necessary.In order to obtain a complete picture of the perfor-
Using a mixture of 24 percent 12C1602, 12 percent 14N2, 6.0 percent He, and 4 percent Xe at 17 torr operating pressure, a maximum output power of 35 W was obtained on several lines in the P branch of the 10.4 (urn band of the 12C1602 molecule, Manuscript received March 3,1981.This work was supported in part PPLICATIONS such as radio astronomy have stimulated by the United States Office of Naval Research.The author was with the Department of Physics, University of Cali-development of low noise receivers for millimeter and fornia, Berkeley, CA 94720.He is now with L,&orato&s, M~~~ submillimeter wavelength electromagnetic radiation.Super-Hill, NJ 07974.conducting tunnel junctions have long been considered as pos-A 0018-9197/81/0700-1151$00.75 0 1981 IEEE