High-Power Low-Threshold Optically Pumped Type-ll Quantum-Well Lasers
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Chih-Hsiang Lin*, S. J. Murry, Rui Q. Yang, and S. S. Pei Space Vacuum Epitaxy Center, University of Houston, Texas 77204-5507
H. Q. Le MIT Lincoln Laboratory, Lexington, Massachusetts 02173 Chi Yan and D. M. Gianardi, Jr. Rocketdyne Technical Services, Boeing Defense & Space Group, Kirtland AFB, NM 871175776 D. L. McDaniel, Jr. and M. Falcon Semiconductor Laser Branch, Air Force Phillips Lab., Kirtland AFB, NM 87117-5776
Abstract Stimulated emission in InAs/InGaSb/InAs/AlSb type-II quantum-well (QW) lasers was observed up to room temperature at 4.5 jtm, optically pumped by a pulsed 2-j.m Tm:YAG laser. The absorbed threshold peak pump intensity was only 1.1 kW/cm2 at 300 K, with a characteristic temperature To of 61.6 K for temperatures up to 300 K. We will also study the effects of internal loss on the efficiency and output power for type-II QW lasers via optical pumping. Using a 0.98ý.m InGaAs linear diode array, the devices exhibited an internal quantum efficiency of 67% at temperatures up to 190 K, and was capable of > 1.1-W peak output power per facet in 6-us pulses at 85 K. The internal loss of the devices exhibited an increase from 18 cm' near 70 K to ~ 60-100 cm' near 180 K, which was possibly due to inter-valence band free carrier absorption.
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also with Applied Optoelectronics Inc., Houston, Texas 77081 107 Mat. Res. Soc. Symp. Proc. Vol. 484 © 1998 Materials Research Society
I. INTRODUCTION High-power high-temperature mid-infrared (MIR) lasers at 2 to 5 jim are highly desirable for a variety of applications such as infrared (IR) countermeasures, medical surgery and diagnosis, covert illumination for night vision, and molecular spectroscopy, etc. In addition, many important atmospheric molecules including industrial pollutants and green house gases (H20, CO, HF, CH4, C2HA, HCI, C0 2, N 20, 03, etc.) have strong, fundamental vibrational transitions in the MIR wavelength range. Even though they also have overtones at shorter, near IR wavelengths, the absorption there are much weaker. For example, the absorption of CH4 is two orders of magnitude stronger at 3.3 jim than at 1.65 pm. Both military and commercial MIR systems are limited mainly due to a lack of adequate sources. Currently, MIR solid state lasers tend to be bulky with little wavelength agility, while optical parametric oscillators, which use a nonlinear crystal to down convert or up convert the output wavelength of pump sources, are complex and expensive. Semiconductor diode lasers have significant advantages in terms of cost, volume, weight, reliability, and power dissipation. The availability of compact high-power MIR semiconductor lasers operating at thermo-electrically (TE) cooled temperatures > 205 K would significantly enhance the capability of current MIR technology. Recently, MIR semiconductor lasers have improved significantly in output power and operating temperature [1-15]. The Sb-based lasers [1-13] demonstrated the best power and temperature performance for 2 pm < X < 4.5 pm, and the InP-based intersubband quantum cascade (QC)
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