M. Maiorov

Temperature dependence of continuous wave threshold current for 2.3–2.6 μm InGaAsSb/AlGaAsSb separate confinement heterostructure quantum well semiconductor diode lasers

The dependence of spontaneous emission intensity on both current and temperature has been studied for 2.3–2.6 μm InGaAsSb/AlGaAsSb separate-confinement-heterostructure quantum well diode lasers operating in the continuous wave and pulsed regimes. We have used the temperature dependence of the nonradiative recombination processes in the active region to determine the dependence of threshold current on temperature for lasers operating in this wavelength range. The high T0 value (T0=110 °C) observed at T 65 °C and for 2.6 μm lasers in the whole temperature range studied has been identified with an enhancement of the Auger recombination process.

New room temperature CW InGaAsSb/AlGaAsSb QW ridge diode lasers and their application to CO measurements near 2.3 μm

In this work the spectral characteristics of a new type of mid-infrared diode laser are discussed and an application for CO trace gas detection is demonstrated. The InGaAsSb/AlGaAsSb QW diode lasers operating in the spectral range of 2.0 - 2.7 micrometer in continuous wave (CW) regime at room temperature (RT) were developed last year. Earlier, the spectral range of RT CW operation for diode lasers was limited by 2.0 - 2.1 micrometer. The extension of wavelength to 2.7 micrometer was achieved for InGaAsSb/AlGaAsSb quantum well (QW) lasers by employing for QWs new quasi-ternary InGaSb(As) compositions that are out of the miscibility gap for InGaAsSb materials. Single spatial mode ridge lasers emitting at 2.2 - 2.7 micrometer have parameters similar to those of the infrared lasers with (lambda) less than 2 micrometer widely used for spectroscopic application. At operating currents about 80 - 200 mA and temperatures up to +50 degrees Celsius, these lasers emit CW output power of several milliwatts. Investigation of the laser spectra has revealed the current and temperature ranges where a single longitudinal mode dominates with side mode suppression of 22 - 25 dB. The dominant mode can be tuned in wavelength by varying current or temperature. The lasers were used to record high-resolution CO absorption lineshapes (2v band near 2.3 micrometer) in a static cell (14.9-cm path). Probed CO transitions were selected for applications to in situ measurements in high- temperature combustion flows. In general, the measured CO absorption lineshapes agreed with theoretical Voigt profiles calculated using the HITRAN database to within 2%. For a minimum detectable absorbance of 0.01% and a 1-meter long path, the CO measurement sensitivity for the probed R30 transition near 2.302 micrometer was 5 - 10 ppm at 1000 K. This value is about two orders of magnitude better than the sensitivity reported for CO detection with conventional diode lasers that probe transitions in the 3v band near 1.56 micrometer.

Super-high-power operation of 0.98-μm InGaAs(P)/InGaP/GaAs-broadened waveguide separate confinement heterostructure quantum well diode lasers

Record high powers of 16.8 W and 23.5 W have been obtained at CW and Quasi-CW (QCW) operation of 200 μm-aperture Al-free broad waveguide 0.98 μm SCH QW InGaAs(P)/InGaP/GaAs lasers. Some new features of diode laser operation at the super high power regime are considered. Non-thermal, purely current-induced mechanism of power saturation decreases the output powers at P>14 W. Influence of thermal-induced power saturation at high CW currents can be reduced by the stabilization of active region temperature. The main portion (-70%) of active region overheating is associated with a temperature gradient in the copper heatsink. The computed temperature distribution across device is in a good agreement with the spectral and direct measurements of the diode laser temperature. Life-testing at an output power level of 6 W CW and 45 °C has shown only about 6% degradation after more than 1200 hours of operation.

Non-thermal saturation of P-I characteristics for InP- and GaSb-based broad-contact SCH-QW lasers

Summary form only given. High-power pulsed eye-safe IR laser diodes are currently of increasing interest for applications including range finders and IRCM systems. The output power for InP-based lasers is limited by power-current (P-I) characteristics saturation (rollover effect) rather than by the catastrophic optical damage of the mirror facets as observed for shorter wavelength devices. The current leakage from the quantum well active region has been considered as one of the main reasons of the rollover effect. We present data on the studies of P-I characteristics in the short pulsed regime for broad-contact InP-and GaSb-based separate-confinement heterostructure double-quantum-well (SCH-DQW) lasers emitting in the wavelength range 1.45-1.95 /spl mu/m.

Reliability assessment of GaAs- and InP-based diode lasers for high-energy single-pulse operation

With the maturing of high-power diode laser technology, studies of laser-assisted ignition of a variety of substances are becoming an increasingly popular research topic. Its range of applications is wide - from fusing in the defense, construction and exploration industries to ignition in future combustion engines. Recent advances in InP-based technology have expanded the wavelength range that can be covered by multi-watt GaAs- and InP-based diode lasers to about 0.8 to 2 μm. With such a wide range, the wattage is no longer the sole defining factor for efficient ignition. Ignition-related studies should include the interaction of radiation of various wavelengths with matter and the reliability of devices based on different material systems. In this paper, we focus on the reliability of pulsed laser diodes for use in ignition applications. We discuss the existing data on the catastrophic optical damage (COD) of the mirrors of the GaAsbased laser diodes and come up with a non-destructive test method to predict the COD level of a particular device. This allows pre-characterization of the devices intended for fusing to eliminate failures during single-pulse operation in the field. We also tested InP-based devices and demonstrated that the maximum power is not limited by COD. Currently, devices with >10W output power are available from both GaAs- and InP-based devices, which dramatically expands the potential use of laser diodes in ignition systems.

Reliability of fuzes based on diode laser assemblies

We present an analysis of a reliability assessment tailored specifically to fuzes based on laser diode assemblies. Fuzes are required to deliver high energy in a single short pulse (micro- to milliseconds) after prolonged storage (tens of years) in thermally non-stabilized environments. The temperature variation could easily exceed 100 degrees, and the transition from one extreme to the other could be slow or rapid, depending on a particular application. The operating requirements for diode laser fuzes are dramatically different from the majority of other diode laser applications and thus a reliability assurance program for laser fuzes should reflect these differences in usage. In this paper we demonstrate that it is possible to build accelerated aging conditions based on thermal cycling. As parameters in the accelerated thermal aging, we used the total temperature difference between the lowest and the highest points in the cycle, and the average rate of temperature change between the extreme points. This accelerated aging technique based on thermal cycling can predict the performance deterioration over time after storage in thermally non-stabilized environments. The basis of this approach can be extended to the analysis of reliability in environments with high vibration and radiation levels.

2.2-2.5 /spl mu/m InGaAsSb/AlGaAsSb QW diode laser with extraordinarily wide (/spl Delta//spl lambda/ = 300 nm) optical gain spectrum

Summary form only given. Spectroscopy and environmental monitoring are among the prospective applications of mid-infrared diode lasers. Achievement of the widest tuning range for these lasers is highly desirable. The typical tuning range of commercially available external cavity tunable lasers is below 100 nm in the 2-/spl mu/m range. To expand this range it is necessary to employ a gain media with a wider optical gain spectrum. The switching of the laser emission wavelength between the ground n = 1 and the first excited n = 2 states in a quantum well has previously been reported in for GaAs/AlGaAs QW lasers. We suggest involving the first excited states into the light amplification in order to expand the gain spectrum bandwidth. In this work we determined the structural design and experimental conditions for GaSb-based lasers in order to attain the widest gain spectrum (the full-width at half-maximum was /spl Delta//spl lambda/ = 300 nm) at reasonable gain flatness: for the structure with quantum well width of 200 A at near-room temperature the depth of the valley between gain peaks did not exceed 10 cm/sup -1/.