Joseph Chavez

High power and high brightness from an optically pumped InAs/InGaSb type-II midinfrared laser with low confinement

We report on optically pumped semiconductor lasers emitting near 3.8 μm that exhibit high power and low output divergence. The lasers incorporate multiple InAs/InGaSb/InAs type-II wells imbedded in an InGaAsSb waveguide that is designed to absorb the pump emission. When operated at 85 K, 0.25 mm×2.5 mm broad area devices produce >5 W of peak power under long pulse conditions. Moreover, these extremely bright devices exhibit a fast axis divergence of only ∼15° full width at half maximum (FWHM), coupled with a slow axis divergence of ∼6° FWHM. The first is due to the reduced optical confinement in the transverse direction, while the latter is attributed to the suppression of filament formation, which is another beneficial consequence of the low optical confinement.

Optically pumped integrated absorber 3.4 μm laser with InAs-to-InGaAsSb type-II transition

We report optically pumped lasing at λ∼3.4 μm from an integrated absorber structure in which the electrons confined in the InAs quantum wells recombine with holes in adjacent InGaAsSb layers to provide the gain. This type-II laser exhibits an estimated photon-to-photon conversion rate of ∼24% at 85 K. The self-consistent empirical pseudopotential method calculations suggest that Coulomb attraction can lead to a strong enhancement in carrier overlap, and the resulting small shift in transition energy is consistent with that observed.

Midinfrared, optically pumped, unstable resonator lasers

The authors describe high-brightness, broad area midinfrared semiconductor lasers. These devices were fabricated in the authors’ laboratory using a commercial solid-source molecular beam epitaxial system. The laser structures incorporated 14 type-II quantum wells embedded in thick waveguide/absorber regions composed of In0.2Ga0.8As0.18Sb0.82. The optically pumped devices achieved higher brightness operation as unstable resonators. Each unstable resonator was realized by polishing a diverging cylindrical mirror at one of the facets. For an unstable resonator semiconductor laser operating at ∼4.6μm, near 84K, and at a peak power of 6.7W, the device was observed to be nearly diffraction limited at 25 times threshold. In comparison, a standard Fabry-Perot laser was observed to be many times diffraction limited when operated under similar conditions.

Controlling the outcoupled power in a dual wavelength optically pumped semiconductor laser

We present a study of a dual wavelength optically pumped midinfrared semiconductor laser. In order to control the outcoupled power of each wavelength, the modal overlap between the adjacent gain regions was minimized while the pump absorbance for each gain region was balanced. The nominal power expectation, based solely on the absorbed power per gain region, was observed to be generally in good agreement with measurement. Improved power accounting can be accomplished if the waveguide loss and internal efficiency at each operational wavelength is known.

Power Sharing in Dual-Wavelength Optically Pumped Midinfrared Laser

We present a study of dual-wavelength optically pumped midinfrared semiconductor lasers, in which the effects of several design parameters are analyzed. We observe that when the short wavelength waveguide mode overlaps the long wavelength gain region, photon re-absorption occurs, favoring long wavelength emission. We demonstrate high power output from a laser emitting at two wavelength bands.

High Power Nd:YAG Spinning Disk Laser

We report on a high power Nd:YAG spinning disk laser. The 6 cm diameter disk generated 181 W CW output with 300 W of absorbed pump. The power conversion efficiency was 67 %.

Multi-parametric data fusion for enhanced object identification and discrimination

Effective fusion of multi-parametric heterogeneous data is essential for better object identification, characterization and discrimination. In this report we discuss a practical example of fusing the data provided by imaging and nonimaging electro-optic sensors. The proposed approach allows the processing, integration and interpretation of such data streams from the sensors. Practical examples of improved accuracy in discriminating similar but non-identical objects are presented.

High-peak power from optically-pumped mid-IR semiconductor lasers

We present work on the high-peak power pumping of optically pumped mid-IR semiconductor lasers. The lasers incorporated 14 type-II InAs/InGaSb/InAs quantum wells (QW). Thick quaternary absorber layers (InGaAsSb) surrounded the QWs, which allowed a large fraction of pump light to be absorbed. The devices were optically pumped with the output of a passively Q-switched Ho:YAG laser at λ = 2.09 μm. The Ho:YAG maximum output power was ~90 kW; this allows the optically pumped semiconductor lasers (OPSLs) to be pumped at several thousand times above threshold. Emission from the QW was observed near 4.1 μm. As the pump power was increased, the QW spectra were observed to broaden and eventually saturate. Under low power pumping conditions, the OPSL pulse tracked the Ho:YAG pulse, which has a 16-ns full-width half-maximum. As the pump power was increased, the OPSL pulse duration increased and the pulse eventually split into two peaks. This may be due to a large increase in the free-carrier absorbance rates in the bulk-like quaternary absorber. Emission from the quaternary was observed near 2.2 μm and its intensity, with respect to the QW intensity, increased significantly as the pump power was increased. This indicates that at the higher pump powers, large fractions of photogenerated carriers are reservoired in the thick absorber layers. The maximum OPSL single-ended peak power was 490 W. This is the highest reported peak power from a mid-IR semiconductor laser. A rate equation model describing the time evolution of the carriers in the QW, the stored carrier population in the reservoir, and the photon population gives good agreement with the data.

Beacon-defined performance of adaptive optics

Achieving a minimal size laser spot (beacon) on a remote object is a major objective of the adaptive optics-based phase conjugations methods used in laser communications and directed energy systems. Achieving this goal not only requires a high quality conjugation of the laser beam wave front relative to the object-returned beacon beam, but also fulfillment of the reciprocity condition. The latter can be defined as precise matching of the intensities and wave fonts of two contrapropagating beams in each cross section along the propagation path. This condition is central for effectively focusing a laser beam on a remote object. Violation of the conditions of reciprocal propagation occurs, for example, when the receiving aperture is of limited size compared to the size of the object-returned beacon beam. Such size disparity between the receiving aperture and beacon returned beam results in decreased power density on the focused spot and reduced intensity of the target-returned beam. When the beacon wave is formed on a rough-surface object there is an additional decrease in the efficiency of the beam focusing. The paper provides a detailed discussion of these phenomena.

High-Brightness from an Unstable Resonator Mid-IR Semiconductor Laser

We describe high-brightness, broad-area mid-IR semiconductor lasers. These devices were fabricated in our laboratory using a commercial solid-source MBE system, configured specifically for antimonide alloy deposition. The laser structures incorporated fourteen type-II quantum wells embedded in thick waveguide/absorber regions composed of In0.2Ga0.8AsySb1-y . Each type-II well is comprised of a ~24 Aring thick In0.4 Ga0.6Sb hole bearing layer, which is sandwiched in between two coupled InAs electron wells; as we vary the InAs thickness from 3 to 30 Aring we tune the laser from 2.5 mum to 9.5 mum