ABSTRACT
We demonstrate active hyperspectral imaging using a quantum-cascade laser (QCL) array as the illumination source and a digital-pixel focal-plane-array (DFPA) camera as the receiver. The multi-wavelength QCL array used in this work comprises 15 individually addressable QCLs in which the beams from all lasers are spatially overlapped using wavelength beam combining (WBC). The DFPA camera was configured to integrate the laser light reflected from the sample and to perform on-chip subtraction of the passive thermal background. A 27-frame hyperspectral image was acquired of a liquid contaminant on a diffuse gold surface at a range of 5 meters. The measured spectral reflectance closely matches the calculated reflectance. Furthermore, the high-speed capabilities of the system were demonstrated by capturing differential reflectance images of sand and KClO3 particles that were moving at speeds of up to 10 m/s.
ABSTRACT
We report on multi-wavelength arrays of master-oscillator power-amplifier quantum cascade lasers operating at wavelengths between 9.2 and 9.8 µm. All elements of the high-performance array feature longitudinal (spectral) as well as transverse single-mode emission at peak powers between 2.7 and 10 W at room temperature. The performance of two arrays that are based on different seed-section designs is thoroughly studied and compared. High output power and excellent beam quality render the arrays highly suitable for stand-off spectroscopy applications.
Subject(s)
Amplifiers, Electronic , Lasers , Oscillometry/instrumentation , Equipment Design , Equipment Failure AnalysisABSTRACT
We report quantum cascade laser (QCL) master-oscillator power-amplifiers (MOPAs) at 300 K reaching output power of 1.5 W for tapered devices and 0.9 W for untapered devices. The devices display single-longitudinal-mode emission at λ = 7.26 µm and single-transverse-mode emission at TM(00). The maximum amplification factor is 12 dB for the tapered devices.
ABSTRACT
A multiwavelength array of distributed feedback (DFB) quantum cascade lasers (QCLs) that spans λ = 8.28 to 9.62 µm is wavelength beam combined (WBC) using both single-grating and dual-grating designs. WBC with a single grating results in a pointing error of 3-times the beam divergence for a single laser and arises from the nonlinear dispersion of the grating. By adding a second grating to compensate for the nonlinear dispersion, the pointing error is reduced to only 13% of the beam divergence for a single laser. A transceiver based on the dual-grating-WBC QCL was used to measure the transmittance of a polymer sheet placed between itself and a retroreflector over a round-trip distance of 70 meters.
Subject(s)
Artifacts , Computer-Aided Design , Lasers , Models, Theoretical , Photometry/instrumentation , Refractometry/instrumentation , Computer Simulation , Equipment Design , Equipment Failure Analysis , Light , Scattering, RadiationABSTRACT
Wavelength beam combining was used to co-propagate beams from 28 elements in an array of distributed-feedback quantum cascade lasers (DFB-QCLs). The beam-quality product of the array, defined as the product of near-field spot size and far-field divergence for the entire array, was improved by a factor of 21 by using wavelength beam combining. To demonstrate the applicability of wavelength beam combined DFB-QCL arrays for remote sensing, we obtained the absorption spectrum of isopropanol at a distance of 6 m from the laser array.
ABSTRACT
Two-dimensional angular optical scattering (TAOS) patterns of droplets composed of a mixture of H2O and D2O are detected in the mid infrared. First, a lens is used in the Abbé sine condition to collect a small solid angle of light, where the scattering pattern matches well numerical simulations based on Mie theory. Next, TAOS patterns from droplets spanning a large (approximately 27pi sr) solid angle are captured simultaneously at two wavelengths. The effects of absorption are evident in the patterns and are discernible without the need for curve matching by Mie theory.
