Utilizing broad gain bandwidth in quantum cascade devices

Abstract

The utilization of the broad gain bandwidth available from quantum cascade (QC) devices is considered. The performance of homogeneous and heterogeneous QC gain media is explored in an externalcavity configuration. Paradigms for realizing fixed wavelength or broad tuning performance of QC devices are considered. C 2010 Society of PhotoOptical Instrumentation Engineers. IntroductionQuantum cascade (QC) devices have become the standard gain media for lasers where high power, room-temperature operation, and continuous wavelength coverage are required in the midinfrared region of 3 to 12 μm. Recently, a tuning range of 432 cm -1 was demonstrated 1 for a QC device run in external-cavity mode. Such a broad gain bandwidth is comparable to results achieved with other semiconductor gain media: For example, 596 cm -1 of tuning has been demonstrated in near-IR diodes, 2 and 444 cm -1 in cryogenically cooled mid-IR Pb-salt diodes. 3 Utilizing the broad gain bandwidth of QC devices is an important consideration in the commercialization of QC-based lasers.Broad gain bandwidth in a gain medium offers potential advantages in the manufacture of lasers. For fixedwavelength lasers, a larger offering of wavelengths can be made without having to create multiple gain media. 4 Broad gain bandwidth can be converted into tuning range to access wider spectral ranges. 5 In both cases, however, a method is needed to restrict the laser operation to a single mode or subset of modes that are useful for the application of interest.Distributed feedback (DFB) structures have been integrated into the QC waveguide to restrict lasing to a narrow wavelength range. 6 This approach has the advantage that an extremely compact single-mode laser can be made with narrow linewidth and low frequency noise. 7 DFB lasers can be used in an intrapulse mode to perform spectroscopy of rotationally resolved gas molecules over a few inverse centimeters. 8 Ultimately, however, DFB QC lasers can only realize broader tuning by changing temperature, which limits their effective tuning range to less than 20 cm -1 , not nearly enough to utilize the full gain bandwidth available in QC devices. Moreover, from a manufacturing standpoint, different DFB QC devices have to be stocked for each fixed wavelength, negating the advantage of broad gain bandwidth in manufacturing.An alternative method, which allows for manufacturing settability of wavelength and broad tuning if required, is an external-cavity configuration. External-cavity QC lasers have been successfully employed to realize both narrow linewidth and broad tuning. 9, 10 A typical external cavity arrangement with grating feedback in Littrow configuration is shown in

Low-Energy CO Scattering at the Gas–Liquid Interface: Experimental/Theoretical Evidence for a Novel Subthermal Impulsive Scattering (STIS) Channel

“…The scattered populations are measured with a tunable laser direct absorption spectrometer operating near the quantum shot-noise limit. This spectrometer consists of (i) a narrow linewidth external cavity quantum cascade laser (ECQCL, Daylight Solutions, 21047-MHF-013-D0724), 37 (ii) frequency calibration/diagnostics, and (iii) an in vacuo multipass cell with quantum shot-noise-limited balanced detection. The ECQCL provides CW output greater than 250 mW over a frequency range of 1960−2200 cm −1 with an optical linewidth Δν < 10 MHz in the experimental detection bandwidth (10 KHz).…”

Quantum State and Doppler-Resolved Scattering of Thermal/Hyperthermal DCl at the Gas–Liquid Interface: Support for a Simple “Lever Arm” Model of the Energy-Transfer Dynamics

“…The scattered DCl number densities are measured via high-resolution Beers law absorption spectroscopy, with light generated by an external cavity quantum cascade laser − (ECQCL, Daylight Solutions MHF-QCL, 4.6 μm laser chip) directed through a 16 pass Herriott cell parallel to the wetted wheel surface. Light intensities are measured differentially before and after the Herriott cell on liquid N 2 -cooled indium antimony (InSb) photodetectors in a fast servo loop subtraction circuit to maintain high bandwidth (60 MHz) rejection of common mode laser noise.…”

Broadly tunable single-mode mid-infrared quantum cascade lasers

“…For instance, a scanning rate of 5 kHz was shown in [146] over a tuning range of 7 cm −1 by tilting the small mirror in the cavity. EC-QCLs with microelectromechanical systems (MEMS)-actuated grating are supposed to allow further device miniaturization and thus a faster scanning speed [147,148]. Among the tuning methods, one interesting approach is to generate the DFB grating by using a surface acoustic wave (SAW) [149,150].…”