Quantum cascade semiconductor infrared and far-infrared lasers: from trace gas sensing to non-linear optics

Abstract

The Quantum cascade (QC) laser is an entirely new type of semiconductor device in which the laser wavelength depends on the band-gap engineering. It can be made to operate over a much larger range than lead salt lasers, covering significant parts of both the infrared and submillimetre regions, and with higher output power. In this tutorial review we survey some of the applications of these new lasers, which range from trace gas detection for atmospheric or medical purposes to sub-Doppler and time dependent non-linear spectroscopy.

High sensitivity gas sensor based on IR spectroscopy technology and application

“…The spectroscopy scanning range was determined both by pulse current tuning and temperature tuning [11]. In order to express the spectrum scanning characteristics, 121 mTorr H 2 CO with the purity of 99.8% was introduced into the gas cell to obtain the absorption spectrum at different temperatures.…”

“…Presently, the usefulness of the laser spectroscopy approach is limited by the availability of convenient tunable sources in the spectroscopically important "fingerprint" region from 3 μm to 20 μm [1]. Recent measurements with QC-DFB (distributed feedback quantum cascade laser) lasers [2,3] have demonstrated the usefulness of these devices for highly selective real-time trace gas concentration measurements based on the absorption spectroscopy with the sensitivity of several ppb [4][5][6][7][8][9][10][11].…”

Non-symmetrical line broadening effects using short-pulse QCL spectrometers as determined with sub-nanosecond time-resolution

“…On the other hand, increased pulse widths lead to a chirp-limited resolution (70 ns, 2.79 GHz [6]). Furthermore, asymmetric line shapes of absorption features have been detected in several studies employing both the short-pulse [9,11,24] and the long-pulse mode [25]. Additionally, the latter method suffers from non-linear absorption effects [26].…”

“…While a theoretical description for the non-linear absorption phenomena based on optical Bloch equations exists [25,26,28], the origin of distorted line shapes in the short-pulse mode is not yet completely understood [9]. The problem is often empirically minimised by finding a compromise between a reasonable signal-to-noise ratio (SNR) and a narrow spectral width [12].…”

Terahertz Quantum Cascaded Laser Based on LO-phonon Scattering Using GaAs∕Al[sub x]Ga[sub 1−x]As (x = 0.15) Material System

“…Even though research in QCL is now matured, there remains many technical and scientific challenges such as obtaining continuous wave performance at high temperature over a larger wavelength range, raising power levels, improving single mode performance etc. [2][3][4][5][6][7] However, there are two major difficulties with THz QCL design: 1) the difficulty of achieving a population inversion for such a small subband separation; and 2) the challenge of obtaining a low-loss waveguide for such long wavelengths. 2 The first problem can be sorted out by the resonant phonon design for terahertz QCLs, which is gaining considerable attention.…”