Abstract
The recent demonstration of external cavity quantum cascade lasers with optical feedback, controlled by an acousto-optic modulator, paves the way to ruggedized infrared laser systems with the capability of tuning the emission wavelength on a microsecond scale. Such systems are of great importance for various critical applications requiring ultra-rapid wavelength tuning, including combustion and explosion diagnostics and standoff detection. In this paper, recent research results on these devices are summarized and the advantages of the new configuration are analyzed in the context of practical applications.
Highlights
The development of quantum cascade laser (QCL) configurations with a broad spectral coverage, and compatible with ultra-fast spectroscopic measurements, is an area of active research, primarily driven by QCL applications in infrared standoff detection and combustion/explosion diagnostics.One of the most promising developments in the field has been the demonstration of QCL-based frequency combs [1] and ultra-fast dual-comb QCL sensors [2]
In the case of QCL DFB arrays, an alternative approach to fast wavelength tuning with a broad spectral coverage, the yield quickly drops with an increase in number of elements
The response time has two components: (1) propagation time of the acoustic wave from the piezoelectric transducer to the edge of the optical beam going through the an electrically controlled optic modulator (AOM); and (2) the propagation time for the acoustic wave across the optical beam
Summary
The development of quantum cascade laser (QCL) configurations with a broad spectral coverage, and compatible with ultra-fast spectroscopic measurements, is an area of active research, primarily driven by QCL applications in infrared standoff detection and combustion/explosion diagnostics. The widest wavelength tunability, covering a substantial fraction of the QCL gain bandwidth, has been demonstrated for lasers in the external cavity configuration with a mechanical grating controlling a wavelength-dependent feedback [3]. This configuration has been in wide use with all types of gain media including solids, liquids and gases for over forty years. Suffer from two important disadvantages arising from the need to physically rotate a macroscopic spectral dispersive component—the diffraction grating These disadvantages are (1) slow wavelength tuning and (2) sensitivity to mechanical vibrations and shocks. Use of electronic key tuning to fastand tuning and of absence ofparts moving parts can assure of electronic tuningtuning could could be the be keythe to fast absence moving can assure immunity immunity to and vibrations to vibrations shocks.and shocks
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