Abstract
We present a method to produce a fast frequency swept laser emission from a monolithic mid-infrared laser. A commercially available Fabry–Pérot cavity quantum cascade laser (QCL) operating at a wavelength of 8.15 μm was electrically driven by a current pulse with a 10 μs duration and a slow front rising time of ∼2 μs. Due to the switching of the lasing emission from the vertical to the diagonal transition in the QCL and a strong quantum-confined Stark effect energy shift of the diagonal transition, the frequency of the emitted light was blue-shifting as the injection current continues to raise above the threshold. The temporal evolution of the laser spectrum was measured by a high-resolution step-scan Fourier transform infrared spectrometer. The blue-chirped emission was strongly influenced by the heatsink temperature due to the high thermal sensitivity of the threshold current and slope efficiency. By optimizing carefully the QCL operating temperature and the amplitude of the current pulse, we demonstrate a high-speed self-sweeping laser emission under room temperature operation conditions, reaching the spectral tuning range of ∼25 cm−1 within 1.8 μs.
Highlights
Techniques can provide a wide wavelength range with high detection sensitivity
By optimizing carefully the quantum cascade laser (QCL) operating temperature and the amplitude of the current pulse, we demonstrate a high-speed self-sweeping laser emission under room temperature operation conditions, reaching the spectral tuning range of $25 cmÀ1 within 1.8 ls
Instead of engineering a specific QCL structure operating on the diagonal transition, which may only provide a broadband emission, or QCL incorporating an independently biased refractive index modulation layer, which enabled an electrically controlled tuning over 0.15 cmÀ1,16 or other alternative approaches for rapid electrical tuning of QCLs and ICLs that can be found in a review,[17] we use the mechanism of lasing wavelength switching and locking from the main broadband vertical transition in the active region QWs to the narrowband diagonal transition from the injector to the low laser level.[18]
Summary
Techniques can provide a wide wavelength range with high detection sensitivity. due to operational complexity and high cost, these approaches are practically limited to academic research applications.
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