Abstract
An efficient mid-infrared frequency comb source is of great interest to high speed, high resolution spectroscopy and metrology. Here we demonstrate a mid-IR quantum cascade laser frequency comb with a high power output and narrow beatnote linewidth at room temperature. The active region was designed with a strong-coupling between the injector and the upper lasing level for high internal quantum efficiency and a broadband gain. The group velocity dispersion was engineered for efficient, broadband mode-locking via four wave mixing. The comb device exhibits a narrow intermode beatnote linewidth of 50.5 Hz and a maximum wall-plug efficiency of 6.5% covering a spectral coverage of 110 cm−1 at λ ~ 8 μm. The efficiency is improved by a factor of 6 compared with previous demonstrations. The high power efficiency and narrow beatnote linewidth will greatly expand the applications of quantum cascade laser frequency combs including high-precision remote sensing and spectroscopy.
Highlights
An efficient mid-infrared frequency comb source is of great interest to high speed, high resolution spectroscopy and metrology
Since the frequency comb is directly generated inside the Quantum cascade laser (QCL) without any extra optical components, QCL frequency combs are monolithic and chip-based comb sources offering great promise for high-speed, high-resolution spectroscopy
The uniformity of power distribution is further improved via Gires–Tournois interferometers (GTI)-coated QCL combs, but the average power on each mode remains the same, about 0.5 mW at −6 °C19
Summary
An efficient mid-infrared frequency comb source is of great interest to high speed, high resolution spectroscopy and metrology. We demonstrate a mid-IR quantum cascade laser frequency comb with a high power output and narrow beatnote linewidth at room temperature. The high power efficiency and narrow beatnote linewidth will greatly expand the applications of quantum cascade laser frequency combs including high-precision remote sensing and spectroscopy. Optical frequency combs[1] emitting a broad spectrum of discrete, evenly spaced narrow lines with well-defined phase, have become attractive laser sources for a variety of applications They provide a unique combination of large wavelength coverage and high spectral resolution, they allow for simultaneous, precise, and rapid spectroscopy of wide wavelength regions of interest[2,3]. The uniformity of power distribution is further improved via Gires–Tournois interferometers (GTI)-coated QCL combs, but the average power on each mode remains the same, about 0.5 mW at −6 °C19
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