Frequency stability characterization of a quantum cascade laser frequency comb

Abstract

Optical frequency combs generated by quantum cascade lasers have recently been demonstrated in the mid and far infrared, but a detailed analysis of the possibility of a fine control of the emission to use them for high-resolution spectroscopy and metrology applications is still missing. In this manuscript the attempt of frequency stabilizing a mid-infrared quantum cascade laser comb (QCL-comb) against a metrological mid-infrared intracavity-difference-frequency-generated comb through a single phase-locking chain acting on the driving current is presented. Following a brief derivation, simple relations between the QCL-comb frequency parameters and optical quantities such as the refractive index have been found and used to observe how the locking affects the physics of the system. The conclusion is that the current locking essentially acts on the effective refractive index to reduce the offset fluctuations (common noise), but does not sensitively affect the group refractive index and the mode spacing. Nonetheless, the overall single QCL-comb tooth linewidth is reduced from 500 kHz down to values ranging from 1 to 23 kHz on a 40 ms time scale.

Laser spectroscopy for breath analysis: towards clinical implementation

“…This device has ready applicability for using breath acetone analysis to provide an alternative to blood testing for ketone measurement, to assist with the management of type 1 diabetes [153]. The fast development of the QCL combs, e.g., achieving higher power levels [154] and improvement in their frequency stability [155,156] promises substantial improvements in the operation of QCL-based dual-comb spectrometers in the near future, making them more interesting for biomedical applications.…”

High efficiency quantum cascade laser frequency comb

“…This is because both the repetition frequency f rep and the carrier-envelope offset frequency f ceo are related to the group index n g , and are sensitive to the current induced temperature change. To realize a “ruggedized” broadband frequency comb for real-world applications, the comb spectrum and power will be stabilized by phase-locking to a reference stabilized frequency comb source23 or adjusting the operating temperature accordingly to stabilize the frequency comb by using the feedback of beatnote frequency change.…”

Frequency stability of a dual wavelength quantum cascade laser

“…A linewidth narrowing by a factor 5.4 was thus achieved for the indirectly-locked mode, which is similar to the factor 6.2 obtained for the directly-locked mode (at 1-ms observation time). The behaviour of a dualmode QCL under current locking can be compared to the one of QCL combs, where it has been demonstrated, that action on the effective refractive index reduces the common noise of laser modes [27]. However, it should be noted, that, whereas in QCL combs all modes are linked together via the four-wave mixing, there is no such process in dual-mode lasers, therefore the correlation mechanism of their modes is different and needs a separate study that is out of the scope of this work.…”