# QCL-based frequency metrology from the mid-infrared to the THz range: a review

## TL;DR

This review discusses the advancements in quantum cascade lasers (QCLs) for frequency metrology across mid-infrared to THz ranges, highlighting recent progress, challenges, and future prospects in achieving ultra-narrow linewidths and multifrequency operation.

## Contribution

It provides a comprehensive overview of recent developments in QCL technology, spectral control, and their applications in high-precision metrology and spectroscopy.

## Key findings

- Demonstration of multifrequency QCLs
- Achievement of ultra-narrow linewidths for metrology
- Progress in microresonators and frequency standards

## Abstract

Quantum cascade lasers (QCLs) are becoming a key tool for plenty of applications, from the mid-infrared (mid-IR) to the THz range. Progress in related areas, such as the development of ultra-low-loss crystalline microresonators, optical frequency standards, and optical fiber networks for time and frequency dissemination, is paving the way for unprecedented applications in many fields. For most demanding applications, a thorough control of QCLs emission must be achieved. In the last few years, QCLs unique spectral features have been unveiled, while multifrequency QCLs have been demonstrated. Ultra-narrow frequency linewidths are necessary for metrological applications, ranging from cold molecules interaction and ultra-high sensitivity spectroscopy to infrared-THz metrology. A review of the present status of research in this field is presented, with a view of perspectives and future applications.

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Source: https://tomesphere.com/paper/1904.13124