Since the introduction of the laser in the 1960s, laser spectroscopy has revolutionized the way scientists study atoms and molecules. The advancements in laser technology have significantly enhanced the capabilities of laser spectroscopy, making it an essential tool for researching the detailed structures and dynamics of these fundamental building blocks of matter.
Frequency comb-based laser spectroscopy is one of the main types of laser spectroscopy that has enabled extremely precise frequency measurements with an accuracy of up to 18 digits. The high precision of frequency combs has led to groundbreaking discoveries in the field of physics and has applications in optical clocks, gravity sensing, and the search for dark matter. However, the low power per comb mode and gaps between the comb modes pose challenges for detecting trace gases and measuring spectrally narrow features. Additionally, maintaining long-term coherence in comb sources requires complex stabilization systems.
Tunable CW lasers offer high photon flux, long interaction paths, and frequency agility, making them ideal for sensitive molecular spectroscopy, gas sensing, and LIDAR applications with high signal-to-noise ratios. Despite their advantages, these systems often face fluctuations in laser frequency scan speed. To address these fluctuations, various methods like interferometric approaches, single-sideband modulation, and optical frequency combs have been developed. Frequency-comb-calibrated tunable laser spectroscopy combines the accuracy of frequency comb with the tunability and high power of a CW laser, but it requires a stable reference frequency comb, which can be challenging to achieve.
Researchers at the Max Planck Institute for the Science of Light have developed a new, straightforward broadband spectroscopy method with Hz-level precision. This technique involves on-the-fly calibration of the laser frequency using a fiber cavity and a dual radio frequency (RF) modulation technique, enabling precise tracking of the laser color and providing calibration markers for measuring optical frequency distances between spectral features with ultra-high precision. This method allows for measuring minuscule deviations in the free spectral range of a fiber loop cavity over a wide frequency range with sub-10-Hz precision, an order of magnitude improvement over existing tunable laser spectroscopy methods.
The new broadband spectroscopy method offers higher optical probe power and better spectral flatness and polarization stability compared to frequency comb-based spectroscopy. It has been successfully used to characterize spectral features of integrated photonic devices and measure the molecular absorption spectrum of gases with exceptional precision. This robust and straightforward method does not require complex locking techniques, making it suitable for various out-of-lab applications such as LIDAR systems, 3D imaging, trace gas sensing, and calibration of astrophysical spectrometers. Its simplicity and robustness make it an excellent choice for use in challenging environments.
The advancements in laser spectroscopy, specifically the development of new methods like the broadband spectroscopy technique from the Max Planck Institute, have significantly expanded the capabilities of studying atoms, molecules, and other fundamental components of matter with unprecedented precision and accuracy. These advancements open up new possibilities for research and applications in a wide range of fields, making laser spectroscopy an indispensable tool for scientific exploration.
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