arXiv subjects

Qizhong Liang

Publications and source records attributed to Qizhong Liang.

4 recordsLinked to original sources

arXiv2024

Modulated Ringdown Comb Interferometry for next-generation high complexity trace gas sensing

Gas samples relevant to health and environment typically contain a plethora of molecular species that span a huge concentration dynamic range. High-concentration molecules impose a strong absorption background that hinders robust identification of low-concentration species. While mid-infrared frequency comb spectroscopy with high-finesse cavity enhancement has realized many of the most sensitive multi-species trace gas detection to date, its robust performance requires gas samples to contain only weak absorption features to avoid dispersing cavity resonances from the comb line frequencies. Here we introduce a new technique that is free from this restriction, thus enabling the development of next-generation multi-species trace gas sensing with broad applicability to complex and dynamic molecular compositions. The principle of Modulated Ringdown Comb Interferometry is to resolve ringdown dynamics carried by massively parallel comb lines transmitted through a length-modulated cavity. This method leverages both periodicity of the field dynamics and Doppler frequency shifts introduced from a Michelson interferometer. Scalable enhancement of both spectral coverage and cavity finesse is enabled with dispersion immune and high-efficiency data collection. Built upon this platform, we realize in the mid-infrared a product of finesse and spectral coverage that is orders of magnitude better than all prior experiments. We demonstrate the power of this technique by measuring highly dispersive exhaled human breath samples over a vastly expanded spectral coverage of 1,010 cm-1 and with cavity finesse of 23,000. This allows for the first time simultaneous quantification of 20 distinct molecular species at > 1 part-per-trillion sensitivity with their concentrations varying by 7 orders of magnitude.

physics.optics↗

arXiv2023

Breath analysis by ultra-sensitive broadband laser spectroscopy detects SARS-CoV-2 infection

Rapid testing is essential to fighting pandemics such as COVID-19, the disease caused by the SARS-CoV-2 virus. Exhaled human breath contains multiple volatile molecules providing powerful potential for non-invasive diagnosis of diverse medical conditions. We investigated breath detection of SARS-CoV-2 infection using cavity-enhanced direct frequency comb spectroscopy (CE-DFCS), a state-of-the-art laser spectroscopic technique capable of a real-time massive collection of broadband molecular absorption features at ro-vibrational quantum state resolution and at parts-per-trillion volume detection sensitivity. Using a total of 170 individual breath samples (83 positive and 87 negative with SARS-CoV-2 based on Reverse Transcription Polymerase Chain Reaction tests), we report excellent discrimination capability for SARS-CoV-2 infection with an area under the Receiver-Operating-Characteristics curve of 0.849(4). Our results support the development of CE-DFCS as an alternative, rapid, non-invasive test for COVID-19 and highlight its remarkable potential for optical diagnoses of diverse biological conditions and disease states.

physics.med-ph↗

arXiv2022

Collision-induced C_60 rovibrational relaxation probed by state-resolved nonlinear spectroscopy

Quantum state-resolved spectroscopy was recently achieved for C60 molecules when cooled by buffer gas collisions and probed with a midinfrared frequency comb. This rovibrational quantum state resolution for the largest molecule on record is facilitated by the remarkable symmetry and rigidity of C60, which also present new opportunities and challenges to explore energy transfer between quantum states in this many-atom system. Here we combine state-specific optical pumping, buffer gas collisions, and ultrasensitive intracavity nonlinear spectroscopy to initiate and probe the rotation-vibration energy transfer and relaxation. This approach provides the first detailed characterization of C60 collisional energy transfer for a variety of collision partners, and determines the rotational and vibrational inelastic collision cross sections. These results compare well with our theoretical modeling of the collisions, and establish a route towards quantum state control of a new class of unprecedentedly large molecules.

physics.atom-ph↗

arXiv2021

Ultra-sensitive multi-species spectroscopic breath analysis for real-time health monitoring and diagnostics

Breath analysis enables rapid, non-invasive diagnostics, as well as long-term monitoring, of human health through the identification and quantification of exhaled biomarkers. Here, for the first time, we demonstrate the remarkable capabilities of mid-infrared (mid-IR) cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) applied to breath analysis. We simultaneously detect and monitor as a function of time four breath biomarkers - CH$_3$OH, CH$_4$, H$_2$O and HDO - as well as illustrating the feasibility of detecting at least six more (H$_2$CO, C$_2$H$_6$, OCS, C$_2$H$_4$, CS$_2$ and NH$_3$) without modifications to the experimental apparatus. We achieve ultra-high detection sensitivity at the parts-per-trillion level. This is made possible by the combination of the broadband spectral coverage of a frequency comb, the high spectral resolution afforded by the individual comb teeth, and the sensitivity enhancement resulting from a high-finesse cavity. Exploiting recent advances in frequency comb, optical coating, and photodetector technologies, we can access a large variety of biomarkers with strong carbon-hydrogen bond spectral signatures in the mid-IR.

physics.chem-ph↗