Calibration-free infrared absorption spectroscopy using cantilever-enhanced photoacoustic detection of the optical power

IF 7.1 1区医学 Q1 ENGINEERING, BIOMEDICAL Photoacoustics Pub Date : 2024-10-09 DOI:10.1016/j.pacs.2024.100655

Jussi Rossi , Markku Vainio

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Abstract

We report on sensitive tunable laser absorption spectroscopy using a multipass gas cell and a solid-state photoacoustic optical power detector. Unlike photoacoustic spectroscopy (PAS), this method readily allows a low gas pressure for high spectral selectivity and a free gas flow for continuous measurements. Our photoacoustic optical power detector has a large linear dynamic range and can be used at almost any optical wavelength, including the middle infrared and THz regions that are challenging to cover with traditional optical detectors. Furthermore, our approach allows for compensation of laser power drifts with a single detector. As a proof of concept, we have measured very weak CO₂ absorption lines at 9.2 µm wavelength and achieved a normalized noise equivalent absorption (NNEA) of 2.35·10⁻⁹ Wcm⁻¹Hz^−1/2 with a low-power quantum cascade laser. The absolute value of the gas absorption coefficient is obtained directly from the Beer-Lambert law, making the technique calibration-free.

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利用悬臂增强型光声探测光功率的免校准红外吸收光谱法

我们报告了使用多通道气体池和固态光声光学功率检测器进行灵敏可调激光吸收光谱分析的情况。与光声光谱法（PAS）不同的是，这种方法可以利用低气体压力实现高光谱选择性，并利用自由气体流实现连续测量。我们的光声光学功率检测器具有较大的线性动态范围，可用于几乎所有光学波长，包括传统光学检测器难以覆盖的中红外和太赫兹区域。此外，我们的方法还允许使用单个探测器对激光功率漂移进行补偿。作为概念验证，我们测量了波长为 9.2 µm 的极弱二氧化碳吸收线，并利用低功率量子级联激光器实现了 2.35-10-9 Wcm-1Hz-1/2 的归一化噪声等效吸收（NNEA）。气体吸收系数的绝对值可直接从比尔-朗伯定律中获得，因此该技术无需校准。

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来源期刊

Photoacoustics Physics and Astronomy-Atomic and Molecular Physics, and Optics

CiteScore

11.40

自引率

16.50%

发文量

审稿时长

53 days

期刊介绍： The open access Photoacoustics journal (PACS) aims to publish original research and review contributions in the field of photoacoustics-optoacoustics-thermoacoustics. This field utilizes acoustical and ultrasonic phenomena excited by electromagnetic radiation for the detection, visualization, and characterization of various materials and biological tissues, including living organisms. Recent advancements in laser technologies, ultrasound detection approaches, inverse theory, and fast reconstruction algorithms have greatly supported the rapid progress in this field. The unique contrast provided by molecular absorption in photoacoustic-optoacoustic-thermoacoustic methods has allowed for addressing unmet biological and medical needs such as pre-clinical research, clinical imaging of vasculature, tissue and disease physiology, drug efficacy, surgery guidance, and therapy monitoring. Applications of this field encompass a wide range of medical imaging and sensing applications, including cancer, vascular diseases, brain neurophysiology, ophthalmology, and diabetes. Moreover, photoacoustics-optoacoustics-thermoacoustics is a multidisciplinary field, with contributions from chemistry and nanotechnology, where novel materials such as biodegradable nanoparticles, organic dyes, targeted agents, theranostic probes, and genetically expressed markers are being actively developed. These advanced materials have significantly improved the signal-to-noise ratio and tissue contrast in photoacoustic methods.