Abstract
We report the design and characteristics of a simple and compact mode-locked Er-doped fiber laser and its application to broadband cavity-enhanced spectroscopy. The graphene mode-locked polarization maintaining oscillator consumes less than 5 W of power. It is thermally stabilized, enclosed in a 3D printed box, and equipped with three actuators that control the repetition rate: fast and slow fiber stretchers, and metal-coated fiber section. This allows wide tuning of the repetition rate and its stabilization to an external reference source. The applicability of the laser to molecular spectroscopy is demonstrated by detecting CO2 in air using continuous-filtering Vernier spectroscopy with absorption sensitivity of 5.5 × 10−8 cm−1 in 50 ms.
Highlights
Optical frequency combs emerged as powerful tools for molecular spectroscopy due to their high spectral brightness, broad spectral coverage, and compatibility with enhancement cavities [1]
A fully self-referenced frequency comb based on an Er-doped fiber laser was reported, with electrical power consumption of only 5 W [7]
The technique that has so far been most successfully used for broadband open path sensing is near and mid-infrared dual-comb spectroscopy (DCS) using both laboratory-based and field deployed platforms based on Er-doped fiber combs and difference frequency generation sources [10,11,12,13]
Summary
Optical frequency combs emerged as powerful tools for molecular spectroscopy due to their high spectral brightness, broad spectral coverage, and compatibility with enhancement cavities [1]. The technique that has so far been most successfully used for broadband open path sensing is near and mid-infrared dual-comb spectroscopy (DCS) using both laboratory-based and field deployed platforms based on Er-doped fiber combs and difference frequency generation sources [10,11,12,13]. A field-deployed platform for broadband in situ sensing has only been demonstrated in the UV range using a system based on a frequency-doubled femtosecond Ti:Sapphire laser, an enhancement cavity, and low-resolution compact spectrograph [17, 18]. We report a simple and compact 125 MHz modelocked Er-doped fiber laser with wide frep tuning capabilities and its application to broadband cavity-enhanced continuous-filtering Vernier spectroscopy. The applicability of the laser to broadband and sensitive spectroscopy was verified by detection of CO2 in laboratory air using a CF-VS spectrometer, with absorption sensitivity similar to that obtained with a commercial Er-doped fiber frequency comb
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