High‐resolution continuous‐wave coherent anti‐Stokes Raman spectroscopy in a CO₂‐filled hollow‐core photonic crystal fiber

Abstract

We demonstrated high‐resolution continuous‐wave (CW) coherent anti‐Stokes Raman spectroscopy of gaseous samples in a single ring hollow‐core photonic crystal fiber. Pump beam and Stokes beam were provided by CW single longitudinal mode lasers. These narrow linewidth lasers brought the benefit of a spectral resolution of 99 MHz. The high resolution allowed a measurement of a linewidth 0.3 GHz of the ν1 transition of CO2 in a gas mixture with partial pressure of 0.15 MPa and total pressure of 0.9 MPa. Pump beam from a tunable dye laser and Stokes beam from an external cavity diode laser were coupled into the fiber containing gaseous CO2. Fundamental mode phase matching was achieved by tuning gas pressure. The long interaction length provided by the hollow fiber yielded a 60‐dB increase in the anti‐Stoke signal. The attained signal to noise ratio of the spectrum of ν1 component of 0.6‐MPa CO2 was ~25,000 with 152‐mW pump power and 1.4‐mW Stokes power.

2 μm Raman laser based on CO2-filled hollow-core silica fiber

“…The distribution has a negative exponential distribution at a low energy of 0.125 μJ which reflects the behavior of quantum noise 30 , and, due to the depletion of the pump power and the CO2 molecules in the ground state during the SRS 31 , it evolves to a Gaussian-like shape as the pulse energy increases. These effects are consistent with the conventional gas-chamber based Raman laser as well as our recent work using a H2-filled ARHCF 22,30 .…”

“…This is because its relatively small Stokes shift coefficient of 1385 cm-1 allows the direct generation of 2 μm laser from the 1.5 μm spectral range. Moreover, the remarkably narrow Raman gain linewidth (∼ 300 MHz at 1 bar) formed by Dicke narrowing and collisional line-mixing effect is an important advantage for the development of ultra-narrow linewidth lasers 22 . Recently, a near-infrared (near-IR) frequency comb has been demonstrated based on cascaded SRS in a CO2-filled ARHCF using a 1064 nm pump laser 23 .…”

Structural Analysis of Nano Core PCF With Fused Cladding for Supercontinuum Generation in 6G Networks

“…Its value may be either positive or negative and it depends on the position of wavelength with respect to the zero‐dispersion wavelength. Group‐velocity dispersion can be calculated using (R. Salgueiro, & A. Ferrando, 2018; D. Xiong, et al., 2021), $$$\text{GVD}=\frac{-2\pi c}{{\omega }^{2}}\times D(\lambda )$$$ where c is the speed of light, ω is the angular frequency, and D signifies the dispersion coefficient.…”

“…Its value may be either positive or negative and it depends on the position of wavelength with respect to the zero-dispersion wavelength. Group-velocity dispersion can be calculated using (R. Salgueiro, & A. Ferrando, 2018;D. Xiong, et al, 2021),…”

Ultraviolet to mid-infrared gas-filled anti-resonant hollow-core fiber lasers

“…Phase matching condition of the anti-Stokes emission can be satisfied with the pressured dependent fiber dispersion property and the dispersion difference of different order modes 10,11 . Contrary to SC generation, the gas-filled fiber Raman laser can achieve a narrow linewidth in few GHz level and even hundreds MHz level [11][12][13] . This is because SRS process in gas has a narrow Raman gain bandwidth 14 , and can occur at a lower laser intensity compared to other nonlinear effects such as self-phase modulation (SPM).…”