We will present our recent work using noble and Raman-active gas-filled anti-resonant hollow-core fiber (ARHCF) technology. First, we will present the generation of supercontinuum spanning from 200 nm to 4000 nm based on nonlinear effects of soliton self-compression and phase-matched deep‑ultraviolet (DUV) dispersive wave (DW) emission in Argon (Ar)-filled ARHCFs pumped at 2.46 μm wavelength with 100 fs pulses and ~8μJ pulse energy. Then we will discuss our recent work on stimulated Raman scattering (SRS) effect in a hydrogen (H2)-filled ARHCF, to achieve near- and MIR Raman lasers. By employing the single-stage vibrational SRS effect, a 4.22 μm Raman laser line is directly converted from a linearly polarized 1.53 μm pump laser. A quantum efficiency as high as 74% was achieved, to yield 17.6 µJ pulse energy. The designed 4.22 μm wavelength is well overlapped with the strongest CO2 absorption, therefore constituting a promising way for CO2 detection. In addition, we report a multi-wavelength Raman laser based on the cascaded rotational SRS effect. Four Raman lines at 1683 nm, 1868 nm, 2100 nm, and 2400 nm are generated, with pulse energies as high as 18.25 µJ, 14.4 µJ, 14.1 µJ, and 8.2 µJ, respectively. The energy of these Raman lines can be controlled by tuning the H2 pressure from 1 bar to 20 bar.
Silica anti-resonant hollow-core fiber (ARHCF) is a promising platform for optofluidic applications because it can act as fluid-cell, permitting intense fluid-light interaction over extended length with low optical loss from ultra-violet to midinfrared region. For this kind of applications, an all-fiberized and compact structure is necessary. However, a prerequisite for this purpose is that micro-channels must be created on the side of the fiber, to provide access for the diffusion of fluids (i.e. liquid or gas) into the core. Several attempts based on femtosecond laser micro-machining technology have been made to create micro-channels through the silica cladding, but significant loss could be induced due to the damage of the cladding capillaries of ARHCF. Here, we report a high-precision and repeatable micro-machining technique using focused ion beam (FIB) milling on a nodeless ARHCF. Ga+ ion beam is employed to bombard a 43 μm thick outer cladding of ARHCF for 30 minutes, to create a 50 μm deep fluidic channel. The micro-channel in the silica cladding is precisely drilled at the middle position of two adjacent capillaries with a 2.8 μm gap, providing direct access for liquid/gas to diffuse into the hollow-core region, while avoiding the damage of the capillaries. Corroborating results from simulation of such a structure are presented to demonstrate that no additional loss is induced by the milled structure.
We demonstrate a high repetition rate (3 MHz) Mid-IR supercontinuum (SC) source spanning whose spectrum spanning 1000-4200 nm using a cascade of different nonlinear fibers. Multi-tone absorption spectroscopy measurements are subsequently carried out using this source and a scanning spectrometer probing various concentrations and a combination of different analytes. We further explore a novel algorithm for rearranging the absorption in the IR-region and the NIR region for three-dimensional modeling. We show this method of analyzing the data is robust, that is being able to predict newly added samples of slightly different nature without having to the recalibrate the model.
We demonstrate a robust photoacoustic medium for measuring the concentration of ammonia in an aqueous solution. We target the near-infrared (NIR) overtone absorption band (~1540 nm) of ammonia with a supercontinuum (SC) laser-based excitation system and an immersion-based acoustic transducer as the detection system. We further present how such a simple system can be used to perform effective in-situ measurements of ammonia over a range of concentrations with a sensitivity of parts per million (ppm) by volume and linearity of <96%. We demonstrate how the sensing system can be readily tailored to monitor the concentrations of other miscible gases in the aqueous solution.
Detection of ammonia based on an all-fiber configuration is reported. The system consists of a hollowcore photonic-bandgap (HC-PBG) fiber with 20μm core diameter and transmission window from 1490 to 1680 nm. Absorption bands of ammonia at ~1538 nm are targeted using a supercontinuum source with central wavelength at 1550 nm. We present the method of achieving a complete fiber system while addressing the gas entry/exit path through the HC-PBG. Analysis of the ammonia absorbance in the fiber with respect to fiber length and response time is investigated. By operating in the near infrared, we demonstrate how the proposed system addresses several challenges associated with fiber-based gas-sensing, using readily available commercial components.
In this work, we report a cost-effective supercontinuum (SC) laser-based multispectral photoacoustic spectroscopy (MSPAS) system for studying spectral characteristics of various analytes. We demonstrate an in vitro label-free monitoring of the analytes in the extended near-infrared (NIR) (1540–1840 nm) spectral range. We further demonstrate how a simple ratiometric analysis in conjunction with linear regression can be used for accurate prediction of glucose over commonly encountered physiological levels inside the human body (0–400 mg/dL). Looking forward, the proposed SC-based MSPAS system provides a framework for the development of label-free and non-invasive monitoring multiple bio-analytes accurately, with potential translation to clinical in vivo applications.
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