Photonic bandgap fiber-enabled Raman detection of nitrogen gas

Abstract

Raman detection of nitrogen gas is very difficult without a multi-pass arrangement and high laser power. Hollow-core photonic bandgap fibers (HC-PBF) provide an excellent means of concentrating light energy in a very small volume and long interaction path between gas and laser. One particular commercial fiber with a core diameter of 4.9 microns offers losses of about 1dB/m for wavelengths between 510 and 610 nm. If 514nm laser is used for excitation, the entire Raman spectrum up to above 3000 cm -1 will be contained within the transmission band of the fiber. A standard Raman microscope launches mW level 514nm laser light into the PBF and collects backscattered Raman signal exiting the fiber. The resulting spectra of nitrogen gas in air at ambient temperature and pressure exhibit a signal enhancement of about several thousand over what is attainable with the objective in air and no fiber. The design and fabrication of a flowthrough cell to hold and align the fiber end allowed the instrument calibration for varying concentrations of nitrogen. The enhancement was also found to be a function of fiber length. Due to the high achieved Raman signal, rotational spectral of nitrogen and oxygen were observed in the PBF for the first time to the best of our knowledge.

Materials and Transducers Toward Selective Wireless Gas Sensing

“…462,463 Advances in direct spectroscopic sensing that do not require a sensing material to generate the signal, are utilizing new physical principles and engineering designs to dramatically reduce the volume of analytical gas cells, improve detection sensitivity, and reduce device size. 464,465 …”

“…For example, advances in miniaturization and ionization sources in mass spectrometry are bringing micromachined mass spectrometry (MS) devices to the point of operating at ambient atmospheric pressure without vacuum pumps . Advances in miniaturization in ion mobility spectrometry (IMS) are bringing these devices to form factors and power requirements similar to conventional packaged sensor systems. , Advances in miniaturization in gas chromatography are establishing the ability to detect and quantify 10 or more volatiles in <1 min with ppb detection limits in cell-phone-sized microgas analyzers (MGAs). , Advances in direct spectroscopic sensing that do not require a sensing material to generate the signal are utilizing new physical principles and engineering designs to dramatically reduce the volume of analytical gas cells, improve detection sensitivity, and reduce device size. , …”

“…462,463 Advances in direct spectroscopic sensing that do not require a sensing material to generate the signal are utilizing new physical principles and engineering designs to dramatically reduce the volume of analytical gas cells, improve detection sensitivity, and reduce device size. 464,465 Although we and other proponents of gas sensor technologies continue to bring the old arguments of low sensor cost and small size, these arguments, eventually, become less valid when comparing sensors with state-of-the-art, fieldable microanalytical instruments based on competing detection concepts. However, newly developed sensors continue to successfully compete with other types of microanalytical instrumentation based on certain performance parameters.…”

A Raman cell based on hollow core photonic crystal fiber for human breath analysis

“…Some provisional tests using Raman scattering of industrial gases trapped in a HC-PCF showed that the concept had great promise. [37][38][39] In this paper, we present the design and test of a simple analyzer for trace gas detection employing Raman scattering and HC-PCF. Using a near-IR optimized, 2.5 m long fiber, we found that a forward scattering measurement configuration leads to a markedly better SNR than a back scattering configuration.…”

“…The minimum detectable concentration was ∼15 ppmv determined by measuring the concentration of carbon dioxide gas in ambient air which was notably lower than previous studies that used a HC-PCF optimized for visible wavelengths. 37,39 In addition, some provisional tests on breath samples were conducted. To the best of our knowledge, this is the first reported Raman-based breath analyzer using HC-PCF.…”