A Novel Airborne Molecular Contaminants Sensor Based on Sagnac Microfiber Structure

Abstract

The impact of airborne molecular contaminants (AMCs) on the lifetime of fused silica UV optics in high power lasers (HPLs) is a critical issue. In this work, we demonstrated the on-line monitoring method of AMCs concentration based on the Sagnac microfiber structure. In the experiment, a Sagnac microfiber loop with mesoporous silica coating was fabricated by the microheater brushing technique and dip coating. The physical absorption of AMCs in the mesoporous coating results in modification of the surrounding refractive index (RI). By monitoring the spectral shift in the wavelength domain, the proposed structure can operate as an AMCs concentration sensor. The sensitivity of the AMCs sensor can achieve 0.11 nm (mg/m3). By evaluating the gas discharge characteristic of four different low volatilization greases in a coarse vacuum environment, we demonstrated the feasibility of the proposed sensors. The use of these sensors was shown to be very promising for meeting the requirements of detecting trace amounts of contaminants.

Characterization of an airborne organic contaminant sensor based on microfibers with sol–gel film

“…The refractive index of sol-gel films is mainly determined by the porosity of the films. Therefore, the refractive index of sol-gel films after adsorbing contaminants is studied using the mixed-medium correlation model [27][28][29][30]. Sol-gel films are regarded as a mixed medium of silicon dioxide and air.…”

“…In the mixed medium, the dielectric constant of the film satisfies the following relationship, as shown in Eq. 1 [27,28]:…”

“…The sensing units were placed into certain concentrations of airborne organic contaminants, and the experimental data were collected every second by the software to monitor the additional losses and changes caused by increasing concentrations of airborne organic contaminants. Different concentrations of airborne organic contaminants were obtained by heating dibutyl phthalate (DBP) [27]. After the sensing process, the sensing units were placed into the alcohol solution to clean organic contaminants adhered to the sol-gel film of MNOFs, and the measurement results were saved, as shown in Figure 7.…”

“…Based on the strong confinement ability and evanescent field characteristics of micro-nano optical fibers (MNOFs) [22,23], a new method of molecular organic contaminant sensor using a micronano optical fiber with surface microstructures was proposed [24]. We have developed many kinds of microstructures to improve the sensing sensitivity of MNOFs and to realize the monitoring of airborne organic contaminations in a vacuum environment [25][26][27]. However, although the amount of molecular organic contaminants on the surface of optics within the sol-gel film is closely related to the amount of airborne organic contaminations in the same environment, there are also significant differences.…”

Micro-/Nano-Fiber Sensors and Optical Integration Devices

“…Zhou et al used the Sagnac microfiber loop to measure the concentration of airborne molecular contaminants (AMCs) in the air environment, which becomes a serious threat to the service life of UV high-energy lasers [ 11 ]. The mesoporous silica was elaborated on the surface of the Sagnac ring by microheater brushing method and dip coating technique.…”