ABSTRACT
A near-infrared broadband (1500-1640â nm) laser heterodyne radiometer (LHR) with a tunable external-cavity diode laser as the local oscillator is developed and the relative transmittance, which represents the absolute relationship between the measured spectral signals and the atmospheric transmittance, is derived. High-resolution (0.0087â cm-1) LHR spectra in the spectral region of 6248.5-6256â cm-1 were recorded for the observation of atmospheric CO2. Combined with the relative transmittance, the preprocessed measured LHR spectra, the optimal estimation method, and the Python scripts for computational atmospheric spectroscopy, the column-averaged dry-air mixing ratio of CO2 of 409.09 ± 8 ppmv in Dunkirk, France on February 23, 2019, was retrieved, which is consistent with GOSAT and TCCON data. The near-infrared external-cavity LHR demonstrated in the present work has a high potential for use in developing a robust, broadband, unattended, and all-fiber LHR for spacecraft and ground-based atmospheric sensing that offers more channel selection for inversion.
ABSTRACT
In this work, we demonstrate and evaluate a new design of micro-structured core erbium-doped few-mode fiber to be used as optical amplifier in the context of mode-division multiplexing. This concept is proposed so as to better control the distribution of the Er3+ ions in the core area, thus permitting to adjust the overall differential modal gains between the different signal modes. The design presented here consists of 19 erbium-doped inclusions embedded in a pedestal geometry guiding 10 modes in the C-band. It has been optimized numerically so as to reach the equalized amplification of all the signal modes. The fiber has been realized and combined with custom-made dual-wavelength mode multiplexers based on multi-plane light conversion to shape the signal and pump beams. Amplification properties have finally been evaluated experimentally.
ABSTRACT
The incorporation of Ce3+ ions in silicate glasses is a crucial issue for luminescence-based sensing applications. In this article, we report on silica glass preforms doped with cerium ions fabricated by modified chemical vapor deposition (MCVD) under different atmospheres in order to favor the Ce3+ oxidation state. Structural analysis and photophysical investigations are performed on the obtained glass rods. The preform fabricated under reducing atmosphere presents the highest photoluminescence (PL) quantum yield (QY). This preform drawn into a 125 µm-optical fiber, with a Ce-doped core diameter of about 40 µm, is characterized to confirm the presence of Ce3+ ions inside this optical fiber core. The fiber is then tested in an all-fibered X-ray dosimeter configuration. We demonstrate that this fiber allows the remote monitoring of the X-ray dose rate (flux) through a radioluminescence (RL) signal generated around 460 nm. The response dependence of RL versus dose rate exhibits a linear behavior over five decades, at least from 330 µGy(SiO2)/s up to 22.6 Gy(SiO2)/s. These results attest the potentialities of the MCVD-made Ce-doped material, obtained under reducing atmosphere, for real-time remote ionizing radiation dosimetry.
