Development of a tunable, narrow-linewidth, cw 2066-μm Ho:YLF laser for remote sensing of atmospheric CO_2 and H_2O

TLDR

The laser was built from a 4.5‑mm TE‑cooled, codoped 5 % Tm/0.5 % Ho YLF crystal pumped by a 500‑mW, 792‑nm Ti:sapphire laser, yielding a 32‑mW, narrow‑linewidth, cw 2.066‑µm output. Using intracavity etalons to narrow the linewidth to ~0.025 cm⁻¹, the tunable Ho:YLF laser enabled laboratory and atmospheric CO₂/H₂O spectroscopy with 5–10 % concentration accuracy, though measurement uncertainty arose from laser mode asymmetry, atmospheric turbulence, beam motion, and background spectral shifts.

Abstract

A smoothly tunable, narrow-linewidth, cw, 32-mW, 2.066-μm Ho:YLF laser was constructed and used for the first time in preliminary spectroscopic measurements of atmospheric CO2 and H2O. The laser was constructed with a 4.5-mm-long, TE-cooled, codoped 5% Tm and 0.5% Ho yttrium lithium fluoride crystal (cut at Brewster's angle) pumped by an Ar+-pumped 500-mW Ti:sapphire laser operating at 792 nm. Intracavity etalons were used to reduce the laser linewidth to approximately 0.025 cm-1 (0.75 GHz), and the laser wavelength was continuously and smoothly tunable over approximately 6 cm-1 (180 GHz). The Ho:YLF laser was used to perform spectroscopic measurements on molecular CO2 in a laboratory absorption cell and to measure the concentration of CO2 and water vapor in the atmosphere with an initial accuracy of approximately 5–10%. The measurement uncertainty was found to be due to several noise sources, including the effect of asymmetric intensity of the laser modes within the laser linewidth, fluctuations caused by atmospheric turbulence and laser beam/target movement, and background spectral shifts.