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EPJ Web of Conferences

Towards Direct Detection Lidar Velocimetry Measurements using Spectral Hole Burning

Robert T. Randolph, Richard B. Miles, Christopher Limbach

Published Jan 1, 2026• 0 citations
Publisher

Abstract

Weather modelling, detection of clean air turbulence, detection of wind shear, and other applications benefit from precise wind speed measurements. This work reports on progress towards a direct detection lidar velocimetry method utilizing an adaptable vapor filter. The method uses spectral hole burning, in which a pump beam excites atoms in a vapor cell moving them from the ground state to a trapping state, creating deep “holes” in the inhomogenously transmission profile. A three-level atomic model was created and experimentally validated to characterize the position and magnitude of the hole in the transmission profile, as well as the time required to reach equilibrium, under different pump frequencies and powers. Work towards using the technique for tabletop velocimetry measurements of an under-expanded jet is described.

DOI
10.1051/epjconf/202636201034

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Weather modelling, detection of clean air turbulence, detection of wind shear, and other applications benefit from precise wind speed measurements. This work reports on progress towards a direct detection lidar velocimetry method utilizing an adaptable vapor filter. The method uses spectral hole burning, in which a pump beam excites atoms in a vapor cell moving them from the ground state to a trapping state, creating deep “holes” in the inhomogenously transmission profile. A three-level atomic model was created and experimentally validated to characterize the position and magnitude of the hole in the transmission profile, as well as the time required to reach equilibrium, under different pump frequencies and powers. Work towards using the technique for tabletop velocimetry measurements of an under-expanded jet is described.
Weather modelling, detection of clean air turbulence, detection of wind shear, and other applications benefit from precise wind speed measurements. This work reports on progress towards a direct detection lidar velocimetry method utilizing an adaptable vapor filter. The method uses spectral hole burning, in which a pump beam excites atoms in a vapor cell moving them from the ground state to a trapping state, creating deep “holes” in the inhomogenously transmission profile. A three-level atomic model was created and experimentally validated to characterize the position and magnitude of the hole in the transmission profile, as well as the time required to reach equilibrium, under different pump frequencies and powers. Work towards using the technique for tabletop velocimetry measurements of an under-expanded jet is described.
Precise wind velocity measurements are of interest for a variety of applications including weather forecasting and detection of clean air turbulence and wind shear. This work investigates a concept known as spectral hole burning to create an actively tunable atomic vapor filter in order to improve the resolution of LIDAR wind velocity profiling. By adjusting the frequency and intensity of a pump beam in an alkali vapor cell, steep slopes in the transmission profile may be used to monitor shifts in frequency of a probe beam. A three-level atomic model to simulate the spectral hole is described and validated experimentally through pump-probe spectroscopy. The model then optimizes parameters including cell length, cell temperature, pump intensity and pump frequency to find the steepest transmission slope obtainable. At this location, frequency resolutions of 0.69 MHz are predicted per 1% change in transmission, corresponding to a 0.27 m/s velocity sensitivity. From this information, the feasibility and limitations of using spectral hole burning as a controllable atomic filter for LIDAR velocimetry measurements are discussed.
Accurate velocimetry measurements with fine spatial resolution are important for weather forecasting and detection of clean air turbulence and wind shear. This work experimentally demonstrates velocimetry measurements using an actively controlled atomic vapor filter, which has applications as an edge-filter-based direct detection Doppler lidar system. Here, the Doppler shift is determined by measuring the change in absorption of the signal along the edge of a transmission line in an atomic vapor medium. A counter-propagating pump beam resonant with a second ground state absorption line results in deep holes in the transmission spectrum near resonant velocity classes of the vapor. The steeper transmission slope gives an increased sensitivity to the Doppler shift of the probe beam. The location of the slope may be shifted by modifying the pump wavelength and power, essentially creating an actively controllable edge filter. The filter is used to estimate the Doppler shift of light scattered from a rotating disk with tangential speeds between 10 and 45 m/s. Improvements up to 70% in the velocity sensitivity are demonstrated when propagating the pump beam through the cell. Further improvements are anticipated with optimized cell and pump beam parameters. The filter is suggested for future lidar measurements of aerosol velocities and can be applied to other wavelengths resonant with energy level transitions in atomic vapors in the UV, visible, and IR regimes.
Methods to separate and filter Mie, Rayleigh and Raman scattering are required in many atmospheric lidar systems and other laser diagnostic applications. This work reports on progress towards a novel filtering technique to spectrally separate components of a backscattered signal through coherent light generation in an atomic vapor cell. Specifically, this work characterizes 420 nm (blue) light generation in a heated rubidium cell arising from the mixing of 776 nm and 780 nm pump beams. The work finds the optimal pump frequencies and cell temperature and detects a signal using pump beams as low as 0.7 μW. Progress towards using the technique to detect scattered light in a lidar application is described.
Methods to separate and filter Mie, Rayleigh and Raman scattering are required in many atmospheric lidar systems and other laser diagnostic applications. This work reports on progress towards a novel filtering technique to spectrally separate components of a backscattered signal through coherent light generation in an atomic vapor cell. Specifically, this work characterizes 420 nm (blue) light generation in a heated rubidium cell arising from the mixing of 776 nm and 780 nm pump beams. The work finds the optimal pump frequencies and cell temperature and detects a signal using pump beams as low as 0.7 μW. Progress towards using the technique to detect scattered light in a lidar application is described.
This poster presents the status of the development of an ultra-frequency stable laser via a spectroscopic technique known as Spectral Hole Burning (SHB). In short, we can use a pump laser to imprint, or ’burn’, transmissive spectral lines, or ’spectral holes’, in the otherwise inhomogeneously broadened absorptive spectral sites of a Eu3+ doped Y2SiO5 crystal. We can then lock a probe laser to these narrow spectral features achieving our frequency stabilized laser. Of great concern is the frequency stability of the spectral holes, such as their sensitivity to temperature changes which we characterize here. Additionally, a challenge this experiment faces is the restriction of probe laser power to avoid damaging the spectral features. This sets a relatively high level of shot noise, limiting the detection sensitivity. Here we present our solution to overcome this difficulty by using a multi-spectral- hole probing scheme to average the probing signals of several burned spectral holes.