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A Four Wave Mixing Approach Towards Generating Coherent 420 nm Light in Heated Rubidium Vapor

Robert T. Randolph, Eric Finberg, Kevin A. Brown, Richard B. Miles

Published Jul 27, 2024• 0 citations
Publisher

Abstract

This work introduces an approach to generate coherent 420 nm (blue) light utilizing narrowband, CW pump beams at 795 nm, 532 nm and 1320 nm in a rubidium vapor cell. The frequencies giving the strongest signal intensity are found. The method is compared to other transition pathways that generate 420 nm light in rubidium vapor, namely using the 776 nm and 780 nm absorption lines. The approach discussed in this work has the potential to be used in a diagnostic measurement capability as a means to spectrally filter a component of a scattered signal.

DOI
10.2514/6.2024-3722

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This work introduces an approach to generate coherent 420 nm (blue) light utilizing narrowband, CW pump beams at 795 nm, 532 nm and 1320 nm in a rubidium vapor cell. The frequencies giving the strongest signal intensity are found. The method is compared to other transition pathways that generate 420 nm light in rubidium vapor, namely using the 776 nm and 780 nm absorption lines. The approach discussed in this work has the potential to be used in a diagnostic measurement capability as a means to spectrally filter a component of a scattered signal.
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 work experimentally demonstrates the conversion of coherent and incoherent green 532 nm light to collimated blue 420 nm light through resonant four-wave mixing in rubidium vapor. The 532 nm light co-propagates with 795 nm and 1320 nm CW pump beams, simultaneously taking advantage of resonances between the 5 P, 10 S, 6 P and 5 S ground states of rubidium. Using a coherent green beam, the intensity of the collimated 420 nm signal is characterized under varying polarizations, cell temperatures, frequency detunings and pump intensities. A 2 d image is up-converted from green to blue light to extend the technique to spatially incoherent light. This excitation pathway has the potential to be used as a narrow linewidth ( < 1 GHz), tunable bandpass filter for lidar or other remote sensing applications. • Narrow linewidth of 532 nm signal up-converted to blue light using four wave mixing. • Demonstration of image up-conversion using hot Rb vapor. • A third applied IR pump beam increases conversion efficiency.
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.
Pulsed collimated blue light at 420.3 nm is generated in hot Rb vapor by upconverting the 778.10 nm pumping beam through four wave mixing process. The energy conversion efficiency exceeds 1% when a 45 cm-long, 170°C heated Rb cell is used. The influence of cell temperature, wavelength, and energy of a pumping laser are fully examined. The efficiency of the photon conversion is found to be more sensitive to the blue detuning of the pump light and less sensitive to the red detuning of the pump light. This phenomenon can be explained by stimulated hyper-Raman scattering involved in the four-wave mixing process.
Pulsed collimated blue light at 420.3 nm is generated in hot Rb vapor by upconverting the 778.10 nm pumping beam through four wave mixing process. The energy conversion efficiency exceeds 1% when a 45 cm-long, 170 degrees C heated Rb cell is used. The influence of cell temperature, wavelength, and energy of a pumping laser are fully examined. The efficiency of the photon conversion is found to be more sensitive to the blue detuning of the pump light and less sensitive to the red detuning of the pump light. This phenomenon can be explained by stimulated hyper-Raman scattering involved in the four-wave mixing process.
We have generated a stable and continuously tunable single frequency (420 nm) coherent blue light (CBL) by the cavity-enhanced four-wave mixing process in Rb vapor. With the bow-tie-type ring cavity, the output power was 3.3 mW, two orders of magnitude higher than that of the CBL generated by the single-pass four-wave mixing process. The measured power stabilities of the 420 nm CBL operated at 2.5 mW and 1.5 mW for 1000 s were 2.89% and 1.88%, respectively. Under the scanning pump laser frequency, the continuously tunable range of the generated CBL reached 1.68 GHz without mode hopping. The measured beam qualities of the generated laser were M x 2 = 1.117 and M y 2 = 1.179 . The excellent performance of the 420 nm CBL was characterized by velocity transfer spectroscopy with 780 nm probe laser. This high quality short wavelength coherent light is potentially applicable to photon-atom interactions in quantum optics and fundamental research fields.