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Mirrorless Lasing in Optically Pumped Rubidium Vapor

Ryan M. Richards

Published Mar 1, 2013• 0 citations
OpenAlex

Abstract

Abstract : Mirrorless lasing has been successfully demonstrated in a Rubidium heat pipe. Lasing was observed on the 6(2)P(sub 3/2)-6(2)S(sub 1/2) energy transition at 2.73 microns and on the 6(2)P(sub 1/2)-6(2)S(sub 1/2) transition at 2.79 microns. The transitions were optically pumped from 5(2)S(sub 1/2)-6(2)P(sub 3/2) at 420.2 nm and from 5(2)S(sub 1/2)-6(2)P(sub 1/2) at 421.7 nm, respectively. The 5(2)S(sub 1/2)-6(2)P(sub 3/2) transition was excited over a 36 GHz band, while the 5(2)S(sub 1/2)-6(2)P(sub 1/2) transition was excited over a 24 GHz band. Both pump transitions showed a high degree of saturation and only a small fraction (1%) of the incident pump energy was absorbed. Output energies of up to 5 nJ were obtained at 2.73 microns and of up to 5.4 nJ at 2.79 microns when pumped at pulse energies of 4 mJ. Both transitions experienced bleaching at this 4 mJ pump energy, limiting further IR output energy. Increasing rubidium concentration at bleached pump energies showed no increase in laser energy after 170 deg. C, likely due to second order processes. Slope efficiency for both transitions, however, increased linearly with rubidium concentration up to 11 x .000001 The addition of small amounts of argon, helium, and ethane (5-45 Torr) were found to fully quench lasing action on both transitions.

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Scaling of an Optically Pumped Mid-Infrared Rubidium Laser

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Abstract : An optically pumped mid-infrared rubidium (Rb) pulsed laser has been demonstrated in a heat pipe along the 62P3/2 - 62S1/2 transition at 2.730 micrometer and the 62P1/2 - 62S1/2 transition at 2.790 micrometer. The bleached limit, slope efficiency, and maximum laser output energy of the mid-IR Rb laser have been shown to scale linearly with increasing Rb density, contrary to prior laser demonstrations. A maximum output energy of 5 nJ per pulse had previously been observed before a rollover occurred in the scaling of output energy with Rb concentration. In this experiment, the maximum laser output energy observed was 100 nJ, with linear scaling to a Rb concentration of 7 x 10 to the 15th power cm-3. A maximum slope efficiency of 1.7 x 0.0001 was observed. Evidence that only a small percentage (2%) of the available pump photons were absorbed at a concentration of 2 x 10 to the 15th power cm-3 and a pump energy of 10 (mu)J. This indicated that there were 20,000 pump photons per Rb atom at a pump energy of 10 mJ, and that the effective laser efficiency was 0.65 percent or higher. The hyperfine structure and absorption spectral profile of the 52S1/2 - 62P1/2 and 52S1/2 - 62P3/2 (blue) pump transitions were studied using a continuous wave (cw) pump source.

•Mar 26, 2015•0 citations

Wavelength diversity in optically pumped alkali vapor lasers

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Alternative wavelengths for optically pumped alkali vapor lasers have been developed using single photon excitation of higher lying P-states, stimulated Raman processes, two-photon excitation of S and D states, and electric quadruple excitation on S-D transitions. Two photon excitation of Cs 72D leads to competing and cascade lasing producing red and infrared lasers operating on the D-P transitions, followed by ultraviolet, blue, the standard near infrared DPAL transitions operating on P-S transitions. The S-D pump transitions are fully bleached at pump intensities exceeding 1 MW/cm2, allowing for lasing transitions that terminate on the ground state. The kinetics of these systems are complex due to competition for population inversion among the many optical transitions. An optically pumped mid-infrared rubidium pulsed, mirrorless laser has also been demonstrated in a heat pipe along both the 62P3/2 - 62S1/2 transition at 2.73 μm and the 62P1/2 - 62S1/2 transition at 2.79 μm with a maximum energy of ~100 nJ. Performance improves dramatically as the rubidium vapor density is increased, in direct contradiction with the prior work. No scaling limitations associated with energy pooling or ionization kinetics have been observed. Practical application for infrared counter measures depends on the further development of blue diode pump sources. Finally, stimulated electronic Raman scattering and hyper-Raman processes in potassium vapor near the D1 and D2 lines have been observed using a stable resonator and pulsed laser excitation. First and second order Stokes and anti-Stokes lines were observed simultaneously and independently for a pump laser tuning range exceeding 70 cm-1. When the pump is tuned between the K D1 and D2 lines, an efficient hyper-Raman process dominates with a slope efficiency that exceeds 10%. Raman shifted laser may be useful as a target illuminator or atmospheric compensation beacon for a high power diode pumped alkali laser.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Jan 13, 2017•1 citation

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Abstract : The Doppler-broadened two-photon absorption (TPA) cross-section for the 52S1/2- 52D5/2 transition in Rb is measured using direct absorption methods. A detailed model of the intensity profile was developed to account for a focused Gaussian beam propagating through a two-photon absorption medium. A peak absorbance of 24% was observed for an intensity of 6.28 kW/cm2 at the focus, a Rb density of 4.6 x 1015 cm-3 concentrations from 1.61-8.52 x 10(15) cm-3 line. Extracting the hyperfine-broadened TPA cross-section from 87 test configurations, while varying the pump power, alkali concentration and focal length, yielded an error weighted average of 6.75x10-21 cm4/W. This cross-section is sufficient for a pulsed dye laser to bleach the pump transition in the Two-Photon Pumped Alkali Laser (TPAL) that lases at 420 nm and 5.2 mum. Additionally, optically pumped atomic rubidium lasers pumped in the blue satellite of the D2 line from the ground Rb-Ar or Rb-Kr collision pair to the dissociative B2 sum 1/2 produce laser emission at 780.2 nm. Lasing is achieved for the Rb-Ar system and 757.1 - 760.4 nm for the Rb-Kr system. Slope efficiencies exceed 0.25% using a heat pipe configuration. The gain is very high with photon build-up times of 1-3.7 ns.

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Applied Physics Letters•Aug 1, 1981•58 citations
Abstract : Mirrorless lasing has been successfully demonstrated in a Rubidium heat pipe. Lasing was observed on the 6(2)P(sub 3/2)-6(2)S(sub 1/2) energy transition at 2.73 microns and on the 6(2)P(sub 1/2)-6(2)S(sub 1/2) transition at 2.79 microns. The transitions were optically pumped from 5(2)S(sub 1/2)-6(2)P(sub 3/2) at 420.2 nm and from 5(2)S(sub 1/2)-6(2)P(sub 1/2) at 421.7 nm, respectively. The 5(2)S(sub 1/2)-6(2)P(sub 3/2) transition was excited over a 36 GHz band, while the 5(2)S(sub 1/2)-6(2)P(sub 1/2) transition was excited over a 24 GHz band. Both pump transitions showed a high degree of saturation and only a small fraction (1%) of the incident pump energy was absorbed. Output energies of up to 5 nJ were obtained at 2.73 microns and of up to 5.4 nJ at 2.79 microns when pumped at pulse energies of 4 mJ. Both transitions experienced bleaching at this 4 mJ pump energy, limiting further IR output energy. Increasing rubidium concentration at bleached pump energies showed no increase in laser energy after 170 deg. C, likely due to second order processes. Slope efficiency for both transitions, however, increased linearly with rubidium concentration up to 11 x .000001 The addition of small amounts of argon, helium, and ethane (5-45 Torr) were found to fully quench lasing action on both transitions.
Abstract : An optically pumped mid-infrared rubidium (Rb) pulsed laser has been demonstrated in a heat pipe along the 62P3/2 - 62S1/2 transition at 2.730 micrometer and the 62P1/2 - 62S1/2 transition at 2.790 micrometer. The bleached limit, slope efficiency, and maximum laser output energy of the mid-IR Rb laser have been shown to scale linearly with increasing Rb density, contrary to prior laser demonstrations. A maximum output energy of 5 nJ per pulse had previously been observed before a rollover occurred in the scaling of output energy with Rb concentration. In this experiment, the maximum laser output energy observed was 100 nJ, with linear scaling to a Rb concentration of 7 x 10 to the 15th power cm-3. A maximum slope efficiency of 1.7 x 0.0001 was observed. Evidence that only a small percentage (2%) of the available pump photons were absorbed at a concentration of 2 x 10 to the 15th power cm-3 and a pump energy of 10 (mu)J. This indicated that there were 20,000 pump photons per Rb atom at a pump energy of 10 mJ, and that the effective laser efficiency was 0.65 percent or higher. The hyperfine structure and absorption spectral profile of the 52S1/2 - 62P1/2 and 52S1/2 - 62P3/2 (blue) pump transitions were studied using a continuous wave (cw) pump source.
Alternative wavelengths for optically pumped alkali vapor lasers have been developed using single photon excitation of higher lying P-states, stimulated Raman processes, two-photon excitation of S and D states, and electric quadruple excitation on S-D transitions. Two photon excitation of Cs 72D leads to competing and cascade lasing producing red and infrared lasers operating on the D-P transitions, followed by ultraviolet, blue, the standard near infrared DPAL transitions operating on P-S transitions. The S-D pump transitions are fully bleached at pump intensities exceeding 1 MW/cm2, allowing for lasing transitions that terminate on the ground state. The kinetics of these systems are complex due to competition for population inversion among the many optical transitions. An optically pumped mid-infrared rubidium pulsed, mirrorless laser has also been demonstrated in a heat pipe along both the 62P3/2 - 62S1/2 transition at 2.73 μm and the 62P1/2 - 62S1/2 transition at 2.79 μm with a maximum energy of ~100 nJ. Performance improves dramatically as the rubidium vapor density is increased, in direct contradiction with the prior work. No scaling limitations associated with energy pooling or ionization kinetics have been observed. Practical application for infrared counter measures depends on the further development of blue diode pump sources. Finally, stimulated electronic Raman scattering and hyper-Raman processes in potassium vapor near the D1 and D2 lines have been observed using a stable resonator and pulsed laser excitation. First and second order Stokes and anti-Stokes lines were observed simultaneously and independently for a pump laser tuning range exceeding 70 cm-1. When the pump is tuned between the K D1 and D2 lines, an efficient hyper-Raman process dominates with a slope efficiency that exceeds 10%. Raman shifted laser may be useful as a target illuminator or atmospheric compensation beacon for a high power diode pumped alkali laser.
Abstract : The Doppler-broadened two-photon absorption (TPA) cross-section for the 52S1/2- 52D5/2 transition in Rb is measured using direct absorption methods. A detailed model of the intensity profile was developed to account for a focused Gaussian beam propagating through a two-photon absorption medium. A peak absorbance of 24% was observed for an intensity of 6.28 kW/cm2 at the focus, a Rb density of 4.6 x 1015 cm-3 concentrations from 1.61-8.52 x 10(15) cm-3 line. Extracting the hyperfine-broadened TPA cross-section from 87 test configurations, while varying the pump power, alkali concentration and focal length, yielded an error weighted average of 6.75x10-21 cm4/W. This cross-section is sufficient for a pulsed dye laser to bleach the pump transition in the Two-Photon Pumped Alkali Laser (TPAL) that lases at 420 nm and 5.2 mum. Additionally, optically pumped atomic rubidium lasers pumped in the blue satellite of the D2 line from the ground Rb-Ar or Rb-Kr collision pair to the dissociative B2 sum 1/2 produce laser emission at 780.2 nm. Lasing is achieved for the Rb-Ar system and 757.1 - 760.4 nm for the Rb-Kr system. Slope efficiencies exceed 0.25% using a heat pipe configuration. The gain is very high with photon build-up times of 1-3.7 ns.
We report the first CW lasing from two-photon pumping via a virtual state. Pulsed and the CW lasing of the 3096 nm 72 P1/2 to 72 S1/2 line are observed from degenerate two-photon pumping of the cesium 72 S1/2 to 62 D3/2 transition. High intensity pulses excite over 17 lasing wavelengths. Under lower intensity CW excitation, 3 μm lasing is still observed with efficiencies of 0.7%. CW experiments utilized a Cs heat pipe at 150 °C to 270 °C, and a highly-focused, single pass, Ti-Sapphire pump with no aid of a cavity. Unlike normal DPALS, this architecture does not require buffer gas, and heat is released optically so a flowing system is not required. Both suggest a very simple device with excellent beam quality is possible. This proof of concept can be greatly enhanced with more optimal conditions such as non-degenerate pumping to further increase the two-photon pump cross section and the addition of a cavity to improve mode volume overlap. These improvements may lead to an increase in efficiencies to a theoretical maximum of 14%. Results suggest two-photon pumping with diodes is feasible.
Mirrorless lasers avoid cavity-pulling effects by generating stimulated emission directly from an atomic gain medium without an optical cavity. However, most superradiant or superfluorescent emissions are transient, limiting their use as steady atom-referenced optical sources. Here, we demonstrate a continuous-wave dual-wavelength mirrorless laser in thermal rubidium vapor. A frequency-stabilized 420 nm laser pumps the 5S1/2→6P3/2 transition and generates directional infrared lasing at 1323 and 1367 nm through the non-cascaded 6S1/2→5P1/2 and 6S1/2→5P3/2 transitions. The emissions exhibit threshold-like pump-power dependence and a near-fundamental transverse mode, supporting CW mirrorless laser in a traveling-wave atomic gain medium. Heterodyne detection gives a 1367 nm linewidth of 32.5 kHz, which is 38 times narrower than the natural linewidth. This work establishes a linewidth-narrowed, cavity-free, atom-referenced dual-wavelength laser platform for precision spectroscopy, optical frequency references, and quantum sensing.