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Two red photon absorption in alkalis producing infrared and blue beams

Greg A. Pitz, Ericka Acosta, Glen P. Perram

Published Jan 1, 2010• 4 citations
OpenAlex

Abstract

uorescence geometry. The threshold for the blue is modest, 0.3 mJ/pulse, and slope eciencies increase dramatically with alkali concentration. Threshold in the infrared is quite small. Although two photon absorption cross-sections are typically quite low, the intensity dependent cross-section for the Rb 5 2 S1=2 ! 5 2 D5=2 has been previously calculated as 0.57 x 10 18 cm 4 /W and measured as 4 x 10 20 cm 4 /W and 1.2 0.5 x 10 18 cm 4 /W. At the threshold pump energy of 0.3 mJ, the corresponding intensity is 80 kW/cm 2 , yielding an eective absorption cross-section of 10 13 cm 2 . This cross-section is about 15 times lower than the value for single photon absorption on the D2 line with broadening associated with 600 Torr of helium. The standard red DPAL typically exhibits a threshold of 1-2 kW/cm 2 , about 40-80 times less than the present results. The two photon absorption cross-section appears to be large enough to bleach the sample.

Related papers

Optically Pumped Atomic Rubidium Lasers: Two-Photon and Exciplex Excitation Mechanisms

Jeffrey Gallagher

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.

•Jun 1, 2013•2 citations

Determining the Two-Photon Absorption Cross-Section for the 52S1/2 --> 52D5/2 Transition in Naturally Occurring Rubidium

Jeffrey Gallagher, Glen P. Perram

Recently we demonstrated lasing at 420 nm and 455 nm inside of rubidium and cesium vapor cells respectively, by non-resonant, two photon absorption at near infrared pump wavelengths. Two photon absorption from the ground S1/2 state to excited D3/2,5/2 or higher lying S1/2 state via virtual states and subsequent infrared stimulated emission pumps the upper laser levels, the second excited P1/2,3/2 states. To better understand the mechanism and phenomenology of this type of laser, this paper presents a method for determining the two-photon absorption (TPA) cross-section for the 5S1/2 −→ 5D5/2 transition in naturally occurring rubidium. For an incident pump intensity of 392 W cm2 and a rubidium concentration of 3.34 × 10 atoms cm3 , a peak absorbance of 0.10 is observed. The concentration of the Rb in the test cell is determined by one photon absorption spectra of the D2, indicating a vapor curve shifted by 14 C from the exterior wall temperature. The incident laser beam is focused to a waist of 75 μm. The beam quality is consistent with an M = 1.05 − 1.09. A model for the intensity as a function of propagation distance is developed to interpret the observed absorption spectrum and determine a cross-section for the two photon absorption.

AIAA Plasmadynamics and Lasers Conference•Jun 1, 2011•1 citation

Wavelength diversity in optically pumped alkali vapor lasers

Glen P. Perram

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

Multi-photon processes in alkali metal vapors

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Achieving population inversion through multi-photon cascade pumping is almost always difficult, and most laser medium work under 1-photon excitation mechanism. But for alkali atoms such as cesium, relatively large absorption cross sections of several low, cascading energy levels enable them properties such as up conversion. Here we carried out research on two-photon excitation alkali fluorescence. Two photons of near infrared region are used to excite alkali atoms to n 2 D5/2, n 2 D3/2 or higher energy levels, then the blue fluorescence of (n+1) 2 P3/2,(n+1) 2 P1/2→n 2 S1/2 are observed. Different pumping paths are tried and by the recorded spectra, transition routes of cesium are deducted and concluded. Finally the possibility of two-photon style DPALs (diode pumped alkali laser) are discussed, such alkali lasers can give output wavelengths in the shorter end of visual spectroscopy (400-460 nm) and are expected to get application in underwater communication and material laser processing.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Feb 3, 2015•0 citations

Absolute Rb one-color two-photon ionization cross-section measurement near a quantum interference

T. Takekoshi, George M. Brooke, Brian M. Patterson +1 more

We observe destructive interference in the ground-state Rb two-photon ionization cross section when the single photon energy is tuned between the $5S\ensuremath{\rightarrow}5P$ and $5S\ensuremath{\rightarrow}6P$ transition energies. The minimum cross section is $5.9(1.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}52}\phantom{\rule{0.3em}{0ex}}{\text{cm}}^{4}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ and it occurs at a wavelength of $441.0(3)\phantom{\rule{0.3em}{0ex}}\text{nm}$ (in vacuo). Relative measurements of these cross sections are made at various wavelengths by counting ions produced when magneto-optically trapped Rb atoms are exposed to light from a tunable pulsed laser. This relative curve is calibrated to an absolute cross-section measurement at $532\phantom{\rule{0.3em}{0ex}}\text{nm}$ using the trap loss method. A simple calculation agrees reasonably with our results.

Physical Review A•May 20, 2004•10 citations

Spectroscopic studies of alkali atom-rare gas systems

Steven J. Davis, Kristin L. Galbally-Kinney, William J. Kessler +1 more

We describe a series of measurements of absorption and laser induced fluorescence on cells that contained cesium and rubidium and a rare gas: He, Ar, Kr, or Xe. These studies showed strong blue wing absorption to the short wavelength side of the alkali atom D2 lines due to collisionally formed Cs- or Rb-rare gas excimers. We also have observed an efficient two photon excitation of higher lying states in Cs and Rb that produces both intense blue emission and IR atomic emission in the 1.3 to 3.8 μm spectral region.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Feb 11, 2010•3 citations
uorescence geometry. The threshold for the blue is modest, 0.3 mJ/pulse, and slope eciencies increase dramatically with alkali concentration. Threshold in the infrared is quite small. Although two photon absorption cross-sections are typically quite low, the intensity dependent cross-section for the Rb 5 2 S1=2 ! 5 2 D5=2 has been previously calculated as 0.57 x 10 18 cm 4 /W and measured as 4 x 10 20 cm 4 /W and 1.2 0.5 x 10 18 cm 4 /W. At the threshold pump energy of 0.3 mJ, the corresponding intensity is 80 kW/cm 2 , yielding an eective absorption cross-section of 10 13 cm 2 . This cross-section is about 15 times lower than the value for single photon absorption on the D2 line with broadening associated with 600 Torr of helium. The standard red DPAL typically exhibits a threshold of 1-2 kW/cm 2 , about 40-80 times less than the present results. The two photon absorption cross-section appears to be large enough to bleach the sample.
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.
Recently we demonstrated lasing at 420 nm and 455 nm inside of rubidium and cesium vapor cells respectively, by non-resonant, two photon absorption at near infrared pump wavelengths. Two photon absorption from the ground S1/2 state to excited D3/2,5/2 or higher lying S1/2 state via virtual states and subsequent infrared stimulated emission pumps the upper laser levels, the second excited P1/2,3/2 states. To better understand the mechanism and phenomenology of this type of laser, this paper presents a method for determining the two-photon absorption (TPA) cross-section for the 5S1/2 −→ 5D5/2 transition in naturally occurring rubidium. For an incident pump intensity of 392 W cm2 and a rubidium concentration of 3.34 × 10 atoms cm3 , a peak absorbance of 0.10 is observed. The concentration of the Rb in the test cell is determined by one photon absorption spectra of the D2, indicating a vapor curve shifted by 14 C from the exterior wall temperature. The incident laser beam is focused to a waist of 75 μm. The beam quality is consistent with an M = 1.05 − 1.09. A model for the intensity as a function of propagation distance is developed to interpret the observed absorption spectrum and determine a cross-section for the two photon absorption.
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.
Achieving population inversion through multi-photon cascade pumping is almost always difficult, and most laser medium work under 1-photon excitation mechanism. But for alkali atoms such as cesium, relatively large absorption cross sections of several low, cascading energy levels enable them properties such as up conversion. Here we carried out research on two-photon excitation alkali fluorescence. Two photons of near infrared region are used to excite alkali atoms to n 2 D5/2, n 2 D3/2 or higher energy levels, then the blue fluorescence of (n+1) 2 P3/2,(n+1) 2 P1/2→n 2 S1/2 are observed. Different pumping paths are tried and by the recorded spectra, transition routes of cesium are deducted and concluded. Finally the possibility of two-photon style DPALs (diode pumped alkali laser) are discussed, such alkali lasers can give output wavelengths in the shorter end of visual spectroscopy (400-460 nm) and are expected to get application in underwater communication and material laser processing.
We observe destructive interference in the ground-state Rb two-photon ionization cross section when the single photon energy is tuned between the $5S\ensuremath{\rightarrow}5P$ and $5S\ensuremath{\rightarrow}6P$ transition energies. The minimum cross section is $5.9(1.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}52}\phantom{\rule{0.3em}{0ex}}{\text{cm}}^{4}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ and it occurs at a wavelength of 441.0(3)nm441.0(3)\phantom{\rule{0.3em}{0ex}}\text{nm}441.0(3)nm (in vacuo). Relative measurements of these cross sections are made at various wavelengths by counting ions produced when magneto-optically trapped Rb atoms are exposed to light from a tunable pulsed laser. This relative curve is calibrated to an absolute cross-section measurement at 532nm532\phantom{\rule{0.3em}{0ex}}\text{nm}532nm using the trap loss method. A simple calculation agrees reasonably with our results.
We describe a series of measurements of absorption and laser induced fluorescence on cells that contained cesium and rubidium and a rare gas: He, Ar, Kr, or Xe. These studies showed strong blue wing absorption to the short wavelength side of the alkali atom D2 lines due to collisionally formed Cs- or Rb-rare gas excimers. We also have observed an efficient two photon excitation of higher lying states in Cs and Rb that produces both intense blue emission and IR atomic emission in the 1.3 to 3.8 μm spectral region.