- Email: [email protected]
Four-wave mixing in gases
Volume 18, n u m b e r 1
OPTICS ('OMMUNICATtONS L5
July I!~ 7¢,
FOUR-WAVE MIXING 1N GASES
(Invited) P. SOROKIN IBM Thomas Z Watson Research ('enter. ~orktow~ Heights, New York 10598, USA Not received
L6
FOUR-WAVE SUM-MIXING IN NO, 1400 to 1510 A
[Invited) Stephen C. WALLACE, K.K. INNES and B.P. STOICHEFF
Department of Physics, University of Toronto, Toronto, Ontario, Canada, M5S IA 7
~
- - , wl-oa2
ub-toe Fig. 1. Three-dimensional plot of X(3)(-tJ3 , WO, COl, - w 2) versus the two intermediate frequencies w o - w 2 and ~ 1 - w2, for the region near two sharp R a m a n resonances of the sample. n o u n c e d change in the shape of one resonance as w 0 - co 2 is varied in steps across the other resonance. Experimentally, about 20 cuts in the 3-D surface in fig. t were scanned. T h e y proved to be virtually identical to the predicted theoretical curves. Similar results were f o u n d in the CuC1 case, where the interference is between uv exciton and ir polariton resonances of the material. Since the two resonances used in the double-resonance experiment do n o t need to be characteristics of the same material or solution, this experiment is useful for making accurate relative m e a s u r e m e n t s of the u n k n o w n strength of a R a m a n or two-photon resonance in terms of a k n o w n R a m a n or t w o - p h o t o n strength. For example, the exciton strength of CuC1 could be compared with the strength of the 1088 cm - I R a m a n line of calcite, or the strength of the 802 cm- 1 R a m a n line of cyclohexane could be compared to the well-known strength of the 992 cm - ! R a m a n line o f benzene. This calibration procedure m a y be very useful, since it avoids the difficulties usually e n c o u n t e r e d in such comparison measurements. In the double-resonance experiment, a strong resonance m a y be used to cancel the n o n r e s o n a n t background susceptibility. This background has been the limiting factor in the sensitivity of the single-resonance experiment to measure weak resonances.
110
Recent progress in sum-frequency mixing to generate coherent light in the vacuurn'ultraviotet (vuv) has been based on the use of atomic vapours, such as Rb [ 1 ], Sr [2], and Mg [3], as the non-linear media. As an alternative to using metal vapours one m a y choose a molecular system as the non-linear material. A molecular gas can be used directly in a simple cell (without the complexities introduced by heat-pipe ovens, necessary for these atomic systems). Moreover, phase matching is simplified and good optical h o m o g e n e i t y over arbitrary lengths is assured. We report the first observations of resonantly enhanced, four wave sum-mixing into the vuv via a molecular gas, nitric oxide (NO). The incident frequencies were provided by two H~insch type dye lasers (0.1 cm - 1 linewidth) p u m p e d by a nitrogen laser (Molectron UV-1000). Nitric oxide was carefully purified by fractional distillation to remove impurities which attenuate the harmonic radiation. The dye laser radiation was focussed to a confocal beam parameter b = 1.2 cm, in the center of a glass cell 13 cm in length. The vuv radiation passed through LiF optics to a one-meter m o n o c h r o m a t o r and was detected with a solarblind photomultiplier. The two-photon transition in NO which provided the resonant e n h a n c e m e n t of the third order, non-linear susceptibility ×(3) was A ( 2 ~ +) - X(2H) in which A ( 2 Z +) is the lowest Rydberg state. Thus, a single dye laser t u n e d over a 170 c m - l ~ f r e q u e n c y range a b o u t 4530 A (the 0,0 band [4] ) or 4300 A (the 1, 0 band), produced strong third harmonic radiation in the region 1510 A and 1433 A. respectively. The peak intensity of the third harmonic was observed at the 2E+ - 2H1/2 sub-band head. Wider tunahility was then obtained by fixing one frequency to the strongest two-photon transition and tuning a second dye laser over other transitions in the Rydberg manifold [5]. Although the third order non-linear susceptibility o f NO is ~ 1 0 - 2 of that observed for the equivalent metal vapour syst e m (Ca, Sr), reasonable conversion efficiencies were realized by choosing higher n u m b e r densities. Thus, with an NO pressure of 200 torr and the appropriate phase matching, a power conversion efficiency o f 3 x 10 - 7 (107 photons per pulse) was obtained at vuv wavelengths of 1508 A and 1422 A. Dye laser powers up to 20 kW were used and no evidence for saturation of the conversion efficiency at higher laser powers was observed.
OPTICS ('OMMUNICATtONS L5
July I!~ 7¢,
FOUR-WAVE MIXING 1N GASES
(Invited) P. SOROKIN IBM Thomas Z Watson Research ('enter. ~orktow~ Heights, New York 10598, USA Not received
L6
FOUR-WAVE SUM-MIXING IN NO, 1400 to 1510 A
[Invited) Stephen C. WALLACE, K.K. INNES and B.P. STOICHEFF
Department of Physics, University of Toronto, Toronto, Ontario, Canada, M5S IA 7
~
- - , wl-oa2
ub-toe Fig. 1. Three-dimensional plot of X(3)(-tJ3 , WO, COl, - w 2) versus the two intermediate frequencies w o - w 2 and ~ 1 - w2, for the region near two sharp R a m a n resonances of the sample. n o u n c e d change in the shape of one resonance as w 0 - co 2 is varied in steps across the other resonance. Experimentally, about 20 cuts in the 3-D surface in fig. t were scanned. T h e y proved to be virtually identical to the predicted theoretical curves. Similar results were f o u n d in the CuC1 case, where the interference is between uv exciton and ir polariton resonances of the material. Since the two resonances used in the double-resonance experiment do n o t need to be characteristics of the same material or solution, this experiment is useful for making accurate relative m e a s u r e m e n t s of the u n k n o w n strength of a R a m a n or two-photon resonance in terms of a k n o w n R a m a n or t w o - p h o t o n strength. For example, the exciton strength of CuC1 could be compared with the strength of the 1088 cm - I R a m a n line of calcite, or the strength of the 802 cm- 1 R a m a n line of cyclohexane could be compared to the well-known strength of the 992 cm - ! R a m a n line o f benzene. This calibration procedure m a y be very useful, since it avoids the difficulties usually e n c o u n t e r e d in such comparison measurements. In the double-resonance experiment, a strong resonance m a y be used to cancel the n o n r e s o n a n t background susceptibility. This background has been the limiting factor in the sensitivity of the single-resonance experiment to measure weak resonances.
110
Recent progress in sum-frequency mixing to generate coherent light in the vacuurn'ultraviotet (vuv) has been based on the use of atomic vapours, such as Rb [ 1 ], Sr [2], and Mg [3], as the non-linear media. As an alternative to using metal vapours one m a y choose a molecular system as the non-linear material. A molecular gas can be used directly in a simple cell (without the complexities introduced by heat-pipe ovens, necessary for these atomic systems). Moreover, phase matching is simplified and good optical h o m o g e n e i t y over arbitrary lengths is assured. We report the first observations of resonantly enhanced, four wave sum-mixing into the vuv via a molecular gas, nitric oxide (NO). The incident frequencies were provided by two H~insch type dye lasers (0.1 cm - 1 linewidth) p u m p e d by a nitrogen laser (Molectron UV-1000). Nitric oxide was carefully purified by fractional distillation to remove impurities which attenuate the harmonic radiation. The dye laser radiation was focussed to a confocal beam parameter b = 1.2 cm, in the center of a glass cell 13 cm in length. The vuv radiation passed through LiF optics to a one-meter m o n o c h r o m a t o r and was detected with a solarblind photomultiplier. The two-photon transition in NO which provided the resonant e n h a n c e m e n t of the third order, non-linear susceptibility ×(3) was A ( 2 ~ +) - X(2H) in which A ( 2 Z +) is the lowest Rydberg state. Thus, a single dye laser t u n e d over a 170 c m - l ~ f r e q u e n c y range a b o u t 4530 A (the 0,0 band [4] ) or 4300 A (the 1, 0 band), produced strong third harmonic radiation in the region 1510 A and 1433 A. respectively. The peak intensity of the third harmonic was observed at the 2E+ - 2H1/2 sub-band head. Wider tunahility was then obtained by fixing one frequency to the strongest two-photon transition and tuning a second dye laser over other transitions in the Rydberg manifold [5]. Although the third order non-linear susceptibility o f NO is ~ 1 0 - 2 of that observed for the equivalent metal vapour syst e m (Ca, Sr), reasonable conversion efficiencies were realized by choosing higher n u m b e r densities. Thus, with an NO pressure of 200 torr and the appropriate phase matching, a power conversion efficiency o f 3 x 10 - 7 (107 photons per pulse) was obtained at vuv wavelengths of 1508 A and 1422 A. Dye laser powers up to 20 kW were used and no evidence for saturation of the conversion efficiency at higher laser powers was observed.