We describe the first observation of stimulated emission at 0.75–0.80 µm and at 1.06–1.14 µm in sodium vapor at 580°C and 0.5-Torr buffer argon pressure by single-UV-photon or two-visible-photon pumping. For our pumping source, we used a XeCl excimer laser (EMG 101)–dye laser (FL2002), wavelengths 3375.93-Å (PTP) and 5772.8- Å (Rh6G) for single-photon and two-photon excitation with 0.16- Å linewidth and 10-nm pulse width; heating zone of the heat-pipe 25 cm.
We describe the first observation of stimulated emission at 0.75–0.80 µm and at 1.06–1.14 µm in sodium vapor at 580°C and 0.5-Torr buffer argon pressure by single-UV-photon or two-visible-photon pumping. For our pumping source, we used a XeCl excimer laser (EMG 101)–dye laser (FL2002), wavelengths 3375.93-Å (PTP) and 5772.8- Å (Rh6G) for single-photon and two-photon excitation with 0.16- Å linewidth and 10-nm pulse width; heating zone of the heat-pipe 25 cm.
Laser excitation and ionization processes in dense (1–10 Torr) sodium vapor have been studied for laser wavelengths near the two-photon allowed nd 2D(n=3, 4, 5) and ns 2S(n=4, 5, 6) states. In particular, the 1 3Σ+g→1 3Σ+u excimer emission in Na2, predicted in 1980 by Konowalow and Julienne and observed recently by Dinev et al, was studied here in greater detail. Strong excimer emission (∼830 nm) was observed for two-photon pumping to both sides of the unresolved 4D states, and weak excimer emission was seen when pumping near the 5D levels. The excimer emission exhibits a complicated pump laser profile with a pronounced ‘‘dip’’ at the 4d 2D two-photon resonance. Similarly, [2+1] photon ionization via the 3d 2D and 4d 2D states shows a dramatic decrease as the sodium density increases. These results can be attributed either to depleted 3d 2D or 4d 2D population due to stimulated electronic Raman scattering (SERS) or to the interference effects recently reported by Malcuit et al. and Krasnikov et al. and treated theoretically by Manykin and Afanas’ev and by Agarwal. It is argued that both mechanisms are operative. Strong ionization and SERS signals were observed at the hybrid resonances corresponding to 3p 2P3/2, 1/2 →4d 2D transitions; however, no excimer lasing at 830 nm was detected. No excimer emission was detected upon two-photon pumping near or at the 3d 2D or ns 2S(n=4, 5, 6) states. Based on these and other observations, the 1 3Σ+g→1 3Σ+u excimer emission is attributed to a molecular Raman process involving stimulated emission or six-wave mixing via a pathway of the type 1 3Σ+u→2hν 3Δu→ j 3Πg→(k 3Πu, l 3Σ +u)→1 3Σ+g→1 3Σ +u .
For the first time by means of two-photon hybrid excitation in the Na2-Na system, which is distinguished from the usual two-photon excitation in atomic vapor, tunable UV coherent radiation (between 337.6 and 339.1 nm and between 358.0 and 359.6 nm) and tunable infrared stimulated radiation (3.38-3.46 µm) were generated. By optically pumping with a pulsed dye laser scanning from 614.5 to 617.4 nm for sodium vapor in a heat-pipe oven, Na2 was excited by the first photon absorption from the X ′ Σ g + to the A ′ Σ u + state. The energy was transferred to Na by Na2*-Na collision to populate the levels 3p1/2,3/2 in Na, which was followed by another photon excitation from the same beam up to near the 5S level, resulting in SERS (3P1/2-4P and 3P3/2-4P) and OPSE(5S → 4P and 4P → 4S) radiation. Assuming the detunings of pumping frequency ω1, from ω(5S,3P3/2) and ω(5s,3p1/2) to be Δ1 and Δ2, respectively, the three UV coherent radiation components were supposed to be generated by the following mixing processes: ωUV = 2ω1 − ω(5S − 4P); ω U V ′ = 2 ω 1 − [ ω ( 5 S → 4 P ) + Δ 1 ] ; ω U V ′ ′ = 2 ω 1 − [ ω ( 5 S → 4 P ) + Δ 2 ] , and also ω U V ′ ′ ′ = 2 ω 1 − ω ( 4 P → 4 S ) . The SERS and the UV signals were tuned as the pumping wavelength was tuned. The measured wavelengths agreed well with the calculated values.
We report the first observation of a cone radiation at 5890–5896 Å (ωL) in sodium vapor pumped by an excimer laser–dye laser tunable over a 334–347-nm (ωP) range. Simultaneously, with the cone radiation two tunable stimulated emissions were detected: the 3S–4S (Ω) stimulated electronic Raman scattering transition at 2.38–2.65 μm (ωS), and the 4S–3P transition at 1.138–1.142 μm (ωT). On the hollow ring of the upward cone radiation three spectral lines appear at 5890, 5896, and 5894 Å. The first two wavelengths are fixed and the third is slightly tunable during the tuning of the dye laser. The cone size varies with the sodium vapor pressure and it disappears, while the buffer argon pressure is higher than 20 Torr.
This paper reports the UV and violet diffuse band radiation generated by two-photon pumping in Na2 by focusing the pumping beam (~ 10 mJ) from a pulsed dye laser into a heat-pipe oven containing sodium. Measurable forward stimulated diffuse band radiation existed at 350.0-385.0 nm and 405.0-460.0 nm over the whole pumping region from 620.0 to 670.0 nm. The radiation corresponded to transitions from different high-lying triplet g states to the lowest triplet state. The signal intensity related to the pumping wavelength. The stronger signals were there where two-photon pumping was enhanced by singlet-triplet mixing levels. The weaker signals were assumed to relate to the collisions either transferring energy from the A ′ Σ u + to the b3Π g state after the first photon excitation and then pumped by the second photon excitation from the b3Π g state to a high-lying state, or were due to collisional transfer from a high-lying singlet to a nearby triplet state.
Laser excitation and ionization processes in dense (1--10 Torr) sodium vapor have been studied for laser wavelengths near the two-photon allowed nd /sup 2/D(n = 3, 4, 5) and ns /sup 2/S(n = 4, 5, 6) states. In particular, the 1 /sup 3//Sigma//sup +//sub g//yields/1 /sup 3//Sigma//sup +//sub u/ excimer emission in Na/sub 2/, predicted in 1980 by Konowalow and Julienne and observed recently by Dinev et al, was studied here in greater detail. Strong excimer emission (/similar to/30 nm) was observed for two-photon pumping to both sides of the unresolved 4D states, and weak excimer emission was seen when pumping near the 5D levels. The excimer emission exhibits a complicated pump laser profile with a pronounced ''dip'' at the 4d /sup 2/D two-photon resonance. Similarly, (2+1) photon ionization via the 3d /sup 2/D and 4d /sup 2/D states shows a dramatic decrease as the sodium density increases. These results can be attributed either to depleted 3d /sup 2/D or 4d /sup 2/D population due to stimulated electronic Raman scattering (SERS) or to the interference effects recently reported by Malcuit et al. and Krasnikov et al. and treated theoretically by Manykin and Afanas'ev and by Agarwal. It is argued thatmore » both mechanisms are operative.« less
STIMULATED EMISSION BASED ON TWO-STEP HYBRID RESONANCE A1Σu+ OR B1Πu STATE OF Na.∗
The first step of the hybrid excitation in the experiment was achieved by using a pulse broadband ($\\sim$200 {\\AA}) dye laser beam through a heat pipe oven. But the total covered pumping wavelength region from 4600 {\\AA} to 6800 {\\AA} the populated upper electronic state in Na2 should be either AprimeSigmau or BprimePiu state. The excited sodium dimers Na2ast transfered their energy to sodium atoms Na by near resonace collisions and the Na then would populate up the 3P level from ground state 3s. The Na were consequentely pumped up to 4D, 5D, 5S or 6S level from 3P by using a narrowband dye laser pumped by the same N2 laser. The infrared stimulated radiation corresponding to the transitions of 4D-4P(2.34 mum). 5D-4P(5.02mum), 5S-4P(3.42 mum) and 6S-5P(7.52 mum) with cascade stimulated emission from 4P to 4S (2.20 mum) and from 5P to 5S (5.43 mum) were then obtained, Furthermore the dependence of the output energy on the pumping wavelengthes was measured and discussed.