Stimulated Electronic Raman Scattering Research Articles

Terahertz emitting and four wave mixing details in 6P3/2→11DJ pumped cesium vapor

Terahertz emitting and FWM (Four wave mixing) processes in 6P3/2→11DJ near-resonating pumped cesium vapor are studied in this work. Using a nanosecond 550 nm pump laser, collimated frequency converted lights around 557 nm and 563 nm are observed in cesium vapor. A detailed analysis shows that the frequency converted lights come from FWM processes driven by the pump laser and stimulated terahertz emissions in the frequency range of 1–7 THz. These stimulated terahertz emissions are generated by cesium atom SERS (stimulated electronic Raman scattering) or ASE (amplified spontaneous emission) under pumping. The terahertz emission iQEs (internal quantum efficiency) are estimated to be on the order of 1 E -3 ~ 1 E -2 as their lower limits. Results of this work will contribute to studies on atom FWM physics, terahertz light source and detector based on atom vapor.

Plasmonic sensors for identification of inorganic microcrystals

A method of applying giant stimulated electronic Raman scattering (SERS) by plasmonic gold nanoparticles for identification of inorganic microcrystals in the structure of works of art is presented. The high signal-to-noise ratio in the SERS spectra, along with the low luminescent background, makes the method promising for implementation in practice of technical expertise of objects of cultural heritage.

Stimulated Electronic X-Ray Raman Scattering

We demonstrate strong stimulated inelastic x-ray scattering by resonantly exciting a dense gas target of neon with femtosecond, high-intensity x-ray pulses from an x-ray free-electron laser (XFEL). A small number of lower energy XFEL seed photons drive an avalanche of stimulated resonant inelastic x-ray scattering processes that amplify the Raman scattering signal by several orders of magnitude until it reaches saturation. Despite the large overall spectral width, the internal spiky structure of the XFEL spectrum determines the energy resolution of the scattering process in a statistical sense. This is demonstrated by observing a stochastic line shift of the inelastically scattered x-ray radiation. In conjunction with statistical methods, XFELs can be used for stimulated resonant inelastic x-ray scattering, with spectral resolution smaller than the natural width of the core-excited, intermediate state.

Effect of the pump absorption on generation of infrared stimulated electronic Raman scattering in alkali-metal vapors

The main properties of infrared stimulated electronic Raman scattering (SERS) at the 62S1/2-72S1/2, 3/2 transitions in cesium atoms are studied theoretically and experimentally as functions of the atomic concentration, which was varied from 1011 to 1016 cm−3. It is found that the efficiency of generation of Stokes radiation strongly depends on one-photon absorption of the pump radiation tuned near frequencies of the 62S1/2-72P1/2, 3/2 transitions. By using the equation for the density matrix, which describes the evolution of a three-level system, the theory of resonance excitation of IR radiation upon one-photon absorption at an adjacent transition is developed. The theory describes well the main features of IR SERS in alkali-metal vapors.

Tunable picosecond infrared pulses generated by stimulated electronic Raman scattering of a mode-locked Ti:Sapphire laser in potassium vapor

A down-conversion to the mid-infrared region by using Stimulated Electronic Raman Scattering (SERS) in potassium vapor is described. The pump radiation is a frequency-doubled regeneratively amplified Ti:Sapphire laser with a pulse duration of 2 ps, pulse energy of 0.2 mJ, and repetition rate of 10 Hz. With the pumping frequency tuned around the potassium 4s-5p transition, nearly transform-limited infrared radiation tunable between 2.2 and 3.4 μm has been generated with a peak infrared energy of 12 µJ, corresponding to a quantum efficiency of 17%, and with a pulse duration of 2 ps. The present tuning range could be extended by extending the tuning range of the pump laser. In comparison, intense infrared radiation of 90 µJ energy but with a very narrow tunability around 2.9 μm has also been generated by SERS in barium vapor.

X-ray-stimulated electronic Raman scattering in neutral gases and inhibited ionization

We theoretically demonstrate the feasibility of resonantly enhanced, stimulated electronic Raman scattering (SERS) of Se x-ray laser radiation in atomic He and Li and estimate the Stokes output. We show that, despite strong photoionization, the conversion efficiency of the Raman process can be considerably high. We despite also found that coherent SERS can significantly inhibit x-ray-induced photoionization.

Observation of cw stimulated Raman emission in the neon 2p→1s manifold

We report previously unobserved cw laser emission from a commercial HeNe laser. This lasing is based on near-resonant stimulated electronic Raman scattering (SERS) involving NeI 1s 5→2p→1s 4, and 1s 5→2p→1s 2, electronic states when the laser cavity is pumped externally by cw dye laser radiation. Two of the emitted lines [2p 2→1s 4 (603.0 nm) and 2p 2→1s 2 (659.9 nm); both pumped at 588.2 nm (1s 5→2p 2)] are explored in some detail. Output power of the Raman laser has been measured as a function of the laser-atom detuning, the Ne discharge current and the pumping laser power. These Raman lines can be several times stronger than the 633 nm HeNe laser output itself. The observations are qualitatively consistent with calculations of Raman gain showing the possibility of all 14 dipole-allowed 2p→1s Stokes-Raman laser lines being observable with commercial HeNe lasers, given mirror coatings of sufficient spectral width.

Laser SRS Diagnostics of HBr in Tungsten Halogen Lamps

The generation of infrared radiation by stimulated electronic Raman scattering (SRS) in a cesium vapor heat pipe is used to obtain diagnostic information on HBr in a tungsten halogen lamp. The IR beam traverses through the center of the coiled filament of a General Electric projection lamp, and spectra are taken of the R branch in the fundamental band for the lamp lit from 0 to 148 W, corresponding to filament temperatures of 296-2387 K. Molecular rotational temperatures and absolute HBr densities are then derived from the spectra. The results demonstrate the method to be a useful diagnostic tool for spatially resolved measurements of a key partner in the tungsten halogen cycle.

Self-induced destructive interference suppression of stimulated electronic Raman scattering

The self-induced suppression (SIS) of stimulated electronic Raman scattering (SERS) is discussed. The nature of SIS is that SERS induces in gaseous media the generation of new fields by a four-wave mixing (FWM) process which destructively interferes with SERS and results in its suppression. The behaviour of Stokes radiation is investigated under SIS of SERS, both in the steady-state case and in the non-stationary regime of interaction with an ultrashort pump pulse. The effect is shown to be absent in the non-stationary case. On the basis of this result the author is able to explain in a simple manner the 'strange' dependence of the Stokes wavelength on pump pulse duration observed experimentally in barium vapours. The author also discusses the possible application of SIS of SERS for Stokes frequency switching. This can be achieved by stimulation of destructive interference between SERS and FWM if, simultaneously with the pump pulse, a signal wave at a frequency of one of the parametrically generated fields is switched on. As a result the FWM is intensified leading to strong suppression of SERS on a given transition and the Stokes radiation is now generated on the other transition with a new frequency. The method can be used to convert the laser frequency into the far-IR region and for a new spectroscopic study of gaseous media.

Two-photon excitation of dense sodium vapor near the n d 2D5/2, 3/2 (n=3, 4, 5) levels: Na2 1 3Σ+g→1 3Σ+u excimer emission

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 .

Generation of nanosecond infrared pulses tunable from 28 to 16 μm by efficient stimulated electronic Raman scattering

A source of nanosecond IR pulses tunable from 2.8 to 16 microm (3500 to 630 cm(-1)) is obtained by stimulated electronic Raman scattering (SERS) on the cesium 6s-5d transition. Reliable rhodamine and DCM dye-laser pulses are frequency shifted with up to 10% quantum conversion efficiency to obtain up to 2 mJ of IR pulse energy, a 5-25x improvement in energy over previous SERS infrared generation. The tuning curve structure and unwanted amplified spontaneous emission lines are also substantially reduced.

Two-photon resonant four-wave mixing and multiphoton ionization of cesium in a heat-pipe oven.

Optical pumping of cesium vapor in a heat-pipe oven in which the energy of two near-infrared photons is close to the 6D states results in high conversion efficiency (up to 1.7%) of the near-infrared pump light to intense blue, forward-propagating radiation. The blue light corresponds to the 7P-6S transition. The dependence of conversion efficiency upon focusing conditions, cell length, and pump intensity is presented. Absorption and gain coefficients are measured in a second heat pipe. The results are discussed in terms of optically pumped stimulated emission (OPSE), stimulated electronic Raman scattering (SERS), and subsequent nonlinear four-wave mixing of two pump-laser photons and one SERS or OPSE infrared photon, leading to parametric generation at \ensuremath{\omega}=2${\ensuremath{\omega}}_{L}$-${\ensuremath{\omega}}_{\mathrm{ir}}$. Two-photon resonant, three-photon ionization cross sections are also studied experimentally and theoretically for the case of resonant enhancement at the 6D levels of cesium. For comparison, similar results for rubidium are also presented for the 5D levels.

Stimulated collision-induced resonance Raman scattering

The passage of strong monochromatic laser radiation through a resonance medium consisting of three-level atoms is investigated. It is shown that if collisions are taken into account in the scattered waves the resonances at combination frequencies occur to first order in the laser field intensity. A numerical analysis of the dependence of the stimulated electronic Raman scattering (SERS) components' gain factors on the pump frequency is carried out. The dispersion curves of the SERS components' gain (absorption) factors for fixed values of pump frequency and intensity are plotted.

A tunable picosecond IR laser generating multi-megawatt pulses in the range 3–8 m

We describe a versatile infrared laser system capable of generating picosecond pulses continuously tunable over the wavelength range 3.3–8.4 μm, with peak powers of 1–20 MW. The IR pulse duration is ∼1.3 ps with a time-bandwidth product of ∼0.3. The system uses stimulated electronic Raman scattering (SERS) in caesium vapour to shift the frequency of a picosecond dye laser into the infrared. The quantum efficiency of the Raman conversion process exceeds 40% over almost the entire tuning range. This technique can be extended to other tuning ranges in the IR by using different atomic vapours and SERS transitions.

Saturation and tuning behavior of stimulated electronic Raman scattering

The saturation behavior of stimulated electronic Raman scattering (SERS) in atomic vapors is studied theoretically and experimentally. Limits to the SERS output energy are imposed by both pump depletion and saturation of the Raman transition. The effects of these on the performance of tunable infrared lasers based on SERS are examined.

Stimulated electronic Raman scattering in Cs vapour: a simple tunable laser system for the 2.7 to 3.5 ?m region

Stimulated electronic Raman scattering (SERS) in atomic vapours provides a simple method of extending the tuning ranges of pulsed dye lasers well into the infrared region. The special advantages of this technique in comparison with other types of tunable infrared lasers are discussed, and are illustrated by describing a SERS system which uses a modest nitrogen laser-pumped dye laser (∼ 20 kW). This produces infrared radiation tunable from 2.67 to 3.47μm by SERS in caesium vapour, which is contained in a heat pipe oven. Photon conversion efficiencies of up to 50% are obtained. The design of the heat pipe oven, operation of the system and optimization of experimental parameters are described in detail.