anti-Stokes Stimulated Raman Scattering Research Articles

Spontaneous and stimulated Raman scattering by the products of the interaction of lithium deuteride with the environment

The processes of spontaneous and multicomponent stimulated Raman scattering (SRS) in a polycrystal consisting of the products of the interaction of lithium deuteride crystals with air molecules are studied. The interaction of lithium deuteride with environmental molecules resulted in a solid polycrystalline mixture of LiOH, LiOD, LiOH·H2O, and Li2CO3 on the crystal surface. Excitation of the sample under study by the third harmonic of a picosecond repetitively pulsed YAG:Nd3+ laser made it possible to detect three Stokes and the second anti-Stokes SRS components with a Raman frequency ν = 3660 cm−1 corresponding to the valence breathing mode of the OH− ion. A feature of the obtained spectra is the smaller spectral half-width of the second and third Stokes components compared to the first. When the studied polycrystals were excited by picosecond radiation with a wavelength λ = 532 nm, two Stokes and one anti-Stokes SRS components corresponding to the internal symmetric vibrational mode of LiOH were detected. The excitation of SRS at the Raman frequency of the OH− vibration ν = 3660 cm−1 in solids is promising due to the high-frequency shift and high quality factor, and is also important for studying the strength of hydrogen bonds.

Generated four-wave mixing in temperature controlled mixtures of carbon disulfide and benzene

Generated four-wave mixing (FWM) from the Cascaded stimulated Raman scattering (SRS) process of the mixtures of carbon disulfide and benzene on temperature was investigated. At the low temperature conditions, the stimulated Brillouin scattering can be significantly suppressed, the beam distortion caused by thermal self-defocusing effect can be reduced, thereby improving the energy conversion efficiency of SRS. Not only the multi-order Stokes and anti-Stokes SRS of CS stretching vibration, CC ring skeleton vibration and CH stretching vibration were obtained, but also the 1st (∼583 nm) and 2nd -order (∼646 nm) FWM was generated by the Stokes light, anti-Stokes light and pump laser. At 20 °C, the highest conversion efficiency is 32%, and the peak intensity of FWM is also the intensest. The results are of great significance for the multi-wavelength Raman laser in liquid medium.

Coherent Raman comb generation in H2O2aqueous solutions by crossing-pump stimulated Raman scattering.

The cascaded stimulated Raman scattering (SRS) of 30% H2O2 aqueous solutions was investigated using a pulsed Nd: YAG laser with a wavelength of 532 nm. The transfer of excess electrons between H2O2 and H2O molecules enhanced the SRS. Together, the decomposition of H2O2 and the intense SRS Stokes led to the generation of the crossing-pump effect of H2O2 aqueous solutions and the appearance of a new peak at 4229 cm-1 that is excited by Stokes as the pump source. Crossing-pump not only reduced the threshold but also generated the broadband-coherent Raman comb, defined as a coherent radiation wavelength ranging from 434 to 831 nm (i.e., a Raman shift ranging from -4225 to 6756 cm-1). The anti-Stokes SRS was attributed to the four-wave mixing (FWM) process.

Resonance enhanced cascaded stimulated Raman and Coherent Anti-Stokes Raman scattering of symmetric and antisymmetric O-D vibrations

Stimulated Raman scattering (SRS) of deuteroxide was investigated using a pulsed Nd:YAG laser with a wavelength of 532 nm. After the pump laser passed through the first sample cell (C1), the output light included the transmitted pump beam and the Stokes SRS lights, and the frequency difference between the two self-matched the O-D symmetric and antisymmetric stretching vibration modes. The 1st and the 2nd-order cascaded Stokes and the anti-Stokes SRS (Coherent Anti-Stokes Raman Spectroscopy-CARS) of both two modes were observed. The 2nd-order Stokes SRS and its CARS were firstly observed at a pump energy of 14.79 mJ. The pure Stokes SRS were always collinear with the pump beam along the axial direction. Some ring-like Stokes SRS and CARS, which originated from the four-wave mixing (FWM) processes, were also observed only in the forward direction along with different angles apart from the pump beam direction, respectively. This method not only reduced the SRS threshold but also increased the SRS intensity of the weak vibration mode, resulting in an energy conversion efficiency reaching up to 54%. The technique can be used in a tunable Raman laser.

Investigated coherent anti-Stokes Raman scattering in the process of cascaded stimulated Raman scattering in liquid and ice-Ih D2O.

Stimulated Raman scattering (SRS) of liquid and ice-Ih D2O was investigated using a pulsed Nd:YAG laser with a wavelength of 532nm. The high-order Stokes peaks and corresponding anti-Stokes SRS [Coherent Anti-Stokes Raman Spectroscopy (CARS)] peaks were obtained. Two symmetric and antisymmetric Raman modes of stretching vibrations were observed in liquid D2O, while only a symmetric stretching vibration mode was observed in ice-Ih D2O. Pure Stokes SRS is always collinear with the pump beam along the axial direction. Some ring-like Stokes SRS and CARS shifts, which originate from four-wave mixing processes, can also be observed only in the forward direction along with different angles meeting the phase-matching criteria, respectively. Simultaneously, the temporal behavior of SRS in liquid and ice-Ih D2O was examined, and the temporal waveforms of the pump laser pulse, transmitted pump pulse, and the forward SRS pulse were measured. In both cases, SRS was the dominant contributor to stimulated scattering. However, the efficiency values drastically decreased due to the self-termination behavior of SRS in liquid D2O, which arose from the thermal self-defocusing of both the pump beam and the SRS beam, owing to the Stokes shift-related opto-heating effect. In contrast, for the SRS process in ice-Ih D2O, the thermal self-defocusing influence was negligible, benefitting from a much greater thermal conductivity and a higher conversion efficiency of SRS generation retained under both of the conditions.

Short-pulse broadband stimulated Raman scattering in carbon disulfide via resonance cascading.

Cascaded stimulated Raman scattering (SRS) of carbon disulfide (CS2) was investigated by a pulsed Nd:YAG laser with a wavelength of 532 nm. The fourth-order Stokes and second-order anti-Stokes lines were generated when the pump laser energy was about 1.909 mJ in one sample cell (C1) only. However, the same result was obtained in the second sample cell (C2) with a pump energy of 0.883 mJ. At the same time, the fifth-order Stokes line was produced in C2 when the pump energy increased to 1.208 mJ, and the coherent radiation wavelength ranged from 498 to 644 nm. The result was attributed to the resonance enhancement effect, where the frequency difference between the pump laser and the Stokes light emitted from the working medium (CS2) self-matched with the vibrational energy level of C=S, which resulted in the generation of the cascaded broadband SRS. The anti-Stokes SRS was attributed to four-wave mixing. Simultaneously, the pulse durations of the Stokes and anti-Stokes were compressed to about 380 ps by SRS and laser-induced breakdown. The resonance effect not only reduced the threshold, but it also generated broadband and short-pulse SRS.

Intramolecular Vibration Energy-Transfer-Driven Cascaded Stimulated Raman Scattering and Four-Wave Mixing in Benzene Series.

Cascaded stimulated Raman scattering (SRS) of benzene, bromobenzene, chlorobenzene, ethylbenzene, and toluene was investigated by a pulsed Nd:YAG laser with 532 nm wavelength. The results showed that the third-order Stokes SRS of the ring skeleton vibration (CC at 3006 cm-1) accompanied by another higher-frequency Stokes SRS of the CH stretching vibration (at 3066 cm-1), which arose only when the third-order Stokes SRS of the ring skeleton was produced, can be attributed to the vibration energy transfer between vibration energy levels of CC and CH. The Stokes and anti-Stokes SRS rings, which originated from the intramolecular energy-transfer-enhanced four-wave mixing (FWM) processes, can be observed only in the forward direction along different angles apart from the pump beam direction. The phenomenon also existed in other derivatives of benzene. We propose the intramolecular energy-transfer-enhanced SRS for the first time, which can be used for a broadband Raman laser.

Stimulated Raman scattering in suspension of submicron diamond particles

We report on the first experimental observation of stimulated Raman scattering (SRS), stimulated low-frequency Raman scattering and multiphoton excited negatively-charged single nitrogen-vacancy (NV-) centers luminescence in ethanol suspension of submicron diamond particles obtained at high pressures and temperatures (HPHT). The Stokes and anti-Stokes SRS components with a frequency shift of 1332 cm−1, corresponding to the fundamental optical mode of diamond crystal were observed. The spectral characteristics and energy thresholds of the studied processes were determined.

Phase-interfacial stimulated Raman scattering generated in strongly pumped water

We have observed unusual blue-shifted radiations in water pumped by a strong 532-nm nanosecond laser. Properties including divergence, polarizations, and pulse shapes of the unusual radiations are measured and compared with those of the regular stimulated Raman scattering (SRS) in water. The unusual radiations are attributed to the parametric anti-Stokes SRS that occurs on the interface of water and ionization plasma (or gas) formed in the laser-induced breakdown of water.

Enhanced stimulated Raman scattering in H2 by seeding an SRS line into an H-ɛ Balmer line: Amplification-coupled laser wavelength shifter

The stimulated Raman scattering (SRS) in H2 gas above the dissociation energy limit was recorded using a 266-nm UV laser. All of the observed Stokes and anti-Stokes SRS lines showed a normal behavior except the third Stokes SRS lines at 397.8 nm, which showed a substantial intensity enhancement of about a 36%-conversion efficiency of the pump energy. This enhancement in the SRS line is attributed to the seeding of the SRS line into the Balmer H-ɛ line at 397 nm in molecular hydrogen. To the best of our knowledge, there is no report of any work on enhanced stimulated Raman scattering in H2 by the seeding of the H-ɛ Balmer line into the SRS line and attaining a very high intensity at the third Stokes SRS lines at 397.8 nm. The cell pressure and the laser pulse energy dependence of these SRS lines substantiate our explanation.

Multiwave stimulated raman scattering under quasi-phase-matching conditions

The effect of the generation of higher Stokes and anti-Stokes components of steady-state and transient stimulated Raman scattering (SRS) on the realization of quasi-phase-matching conditions in the course of generation of the first anti-Stokes SRS component is numerically analyzed by using a system of coupled equations derived with regard to diffraction effects. The calculations show that the application of a periodic layered structure in order to realize quasi-phase-matching conditions virtually does not reduce the anti-Stokes SRS efficiency and allows efficient conversion of pulses with a duration of 3 ns or longer. It is found that focusing of waves inside the medium allows partial compensation for diffraction spreading and provides for an increase in the efficiency of anti-Stokes SRS conversion, and, at a Fresnel number above three, the effect of diffraction on the realization of quasi-phase-matching conditions during SRS can be disregarded.

Self-Induced Phase Matching in Parametric Anti-Stokes Stimulated Raman Scattering

We show through the experiments of parametric anti-Stokes stimulated Raman scattering for solid hydrogen that the phase matching in a parametric process can be self-induced without the stringent restriction of the medium. We explain this self-induced phase matching as a consequence of strong coupling between radiation fields and medium spontaneously established through the stimulated Raman scattering process.

Double raman scattering scheme for an XUV laser

A new method is proposed to achieve XUV generation in an He-K mixture medium excited by an electrical discharge by means of a double stimulated Raman scattering (SRS) process. First a dye laser of 404 nm radiation is down-converted to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda_{s} = 1.209 \mu</tex> m in a Stokes SRS and then the produced IR radiation is up-converted to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda_{as} = 64</tex> nm in an anti-Stokes SRS. The overall calculated efficiency of conversion of violet pulse energy into XUV pulse energy reaches <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 \cdot 10^{-4}</tex> in a traveling-wave-type regime with tight focusing and 22 MW pumping power. The XUV pulse energy may reach 12.3 μJ and is limited by excited potassium quartet atoms density ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8 \cdot 10^{11}</tex> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> for this case). The pump power may be lowered by using an IR resonator. Then with 6 ns pulse duration, the same XUV output energy as in the traveling-wave regime may be achieved with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.7 \cdot 10^{-4}</tex> efficiency and a violet pump power of 14 MW.

Angular distribution of anti-Stokes stimulated Raman scattering components from ground and excited vibrational levels of the hydrogen molecule

An investigation was made of the angular distribution of anti-Stokes components of stimulated Raman scattering (STRS) from the ground and excited vibrational levels of the hydrogen molecule. It was established that as the divergence of the pump radiation increases, the angles of emission of the first and second anti-Stokes STRS components due to the 01 (1) transition increased up to twice the angle deduced from the normal phase-matching conditions. The angular spectrum of the anti-Stokes STRS component due to the 12 (1) transition was similar to the angular spectrum observed for STRS in liquids.

Anti-Stokes stimulated Raman scattering of light by polaritons

A theoretical analysis is made of anti-Stokes stimulated Raman scattering (STRS) of light by polaritons in noncentrosymmetric crystals. This is due to the superposition of parametric four-photon and two-stage three-photon processes, in addition to three-photon processes associated with the possible existence of thermal polariton excitations. These processes are mutually coherent and their contributions interfere. The fluctuation-dissipation theory of polariton STRS is applied to derive and analyze general formulas for the frequency-angular distribution of the Stokes and anti-Stokes radiation intensity at the exit face of a plane-parallel crystal layer pumped by a given plane monochromatic wave. Unlike the phonon process, frequency-tunable polariton anti-Stokes STRS is found in scattering at any angles within the polariton range of scattering angles. The anti-Stokes processes also affect the Stokes scattering. In particular, a doublet fine is observed near the center of the gain line with a dip on one side and a on the other. If the is sufficiently large, it may determine the line observed in strong STRS. The anti-Stokes lines are generally considerably narrower than the Stokes lines but their peak intensities are of the same order of magnitude. They also have a doublet structure with a dip and whose width, in this case, is of the order of the total line width. Spontaneous anti-Stokes scatterng is attributable only to thermal polariton excitations in the medium.

Amplifiers involving two-photon energy-extraction schemes

Amplifiers based on two-photon decay channels of inverted metastable species are examined from a rate-equation and practical-feasibility viewpoint. Approximate analytical solutions, within the rate-equation approximation, predict that resonant parametric generation coupled with anti-Stokes-stimulated Raman scattering (ASRS) is a strong competitor to straight two-photon emission. Expressions for initial growth rates indicate that large linear chromatic dispersion, proper linear absorptions, and resonant enhancements can initially favor two-photon emission, but that ASRS will ultimately dominate in most practical situations if inversion depletion does not occur early. For an amplifier based on degenerate two-photon processes, this situation has led to the proposal of running the system as an odd-harmonic generator, first extracting energy via two-photon emission followed by greater-than-100% conversion to the third, fifth, seventh, etc., harmonics. This type of amplifier response has important potential applications for laser-induced thermonuclear fusion as well as for the production of coherent vacuum-uv soft-x-ray systems. An examination of practical constraints provides further analytical relationships between various physical properties of prospective metastable species. Combining these results, several two-photon schemes are pointed out. Based on current technology, atomic iodine, which is inverted to the $^{2}P_{\frac{1}{2}}$ state, appears to be the best medium for experiments, but other materials, such as atomic oxygen, show greater promise if absolute population inversions of high-density material are created at high efficiency.