Stimulated vibrational Raman scattering in HD

This letter reports an observation of stimulated vibrational Raman scattering in HD gas. The Raman threshold data are compared to those of H2under similar conditions, and the difference in their gain coefficients is discussed.     

Surface vibrational spectroscopy using stimulated Raman scattering

We propose a new method for studying surface vibrational spectroscopy based on an extension of the picosecond stimulated Raman gain technique. This technique is extremely surface sensitive and can detect coverages of 1 percent of a monolayer. This technique does not require ultrahigh vacuums (as do electron spectroscopies), is an extremely sensitive probe of surface local fields, has very high frequency resolution (<1 cm^-1) and very short time resolution (∼ 1 ps).     

Stimulated rotational Raman scattering in the atmosphere

Theoretical and experimental information in the literature is used to calculate the gain coefficient for stimulated rotational Raman scattering by atmospheric N2and O2. The dependence on laser wavelength and polarization, as well as on the pressure and altitude is discussed. It is pointed out that because of pressure broadening, the gain coefficient is independent of altitude up to an altitude of 40-50 km, where the Raman transition becomes Doppler broadened. The 1 percent conversion threshold for vertical propagation from the ground up is calculated for various transitions and laser beam characteristics. The highest-gain transition, theS(8) transition of N2, is shown to have a 1 percent conversion intensity threshold of ∼ 1.2 MW/cm2for linearly polarized light at a wavelength of 400 nm.     

First results from the OMI rotational Raman scattering cloud pressure algorithm

We have developed an algorithm to retrieve scattering cloud pressures and other cloud properties with the Aura Ozone Monitoring Instrument (OMI). The scattering cloud pressure is retrieved using the effects of rotational Raman scattering (RRS). It is defined as the pressure of a Lambertian surface that would produce the observed amount of RRS consistent with the derived reflectivity of that surface. The independent pixel approximation is used in conjunction with the Lambertian-equivalent reflectivity model to provide an effective radiative cloud fraction and scattering pressure in the presence of broken or thin cloud. The derived cloud pressures will enable accurate retrievals of trace gas mixing ratios, including ozone, in the troposphere within and above clouds. We describe details of the algorithm that will be used for the first release of these products. We compare our scattering cloud pressures with cloud-top pressures and other cloud properties from the Aqua Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument. OMI and MODIS are part of the so-called A-train satellites flying in formation within 30 min of each other. Differences between OMI and MODIS are expected because the MODIS observations in the thermal infrared are more sensitive to the cloud top whereas the backscattered photons in the ultraviolet can penetrate deeper into clouds. Radiative transfer calculations are consistent with the observed differences. The OMI cloud pressures are shown to be correlated with the cirrus reflectance. This relationship indicates that OMI can probe through thin or moderately thick cirrus to lower lying water clouds.     

Subnanosecond pulse generation in the VUV by dual-wavelength pumpedstimulated rotational Raman scattering

A novel scheme to generate a subnanosecond pulse in VUV spectral region is proposed, by applying a dual-wavelength pumping method in conjunction with polarization switching technique to the stimulated rotational Raman scattering process. Optimum conditions for the efficient conversion and short pulse generation are presented through numerical model calculations. It is theoretically shown that the duration of the first anti-Stokes pulse of a VUV pump laser can be shorten to 0.72 ns. Since the anti-Stokes pulse is generated at a frequency within the gain profile of the pump laser, the proposed process is applicable to a seed pulse generation for subnanosecond pulse amplification by the pump laser medium in the VUV region     

连续调谐波导型H_2受激振动喇曼散射的研究

设计和研制了一台石英毛细管波导型H_2喇曼池,用450nm染料激光研究了H_2的受激振动喇曼散射,测定了一阶Stokes波输出能量与H_2气压之间的依赖关系。最高能量转换效率为20％。用Oxazine-1染料激光作泵浦源获得三阶Stokes信号,得到的红外喇曼散射最长波长达6.57μm。     

Stimulated rotational Raman scattering in CO2-pumped para-H2

Stimulated rotational Raman scattering in a 300 K multipass cell filled with para-H2with a single-mode CO2pump laser was studied using a single-mode OPO as a probe laser at the Stokes frequency for the So(0) transition. Amplification and pump depletion are examined as a function of incident pump energy. For an incident CO2pump laser energy of 1.5 J, a photon conversion efficiency of 47 percent is observed.     

Dependence of the efficiency of Raman scattering in silicon nanowire arrays on the excitation wavelength

The features of Raman scattering in layers of silicon nanowires from 50 to 350 nm in diameter, obtained by the chemical etching of crystalline silicon (c-Si) wafers with preliminarily deposited silver nanoparticles in fluoric acid solutions are studied. c-Si wafers with various crystallographic orientations and doping levels are used, which is conditioned by the different sizes and degrees of ordering of the formed nanostructures. It is found that the radiation of the Raman scattering of samples is depolarized, and its efficiency depends strongly on the excitation wavelength. Upon excitation by light with a wavelength of 1064 nm, the ratio of Raman-scattering intensities of silicon nanowire samples and c-Si is 2 to 5; as the wavelength decreases, this ratio increases for structures with larger silicon-nanowire diameters and higher degrees of ordering and decreases for less ordered structures. The results obtained are explained by the effect of partial light localization in silicon nanowire arrays.     

Amplified spontaneous Raman scattering in fiber Raman amplifiers

Amplified spontaneous Raman scattered light power in forward and backward Raman amplifiers is theoretically and experimentally studied under the assumption of the constant Raman gain coefficient in the bandwidth of an optical filter. On the basis of the results, the power ratio of the amplified signal to amplified spontaneous scattering is discussed. As a result, it is clarified that the effect of amplified spontaneous Raman scattering on the signal to noise ratio for backward Raman scattering is larger than for forward Raman scattering.     

Amplified spontaneous Raman scattering and gain in fiber Raman amplifiers

The spectrum of amplified spontaneous Raman scattering and gain in a fiber Raman amplifer has been calculated analytically as a function of distance and pump power. The model used makes no assumptions on the magnitude of the gain and considers the pump nondepletion region. From the results, the on/off ratio has been calculated and is found to have a variation with length that depends on frequency detuning. An enhancement in on/off ratio is also found for small fiber lengths but at limited gain. The use of a narrow-bandpass optical fiber leads to quite different behavior of the on/off ratio than for the unfiltered case.     

High power pure rotational laser due to vibrational excitation

It is suggested for the first time to use VRT-relaxation for the excitation of high power laser laser action on rotational transitions in FIR spectral range. It is shown, that the required conditions can be achieved by the free expansion of the previously heated mixture of hydrogen halides molecules and slowly relaxing molecules.     

Li-inserted carbon nanotube Raman scattering

The possibility of inserting lithium into single wall carbon nanotube bundles during the growth process is analyzed in this work by using the Raman technique as probe. The nanotubes were prepared by the arc discharge method by using catalysts prepared by mixing compounds containing lithium and as their counterpart, a similar mixture without this alkali-metal. The two pair of samples studied in this work were obtained with the following catalysts: (i) Li₂CO₃/NiO/CoO and NiO/CoO; or (ii) LiCo_0.5Ni_0.5O₂ and Ni/Co. Raman spectra reveal that the tangential bands profiles of the samples prepared with the catalyst containing lithium is considerably modified in both cases. In the case of the carbon nanotubes obtained using the LiCo_0.5Ni_0.5O₂ catalyst a down shift and severe broadening are observed in addition. Comparison of our results with those published previously for alkali-metals doped single wall carbon nanotubes allowed to conclude that lithium incorporation, actually, occurs during the growth process.     

Raman scattering characterization on SiC

Raman scattering is a powerful non-contact and non-destructive characterization tool for SiC polytypes for both the lattice and electronic properties. Here, I will briefly review two recent Raman experiments on SiC; metal/SiC interface reactions probed by visible lasers and ion-implantation damages probed by deep UV lasers. These studies utilize the opposite aspects of the probe laser, i.e. deep and shallow penetration depth into SiC.     

Stimulated Raman scattering in quartz

Stimulated Raman scattering (SRS) from infrared-active phonons in quartz is discussed. The scattering is concluded to be from a different region ofkspace than that previously stated in the literature. The possibility of producing a broadly tunable parametric oscillator via SRS in quartz is viewed with pessimism.     

Time behavior of stimulated Raman scattering

The time relationship between the 1st Stokes, 2nd Stokes, 3rd Stokes, 1st anti-Stokes radiations, and the exciting laser radiation for stimulated Raman scattering in self-focusing liquids has been investigated theoretically and experimentally. A model is presented for calculating the output power and time behavior of the different orders of Stokes radiation when self-focusing occurs. Experimentally, good agreement is found between predicted and measured output powers, but some apparent anomalies are observed in the time behavior for the 2nd and 3rd Stokes radiations and 1st anti-Stokes radiation, especially in carbon disulfide. There are strong indications of dielectric breakdown occurring in the liquids, and it is shown qualitatively that the observed time behavior of the higher order Stokes radiation can be caused by the dielectric breakdown.     

Surface-enhanced Raman scattering from semiconductor nanostructures

正Developing the surface-enhanced Raman scattering(SERS)substrate from noble metals to semiconductors would bring the SERS more promising applications in biomedicine detection.Based on the photo-induced charge transfer(PICT)mechanism the SERS model in the semiconductor-molecule system was built up.The analytical solution of the contribution from PICT to the molecular polarizability tensor was presented according to calculation of quantum mechanics,and the results suggested that arising SERS from the nanostructured Si substrate is possible.Experimental observation revealed that the numerous hydrogen atoms on the surface of the Hterminated Si nanowire(H-SiNW)arrays may serve as electron sink,and play a critical role in promoting efficient PICT and enable the SERS effect.The evident Raman enhancement of the standard probe Rodamine 6G(R6G),dye(Bu4N)2[Ru(dcbpyH)2-(NCS)2](N719),and the 4-aminothiophenol(PATP)from such substrates were detected.1 A significant enhancement of b2 modes could be observed from PATP chemisorbed on the H-SiNWs substrate,which indicated that a strong PICT process had taken place in the system.     

Analysis of stimulated Raman scattering in waveguides

Stokes radiation, excited by a giant pulse radiation propagating along a rectangular wavegulde, is analyzed in this paper. Equations are established and solved for an arbitrary shape of the giant pulse. At high gains the stimulated radiation is emitted at all angles. The maximum output is almost perpendicular to the exciting beam, and it decreases as the forward and backward directions are approached. Forward-backward ratios are sensitive to the detailed shape and magnitude of the laser pulse. The large forward-backward ratio for intense short laser pulses accounts for the observed results, which are illustrated for a square and a parabolic pulse. In practice, a large number of waveguide modes are simultaneously excited, resulting in intense excitation of vibrational modes in the medium, and enhancement of the inverse Raman effect and of anti-Stokes generation.     

Oblique Raman and polariton scattering in lithium iodate

We have predicted and measured tuning of the LO and TO oblique Raman and the oblique polarition frequencies in the 769-848 cm^-1spectral region in lithium iodate. Oblique scattering in LiIO3is produced by coupling ofAandEsymmetry crystal modes. The resulting LO and TO frequencies lie between the frequencies of the contributing modes. The intensity of the scattered light observed indicates that construction of CW or quasi-CW stimulated oblique Raman and polariton oscillators are possible.