Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “RAMAN EFFECT”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

40-fs hydrogen Raman laser

40-fs first Stokes pulses at a wavelength of 1.2 μm were generated in a hydrogen SRS-converter pumped by orthogonally polarised double chirped pulses of a Ti : sapphire laser. To obtain a Stokes pulse close to a transform-limited one, a programmed acousto-optic dispersive delay line was placed between the master oscillator and regenerative amplifier. The energy efficiency of Stokes radiation conversion reached 22%. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

1-kHz-repetition-rate femtosecond Raman laser

A femtosecond Raman laser utilising compressed hydrogen is experimentally investigated under pumping by radiation from a 1-kHz-repetition-rate Ti : sapphire laser. In the regime of double-pulse pumping, the conditions are determined, which correspond to the minimal energy dispersion of Stokes pulses. The optical scheme is realised, which is capable of ensuring the long-term stability of the average power of the first Stokes component with a variation of less than 2%. The Stokes pulses are produced with a pulse duration of 60 fs and energy of 0.26 mJ at a conversion efficiency of 14%. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Simulation of an intracavity Q -switched optical parametric oscillator using rate equations

Based on rate equations we have refined the model of an intracavity Q -switched optical parametric oscillator (IOPO) by taking into account the influence of self-Raman stimulated scattering. The rate equations are solved and analysed in the plane-wave approximation for a Gaussian spatial beam distribution profile under various conditions. The spatial rate equations are also solved numerically for a beam with a field distribution of the TEM{sub 00} mode. The numerical analysis shows that stimulated self-Raman scattering leads to a decrease in the output signal power and an increase in the signal pulse width. This model allows one to predict that the output signal power can be increased with increasing ratio of Raman to fundamental photon lifetimes. This suggests a practical method for determining the self-Raman gain coefficient experimentally. In addition, a multi-pulse process for the signal beam of the IOPO can be regenerated by the presented model. However, in comparison with the previous research, the presented model is more accurate and allows one to design and optimise single-resonator IOPOs.The bibliography includes 25 references. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Generation of linearly polarised light near 1.4 μm in a cascaded, random distributed feedback Raman laser

We have demonstrated efficient generation of linearly polarised light by a random distributed feedback laser based on stimulated Raman scattering in a 1.8-km-long fibre, pumped by linearly polarised radiation of an ytterbium-doped fibre laser with a lasing wavelength near 1.06 μm. Cascaded generation up to the fifth Stokes component (1.4 μm) with wavelength tuning by changing the pump wavelength is obtained. The output power of the fourth Stokes component reached 5 W at λ=1.34 μm. The problems related to the further mastering of the long-wavelength region are discussed. (paper)

42 ENGINEERING↗
DOE OSTI2017

Femtosecond compressed-nitrogen Raman laser

We have estimated the minimum laser pulse duration at which stimulated Raman scattering in gases is possible. Femtosecond Ti : sapphire laser pulses have been converted to the first Stokes in compressed nitrogen using double-pulse pumping of a gas-filled capillary tube by orthogonally polarised chirped pulses. We have obtained 980-nm Stokes pulses of 51 fs duration. The energy conversion efficiency was 12 % at a pulse repetition rate of 1 kHz and average laser output power of 2 W. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Study of the formation of thermochemical laser-induced periodic surface structures on Cr, Ti, Ni and NiCr films under femtosecond irradiation

The formation of femtosecond laser-induced periodic surface structures (LIPSS’s) on Cr, Ti, Ni and NiCr films (with different Cr contents) is investigated. It is established that thermochemical LIPSS’s with periods of 950, 930 and 980 nm are formed, respectively, on the surfaces of titanium, chromium, and nichrome (with a chromium content of 20%); however, thermochemical LIPSS’s are not formed on the surfaces of nickel and nichrome with a low chromium content, although Raman data indicate that oxidation occurs in all cases. A weakly ordered ablated structure with a period of 250 – 300 nm is found to be formed on oxidised areas of thermochemical LIPSS’s in the case of chromium and nichrome (80/20). Experimental data on selective etching of thermochemical LIPSS’s on titanium and chromium films are presented. (paper)

36 MATERIALS SCIENCE↗
DOE OSTI2017

Population difference gratings produced by unipolar subcycle pulses in a resonant medium

We demonstrate the possibility of inducing, erasing and extra rapidly controlling population difference gratings resulting from coherent interaction of unipolar subcycle pulses with a resonant medium. Gratings can be produced without overlap of pulses in the medium, which is an important distinction of the proposed approach from the traditional one, in which gratings are produced using interference of two or more overlapping quasi-monochromatic light beams. The use of unipolar subcycle pulses ensures faster control over gratings in comparison with bipolar pulses studied by us previously.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

4.4-μm Raman laser based on hollow-core silica fibre

A Raman laser with a wavelength exceeding 4 μm is designed for the first time. Using a revolver silica fibre with a hollow core filled with molecular hydrogen ({sup 1}H{sub 2}) as an active medium, we have obtained SRS lasing at a wavelength of 4.4 μm under pumping by a pulsed erbium fibre laser ( λ = 1.56 μm, τ = 2 ns). The SRS conversion quantum efficiency reaches 15 %, and the maximum output peak power at a wavelength of 4.4 μm is 0.6 kW.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Minimum possible laser pulse duration for SRS

The minimum laser pulse duration for transient stimulated Raman scattering is shown to be limited as a consequence of nonlinear phase modulation of the laser and Stokes waves. It is determined by the ratio of the nonlinear refractive index to the spontaneous Raman scattering cross section. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

FBG array-based random distributed feedback Raman fibre laser

We have demonstrated the possibility of making a Raman laser with a random distributed feedback ensured by an array of 57 fibre Bragg gratings with random phases and amplitudes inscribed in a 13-m-long polarisation-maintaining passive fibre. The linearly polarised cw output power at a wavelength of 1092.3 nm reaches 5.7 W. The laser linewidth at the highest output power is about 80 pm. In the nearthreshold regime, we observe single-frequency lasing with a linewidth under 100 kHz as determined by self-heterodyne measurements. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Ultralong fibre-optic distributed Raman temperature sensor

We have demonstrated an ultralong (up to 85 km in length) all-fibre Raman temperature sensor which utilises SMF-28 standard single-mode telecom fibre and a 1.63-μm probe signal source. The probe signal from the laser diode is amplified by a Raman fibre amplifier. The temperature along a 85-km-long fibre line has been measured with an accuracy of 8 °C and spatial resolution of 800 m or better. (laser applications and other topics in quantum electronics)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Variation in the structure of a time-dependent SRS spectrum in microfiltered water

The time-dependent stimulated Raman scattering of light in water subjected to structural transformation by track membrane microfiltration is investigated. It is shown that the probability of SRS at the frequency of the ice spectral component in the band of stretching OH vibrations of water molecules decreases as a result of water filtration. (nonlinear optical phenomena)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Off-resonant Raman quantum memory in impurity crystals: signal-to-noise ratio analysis

The possibility of implementing an off-resonant Raman scheme of optical quantum memory on the basis of an ensemble of three-level atoms is investigated under the condition of equal polarisations of resonant transitions forming the Λ-scheme. The developed model is used to analyse the signal-to-noise ratio at the output of an optical quantum memory device in {sup 143}Nd{sup 3+} : Y {sup 7}LiF{sub 4}. It is shown that this ratio can significantly exceed unity for single-photon input pulses. The required values of the parameters can be obtained by using an impurity crystal in the form of a whispering-gallery mode ring resonator. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Precision measurement of the forbidden 2{sup 1}S{sub 0} – 2{sup 3}S{sub 1} transition frequency in a helium atom

We demonstrate the possibility of measuring the forbidden 2{sup 1}S{sub 0} – 2{sup 3}S{sub 1} transition frequency (λ = 1557 nm) of a helium atom by the method of stimulated Raman scattering through the intermediate 2{sup 3}P{sub 1} level. Singlet (2{sup 1}S{sub 0}) and triplet (2{sup 3}S{sub 1}) states have long lifetimes of 20 ms and 8000 s, respectively. The transition is important for the spectroscopy of the helium atom because it relates the singlet and triplet parts of the spectrum. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Diamond Raman laser emitting at 1194, 1419, and 597 nm

A Raman laser based on a synthetic diamond crystal pumped by nanosecond pulses of a 1030-nm Yb : YAG laser and emitting in the IR region at the first and second Stokes wavelengths of 1194 and 1419 nm, respectively, was developed. The conversion efficiency was 34 % with a slope efficiency of 50 % and an average power of 1.1 W at a wavelength of 1194 nm; the average power at 1419 nm was 0.52 W. Frequency doubling of the first Stokes component in a nonlinear BBO crystal resulted in orange (597.3 nm) radiation with a pulse energy of 0.15 mJ, an average power of 0.22 W, and a maximum efficiency of 20 %. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Experimental investigation of nonlinear operation mode of a DP-QPSK 100G link with co-propagating-pump Raman amplification

The nonlinear interference noise in a coherent single-span fibre-optic communication link (FOCL) with co-propagating Raman amplification is investigated at different levels of input Raman pump and channel powers and dispersion. A simple phenomenological expression for calculating the nonlinear noise power at the output of a single-channel FOCL is presented. The merit of using a distributed Raman amplifier with co-propagating pump up to 1 W in a single-span single-channel FOCL is experimentally investigated. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Parametric stimulated Raman scattering in barium nitrate crystals

The spectra of multifrequency parametric stimulated Raman scattering in a barium nitrate single crystal is investigated. When this single crystal is excited by ultrashort (80 ps) YAG : Nd{sup 3+} laser pulses with a wavelength of 1064 nm, a frequency comb of eight anti-Stokes components is observed in the visible spectral range. The Raman satellites are due to the totally symmetric vibrational modes of barium nitrate single crystal. The frequencies of the corresponding Raman Stokes components in the IR range (from 1193 to 9662 nm) are calculated. The results of the study open the way to form an array of laser frequencies from the IR to green spectral range with a period of 1047 cm{sup –1}. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Enhancement of local electromagnetic fields by periodic optical resonators

The periodically profiled metasurfaces of silicon and of the same surfaces coated with a thin layer of silver are experimentally investigated to improve the signal-to-noise ratio in the observation of Raman light scattering from molecular compounds. The noise in this case is the unavoidable background molecular luminescence. Our experimental and computer simulation data demonstrate an anomalous optical response due to the excitation of metal-dielectric surface resonances. An enhanced Raman scattering signal is observed from 5,5′-dithiobis(2-nitrobenzoic) acid (DTNB) organic molecules deposited on the metasurface. The proposed metasurface provides a significant enhancement of the RS signal in comparison with the luminescence signal and is an efficient substrate for realising giant Raman scattering of light. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗