Stokes Radiation Research Articles

Study of Stokes Drag and Radiation Pressure in the Restricted Four-Body Problem with Variable Mass

Study of Stokes Drag and Radiation Pressure in the Restricted Four-Body Problem with Variable Mass

Multiwavelength Generation of Stokes Radiation Components with a Small Wavelength Spacing under Stimulated Raman Scattering in a SrMoO4 Crystal

Multiwavelength Generation of Stokes Radiation Components with a Small Wavelength Spacing under Stimulated Raman Scattering in a SrMoO4 Crystal

Optical properties of γ-sensing β-GaLaS3:Er crystal

An erbium-doped β-GaLaS3 crystal has been grown by the solution-melt method, and the effect of γ-irradiation on their vibrational and radiative properties has been investigated. Experiments have demonstrated that the crystal is transparent in the near and mid-infrared (IR) regions (transparency ∼62% in the range of 350–7100 cm−1), which allows it to be used as an effective matrix for creating lasers in this spectral range. For the first time, the vibrational spectrum of the crystal and the density of phonon states have been calculated using the density-functional theory (DFT) method. Both the original and γ-irradiated β-GaLaS3:Er crystals were investigated by Raman and IR spectroscopy. It has been established that irradiation with a dose of up to 5000 Gray does not lead to structural changes in the crystals. The effect of the formed defects is more clearly manifested in the IR reflection spectra, compared to the Raman spectra. The mechanism of the occurrence of excited states and the emission of Er ions embedded in the lattice has been established, and the effect of γ-irradiation on the radiative properties of β-GaLaS3:Er due to the occurrence of radiation-induced defects has been analyzed. A model has been constructed that explains the Stokes and anti-Stokes radiation of the erbium ions in the crystal. It has been demonstrated that the grown crystal has good prospects for sensor and laser technology of the near and mid-IR ranges due to relatively high values of optical transparency and the intense radiative capacity of the erbium ions.

Locked-energy at first-order Stokes stimulated Raman scattering for an aqueous sulfuric acid solution

We introduced a locked-energy coherent Stokes radiation scheme based on multi-mode stimulated Raman scattering (SRS) of aqueous sulfuric acid solutions. SRS of pure sulfuric acid has only one vibrational characteristic peak. Mixing sulfuric acid with water leads to the appearance of bisulfate, and the energy transfer between adjacent vibrational energy levels in a 17.0 mol/l aqueous sulfuric acid solution leads to generation of five different vibrational modes in a solution. The competition between these five SRS modes prevents the vibrational energy from being transferred to high-order Stokes waves, thereby locking most of the energy in the first-order Stokes SRS and outputting a very strong, broadband, and coherent Raman radiation ranging from 555 to 570 nm. This study demonstrates the possibility of producing an intense single longitudinal mode laser.

Natural Convection With Surface Radiation From the Infrared Suppression Device and Estimation of Cooling Time: A Computational Analysis

AbstractThe thermofluid characteristics of the infrared suppression (IRS) device used in the marine gas turbine as an exhaust system are numerically investigated here. The prime objective is to observe the impact of convection united with surface radiation on the cooling of the IRS. Furthermore, the time taken to cool down the device is also estimated. A comparison exercise is also carried out to elucidate the impact of radiation considering the surface radiation and without it (taking only convection). The numerical solution of the Navier–Stokes equation, energy equation, and radiation equation, along with the turbulence equations, are performed using ANSYS FLUENT 15.0. Various relevant parameters are taken for the analysis, namely, Rayleigh number (Ra) (1 × 1010 ≤ Ra ≤ 1 × 1012), diameter ratio (DR) (1.01 ≤ DR ≤ 1.3), funnel overlapping (OL) (−20% ≤ OL ≤ 20%), and emissivity of the surface (ε) (0 ≤ ε ≤ 1). It is noticed that surface radiation has an enormous contribution to the total heat transfer and, thus, could not be neglected. The total heat transfer rate and mass flowrate increase with Ra and DR. Also, the contribution of convective heat transfer drops with the rise in emissivity. In addition, the convection united with surface radiation case reduces the cooling time (almost half) than the natural convection alone case.

Cascaded Generation in Multimode Diode-Pumped Graded-Index Fiber Raman Lasers

We review our recent experimental results on the cascaded Raman conversion of highly multimode laser diode (LD) pump radiation into the first- and higher-order Stokes radiation in multimode graded-index fibers. A linear cavity composed of fiber Bragg gratings (FBGs) inscribed in the fiber core is formed to provide feedback for the first Stokes order, whereas, for the second order, both a linear cavity consisting of two FBGs and a half-open cavity with one FBG and random distributed feedback (RDFB) via Rayleigh backscattering along the fiber are explored. LDs with different wavelengths (915 and 940 nm) are used for pumping enabling Raman lasing at different wavelengths of the first (950, 954 and 976 nm), second (976, 996 and 1019 nm) and third (1065 nm) Stokes orders. Output power and efficiency, spectral line shapes and widths, beam quality and shapes are compared for different configurations. It is shown that the RDFB cavity provides higher slope efficiency of the second Stokes generation (up to 70% as that for the first Stokes wave) with output power up to ~30 W, limited by the third Stokes generation. The best beam quality parameter of the second Stokes beam is close to the diffraction limit (M2~1.3) in both linear and half-open cavities, whereas the line is narrower (<0.2 nm) and more stable in the case of the linear cavity with two FBGs. However, an optimization of the FBG reflection spectrum used in the half-open cavity allows this linewidth value to be approached. The measured beam profiles show the dip formation in the output pump beam profile, whereas the first and second Stokes beams are Gaussian-shaped and almost unchanged with increasing power. A qualitative explanation of such behavior in connection with the power evolution for the transmitted pump and generated first, second and third Stokes beams is given. The potential for wavelength tuning of the cascaded Raman lasers based on LD-pumped multimode fibers is discussed.

SRS of ultrashort laser pulses with nonlinear phase modulation

The SRS process in the regime of nonlinear phase modulation of laser and Stokes radiation waves is studied experimentally. The effect of the relationship between the laser and Stokes wavelengths on the value of the minimum laser pulse duration, at which an efficient SRS process is possible, is ascertained. The possibility of obtaining maximally broadband Stokes radiation pulses by matching the group velocities of the laser and Stokes pulses is demonstrated.

Stimulated Acoustic Light Scattering in the Externally Excited Optical Resonator

Dynamics of Stokes radiation generation in a nanodispersed medium within an optical resonator excited by external monochromatic radiation is investigated for the first time. Conversion of incident radiation results from ponderomotive buildup of intrinsic acoustic pulsations of the dispersed particles. It is assumed that the resonator mirrors reflect well the frequencies of the incident radiation and the first Stokes component.

2 kW high-efficiency Raman fiber amplifier based on passive fiber with dynamic analysis on beam cleanup and fluctuation.

In this paper, we study the power scaling in high power continuous-wave Raman fiber amplifier employing graded-index passive fiber. The maximum output power reaches 2.087 kW at 1130 nm with an optical conversion efficiency of 90.1% (the output signal power versus the depleted pump power). To the best of our knowledge, this is the highest power in the fields of Raman fiber lasers based merely on Stokes radiation. The beam quality parameter M2 improves from 15 to 8.9 during the power boosting process, then beam spot distortion appears at high power level. This is the first observation and analysis on erratic dynamic properties of the transverse modes in high power Raman fiber amplifier.

Combined effect of Stokes drag, oblateness and radiation pressure on the existence and stability of equilibrium points in the restricted four-body problem

This paper studies numerically the existence of collinear and non-collinear equilibrium points and their linear stability in the frame work of photogravitational circular restricted four-body problem with Stokes drag acting as a dissipative force and considering the first primary as a radiating body and the second primary as an oblate spheroid. The mass of the fourth body is assumed to be infinitesimal and does not affect the motion of the three primaries which are always at the vertices of an equilateral triangle (Lagrangian configuration). It is found that at constant dissipative force, and a simultaneous increase in both radiation pressure and oblateness coefficients, the curves that define the path of the motion of the infinitesimal body are found to shrink due to shifts in the positions of equilibrium points. All the collinear and non-collinear equilibrium points are found to be linearly unstable under the combined effect of radiation pressure, oblateness and Stokes drag. The energy integral is seen to be time dependent due to the presence of the drag force. More so the dynamic property of the system is investigated with the help of Lyapunov characteristic exponents (LCEs). It is found that the system is chaotic as the trajectories locally diverge from each other and the equilibrium points are chaotic attractors. We justified the relevance of the model in astronomy by applying it to a stellar system (Gliese 667C) and another found that both the existence and stability of the equilibrium points of any restricted few body system greatly depend of the value of the mass parameter.

Using polarization control plate to suppress transverse stimulated Raman scattering in large-aperture KDP crystal

AbstractTransverse stimulated Raman scattering (TSRS) is strongly generated in the third-harmonic-generation crystal potassium dihydrogen phosphate (KDP) and can even damage the KDP crystal in inertial confinement fusion drivers. In this work, a method to suppress TSRS is proposed in which the polarization control plate (PCP) is moved to a new position in the existing optical path. The proposed method can suppress TSRS significantly and doubles the laser threshold intensity in KDP crystal when the order of the PCP is 16. This result is attributed to the reduction of the gain length for the Stokes radiation. The proposed method may also be used to suppress other nonlinear effects, including transverse stimulated Brillouin scattering in large-aperture optical components.

Linearly Polarized Multi-Wavelength Fiber Laser Comb via Brillouin Random Lasing Oscillation

A linearly polarized multi-wavelength Brillouin laser comb in the 1.5- $\mu \text{m}$ telecom spectral window is established by cascading multiple Brillouin random lasing oscillations in a semi-open polarization maintaining fiber (PMF)-based composite cavity. Distributed Rayleigh scattering offers a broadband random reflector to build up efficient Brillouin lasing resonance along kilometer-long PMFs, yielding four orders of Stokes radiation with high degree of polarization (>99.67%) and polarization extinction ratio of >20 dB. Each Stokes component with kilohertz linewidth as well as over 40-dB optical signal-to-noise ratio has been validated. Compared with single mode fiber-based laser design, the proposed PMF-based laser comb exhibits highly suppressed relative intensity noise, thanks to the immunity to external perturbation and random modes density reduction within polarization-matched Brillouin gain.

250 W clad pumped Raman all-fiber laser with brightness enhancement.

We report a strictly all-fiber clad pumped Raman fiber laser with a CW power of 250W. To the best of our knowledge, this is the highest power Raman fiber laser demonstrated in any configuration allowing brightness enhancement. In addition, this is the first report of a Raman clad pumped all-fiber laser. The brightness of the pump source was enhanced by a factor of ∼3.8. This result was achieved by the design of a novel triple-clad fiber, with tight pump power inner confining clad that both maximized the Raman gain and inhibited the second Stokes radiation. We discuss power-increase effects on the beam quality, efficiency, and brightness enhancement.

Integrated continuous-wave aluminum nitride Raman laser

Wurtzite aluminum nitride (AlN) is known to exhibit six Raman-active optic phonons, making it appealing for Raman lasing. Here, we demonstrate continuous-wave Raman lasers with a low threshold and a high slope efficiency in high quality factor AlN-on-sapphire microrings. Stokes radiations around 1.7–1.8 μm and cascaded operation into 1.9–2.0 μm are identified with a telecom pump. Two types of Stokes lights with distinct Raman shifts and polarizations are recorded via selective excitation of corresponding optic phonons, in accordance with the Raman selection rules in AlN. The observed lasing behavior is satisfactorily accounted for by a theoretical analysis. Our results indicate that AlN-on-sapphire should be promising for integrated nonlinear optics.

Investigation of pre-pulse pumping laser for preserving temporal waveform of stimulated Raman scattering

A modified polarized beam combination technique is proposed for preserving the temporal waveforms of stimulated Raman scattering. 1064 nm pre-pulse pumping lasers prior to the main pumping laser with a delay time are generated and injected into a Ba(NO3)2 Raman medium to excite the crystal firstly. The influences of pre-pulse lasers with various energy levels on the temporal shapes of Raman lasers are investigated, and it is demonstrated that the temporal waveforms of the Raman laser are distorted once the energies of the pre-pulse are below and above the required energy for preserving the temporal shapes of Stokes radiation. It is also discovered that the temporal shape of the 1197 nm Raman laser cannot be perfectly preserved if the energy of the 1064 nm main laser is too low or the relative delay time is too large. Moreover, the optical conversion efficiency and Stokes laser energy obtained under pumping lasers with single and double intensity peaks are compared.

Multi-wavelength Yb:YAG/Nd3+:YVO4 continuous-wave microchip Raman laser.

Multi-wavelength continuous-wave (CW) Raman lasers in a laser diode pumped Yb:YAG/Nd3+:YVO4 microchip Raman laser have been demonstrated for the first time to our best knowledge. The multi-wavelength laser of the first Stokes radiation around 1.08 μm has been achieved with a Raman shift of 261 cm-1 for a-cut Nd:YVO4 crystal corresponding to the fundamental wavelength at 1.05 μm. Multi-wavelength laser operation simultaneously around 1.05 and 1.08 μm has been achieved under the incident pump power between 1.5 and 1.7 W. Multi-wavelength Raman laser with frequency separation of 1 THz around 1.08 μm has been obtained when the incident pump power is higher than 1.7 W. The maximum Raman laser output power of 260 mW at 1.08 μm is obtained and the corresponding optical-to-optical conversion efficiency is 4.2%. Elliptically polarized fundamental laser and linearly polarized Raman laser were observed in an Yb:YAG/Nd:YVO4 CW microchip Raman laser. The experimental results of linearly polarized, multi-wavelength Yb:YAG/Nd:YVO4 CW microchip Raman laser with adjustable frequency separation provide a novel approach for developing potential compact laser sources for Terahertz generation.

Transverse mode locking of Stokes radiation in diode end-pumped Nd:YVO4 laser passively Q-switched by Cr4+:YAG

Transverse mode locking of the Stokes component generated in the mode of stimulated Raman scattering self-conversion by a pulsed diode end-pumped Nd:YVO4/Cr:YAG laser is implemented for the first time under conditions of frequency degeneracy of cavity modes.

Accounting for Transverse Inhomogeneity of Radiation Beams in Laser Raman Scattering

A simple method of accounting for transverse inhomogeneity of the pump and Stokes radiation beams in the description of stimulated Raman scattering (SRS) using intensity-transfer equations for interacting beams is proposed. Features of the method are illustrated using the calculated dependences of the Raman laser efficiency on the output mirror reflectivity and the pump pulse energy as examples.

Dual-wavelength Nd:LGGG laser intracavity pumped simultaneous OPO and SRS processes in single KTP.

Simultaneous optical parametric oscillation (OPO) and stimulated Raman scattering (SRS) in a single KTiOPO₄ (KTP) intracavity pumped by a dual-wavelength Nd:LGGG laser were demonstrated for the first time, to the best of our knowledge. A maximum output power for the signal beam was 448 mW, while for the Stokes radiations it was 40 mW, corresponding to an overall conversion efficiency of about 4.65%. The shortest pulse durations for OPO and SRS waves were directly measured to be 850 ps and 1.526 ns, respectively. The highest peak power of 30.6 kW and the pulse energy of 26 μJ for the signal beam were also obtained. A set of coupled rate equations for the dual-wavelength pumped OPO and SRS was also established. The numerical solutions fit with the experimental results.

Theoretical and experimental studies on coexistent OPO and SRS from a KTiOPO4 pumped by an AO Q-switched Nd:LGGG laser

Coexistent intracavity KTiOPO4 optical parametric oscillator (OPO) and stimulated Raman scattering (SRS) processes pumped by an acousto-optical Q-switched Nd:LuxGd3−xGa5O12 (Nd:LGGG) laser were presented for the first time. The Stokes radiations at 1093.2/1125.8 nm and a signal wave of 1570 nm were generated. At an incident pump power of 9.25 W and pulse repetition rate of 3 kHz, the maximum output powers of 375 mW at 1570 nm and 98 mW at 1093.2/1125.8 nm were obtained for the signal wave and Stokes radiations, respectively, corresponding to a total conversion efficiency of 5.1 %. A set of coupled rate equations for coexistent OPO and SRS processes was developed, and the numerical solutions agreed with the experiment results.