Stokes Components Research Articles

Multiwavelength highly transient stimulated Raman scattering on dual Raman modes in Sr(MoO4)0.8(WO4)0.2 and Sr(MoO4)0.4(WO4)0.6.

For the first time to our knowledge, multiwavelength, highly transient, single-pass stimulated Raman scattering with a low wavelength spacing on dual (stretching and bending) Raman modes in Sr(MoO4)0.8(WO4)0.2 and Sr(MoO4)0.4(WO4)0.6 solid solutions in a range of 1000-1300 nm (transparence window of biological tissue) under ultrafast chirped pulse laser pumping is comparatively investigated in the interests of multicolor two-photon imaging of a living tissue. For both the solid solutions, the optimum range (1-5 ps) of chirped pump pulse durations for multiwavelength Raman conversion on dual Raman modes was wider than for SrMoO4 (2-3 ps) due to the higher integral cross section of the bending Raman mode. Higher efficient SRS conversion took place at negative chirping of the pump pulse with its stretching from 0.25 ps up to 5 ps due to the compensation of a positive chirp caused by nonlinear phase modulation with total Raman conversion efficiency of up to 36% for Sr(MoO4)0.8(WO4)0.2 and 49% for Sr(MoO4)0.4(WO4)0.6. The highest number (five) of Stokes components in the desired range (1000-1300 nm) was observed in the optimum Sr(MoO4)0.4(WO4)0.6 solid solution, which has the Raman modes with comparable intensities.

Observation and all-optical manipulation of replica symmetry breaking dynamics in a multi-Stokes-involved Brillouin random fiber laser photonic system

In this paper, we propose and demonstrate an all-optical control of RSB transition in a multi-wavelength Brillouin random fiber laser (MWBRFL). Multi-order Stokes light components can be subsequently generated by increasing the power of the Erbium-doped fiber amplifier (EDFA) inside the MWBRFL, providing additional disorder as well as multiple Stokes-involved interplay. It essentially allows diversified laser mode landscapes with adjustable average mode lifetime and random mode density of the 1st order Stokes, which benefits the switching between replica symmetry breaking (RSB) and replica symmetry (RS) states in an optically controlled manner. Results show that the average mode lifetime of the 1st order Stokes component gradually decreases from 250.0 ms to 1.2 ms as high orders from the 2nd to the 5th of Stokes components are activated. Meanwhile, the order parameter q of the 1st order Stokes random lasing emission presents distinct statistical distributions within the selective sub-window under various EDFA optical powers. Consequently, all-optical dynamical control of the 1st Stokes random laser mode landscapes with adjustable average mode lifetime turns out to be attainable, facilitating the RSB transition under an appropriate observation time window. These findings open a new avenue for exploring the underlying physical mechanisms behind the occurrence of the RSB phenomenon in photonic complex systems.

All-fiber amplification of highly chirped dissipative solitons around a 1.3 micron using stimulated Raman scattering

An all-fiber amplification of highly chirped dissipative solitons (DSs) by stimulated Raman scattering in a standard passive fiber with continuous-wave pumping is demonstrated for the first time to our knowledge. DSs with a duration of 20 ps and a repetition rate of 15.6 MHz at a wavelength of 1275 nm are amplified by a pump wave at 1205 nm. On–off Raman gain dependence on the amplifier length and pump power, as well as the pumping configuration, are experimentally studied. Uniform amplification has been achieved with a net gain of 10 dB resulting in a pulse energy of 13 nJ at backward pumping. Further Raman amplification is limited by emerging the next Stokes component. The output pulses are compressed by a factor of 50 down to a duration of 400 fs. As a result, the peak power reached the level of 9 kW. The demonstrated scheme can be a simple and robust alternative to the widely used parametric amplification of chirped pulses outside the dopant amplification band, and the resulting pulses can be used in multiphoton microscopy and other applications.

Confirming the stimulated Raman origin of singlet‐oxygen photogeneration

AbstractWe confirm the Raman origin of the singlet oxygen photogenerated in water environments without using photosensitizers. Nanosecond light pulses in the blue region of the spectra (405–480 nm) generate Raman Stokes excitation of singlet oxygen in the red region (600–670 nm) when focusing on pure distilled water. The excitation also produces Stokes components corresponding to the stretching modes of water molecules. The time evolution of both types of Stokes components, singlet oxygen, and stretching modes correspond to the time duration of the excitation pulse as expected for a Raman process. Their power dependences are also similar. Finally, both signals exhibit high refractive ring structures due to the nonlinear optical interaction generated by the stimulated Raman process.

The Mechanism of the Formation of the Spin Hall Effect in a Sharp Focus

We have shown how the spin Hall effect is formed in a tight focus for two light fields with initial linear polarization. We have demonstrated that an even number of local subwavelength regions appear in which the sign of the longitudinal projection of the spin angular momentum (the third Stokes component) alternates. When an optical vortex with topological charge n and linear polarization passes through an ideal spherical lens, additional optical vortices with topological charges n + 2, n − 2, n + 1, and n − 1 with different amplitudes are formed in the converged beam. The first two of these vortices have left and right circular polarizations and the last two vortices have linear polarization. Since circularly polarized vortices have different amplitudes, their superposition will have elliptical polarization. The sign of this elliptical polarization (left or right) will change over the beam cross section with the change in the sign of the difference in the amplitudes of optical vortices with circular polarization. We also have shown that optical vortices with topological charges n + 2, n − 2 propagate in the opposite direction near the focal plane, and together with optical vortices with charges n + 1, n − 1, they form an azimuthal energy flow at the focus.

Highly transient stimulated Raman scattering in SrMoO4 under ultrafast laser pumping with a controllable chirp.

For the first time, to the best of our knowledge, we demonstrate highly transient, multiwavelength, single-pass Raman generation with combined frequency shifts on two Raman modes of an SrMoO4 crystal with high total Raman conversion efficiency of up to 48% in conditions of competition with self-phase modulation (SPM). A 58-mm-long SrMoO4 crystal was used as the active medium under pumping by the 1030-nm, 40-µJ laser pulses with controllable dispersive stretching in a range of 0.25-6 ps at negative and positive chirping. The pump pulse chirping was optimized for both high- and low-frequency Raman shifts on the primary (888 cm-1) and secondary (327 cm-1) Raman modes of the crystal. At the optimal conditions, four Stokes components of stimulated Raman scattering (SRS) radiation with high- and low-frequency Raman shifts at the wavelengths of 1066, 1134, 1177, and 1261 nm were efficiently generated.

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.

Maximum Pump Power Coupled in Raman Resonator for Maximum Power Delivered at 1115 and 1175 nm

In this report, we present our analysis of the relationship between critical power and stimulated Raman scattering in Raman fiber lasers. Through our research, we have established a connection between the R.G. Smith constant at critical power and the necessary pump power required to reach the maximum power delivered by the first Stokes just prior to the generation of the second Stokes. In our experiments, two setups were successful in reaching the second Stokes generation, one utilizing a glass–air interface as the output coupler without HR mirrors and the other using HR-FBGs for both Stokes in conjunction with a glass–air interface. We found that the 1 Km 1060-XP fiber has an R.G. Smith constant of ~4.94 at critical power, which when multiplied by 2 gives ~9.88, a value close to the R.G. Smith constant (9.75) for maximum Stokes corresponding to a pump power of 5.5 W, with an approximation of ~98.6%. Our results demonstrate the importance of knowing the R.G. Smith constant at critical power in estimating the necessary pump power to achieve maximum power delivery in any Stokes component.

Wide-field Stokes polarimetric microscopy for second harmonic generation imaging.

We employ wide-field second harmonic generation (SHG) microscopy together with nonlinear Stokes polarimetry for quick ultrastructural investigation of large sample areas (700 μm × 700 μm) in thin histology sections. The Stokes vector components for SHG are obtained from the polarimetric measurements with incident and outgoing linear and circular polarization states. The Stokes components are used to construct the images of polarimetric parameters and deduce the maps of ultrastructural parameters of achiral and chiral nonlinear susceptibility tensor components ratios and cylindrical axis orientation in fibrillar materials. The large area imaging was employed for lung tumor margin investigations. The imaging shows reduced SHG intensity, increased achiral susceptibility ratio values, and preferential orientation of collagen strands along the boarder of tumor margin. The wide-field Stokes polarimetric SHG microscopy opens a possibility of quick large area imaging of ultrastructural parameters of tissue collagen, which can be used for nonlinear histopathology investigations.

Picosecond random Raman lasing in the spectral range of 360–630 nm using powders of potassium, sodium and strontium nitrates

Stimulated Raman scattering (SRS) of picosecond laser radiation at 532 and 355 nm in microcrystalline powders of potassium, sodium, and strontium nitrates has been studied. One anti-Stokes and three Stokes components were generated in all samples when pumping at 532 nm. For the first time to our knowledge, random Raman lasing in the used nitrates has been obtained upon their excitation at 355 nm. In this case, the multifrequency Stokes SRS is also observed in all nitrates. We have analyzed all possible loss channels when ultraviolet radiation is used for excitation of SRS. In general, picosecond random SRS generation has been obtained at 19 spectral lines in the spectral range of 360–630 nm. In all cases, the SRS process is due to the internal symmetric mode of the (NO3)− ion with the frequency shifts of 1050 cm−1 (KNO3), 1069 cm−1 (NaNO3), and 1057 cm−1 (Sr(NO3)2).

Вынужденное комбинационное рассеяние 0.3-ps лазерных импульсов с длиной волны 515 nm в кристаллах Ca-=SUB=-3-=/SUB=-(VO-=SUB=-4-=/SUB=-)-=SUB=-2-=/SUB=- и Ca-=SUB=-0.27-=/SUB=-Sr-=SUB=-0.3-=/SUB=-(VO-=SUB=-4-=/SUB=-)-=SUB=-2-=/SUB=-

The prospects of SRS-active calcium/strontium orthovanadate crystals, Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2, for spectral conversion of ultrashort visible-range laser pulses evaluated in a single-pass scheme with pump focusing into the samples. For the ~3 J incident laser pulses of 0.3 ps duration at wavelength of 515 nm the energy conversion efficiency of up to ~3.5% to the Stokes component shifted in frequency by ~850 cm–1 obtained in a 1.3 cm long sample of Ca2.7Sr0.3(VO4)2 crystal. Simultaneously, in the transmitted radiation spectrum the amplitude of Stokes component reached 1/3 of the amplitude at the pump wavelength. Under the same conditions, SRS in a Ca3(VO4)2 crystal was not detected at all. It was shown that the observed differences can be explained by the attenuation of pump pulse due to difference in two-photon absorption in these crystals.

Highly efficient transient stimulated Raman scattering on secondary vibrational mode of BaWO4 crystal due to its constructive interference with self-phase modulation

An exceptionally high stimulated Raman scattering (SRS) conversion efficiency to the first Stokes component associated with the secondary (low-frequency and low intensity) vibrational mode ν2 (∼330 cm-1) was observed in a BaWO4 crystal in a highly transient regime of interaction. The effect takes place in the range of pump pulse energy from ∼0.1 to ∼0.5 µJ with maximum energy conversion efficiency up to 35% at 0.2 µJ. The nature of the observed effects is explained by interference of SRS and self-phase modulation, where the latter is related to a noninstantaneous orientational Kerr nonlinearity in the BaWO4 crystal.

Фазовые эффекты при вынужденном рассеянии Мандельштама-Бриллюэна

In the study of stimulated Brillouin scattering (SBS) in the constant intensity approximation, the spatial behavior of the intensity of the Stokes scattering wave in a medium was investigated. It was found that as a result of nonlinear interaction of waves, the period of spatial beats changes. The intensity of the Stokes scattering component is considered as a function of the phase mismatch, pump and acoustic wave intensities. It is found that the efficiency of the scattering of the backward Stokes wave is affected by the total length of the nonlinear medium. According to the analytical expressions obtained in this work, the choice of the optimal parameters of the problem makes it possible to implement the regime of efficient generation of the Stokes scattering component in SBS. The process of generation and amplification of the Stokes scattering component is compared with experiment. By varying the pump intensity, one can control and manipulate the intensity of the output radiation of the Stokes component.

Phase effects at stimulated Brillouin scattering

In the study of stimulated Brillouin scattering (SBS) in the constant intensity approximation, the spatial behavior of the intensity of the Stokes scattering wave in a medium was investigated. It was found that as a result of nonlinear interaction of waves, the period of spatial beats changes. The intensity of the Stokes scattering component is considered as a function of the phase mismatch, pump and acoustic wave intensities. It is found that the efficiency of the scattering of the backward Stokes wave is affected by the total length of the nonlinear medium. According to the analytical expressions obtained in this work, the choice of the optimal parameters of the problem makes it possible to implement the regime of efficient generation of the Stokes scattering component in SBS. The process of generation and amplification of the Stokes scattering component is compared with experiment. By varying the pump intensity, one can control and manipulate the intensity of the output radiation of the Stokes component. Keywords: SBS, backward Stokes scattering wave, constant intensity approximation.

Влияние фокусировки на нестационарное ВКР 0.3 ps лазерных импульсов в кристалле BaWO-=SUB=-4-=/SUB=- с самозаправкой ФСМ

The effect of focusing, taking into account self-focusing, on the interference of SRS (stimulated Raman scattering) and self-phase modulation in a 8-mm BaWO4 crystal pumped by laser pulses with a duration of 0.3 ps and a wavelength of 515 nm is experimentally studied. The maximum efficiency of SRS conversion (~23%) to the Stokes component of the ν1 = 925 cm–1 strongest mode is obtained with a lens with a focal length of 40 mm at the linear focus shift towards the rear facet of the crystal. The increase in efficiency, when the linear focus is shifted to the rear facet, is associated with an increase in the distance between the linear and nonlinear foci, which results in an increase in the effective length of the nonlinear interaction.

Error analysis of multi-scale aerosol optical properties in shortwave radiative transfer

Atmospheric aerosols can significantly affect atmospheric radiative transfer, especially for shortwave radiation. In this paper, the differences between the bin method and the parameterization method for determining the aerosol optical properties using particle size distribution on the effect of solar shortwave radiation have been discussed according to the developed vector radiative transfer model. The aerosol particle size is divided into multiple regions in the bin method and each region has separate optical properties, while the optical properties of the parameterization method are obtained by integrating the entire size distribution and remain constant. Firstly, the accuracy of the model has been verified by Rayleigh scattering and field distribution simulations, and the validation results show that the average errors of normalized radiation intensity, Stokes components Q and U are 1.36%, 0.79%, and 5.82%, respectively. Subsequently, the angular distribution of radiation, the radiation characteristics of different model parameters, and the field distribution of polarization characteristics under the two methods have been calculated, and the relative errors between the methods have been discussed. The results show that the differences between the two methods are significant, and the angular radiation intensity of the bin method is generally larger than that of the parameterization method, with an average error of about 5%. The transmissivity decreases, and reflectivity increases with the increasing SZA (AOD), respectively, but both decrease with the increasing wavelength. For all model parameters, the transmissivity calculated by the bin method is generally smaller than that of the parameterization method, while the reflectivity is larger, indicating that the forward scattering determined by the bin method is weaker and the lateral (backward) scattering is stronger. Besides, the field distribution results show differences in the scattering phase matrix determined by the two methods. This research contributes to the knowledge of climate assessment and target detection.

Cascaded amplification via three-beam double stimulated Raman scattering in benzene

As stimulated Raman scattering (SRS) microscopy has emerged as a powerful tool for label-free imaging of biomolecules in biological systems, SRS has also received much attention in the field of nonlinear optics. Here, we enhanced the cascade SRS of benzene through an energy competition mechanism in the three-beam double SRS processes. A three-beam (pump, Stokes, and anti-Stokes beam) SRS scheme was formulated and demonstrated to simultaneously induce the parallel and cascaded SRS processes, which were related to the Raman active modes in the same molecule. Both two SRS processes generated high-order Stokes SRS through resonance enhancement of the double sample cell configuration, which effectively suppressed the CARS (Coherent anti-Stokes Raman Scattering) signal. It was shown in the experimental results that the cascaded SRS up to six orders from 562 to 780 nm were generated, and the SRS threshold of the multi-order Stokes components was lowered. The present work can potentially contribute to the development of super-resolution SRS microscopy.

All-SBS fiber-based setup for optical frequency comb generation utilizing a pump recycling technique and comb line isolation by implementing Brillouin amplification.

We describe an all-stimulated Brillouin scattering (SBS) fiber-based setup for the generation, amplification, and isolation of frequency components from an optical frequency comb (OFC). The cascaded SBS-OFC is obtained by utilizing pump and Stokes power recycling techniques. A total of >15 comb lines within a 45 dB bandwidth, having an average power of 16 dBm, is observed in the 1550 nm wavelength region of operation. By implementing a polarizer-analyzer setup exploiting the weak birefringence in silica fibers, we amplified and isolated the first Stokes component of the generated comb. The isolated component at 1550.03 nm was amplified by ≈55dB. In order to verify the isolation of a single comb line, the SBS-OFC is intensity modulated using sinusoidal signals of different frequencies, and the modulation is detected after the comb line isolation. We also observe that with the increase in Brillouin pump power during comb line isolation, the spontaneous Brillouin noise acts as a limitation to the selective amplification process.

Generation of dual-supercontinuum coherent radiation in acetone mixed with carbon disulfide by stimulated Raman scattering.

Stimulated Raman scattering (SRS) in a liquid has been a major focus of nonlinear optics. Traditional SRS generates single or cascaded Stokes components arising from spontaneous Raman noise. Herein, we report the formation mechanism of a specific spectrum-continuous spectroscopy technique based on SRS of mixed liquids. SRS of a mixed acetone and carbon disulfide solution is investigated by a pulsed Nd:YAG laser with a wavelength of 532 nm. Two remarkably asymmetric broadened SRS lines are obtained. When the volume ratio is 7:3, the broadened spectral bands are optimized. The supercontinuum spectroscopy phenomenon is explained by hydrogen bond formation, adjacent vibrational modes coupling, and laser-induced plasma generation. This technique has the potential to contribute to the development of a supercontinuum Raman laser.

Spatial weighted fusion based on polarisation image

ABSTRACT This paper uses the principles of polarisation to calculate the Stokes component of the polarisation image. It designs the spatial weighted fusion algorithm, focusing on the research and evaluation of the accuracy and time complexity of the spatial weighted fusion algorithm in the polarisation image fusion processing. The spatial weighted image fusion algorithm is used to fuse the polarisation degree image, the polarisation angle image, and the light intensity image. Finally, the algorithm function is realised through software programming to verify the effect and accuracy of the algorithm. Experimental results show that the spatial weighted fusion algorithm can keep the pixel value of the polarisation source image unchanged, avoid image distortion, artefacts and ringing effects algorithm is stable and efficient, with low time complexity.