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Using different products of disc thickness and Yb ions concentration, we report on the laser performance of Yb:YAG crystals under room and cryogenic temperatures. The optimum crystal parameters have been realized. With a thickness of 0.8 mm, 15 at. % Yb ions doping concentration laser crystal, high optical to optical efficiency of 85.2% and slope efficiency of 89.0% have been achieved and the maximum output energy was 75.6 mJ at ∼ 80 K. Furthermore, the wavelength-switching phenomenon was observed owing to a lower loss cavity with the temperature reduction. Calculation results from the model based on the rate equations were well consistent with the laser output performance. The wavelength-switching effect was also explained by this model.

Random lasing in a lotus leaf, with a wide tunable spectrum from planar liquid waveguide gain channels is described. The lotus leaf shows multiple scattering from the micro-papilla and nanoscale coralloid tomentum on its surface. The Fraunhofer diffraction pattern demonstrates excellent coherence and directionality for our random laser. The emission spectrum wavelength can be tuned by changing the pump position due to the random distribution of the micro/nano-scale features on the lotus leaf. Potential applications of the random laser include probing micro/nano-scale structural alterations, optical biosensors on chips, and developing a multi-color random laser.

The effects of transient temperature variation of gain medium on quasi-three-level microchip laser were investigated. Firstly, the dynamic behavior with temperature variation and the characteristic of the output power were reported. The numerical simulation results revealed not only the dynamics characteristic of lasing levels, but also the relationship between pump pulse width and output power in equivalent duty cycle. The increments of output power deviated significantly from linear increasing with the pump pulse width. The characteristic of the output power with different duty cycle was compared. Because the heat load was rising with the increase of the duty cycle and high heat load reduced population inversion density, the optical-to-optical efficiency of 9.7% at 50% duty cycle was lower than optical-to-optical efficiency of 15.6% at 7% duty cycle. The calculated and experimental pump power thresholds for output of 1030 nm were discussed. Particularly, the output power calculated by the model with the addition of temperature terms was significantly lower than that simulated by the model without temperature terms. Experimental results have shown a good agreement with the theoretical predictions.

Gaseous Raman lasers cover a range of wavelengths but lack wavelength tunability. Here, a 1 c m − 1 linewidth 532 nm laser was used as a pump laser, and with a narrow-linewidth seed laser injection, a narrow-linewidth first Stokes (S1) Raman laser was achieved. By tuning the wavelength of the seed laser, a tuning range of S1 up to 1 c m − 1 was obtained. The wavelengths of the first anti-Stokes and second Stokes lasers could also be tuned. A theoretical model was developed, and spectral profiles of Raman lasers from experiments and simulations agreed well; further simulation predicted that the linewidth of S1 could be compressed to as narrow as 0.01 c m − 1 under optimal conditions. A universal method of fine-tunable Raman lasers is presented that can be utilized in several important applications.

This paper reports the simultaneous output of 358.7nm and 420.3nm laser generated by two-photon excitation (52 S1/2→62 D5/2, TPE) and four-wave mixing effect (FWM) in rubidium system for the first time. Unlike some fluorescent signals, this four-wave mixing beam has a high monochromaticity and extreme directivity and can be used as a laser source. In this study, we also measured the fluorescence lines in the range of 300-820 nm under 52 S1/2→62 D5/2 TPE, and studied other transitions that may occur. The experimental results show that the blue-violet laser produced by this alkali metal rubidium four-wave mixing can provide a new laser source for underwater laser communication, display technology, fluorescence excitation, Raman spectroscopy, marine resource detection, laser biomedicine, lithography, high density information storage and other fields.

In this work, Random laser (RL) and stimulated Raman scattering (SRS) are investigated using Rhodamine 6G ethanol solution in poly (melamine formaldehyde) foam with micro/nano-sized porous structures. At low dye concentration, the RL containing multiple discrete narrow peaks is observed in both its natural and compressed state of foam. It is found that the cavity length in the compressed state is significantly shorter through the power Fourier transform of the spectra. At high dye concentration, in the natural state of the foam, the coexistence of the RL and SRS is observed, while only the SRS peaks appear in the compressed state. It may provide a novel approach to achieving mode-controllable RL emission.

Collimated ultraviolet (UV) light is generated via four-wave mixing (FWM) in cesium vapor by continuously tuning the wavelength of the pump laser. Terahertz (THz) Stokes light is generated by the stimulated Raman scattering (SRS) effect in the FWM process, and its frequency is adjustable. When exciting the cesium atom to a virtual level using different combinations of pump lasers (P1 and P2), the strength distribution of UV light is asymmetric, which can be explained through a phase-matching mechanism. Furthermore, the SRS effect and phase matching influence the FWM.

In this work, single cylindrical lens, an extreme of the astigmatic case, is used to study Stimulated Raman scattering (SRS) in CH4 gas. In comparison with the conventional spherical optics case, single cylindrical lens focusing has three obvious advantages: (1) an increase of the dimension of the focus will decrease pump power density, and the laser-induced breakdown is suppressed. (2) It will efficiently disperse the heat generated in the SRS process, and benefit for the heat management for SRS. Consequently, SRS with cylindrical lens focusing configuration shows stronger resistance to thermal defocusing effect. (3) The forward high-order Stokes and backward SRS are suppressed. Therefore, the utilization of cylindrical lens has improved forward first Stokes in CH4, acquiring the maximum photon conversion efficiency of 67.1% at 188.5 mJ pump energy and 1Hz, and 44.9% at 109.4 mJ pump energy and 10 Hz, for the condition of 3 Mpa pressure. This effect has great potential for the gaseous SRS with high repetition rates and high pressure.

Multi-line frequency up-conversions are realized in Cs vapor using 718.8 nm pumping laser resonating with the two-photon transition 62S1/2 → 82D5/2 of Cs atom. The pumping beam is converted into a beam including wavelengths of 361.2, 387.7, 455.7 and 621.5 nm. Experiments with collimated and focused pumping configurations are carried out and compared. Spectrum peak at 361.2 nm is strongest under collimated pumping condition, while 387.7 nm is strongest under focused pumping beam. The output beam under focused pumping is more stable than that under collimated pumping. Results in this work may be useful in laser frequency standard, beacon light, laser measuring and optics communications, etc.

Stimulated Raman scattering (SRS) in compressed D 2 gas pumped with nanosecond laser radiation at 1064 nm in a multi-pass configuration has been studied. The influence of D 2 pressure and pass number on Raman thresholds and the conversion efficiencies for the first Stokes ( S1 ) and second Stokes ( S2 ) components has been investigated. It is shown that multi-pass configuration is very efficient for the substantial reducing of SRS thresholds for both S1 and S2 components and increasing their conversion efficiencies. In our work, the S1 threshold is approximately one order of magnitude lower than that reported in previous studies; the S1 conversion efficiency reached (56.1±4.4)% at pump energy of 33 mJ. The lowest S2 threshold in the experiment is 15 mJ (with a peak power of 3 MW), and the S2 conversion efficiency reaches (32.9±3.8)%.

It is attractive to investigate the interaction mechanism between metal and rare gas atoms within ionization process, especially for the mixture of metal vapor and rare gas. In this paper, laser-induced breakdown spectroscopy is used to study the ionization and recombination kinetic processes in sodium-argon mixture. Sodium-argon excimer is formed by the atomic collision, and it plays an important role in the ionization process, sodium atoms on 3P state are produced after the dissociation of excimer, then multiphoton ionization happens, the electrons in plasma are accelerated to collide with argon atoms, electron-impact ionization of argon will take place, identified with time-resolved atomic emission spectrum. Population accumulate on 3D,4P, and 5S states after the recombination process of Na+ with electron, then most population will transit to 3P state mainly by collisional relaxation.

Stimulated Raman Scattering (SRS) is important method of laser frequency conversion. Optical frequency-comb is a special kind of SRS which output multiple Stokes beam simultaneously, and lasers with mutiple wavelength have broad applications. In this paper, the optical frequency-comb generated by SRS of CO2 is presented and the spectral range covers from 0.4 μm to 1.5 μm. Research also indicates that the characteristics of optical frequency-comb depends on the wavelength of pumping laser. For instance, the SRS photon conversion efficiency pumped by 1064 nm laser is high at 1248nm, 1510nm but that pumped by 532 nm laser is high at 574nm, 624nm 683nm. The different features are compared and analyzed by the use of the mechanism of four-wave mixing and the change of SRS gain coefficient with Stokes wavelength.

A blue random laser based on solid waveguide gain films with silver nanoparticles (NPs) and SiO2 NPs is demonstrated. Located surface plasmon resonance (LSPR) property and multiple scattering are proven playing an important role simultaneously.

After the multiphoton ionization of sodium-argon mixture, time-resolved atomic emission spectrum is used to experimentally study the unusual phenomenon of the obviously different broadening between Na D1 and D2 lines spectra. The primary reason for the unusual broadening of Na D2 line is that the spectral line of Ar I 588.9 nm overlays with Na D2 line (589.0 nm) after ionization, and the serious self-absorption on Na D2 line is the secondary reason. Although there is difference of population between 32P3/2 and 32P1/2 states, the experiment result demonstrates that the difference between Na D lines in radiation channel will not affect the broadening of spectral profile.

The sum-frequency generation (SFG) in potassium dihydrogen phosphate (KDP) powder with μm-grade particle size is successfully demonstrated under various experimental conditions. Two focused beams of 870 nm and 1369 nm are used for SFG excitation. SFG is observed under different excitation energies. The SFG intensity shows isotropy with different observation azimuths. The intersection angle between two excitation beams is not limited by conventional phase-matching conditions, and it owns the flexibility of a very large allowed range, e.g., it can be 0°∼100° in this work. The polarization combination of excitation beams is not limited either. Thanks to the non-toxicity, low price, and low SFG threshold properties of KDP material and the optical flexibility, this powder SFG technology is a versatile method and is expected to be applied to various situations of optical alignment, e.g., surface SFG, four-wave mixing, coherent anti-Stokes Raman spectroscopy, multi-color laser excitation, etc. The effect of potential powder SFG-assisted optical alignments is also discussed. Extension of this method to multi-beams, tight focusing beams, and plasmonic polariton devices is proposed.

We have established a new method for realizing a typical “2-color” collinear CARS (coherent anti-Stokes Raman scattering) system. The system mainly consists of a laser source, a D2O cell, and a spectrometer. The pump/probe beam and the Stokes beam are provided by SBS (stimulated Brillouin scattering) and BSRS (backward stimulated Raman scattering) of D2O, respectively. The CARS system is statistically stable, and it is also a broadband and alignment-free system. Measurement of N2 signal in air with this system is demonstrated. Detection of N2 in 0.006 bar air is realized with this system. Time-resolved pulse shapes of SBS and BSRS are measured to confirm their generation. Transference of energy from the SBS pulse to the BSRS pulse is realized with a Rhodamine 101 dye cuvette and discussed. This results in a better energy distribution between the pump/probe and Stokes pulses for CARS.

In this work, SF6 as a Raman-active medium is investigated to generate a multispectral Raman laser by the combination of cascade stimulated Raman scattering (SRS) and four wave mixing. The Raman frequency comb from the 10th-order anti-Stokes to the 9th-order Stokes was generated, and its spectral range covered 377–846 nm. The photon conversion efficiency of 16.4% for the first Stokes was achieved, and the Raman gain coefficient at 1.5 MPa of SF6 under the 532 nm pump laser was calculated to be 0.83 cm/GW by the SRS threshold comparison with H2. Using helium as the carrier gas, the thermal effect of the SF6 Raman laser was improved dramatically under a repetition rate of 10 Hz.

A new method to improve the resolution of a slightly non-parallel solid etalon is proposed. The method is aimed to reduce the spectrum broadening caused by non-parallel surfaces; it contains a theoretical formula for adjusting image distances, and an algorithm for processing the corresponding fringe patterns. Theoretical consideration, computer simulation, experimental results, and application demonstration are given. The fringe patterns captured by a CCD showed good agreement with the computer simulation, and the resolution of a λ/10-wavefront-error etalon was improved from 3.1 GHz to 0.51 GHz. In comparison with other methods, this new method is convenient and economical.

In this work, the anisotropy of nonlinear absorption in a crystal Q-switch was considered when we established coupled rate equations of a passively Q-switched laser. A [100]-cut Cr4+:YAG crystal, with initial transmission T0=40%, was used as the Q-switch to evaluate the theoretical model, and the results of the simulation were in good accordance with the experiment. In order to control timing jitter of the passively Q-switched laser, an actively Q-switched Nd:YAG laser was applied to directly bleach the [100]-cut Cr4+:YAG crystal. The timing jitter was more than 1 μs without bleaching light. While there was a bleaching light, the time lag between the laser pulse and the bleaching light was less than 100 ns, which meant the timing jitter decreased. The pulse width of the passively Q-switched laser was found to decrease from 45 to 35 ns due to the existing of bleaching light. As the peak power of bleaching light was increased, the laser pulse energy increased from 18.2 to 24.6 mJ, which meant a 35% increment in the pulse energy. The increase in pulse energy can be explained by the increase of α coefficient, and the results of simulation agreed well with the experiment.

The experimental study of the amplification of stimulated Raman scattering (SRS) in high purity H 2 gas was demonstrated employing a Q-switched Nd:YAG laser at 1064 nm as the pump source. A part of the 1064 nm pump light (20% in energy) was focused into the first H 2 gas cell to generate the backward first Raman Stokes light (BS1), which is taken as the Raman seed light. The BS1 seed light combined to the residual pump light were focused into the second H 2 gas cell to get the amplification of the S1 1900 nm infrared Raman light. In this study, the maximum quantum conversion efficiency of the S1 light was estimated to be 76%. Under the condition of the same pump energy, especially for the low pump energy (lower than 40 mJ), the quantum conversion efficiency of the S1 light with the Raman seed light was significantly increased comparing to the single focus geometry (without the Raman seed light).

Stimulated Raman Scattering (SRS) is an effective means of laser wavelength conversion. Hydrogen is an excellent Raman medium for its high stimulated Raman gain coefficient and good flowability which can rapidly dissipate the heat generated by SRS process. In this paper we reported the H 2 SRS in multiple-pass cell pumped by the fundamental frequency output of a Q-switched Nd: YAG laser. Two concave reflection mirrors (with 1000 mm curvature radius and 50 mm diameter) were used in our experiment, both mirrors with a hole near the edge and were positioned to form co-center cavity, therefore the laser could repeatedly pass and refocus in the Raman cell to achieve a high SRS conversion efficiency and reduce SRS threshold for pump laser. By changing the pass number (1～17) of optical path in the Raman cell and the pump power(0～2.5MW), the Stokes conversion efficiency is optimized. Experimental results indicated that the Raman threshold was 0.178MW and the highest photon conversion efficiency was 50 %.

Sodium-ethane excimer pairs are studied and proved to be a great choice of excimer pumped sodium laser (XPNaL) gain media. The lifetime of the sodium D2 line is studied in a sodium-ethane excimer system excited by a 553 nm laser, and the observed phenomenon of lifetime lengthening is discussed. Amplified spontaneous emission (ASE) of the sodium D2 line is successfully obtained, and its time-resolved and spectroscopic characteristics are studied experimentally. According to the intensity of the ASE signal under different sodium vapor atom densities, the sodium D2 line gain feature of sodium-ethane excimer pairs excited by the 553 nm laser is concluded.

Stimulated raman scattering (SRS) is an effective method for expanding the spectral range of high power lasers, especially in the regime of near IR and middle IR. We report the SRS of high pressure H2 with a multiple-pass cell configuration. The SRS with the multiple-pass cell configuration is found to be very efficient for reduction of threshold of the first Stokes (S1). Due to the coherent SRS (CSRS) process, the multiple-pass cell configuration is more effective for reduction of the threshold for the second Stokes (S2) SRS and for increasing the conversion efficiency of S2. This contributes to the relatively low conversion efficiency of S1 for the multiple-pass cell configuration. Multiple-pass cell SRS is also found to be very effective for improving the beam quality and the stability of S1.