Stimulated Raman scattering (SRS) is a powerful tool for the extension of the spectral range of lasers. To obtain efficient Raman conversion in SRS, many researchers have studied different types of Raman laser configurations. Among these configurations, the intra-cavity type is particularly attractive. Intra-cavity SRS has the advantages of high intra-cavity laser intensity, low-SRS threshold, and high Raman conversion efficiency. In this paper, An Q-switched intra-cavity Nd: YAG/CH<sub>4</sub> frequency-doubled Raman lasers is reported. A negative branch confocal resonator with M= 1.25 is used for the frequency-doubling of Nd: YAG laser. The consequent 532nm light is confined in intra- cavity SRS with travelling wave resonator, and the focal of one mirror of cavity is overlap with the center of the other mirror of the cavity. We found this design is especially efficient to reduce the threshold of SRS, and increase conversion efficiency. The threshold is measured to be 0.62 MW, and at the pump energy of 16.1 mJ, the conversion efficiency is 34%. With the smaller magnification M, the threshold could further decrease, and the conversion efficiency could be improved further. This is a successful try to extend the spectral range of a laser to the shorter wavelength by SRS, and this design may play an important role in the fulfillment of high power red lasers.
We have demonstrated an average output power of 10 W quasi-continuous-wave mid-infrared laser at 2.94 μm from a diode laser (LD) side-pumped Er-doped yttrium aluminum garnet (YAG) crystal. The Er:YAG crystal was composed of Er-doped (50% doped) (YAG) bonded to undoped YAG. The LD was operated at a repetition rate of 150Hz and a pulse-width of 300 μs. The optical-optical conversion efficiency and the slope efficiency were 5.6% and 9.1%, respectively. The slope efficiency was not saturation yet, a higher output power can be expected with a higher LD pump power and colder temperature of the Er:YAG crystal.
Excimer pumped sodium laser (XPNaL) can accurately achieve lasing at 589.16 nm without any complicated control system to reduce the wavelength error, so XPNaL will provide a novel technical system for sodium beacon laser. In this paper, we studied the Na-C<sub>2</sub>H<sub>6</sub> system, which was an efficient excimer pair. We excited the Na-C<sub>2</sub>H<sub>6</sub> system using a pulsed dye laser with wavelength of 553 nm, and measured lifetime of sodium D<sub>2</sub> line based on the fluorescence spectra. Meanwhile, we have also detected strong amplified spontaneous emission (ASE) signal in Na-C<sub>2</sub>H<sub>6</sub> system, through the experimental study, the Na-C<sub>2</sub>H<sub>6</sub> system is considered to own the potential to be utilized in high power XPNaL.
SRS (Stimulated Raman Scattering) is a very effective method to expand the spectrum range of high power laser, especially in the regime of near IR and middle IR. In this paper SRS of high pressure H<sub>2</sub> and D<sub>2</sub> with MPC (multiple-pass cell) configuration were reported. Relation of (FS1) first forward Stokes and (BS1) first backward Stokes has been analysis. The process of gain of FS1 was explained. Experimental results also indicated the second Stokes was also generated. D<sub>2</sub> SRS of the fundamental output of Nd:YAG laser generates the second Stokes light of 2.92 m. The lasers with wavelength of 2.9 μm have broad applications. Finally, multiple-pass SRS was better for complete conversion of pump laser.
Recently, the optically pumped rare gas lasers have been attracted extensive attention. Rare gas laser systems with Ne (2p<sup>5</sup>3p), Ar (3p<sup>5</sup>4p), and Kr (4p<sup>5</sup>5p) atoms have been investigated. However, there are sparse studies based on Xe. In this work, new phenomena, intensive mid-infrared amplified spontaneous emissions (ASEs), are found after two-photon excitation of Xe from the ground state to the 6p[1/2]<sub>0</sub> state. Simultaneously, substantial 6p[1/2]<sub>1</sub> atoms are populated. The thresholds of ASE peak 1 and the generation of 6p[1/2]<sub>1</sub> atoms are both about 1.5 mJ. It indicates that there should exist the relationship between these two phenomena. The ASE signals show broadband spectra. Therefore, it must be yielded by the superposition of Xe<sub>2</sub>* excimer transitions. The mid-infrared ASEs lead to excimers correlating to the 6s’[1/2]<sub>1</sub> enormously generated. Then these excimers dissociate to produce substantial 6p[1/2]<sub>1</sub> atoms. Under some circumstance, the ratio of the 6p[1/2]<sub>1</sub> to 6p[1/2]<sub>0</sub> atoms reaches about 80%. It indicates that the 6p[1/2]<sub>0</sub> atoms strongly tend to decay through the emissions between the excimer states. Using these emissions, continuous-tunable mid-infrared laser with metastable Xe can be promisingly produced.
<sup>1 </sup>Δ<sub>g </sub>oxygen was the active medium of chemical oxygen iodine laser (COIL), the concentration and distribution of <sup>1</sup> Δ<sub>g</sub> oxygen was important for the output power and beam quality. However, the current test technique, such as fluorescence detection method, absorption spectrum method could not get accurate <sup>1</sup> Δ<sub>g</sub> oxygen information, due to the interference from the iodine fluorescence or the rigorous request of the laser source and optics and detection elements. The anti-stokes Raman spectrum of <sup>1 </sup>Δ<sub>g</sub> oxygen was regarded as a potential technique to obtain desirable signal, and the coherent anti-stokes Raman scatter (CARS) was the most feasible technique to get better signal to noise ratio (SNR). In this paper, we reported a broadband nanosecond coherent anti-stokes Raman scatter (CARS) detecting system built up for the detection of the concentration and distribution of O<sub>2</sub>( <sup>1 </sup>Δ<sub>g</sub>) in COIL：The second harmonic of a Nd: YAG pulse laser was separated into two parts, one part was used to pump a broadband nanosecond dye laser to generate light of 578-580 nm, which covered both stokes lines of O<sub>2</sub> ( <sup>1</sup> Δ<sub>g</sub>）and O<sub>2</sub> (<sup>3 </sup>∑）; The other part was combined with dye laser output by a dichroic mirror, and then introduced into the detection region of COIL through a focus lens. CARS signals for O<sub>2</sub>（<sup>1</sup> Δ<sub>g</sub>）and O<sub>2</sub> （<sup>3</sup> ∑）have different wavelengths, and their intensity was proportional to the square of the concentration of O<sub>2</sub>（<sup>1 </sup>Δ<sub>g</sub>） and O<sub>2</sub>( <sup>3</sup> ∑). By changing the focus spot of pump and stokes laser, the concentration distribution of O<sub>2</sub>（<sup>1</sup> Δ<sub>g</sub>） and O<sub>2</sub>（<sup>3</sup> ∑）at different position could be obtained.
The experimental study of the amplification of stimulated Raman scattering (SRS) in high purity H<sub>2 </sub>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<sub>2</sub> 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<sub>2 </sub>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).
Oxygen molecules existed in pairs under liquid condition, the radiation from vibrational ground state of <sup>1</sup> Δ state to the first vibrational excited state of <sup>3</sup> ∑ state was electronic dipole moment transition allowed, and a photon with wavelength of 1580 nm was emitted. In our experiment, dye laser with wavelength of 581 nm, 634 nm, 764 nm was used to excite liquid oxygen to different excited states, while a tunable OPO was used as the seeder laser, and the small signal gain was measured to be 0.23 cm<sup>-1</sup>, 0.3 cm<sup>-1</sup> and 0.076 cm<sup>-1</sup> respectively. The small signal gain (pump by photon of 634 nm) was significantly higher than that of common solid state lasers and chemical lasers. When the fundamental output of a Q-switched Nd:YAG laser was used as the pump source, the corresponding small signal gain was 0.12 cm<sup>-1</sup>. The profiles of small signal gain form 1579.2 nm to 1580.8 nm were also presented. These results were consistent with theoretical calculation. The high positive gain indicated that the liquid oxygen was a potential medium for high energy laser. A comprehensive parameter optimization was still necessary in order to improve the mall signal gain.
Based on two-photon absorption, a 420nm blue laser of alkali Rb vapor was demonstrated, and a dye laser was used as the pumping laser. Utilizing the energy level structure of Rb atom, lasering mechanism and two-photon absorption process are analyzed. Absorbing two 778.1nm photons, Rb atoms were excited from 5<sup>2</sup> S<sub>1/2</sub> to 5<sup>2</sup> D<sub>5/2</sub>, then relaxed to 6<sup>2</sup> P<sub>3/2 </sub>with mid infrared photon radiation. 420nm blue laser was achieved by the transition 6<sup>2</sup> P<sub>3/2</sub>→5<sup>2</sup> S<sub>1/2</sub>. To improve efficiency of the blue laser, two-photon resonant excitation pumped alkali vapor blue lasers are proposed, which will be good beam quality, high efficiency and scalable blue lasers. The development of diode pumped alkali vapor blue laser is expected.
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<sub>2</sub> 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 %.
High press, gravity-independent, singlet oxygen generator (HGSOG) <sup></sup> with small reaction zone and high chemical efficiency was designed and fabricated. The mixing, reaction and separation processes happened simultaneously in the reaction zone of HGSOG. The size and the configuration of reaction zone are very important for HGSOG. In this paper, p-τ value was calculated to determine the upper limit of the volume of reaction zone. The condition of gas-liquid separation was calculated to determine the lower limit of the volume of reaction zone. The utilization rate of Cl<sub>2</sub> achieved 90% and the yield of O<sub>2</sub>(<sup>1</sup>Δ) reached 70%.
A novel conception of iterative pump number was introduced in this work for the first time. Based on the conservation of energy, the equivalent model for the lasering of solid state laser was built up, the iterative pump number was calculated, and a formula for the output power of laser was given. This formula presented the relationships among the output power of laser, pumping power of diode and the thickness of laser medium. The output power predicted by this formula is consistent with experimental results, so this formula could be an important tool for the designing of parameter for diode pumped solid state laser.
Sodium based excimer-pump alkali laser (Na-XPAL) is expected to be an efficient method to generate sodium beacon light, but the information about the spectroscopic characters of Na-XPAL remains sparse so far. In this work, we utilized the relative fluorescence intensity to study the absorption spectrum of blue satellites of complexes of sodium with different collision partners. The yellow fluorescence of Na D<sub>1</sub> and D<sub>2</sub> line was clearly visible. After processing the fluorescence intensity and the input pumping laser relative intensity, we obtained the Na-CH<sub>4</sub> system’s blue satellites was from 553nm to 556nm. Meanwhile, we experimentally demonstrated the Na-Ar and Na-Xe system’s wavelength range of blue satellites. Also, it was observed that the Na-Xe system’s absorption was stronger than the other two systems.
Achieving population inversion through multi-photon cascade pumping is almost always difficult, and most laser medium work under 1-photon excitation mechanism. But for alkali atoms such as cesium, relatively large absorption cross sections of several low, cascading energy levels enable them properties such as up conversion. Here we carried out research on two-photon excitation alkali fluorescence. Two photons of near infrared region are used to excite alkali atoms to n <sup>2</sup> D<sub>5/2</sub>, n <sup>2</sup> D<sub>3/2</sub> or higher energy levels, then the blue fluorescence of (n+1)<sup> 2</sup> P<sub>3/2</sub>,(n+1) <sup>2</sup> P<sub>1/2</sub>→n <sup>2</sup> S<sub>1/2</sub> are observed. Different pumping paths are tried and by the recorded spectra, transition routes of cesium are deducted and concluded. Finally the possibility of two-photon style DPALs (diode pumped alkali laser) are discussed, such alkali lasers can give output wavelengths in the shorter end of visual spectroscopy (400-460 nm) and are expected to get application in underwater communication and material laser processing.
A converging cavity is introduced in the frequency-doubling experiment to increase the efficiency. In this experiment, an annular collimated laser beam produced by Nd:YAG laser with confocal resonator is introduced into the converging cavity as fundamental light. A BBO is positioned in the converging cavity. As propagating in the converging cavity, the fundamental beam profile becomes smaller and smaller. In the theory, the conversion efficiency could be approach 100%. Our experimental result shows that the conversion efficiency is improved significantly compared with the single pass configuration.