We report on the multiple wavelengths Raman laser output, the laser wavelength span from violet to mid-infrared, 359nm~9.2μm have been detected and recorded on spectrum and energy meter. In this investigation, 222mJ Q-switch Nd:YAG 1064nm laser set as pump laser, 737/770nm and 1.1/1.7/1.9/2.1/2.4/9.2μm Raman laser is high gained and takes a measure of the energy. 1.9μm laser maximum 28mJ, 2.1μm laser maximum 30mJ, laser pulse width is 4ns. And 9.2μm mid-infrared laser gets 0.8mJ. The pressurized hydrogen is pumped by a 1064nm laser and 737/770nm anti-Stokes Raman laser are generated. The 737nm laser is generated by stimulated vibrational Raman Scattering (SVRS); while the 770nm laser is generated by the combination processes of SVRS and stimulated rotational Raman scattering (SRRS). The maximum pulse energies of 6.42mJ at 737nm and 4.42mJ at 770nm are achieved by the optimization of anti-Stokes Raman laser. The energy efficiency is 2.6% at 737nm and 1.8% at 770nm.
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.
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.
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.
The kinetic behaviors of 6p[1/2]0, 6p[3/2]2 ,and 6p[5/2]2 were examined under the ultrahigh pumped power. These processes were detected by the way of time-resolved fluorescence and ASE spectra. A theory of energy-pooling is presented under the focused condition. There are three types of energy-pooling processes. The first type is energy-pooling ionization. The obvious ionization can be observed whenever the laser prepared state is the 6p[1/2]0, 6p[3/2]2, or 6p[5/2]2 state. The second type is energy-pooling with big energy difference. The energy-pooling collision between the two 6p[1/2]0 atoms can produce one 5d[3/2]1 atom and one 6s’[1/2]0 atom when the prepared state is 6p[1/2]0. The third type is energy-pooling with small energy difference. The way of generation of five secondary 6p states is energy-pooling instead of collision relaxation.
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/CH4 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.
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-C2H6 system, which was an efficient excimer pair. We excited the Na-C2H6 system using a pulsed dye laser with wavelength of 553 nm, and measured lifetime of sodium D2 line based on the fluorescence spectra. Meanwhile, we have also detected strong amplified spontaneous emission (ASE) signal in Na-C2H6 system, through the experimental study, the Na-C2H6 system is considered to own the potential to be utilized in high power XPNaL.
KEYWORDS: Oxygen, Chemical oxygen iodine lasers, Raman spectroscopy, Dye lasers, Signal detection, Signal processing, Carbon dioxide, Iodine, Carbon dioxide lasers, Signal to noise ratio
1 Δg oxygen was the active medium of chemical oxygen iodine laser (COIL), the concentration and distribution of 1 Δg 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 1 Δg 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 1 Δg 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 O2( 1 Δg) 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 O2 ( 1 Δg)and O2 (3 ∑); 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 O2(1 Δg)and O2 (3 ∑)have different wavelengths, and their intensity was proportional to the square of the concentration of O2(1 Δg) and O2( 3 ∑). By changing the focus spot of pump and stokes laser, the concentration distribution of O2(1 Δg) and O2(3 ∑)at different position could be obtained.
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 D1 and D2 line was clearly visible. After processing the fluorescence intensity and the input pumping laser relative intensity, we obtained the Na-CH4 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.
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 H2 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 %.
Oxygen molecules existed in pairs under liquid condition, the radiation from vibrational ground state of 1 Δ state to the first vibrational excited state of 3 ∑ 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-1, 0.3 cm-1 and 0.076 cm-1 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-1. 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.
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