Ld Pumped Passive Tuning Q Intracavity Frequency Doubling Laser Raman Yellow Theoretical And Experimental Research

All-solid-state lasers have the advantages of small scale, high efficiency and long life. Thewavelength of laser sources between550nm and600nm has a wide range of applications inbiomedical, medical beauty, visual display, information storage, communications, military,atmospheric and remote sensing et al. But it is difficult to produce laser emission in these spectraefficiently by frequency-doubling Nd-doped lasers for the absence of fundamental lasers that canoperate efficiently in the range of1110-1200nm. However, stimulated Raman scatting （SRS）process in crystals has been proved to be an effective way to obtain all-solid-state lasers, and obviousdevelopments have been made in recent years. Compared with the traditional gas and liquid Ramanmedia, Raman crystals could offer high Raman gain, large molecule density, small scale, goodthermal and mechanical properties. The lasers using Raman crystals have the advantages ofcompactness, high efficiency, and high stability. They have wide applications in such fields asinformation, communication, measurement, military affairs, medical treatment, agriculture, industry,and so on. Recently, employing the intracavity doubling-frequency Raman lasers to obtain yellowlaser output has become a hot research field of yellow laser.The technology of Q-switching is capable of producing pulses with high efficiency and highpeak power. Passively Q-switching with a saturable absorber as the Q-switch, compared withactively Q-switching, has the advantages of simplicity, compactness, and low cost. Besides, thissystem can realize frequency-conversion in a short cavity, and produce narrow pulses with high peakpower. Even so, there have been few reports about passively Q-switching Raman yellow laser untilnow.One of theoretical tools of describing the intracavity frequency doubling yellow Raman laser israte equations. In the normalized rate equations, we consider the space-dependence of pump laserand intracavity beams, and beam sizes in the axial direction of the resonator cavity. The theoreticalanalysis and numerical calculations are carried out to investigate the effects of some compositevariables on the performance of passively Q-switched intracavity frequency doubling yellow Ramanlasers. From the numerical calculated curves, we can understand clearly the relationship between thecomposite variables and normalized frequency doubling pulse parameters. These curves can be adopted to help the design and optimization of passively Q-switched intracavity frequency Ramanlasers.Self-Raman lasers have the advantages of short cavity and making the resonator structurecompact. The laser media with smaller stimulated cross emission is in favor of good passivelyQ-switched pulses output. For efficiently yellow laser, the efficient and stable outputs of fundamentaland Raman laser are prerequisites. In this paper, The LD-pumped passively Q-switched c-cutNd:YVO₄self-Raman laser is investigated experimentally, in which Cr4+:YAG crystal is taken assaturable absorber. The influences of the curvature of input mirrors and the reflectivity atfundermental laser of output couplers on output characteristics of fundamental laser are studied. Andthe influences of the initial transmission of Cr⁴⁺:YAG and the reflectivity at Raman laser of outputcouplers on output characteristics of Raman laser are studied, too. The average output power, pulserepetition frequency and pulse width of Raman laser with respect to the pumped power are measured.The obtained maximum output average power of Raman laser is370mW at4.8W of pumpedpower and the corresponding conversion efficiency is7.7%. As we know, this is the highest averageoutput power and efficiency of LD-pumped passively Q-switched c-cut Nd:YVO₄self-Raman. Theself-Raman laser could produce pulses in the sub-nanosecond level, and the maximum single pulseenergy and peak power are54μJ and47kW, respectively.We introduce the method of frequency doubling phase-matching for biaxial crystals, andcompare the characteristics of KTP and LBO, then calculate the phase-matching angle of KTP andthe phase-matching temperature of LBO for frequency doubling.By using LBO as doubling frequency crystal, the LD-pumped passively Q-switched intracavitydoubling frequency Raman yellow lasers are studied. In the experiments, three-mirror linear cavitystructure is explored and there are three different scheme as follows:1) Utilizing c-cut Nd:YVO₄asSelf-Raman media,2) Utilizing c-cut Nd:YVO₄as laser and Raman media, the composite a-cutYVO₄/Nd:YVO₄crystal as Raman media,3) Utilizing the composite a-cut YVO₄/Nd:YVO₄crystal as Self-Raman media. The first two schemes are effective to obtain yellow laser output, and inthe schme1) the average output power of yellow laser is117mW at4.43W of the pumped powerand the corresponding conversion efficiency is2.64%. In scheme2), we can observe bright yellowlight spot at4.03W of the pumped power, and the corresponding yellow laser pulse width is6.7ns. It shows that this scheme is able to get yellow laser output width narrow width. In addition, the factorsthat affect the yellow laser in the experiments are analyzed, such as lager Raman gain, shorterresonate cavity length, smaller stimulated emission cross section et al. are important to get goodpassively Q-switched yellow laser.