Dissertation > Excellent graduate degree dissertation topics show
Allsolidstate Singly and Doubly Qswitched, Laserdiodepumped Intracavity Optical Parametric Oscillators
Author: WangJing
Tutor: ZhaoShengZhi
School: Shandong University
Course: Optical Engineering
Keywords: Optical parametrical oscillator EO switch doubly Qswitched KTA crystal rate equations Gaussian distribution conversion effeciency
CLC: TN248
Type: PhD thesis
Year: 2008
Downloads: 344
Quote: 2
Read: Download Dissertation
Abstract
Much interest in intracavity optical parametric oscillators （OPOs） has been stimulated due to the current interest in efficient, eyesafe coherent light sources for their applications such as telemetry, laser radar, communications and active imaging.It is efficient to predict the performance of Optical Parametric Oscillators （OPOs） by means of rate equations. Many researchers have been working on the rateequation model since Oshman and Harris firstly derived the rate equations for a CW pumped Extracavity Optical Parametric Oscillator （EOPO） in 1968. The derived models can describe the operation of all possible OPOs, including the Qswitched pulse pumped Intracavity Optical Parametric Oscillators （IOPOs） which are preferred by the researchers because of its high efficiency. But all of these works based on the theory that the spatial distribution in the transverse section of the pump light, the fundamental light and the signal light is uniform or under the planewave approximation. For LDpumped IOPOs, this assumption is not properly satisfied because the three beams are all Gaussian transversal distributions. For LDpumped actively and passively Qswitched lasers, when the Gaussian distribution of the intracavity laser intensity is considered in rate equations, it has been shown that the numerical solutions of the equations are more close to the experimental results than those obtained under the planewave approximation. Therefore, for an LDpumped IOPO, it is reasonable to take the spatial variations of the intracavity photon density, the populationinversion density of the gain medium into account.In order to make an OPO work more efficiently, the high peak intensity of the pumped fundamental laser is one of the most important factors. Therefore, it is very important to apply a highquality Qswitch to obtaining the short pulses of the fundamental laser. An actively Qswitched laser （AO and EO switched） can obtain stable pulse train output, but the pulse width of it is usually wide. Passively Qswitched lasers with a saturable absorber can generate shorter pulse than actively Qswitched laser, but the pulse repetition rate is not very stable. When an actively and passively Q switches are simultaneously used in the cavity, it has been shown that this doubly Qswitched can generate shorter pulse with stable repetition rate and high peak power. So it is possible for LDpumped doubly Qswitched IOPOs to obtain signal light with shorter pulse width and higher peak power.Among active Qswitching techniques, electrooptic （EO） Qswitching and acoustooptic （AO） Qswitching are often used, and the former is known to be advantageous over the latter in its faster switching and better holdoff ability. The traditional EO crystals, such as DKDP （KH_{2}PO_{4}） and LN （LiNO_{3}）, are often used in low repetition rate （<1 KHz） Qswitched lasers. Although the crystal BBO （βBaB_{2}O_{4}） as an EO crystal is attractive because of its low damage threshold and low piezoelectric effect, it is still insufficient for an efficient OPO due to its several kHz limit in repetition rate. The excellent frequencydoubling crystal KTP （KTiOPO_{4}） has large electrooptic coefficient and can be used as EO modulator at highrepetitionrate operation, but its application is limited due to its low resistivity.The new type of EO crystal RTP （RbTiOPO_{4}） has high resistivity (10^{10}10^{12}Ω·cm), large electrooptic coefficient, high damage threshold and low piezoelectric effect, so RTP crystal is considered to be promising for high repetition rate EOQswitching lasers. Though some reports on EOswitched IOPOs with several kHz repetition were presented, as far as we know, there is no the related report on a high repetition rate EOswitched IOPO.As far as the nonlinear crystal, compared with the similar and more common OPO crystal KTiOPO_{4} （KTP）, the new crystal KTiOAsO_{4} （KTA） has large nonlinear optical coefficient and the advantage of enhanced transparency in the midinfrared region （35μm）, allowing highpower operation with minimal thermally induced refractive distortion in the OPO crystal. Because of the abovementioned advantages of KTA crystal, the KTA OPO can generate the higher signal output and the shorter pulse than the KTP OPO at some experimental condition.Based on the abovementioned thoughts, the main contents of this dissertation include:（Ⅰ） In the experiment, a laserdiodepumped （LD pumped） actively Qswitched Nd:GdVO_{4}/KTP IOPO with acoustooptic （AO） modulator is realized. The pulse width, the output power and the temporal profile are measured. The rate equations under Gaussian assumption are derived to fit the experimental data. It is found that the Gaussian rate equations agree with the experimental results better than the planewave equations. （ⅡI） By using RTP crystals as EO modulator, a flashpumped high repetition rate （10 kHz50 kHz） EOQswitched Nd^{3+}:YAG/KTP IOPO is realized. The dependences of pulse width, the singlepulse energy and the peak power on flashpump energy for the generatedsignal light are obtained. By considering the gradual loss from the delayed switched time of the EO switch, the coupled rate equations of IOPO under the assumption of the Gaussian distributions of the intracavity photon densities are given and the numerical solution of the equations fits the experimental data well.（Ⅲ） In the experiment, a laserdiodepumped doubly switched Nd:GdVO_{4}/KTP IOPO with AO and a Cr^{4+}: YAG saturable absorber is realized. In the rate equations, the intracavity photon densities and the initial populationinversion density are assumed to be Gaussian spatial distributions. By numerically solving the introduced rate equations based on Gaussian assumption, the dependences of pulse width, singlepulse energy and peak power on pump power for the generatedsignal light are obtained. For a comparison, the experimental results of the AO singly Qswitched Nd:GdVO_{4}/KTP IOPO, involving the pulse width, the peak power and the pulse energy, are measured. It can be found that when the other conditions are the same, the doubly Qswitched IOPO can generate the shorter pulse width and higher peak power than that of the singly AOswitched one. The experimental results agree with the theoretical values well.（Ⅸ） By simultaneously using both an EO modulator and a Cr^{4+}:YAG saturable absorber in the cavity, a xenon flashlamppumped doubly Qswitched Nd:YAG/KTP/IOPO is presented. The dependences of the singlepulse energy, the pulse width, and the peak power on flashpumping energy for the generatedsignal light are obtained. The output characteristics of the doubly Qswitched IOPO with an EO switch and a Cr^{4+}:YAG crystal are compared with those of the singly Qswitched IOPO with an EO switch. The coupled rate equations of doubly Qswitched IOPO under the assumption of the Gaussian distributions of the intracavity photon densities are given and the numerical solution of the equations fits the experimental data well.（Ⅴ） A laserdiodepumped doubly switched Nd:GdVO_{4}/KTA IOPO with an AO and a Cr^{4+}: YAG saturable absorber is realized. For a comparison, the experimental results of the AO singly Qswitched Nd:GdVO_{4}/KTA IOPO, involving the average power, the pulse width, the peak power and the pulse energy of the signal light, are measured. Gaussian equations are used to fit the experimental data and the numerical solutions of the coupled rate equations agree with the experimental results well.（Ⅵ） The wavelength of the output signal light from the LD pumped KTP / KTA IOPO is measured. The signal wavelengths with different crystal temperature for a LD pumped KTA IOPO are obtained. It is found that, in the experimental temperature range （1029℃） the value of wavelength is the lest at T_{KTA} = 23℃.The main innovations of this dissertation are as follows:（Ⅰ） When the intracavity photon densities and the initial populationinversion density are assumed o be Gaussian spatial distributions, the Gaussian rate equations describing the performance of IOPO are firstly derived. In the equations, the influence of the pump rate, the thermal effect in the gain medium and the diffraction loss of the actively Qswitch are considered. Also the different photon densities at different positions in the laser cavity are taken into account. Finally, the average radius of the pump light, the average populationinversion density of the gain medium and the population densities of the excitedstate of the saturable absorber are considered to be Gaussian spatial distributions. The calculated values are compared with that from the plane wave assumption. It is found that the Gaussian theory fits the experimental data better, especially when the pump power is high in our experiment.（Ⅱ） A high repetition rate electroopticalQswitched intracavity optical parametric oscillator （IOPO） is realized by using two RbTiOPO_{4} （RTP） crystals as electrooptic （EO） modulator. By considering the gradual loss from the delayed switched time of the EO switch, the coupled rate equations of IOPO under the assumption of the Gaussian distributions of the intracavity photon densities are given.（Ⅲ） A laserdiodepumped doubly switched Nd:GdVO_{4}/KTP IOPO with AO and a Cr^{4+}: YAG saturable absorber is firstly reported in experiment. The experimental results are compared with those of singly actively Qswitched IOPO. The doubly Qswitched IOPO can generate the shorter pulse width and higher peak power than that of the singly switched one.（Ⅳ） A xenon flashlamppumped doubly Qswitched Nd:YAG/KTP/IOPO is presented in experiment. The experimental results are compared with those of singly actively Qswitched IOPO. The doubly Qswitched IOPO can generate the shorter pulse width and higher peak power than that of the singly switched one and have high conversion efficiency. （Ⅴ） By using the new crystal KTA as the nonlinear material, a Qswitched KTA IOPO is realized. The output characteristic of it is compared with that of a KTP IOPO. The KTA IOPO can generate shorter signal pulse and higher peak power.

Related Dissertations
 Research on 1.53μm EyeSafe Laser Optical Parametric Oscillator,TN248
 Spectral Properties and Frequency Upconversion Characteristics in Rare Earth Doped KYW Crystal,O734
 The Research of Keystroke Dynamics Based on Statistical Method,TP393.08
 Research on Optimization of Transform and Quantization Arithmetic in H.264,TN919.81
 The Detection Algorithm of Marine Oil Spill Based on Time Series Using MODIS,X834
 MultiwaveletBased Digital Image Watermarking,TP309.7
 The Study on the Kinetic Scaling Behavior of ExchangeDriven Aggregation Processes,O469
 Theoretical and Experimental Research on Erbiumdoped Fiber Ring Laser Applied to Gas Sensor,TN248
 Study on the Characteristics of Passively Qswitched Laser Using AlGaInAs as the Saturable Absorber,TN248
 Extension of injection locking theory and their dynamic behavior analysis,TN248
 Research of VideoBased Vehicle Detection Algorithms Through Background Subtraction,TP391.41
 Technical Development of Random Pulse Generator Simulated Nuclear Signal,TL82
 Research on Nonuniformly Injected Semiconductor Optical Amplifiers,TN722
 Theoretical Research of an End Pumped Doubleclad Fiber Lasers Doped with Quasi Twoenergylevel Ions,TN253
 Theoretical lnvestigation on the Tuning Characteristics of High Power TE（A） CO_{2} Lasers,TN241
 All solidstate Raman laser theory and experimental research,TN248
 Design and Implementation of Bugs Analysis and Quality Measurement System,TP311.52
 Contentbased Image Retrieval Method,TP391.41
 Computer Simulation for the Effect of the Dormant Time Distribution on the Structure of Atom Transfer Radical Polymer,O631.3
 The Effect of Different Dust Size Distribution to the Dust Acoustic Wave,O534
CLC: > Industrial Technology > Radio electronics, telecommunications technology > Photonics technology,laser technology > Laser technology, the maser > Laser
© 2012 www.DissertationTopic.Net Mobile
