【作者】 王垚廷；

【导师】 张宽收；

【作者基本信息】 山西大学 ， 光学， 2010， 博士

【摘要】 随着激光技术的飞快发展,全固态蓝光激光器在高密度光学数据存储、彩色激光显示、水下通信和探测、激光医学、激光微加工、激光制冷、材料分析、环境检测、高分辨率激光印刷及广告娱乐等领域有着广泛的应用,因此目前已成为人们的研究热点。对于全固态连续单频激光器来说,由于其具有可以长期稳定运转、输出线宽窄、频率可调、相干长度长、噪声低等特点,广泛应用于科学研究领域、仪器领域、光通信领域、超远距离、超高精度和超高敏感度探测领域、光学全息、干涉、光存储领域、绝对频率稳定及绝对频标等领域中,因此,全固态连续单频蓝光激光器在高精度激光测量、高密度光学全息数据存储、生物技术、紫外频标及科学研究等方面有着优越的用途,也是人们目前研究的热点。根据我们实验室的研究特色,并在已有研究成果的基础上,我们开展了大功率全固态连续单频蓝光激光器的研究。基本设计方案为,以Nd:YAG为激光晶体首先得到连续单频的946nm基频光,然后通过内腔倍频技术得到473 nm的连续单频蓝光。具体研究内容如下：1.在理论上通过把能量传输上转换效应引入准三能级系统的速率方程,对Nd：YAG激光晶体中946 nm跃迁的准三能级系统性质进行了详细的分析。关于准三能级系统的性质,包括自吸收损耗严重,受激辐射截面小及能量传输上转换效应相对明显等,通过从理论上对自吸收损耗表达式进行推导,表明自吸收损耗与激光晶体温度和长度,及激光晶体中泵浦光斑大小成正比。对包括能量传输上转换效应的速率方程进一步研究发现：一方面,能量传输上转换效应的出现使激光器的性能大大改变,包括阈值泵浦功率升高及输出功率下降等；另一方面,能量传输上转换效应(或者参与能量传输上转换过程的粒子数)是一个和激光转换效率有关,即和激光晶体温度、输出耦合透射率及倍频效率等成正比的物理量。2.对激光晶体的热效应进行了详细分析,包括激光晶体的热透镜效应、热致衍射损耗效应及热退偏效应,并把能量传输上转换效应引入分析,结果表明能量传输上转换效应的出现将会给激光晶体带来更严重的热效应,并且能量传输上转换效应感应的热沉积百分比随激光转化效率的变化而变化,即总的热沉积百分比不再是一个常量,而是一个随激光转换效率,包括激光晶体温度、输出耦合透射率及倍频效率等变化的量,因此,热透镜效应、热致衍射损耗效应及热退偏效应也是与激光转换效率有关的物理量。3.以理论分析为基础,并在实验上通过对激光晶体热焦距的测量,设计了一个四镜环形腔,考虑到Nd:YAG晶体各项同性的性质,在腔内插入布儒斯特片用来起偏,同时在腔内插入半波片和TGG晶体组成的光学单向器,迫使振荡激光单向运转,从而实现单频输出。考虑到Nd:YAG激光晶体自吸收损耗与激光晶体温度和长度,及激光晶体中泵浦光斑大小的关系,我们降低了激光晶体温度、优化了激光晶体长度、并采用了芯径为400μm的光纤耦合半导体激光器为泵浦源。考虑到能量传输上转换效应及其感应的热效应和激光转换效率的关系,我们通过优化激光谐振腔腔长和输出耦合透射率,最终得到了1.5W的连续单频946nm激光输出。4.在已得到的连续单频946nm激光器的基础上,将PPKTP倍频晶体插入谐振腔中,通过内腔倍频技术得到了473nm的连续单频蓝光输出。为了提高倍频效率,并考虑到能量传输上转换效应感应的热透镜效应和倍频效率的关系,我们优化了激光谐振腔腔长、PPKTP倍频晶体温度及长度,最终得到了1.01W的连续单频473 nm蓝光输出。5.实验中,由于激光晶体的热致双折射效应导致了热退偏损耗,使得一部分基频光从布儒斯特片反射出来,而且泵浦功率越大反射的越多,这对激光转化效率的提高显然是不利的,但我们也能对反射出来的946nm激光进行利用,并和输出镜输出的473 nm蓝不一·起来得到双波长激光器,以此为基础我们得到了连续单频946nm输出功率为450 mW,同时连续单频473nm蓝光输出功率为1.0l W的双波长激光器。其中,创新性工作包括：1.建立了能量传输上转换效应(或者参与能量传输上转换过程的粒子数)是和激光转化效率,包括激光晶体温度、输出耦合透射率及倍频效率等相关的理论模型,这就说明了能量传输上转换效应感应的热效应,包括激光晶体的热透镜效应、热致衍射损耗效应及热退偏效应也是和激光转化效率有关的物理量。以此理论模型为基础,理论计算和实验结果符合的很好。2.得到了输出功率为1.5W的连续单频946 nm红外激光器,输出功率长期稳定性优于±1%,利用电子伺服系统将激光的频率锁定在共焦法-珀(F-P)腔的共振透射峰上,946 nm激光的频率稳定性优于±1.5 MHz/min。3.得到了输出功率为1.01w的连续单频473nm蓝光激光器,输出功率长期稳定性优于±1.8%,利用电子伺服系统将激光的频率锁定在共焦法-珀(F-P)腔的共振透射峰L473 nm蓝光激光的频率稳定性优于±4 MHz/min。4.考虑到激光晶体热退偏效应的影响并对布儒斯特片反射的946nm激光加以利用,提出了在得到倍频光输出的同时再利用布儒斯特片反射的基频光来得到双波长激光器的方法,最终从实验上得到了连续单频946nm激光输出功率为450mW,同时连续单频473nm蓝光输出功率为1.01W的双波长激光器。更多还原

【Abstract】 With the development of laser technology, all-solid-state blue laser can be applied in high density optical data storage, color display, underwater imaging and detecting, laser medicine, laser micro-processing, laser cooling, high-resolution laser printing and so on. For the all-solid-state cw single-frequency laser, it has many merits such as good power stability and frequency stability, narrow linewidth, tunable frequency, lower noise, so it can be applied in scientific research, instrument, optical communication, super-long-range, super-high-precision, super-high-sensitivity detection, optical holography, interference, optical storage, absolute frequency stability and absolute frequency standard. For the all-solid-state cw single-frequency blue laser, it can be applied high-precision laser measurement, biological technology, ultra-violet frequency-standard, scientific research and so on.Based on the research character and the studying foundation, we start the investigation of high-power all-solid-state cw single-frequency blue laser, and the method is that using the Nd:YAG for laser crystal to obtain the 946 nm laser, then obtain the 473 nm blue laser by intra-cavity frequency doubling technology. We carried out a series of research jobs as follows.1. In theory we analysised the characters of quasi-three-level of Nd:YAG laser operating on 946 nm by the rate equation including energy transfer upconversion, and the result shows that the energy transfer upconversion effect can influent the laser performance such as increase the threshold pump power and reduce the output power and so on. For the quasi-three-level laser system, it has some natures such as serious reabsorption losses, lower stimulated-emission cross section, and serious energy transfer upconversion effect and so on. The theoretical result also shows that the reabsorption losses is indirect proportion to the temperature and length of laser crystal and the spot radius of pump beam in laser crystal. Besides, the result shows that the energy transfer upconversion effect (or the ions including energy transfer upconversion process) is indirect proportion to the laser conversion efficiency, including the temperature of laser crystal, the transmission of output coupler and frequency doubling efficiency.2. In theory we discussed the thermal effect of laser crystal in detail, including thermal lensing effect, thermal-induced diffraction losses and the thermal-induced depolarization effect. Since the energy transfer upconversion effect can make the thermal effect of laser crystal more serious and the thermal effect indued by energy transfer upconversion effect is related to the laser conversion, the whole fractional thermal loading is related to the laser conversion and the thermal lensing effect, thermal-induced diffraction losses and the thermal-induced depolarization effect are also related to the laser conversion.3. Based on the theoretical analysis, in experiment we designed a six-mirror ring cavity, and inserted a Brewster plate into cavity as the isotropy of Nd:YAG crystal. We inserted a half wave plate and a TGG crystal that compose of an optical diode which can make the laser unidirectional operating, that make the output laser operating in single frequency. To reduce the reabsorption losses of Nd:YAG laser crystal, we decreased the temperature of Nd:YAG and optimized the length of it, besides, we also used a laser diode with fiber-core diameter of 400mm for pump source. Considering the thermal effect induced by energy transfer upconversion effect, we optimized the cavity and the transmission of output coupler. As a result of it, an output power of 1.5 W cw single frequency 946 nm laser was obtained.4. Based on the cw single frequency 946 nm laser, and inserted the PPKTP frequency doubling crystal into cavity to obtain the cw single frequency 473nm blue laser. To improve the frequency doubling efficiency and considering the thermal lensing effect induced by energy transfer upconversion effect, we optimized the laser cavity length, the temperature of PPKTP and the length of it, finally we obtained an output power of 1.01 W cw single frequency 473 nm blue laser. 5. In experiment, we investigated some 946 nm laser reflected from the Brewstwe plate that is because of the thermal-induced depolarization losses. According to the principle, we designed and obtained a dual-wavelength laser with an output power of 450 mW at 946 nm and an output power of 1.01 W at 473 nm.The creative works are as follows:1. We founded a theoretical model that the energy transfer upconversion effect (or the ions involving energy transfer upconversion process) is related to the he laser conversion efficiency, including the temperature of laser crystal, the transmission of output coupler and frequency doubling efficiency. It means that the thermal effect of laser crystal including thermal lensing effect, thermal-induced diffraction losses and the thermal-induced depolarization effect is also related to the he laser conversion efficiency. Based on the theoretical model, the theoretical calculation obtained a good agreement with the experimental result.2. In experiment, we obtained a cw single frequency 946 nm laser with an output power of 1.5 W. The long term power stability is less than±1%. After the laser was locked to the confocal Fabry-Perot cavity resonance, the measured frequency stability of 946 nm laser is better than±1.5 MHz.3. In experiment, we obtained a cw single frequency 473 nm blue laser with an output power of 1.01 W. The long term power stability is less than±1.8%. After the laser was locked to the confocal Fabry-Perot cavity resonance, the measured frequency stability of 473 nm blue laser is better than±4 MHz.4. Considering the thermal-induced depolarization effect of Nd:YAG laser crystal and suggesting a method of achieving dual-wavelength laser with the frequency doubling laser and fundamental-wave laser, we obtained a dual-wavelength laser with an output power of 450 mW at 946 nm and an output power of 1.01 W at 473 nm.更多还原