【作者】 卢华东；

【导师】 彭堃墀；

【作者基本信息】 山西大学 ， 光学， 2011， 博士

【摘要】 紧凑稳定高效的全固态连续单频可调谐钛宝石激光器,以其较宽的输出光谱、较高的输出功率、较低的强度噪声等优点,可广泛应用于高灵敏度的干涉仪、高分辨率激光光谱、引力波探测、量子通讯、原子冷却等领域。一方面,我们可以通过对钛宝石晶体本身特性进行分析,设计并优化光学谐振腔,以及在谐振腔内插入激光器必须的光学元件等手段,获得高效稳定的连续单频可调谐钛宝石激光器。另一方面,随着科学技术的发展,人们对激光器的强度噪声更加关注,因为激光器强度噪声的存在对许多实验结果产生不利的影响,进而阻碍了钛宝石激光器在科研领域中的应用。因此,提高全固态连续单频可调谐钛宝石激光器的相关指标和降低钛宝石激光器的强度噪声就成为了发展全固态连续单频可调谐钛宝石激光器的主要内容。为此,我们主要从设计和优化激光器谐振腔,降低激光器强度噪声等方面对全固态连续单频可调谐钛宝石激光器进行了研究,其主要工作如下：1.通过对具有宽带吸收光谱和宽带发射光谱的增益介质钛宝石晶体的分析,设计了消除像散的四镜环行谐振腔。利用传输矩阵,分析了四镜环行谐振腔的稳区和腰斑的变化特性,合理选择谐振腔参数,使激光器工作在最佳状态。在谐振腔内插入了由外加磁场的TGG晶体和消色差半波片组成的宽带该光学单向器后,激光器在可调谐的波长范围内均实现了单向运转。2.理论上分析了最大输出功率与腔内损耗以及输出耦合镜透射率之间的关系,得到了不同泵浦功率下的输出耦合镜最佳透射率。实验上利用腔内插入薄熔融石英片和更换输出耦合镜透射率的方法,测量了腔内损耗,在此基础上得到不同泵浦功率下的输出耦合镜最佳透射率,进而优化了激光器。最后,将激光器锁定在高稳定度的光学参考腔上,提高了激光器的输出稳定性。3.分析了双折射滤波片和标准具以及压电陶瓷在钛宝石激光器中的调谐特性。在钛宝石激光器中,钛宝石晶体的发射谱决定了最大调谐范围；双折射滤波片在激光器中起粗调作用,其最薄一片决定其最大调谐的范围,而最厚一片决定其调谐的精度；标准具是一种选模调谐,尽管其调谐精度很高,但其仍是非连续的调谐；而要想获得真正的连续调谐,还需要改变谐振腔上的压电陶瓷的电压,通过改变压电陶瓷的电压,进而改变谐振腔腔长,最后达到连续调谐的目的。4.在获得高稳定性的全固态连续单频可调谐钛宝石激光器后,我们研究了钛宝石激光器的强度噪声特性。首先,我们研究了泵浦源的纵模结构对钛宝石激光器的影响,发现以单频绿光激光器取代单横模绿光激光器作为钛宝石激光器的泵浦源时,钛宝石激光器的强度噪声明显降低。在此基础上,我们还研究了泵浦源的泵浦速率等因素对钛宝石激光器的影响。随着泵浦速率的增大,激光器的弛豫振荡频率向高频方向移动,而弛豫振荡的幅度减小。最后,我们用一种理论模型拟合了钛宝石激光器的强度噪声,该模型适用于泵浦源有一定分布特点的激光器。5.尽管采用单频绿光激光器作为钛宝石激光器的泵浦源,钛宝石激光器的强度噪声在2.5MHz处已达到量子噪声极限,然而在低频段,钛宝石激光器的强度噪声仍然高于量子噪声极限。为了获得低噪声的钛宝石激光器,我们采用光电负反馈来抑制钛宝石激光器的强度噪声。通过选取合适的反馈增益,位相延时及带通滤波,在频率为1.125MHz处,钛宝石激光器由原先的8.7dB降到了抑制后的1.4dB,抑制程度达7.3dB。而且通过选择不同的位相延时和带通滤波可以获得不同频率点的强度噪声抑制。创新性的工作：A.设计并获得了结构紧凑,稳定性好的钛宝石激光器,其相关指标基本上达到目前国外产品的水平。B.利用腔内插入熔融石英片的方法测量了腔内损耗,研究了激光器在不同泵浦功率下的最佳透射率,优化了谐振腔。C.通过对调谐元件的设计,在达到调谐宽度的基础上,提高了调谐精度。D.研究了泵浦源的纵模结构以及泵浦速率等因素对钛宝石激光器强度噪声的影响,提出了一种适合泵浦源强度噪声有一定分布特点的理论拟合方法。E.利用光电负反馈抑制了钛宝石激光器的强度噪声。更多还原

【Abstract】 All-solid-state continuous-wave single-frequency tunable Ti:sapphire lasers with compact configuration, high stabilization and high efficiency have been extensively applied to high-precision interferometry, high-sensitive laser spectroscopy, gravity-wave detection, quantum communications, atom cooling and so on owing to their broad tunable wavelength range from 700 nm to 1000 nm, high output power and low intensity noise. It has been demonstrated that the Ti:sapphire laser with high-efficiency and high-stabilization can be achieved by analyzing the characteristic of the Ti:sapphire crystal, designing and optimizing the resonant cavity and inserting the necessary optical devices into the laser cavity. However, when Ti:sapphire lasers are used in the experimental researches for laser cooling of atoms, quantum optics and quantum information, more and more attentions have to be paid in reducing intensity noises of their output light since the extra noises of laser sources will severely influence the experimental results. During the period of my Ph. D study, we designed and constructed a CW Ti:sapphire laser firstly. Then, we experimentally analyzed the noise characteristics of the Ti:sapphire laser. The accomplished main works are as following:1. Based on analyzing the absorption and emission spectra of Ti:sapphire crystal, we design a ring laser resonantor with four mirrors, in which the optical astigmatism is compensated. Using the transmission matrix the stable operation conditions of the laser and the properties of the beam-waist are calculated. By optimized the parameters of the laser resonantor the unidirectional operation of the laser can be realized in the required tunable range.2. The dependences of the Ti:sapphire laser output power on the intracavity losses and the transmission of the output coupler are theoretically analyzed and experimentally investigated. According to the experimentally measured intracavity losses and the given transmission of the output coupler, the design of the laser is optimized and the stable laser output with higher power is obtained. In order to improve further the frequency stability of the Ti:sapphire laser, a confocal reference cavity and an electronic servo-system are used for the laser frequency locking on.3. The tuning properties of the Ti:sapphire laser are analyzed. The maximum tuning wavelength range is limited by the bandwidth of the Ti:sapphire crystal. A set of BRF inserted in the resonant cavity serves as the tuning element of the laser. The tuning range and the tuning precision are determined by the thinnest and the thickest plate of the BRF, respectively. Besides, an etalon inserted in the resonant cavity can improve further the tuning precision in a noncontinuous tuning fashion. In order to achieve the continuous tuning, we change the voltage of the PZT attached on a cavity mirror to adjust the resonant frequency of the cavity, continuously.4. To research the intensity noise of the built Ti:sapphire laser, its intensity-noise dependence on the longitudinal-mode structure of the pumping source is experimentally studied, firstly. We find that the intensity noise is significantly reduced when a single-longitudinal-mode green laser is utilized as pumping source instead of the multi-longitudinal-mode green laser. Then the influences of the pumping rate and the wavelength of the laser on the intensity noise of the Ti:sapphire laser are studied. Increasing the pumping rate, the frequency of the relaxation resonant oscillation (RRO) moves toward higher frequency and the amplitude of RRO peak decreases. Finally, we theoretically analyzed the spectra of the intensity noise of the output laser and the theoretical calculation and the experimental result are in good agreement. The theoretical model can be applied to calculate the intensity noise spectra of the laser pumped by a pumping source with a noise distribution.5. In order to suppress the intensity noise at the low frequencies of the all-solid-state continuous-wave single-frequency tunable Ti:sapphire laser, the characteristic of the optoelectronic feed-forward is theoretically analyzed. The calculated result shows that the best gain of the feedback circuit depends on the injected noise. Then, the characteristic of the intensity noise suppression at the low frequencies by means of the optoelectronic feed-forward is experimentally investigated. By tuning carefully the gain of the feedback circuit the suppression of the intensity noises can be optimized. The decrease of the amplitude of the intensity noise from 8.7 dB to 1.4 dB is experimentally observed, and the maximum noise suppression of 7.3 dB is obtained at 1.125 MHz. It has been demonstrated that by selecting the best delay time and feed-forward gain, the intensity noise can be suppressed almost to the quantum noise level at any sideband frequency.The creative works are as following:A. We designed and built an all-solid-state CW single-frequency tunable Ti:sapphire laser.B. The Ti:sapphire laser was optimized by inserting a silicon plate to measure the intracavity losses and studying the relationship bwtween the output power and transmission of the output coupler.C. The tuning precision was improved by designing and selecting a suitable tuning device.D. Influences of the longitudinal-mode structure of the pumping source and a variety of factors on the intensity noise of the Ti:sapphire laser were studied and a method for theoretically calculating the intensity noise spectra was applied. E. Intensity noise at the low frequencies of the Ti:sapphire laser was suppressed by optoelectronic feed-forward control.更多还原