Exploring Polarization States and Longitudinal Modes in Nd-Doped Lasers in Continuous-Wave and Passively Q-Switched Operation

• Main Authors: Cheng, Hao-Ping, 鄭浩平
• Other Authors: Chen, Yung-Fu
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/t6ejmd

博士 === 國立交通大學 === 電子物理系所 === 107 === Light beam polarization is a basic characteristic of laser radiation. Solid-state lasers usually generate linearly polarized or random polarized output. Orthogonally polarized laser sources have attracted intensive attention due to their wide applications in laser interferometry, holographic microscopy, differential absorption lidar, and precision measurement. This dissertation presents several optical experiments to investigate the orthogonally polarized states and longitudinal modes in diode-pumped Nd-doped solid-state lasers (DPSSLs) in continuous-wave (CW) and passively Q-switched (PQS) operation. Several studies have confirmed that the anisotropic and isotropic gain media can generate simultaneous emissions of two orthogonal polarizations. The orthogonally polarized laser can be generated by introducing the induced birefringence into an isotropic gain medium, such as Nd:YAG crystal. The induced birefringence that may come from the thermal stress or external force can lead to a frequency splitting between two orthogonally polarized modes. Moreover, the Nd-doped gain media are suitable to generate single- or multi-wavelength lasers in different transition level due to its abundant fluorescent lines. First of all, we utilize a monolithic Nd:YAG crystal to realize the self-mode-locked (SML) operation with orthogonal polarizations. The beat frequency between two orthogonally polarized states can be widely adjusted by controlling the water temperature. Next, we demonstrate a short linear cavity to explore the frequency splitting in the laser crystal by tuning the absorbed pump power from pump light. Furthermore, we put the monolithic SML laser into a cryogenic system to realize dual-wavelength operation. The relationship between the beat frequency and cooling temperature is further investigated. We also demonstrate the orthogonally polarized single-longitudinal-mode (SLM) and SML lasers by applying the mechanical stress on the Nd:YAG crystals with two crystal length. Moreover, we successfully design two types of coating specification for monolithic-coated Nd:YAG crystal to realize the single-wavelength or dual-wavelength lasers. Next, the synchronously dual SML operations at 946 nm and 1064 nm has been accomplished by physically combining the monolithic-coated Nd:YAG crystal to the Nd:YVO4 crystal as a composite gain medium. Finally, we explore the performance of orthogonally polarized PQS lasers. It has been found that the pulses of two orthogonally polarized states display the classical antiphase dynamics for two equal intensities.