Abstract
Basically speaking, light detection and ranging (LIDAR) is the most accurate technique for observing the orbits of artificial satellites or geodesy. On the other hand, it is also very useful in military application, for example, the radar system of missiles. However, the light source is usually at infrared wavelength such as 1064-nm, and this kind of wavelength could make serious damage to human naked eyes easily. Therefore, it is important to develop a laser source which is at eye-safe wavelength for further application. Since the ranging distance depends on the laser energy, the main scope of thesis will also be focused on generating large-energy eye-safe laser source.We use two kinds of methods to achieve this goal. One is to use stimulated Raman scattering (SRS) and the other is to use diffusion-bonded PPLN (periodic poled lithium niobate) technique. Although PPLN crystals have high efficiency in frequency conversion, the low damage threshold (2.7J/cm2 in a 10ns pulse at 1064nm) makes it hard to get high-energy (~mJ) signal. By increasing laser aperture on the surface of PPLN crystals, we can avoid the damage problem and get larger-energy output. In our research, the air gap in the interface of two pieces of lithium niobate is invisible under the microscope with 1000 magnification. Preliminary optical scattering experiments by using a HeNe laser shows outstanding laser transmission and material homogeneity. It is believed that diffusion-bonded PPLN can be achieved based on the successful experience of diffusion-bonded lithium niobate in the future. We also report the demonstration of 1.5-mJ/pulse eye-safe laser generation by using a 30-mJ/pulse Nd:YAG laser to excite SRS in acetone. The single-path gain length in acetone is 10-cm. Furthermore, the Raman shift of acetone is 2921-cm-1 and the corresponding first Stoke wavelength is at 1544-nm. The single-path efficiency is nearly 5%. Again, acetone is an anisotropic medium which has obvious self-focusing effect, and performance of SRS depends on the self-focusing effect. Thus, the observation of self-focusing effect is also described in this thesis. On the other hand, since the resonator is an efficient structure in laser generation, the concept and the limitation of Raman resonator are also discussed in detail.