Investigation On The Thermal Effect And Laser Characteristics Of Neodymium-doped Multi-segment Bonding Crystals

Laser Diode(LD)pumped solid-state laser has the characteristics of simple structure,strong stability,high pump efficiency and good beam quality,so it has wide practical applications.We can find its adhibition in the fields such as laser spectroscopy,genetic energy transfer,industrial cutting,advanced medical operation as well as communication spectral coding.Due to its advantages,the focus of research in recent years has been paid much attention on.The thermal lensing effect and thermal birefringence caused by the increase of pump power in the gain medium are two of the key factors that prevent the laser from obtaining higher output power and better beam quality.In recent years,the research shows that the multi-segment bonding crystals with the different Nd3+ concentration can effectively reduce the heat loss which induced by the internal thermal deposition of the gain medium,thus reduce the thermal effect.In this thesis,the pump source is a the fiber coupled lasers,and we choose multi-segment bonding Nd:GdVO4 and Nd:YVO4 crystals as the work materials and we have studied the thermal loss and effect and the performance of the lasers.The contents and views of this dissertation are presented as below:(I)The thermal effects of ordinary crystals and multi-segment composite crystals are studied.By using finite element method,the differential form of the heat conduction equation is transformed into a difference form.By means of MATLAB software,the numerical simulation method is used to simulate the thermal focal length of the gain medium and the distribution of the temperature field inside the crystal and at the pump end.We measure the thermal focal length of the crystal.The results which we get through the experiments show that the measured results are in accordance with the theoretical simulation data,and the variation trends of these two are consistent with each other when the pump power increases.(II)The passively Q-switched laser characteristic of GaAs wafer saturable absorber was experimentally analyzed.We measured the average output power,pulse duration,pulse repetition rate versus incident pump power.The relationship between single pulse energy,peak power and pump power is calculated by using the formula.(III)LD-pumped multi-segment bonding Nd:YVO4 passively Q-switched laser at 1064 nm with Cr4+:YAG as the saturable absorber was realized successfully.The experiment employed the compact plane-concave cavity.In order to observe the data which the parameters of the laser change with the incident pump power,we use different small-signal transmission of Cr4+:YAG and identical transmission of OCs.We can get the variation trend which the parameters such as the average output power and pulse width change with the pump power.(IV)Employed the plane-concave cavity and with EO modulator,the LD pumped multi-segment bonding Nd:YVO4/Nd:YVO4/Nd:YVO4 actively Q-switched laser at 1064 nm was achieved.We investigate the actively Q-switched laser performances of two composite crystals.The average output power,the pulse repetition rate and the pulse duration versus incident pump power were achieved.Then the changes of single pulse energy and peak power with pump power are calculated.(V)Employed the W-shape resonator and X-shape resonator with five mirrors,LD pumped multi-segment bonding Nd:YVO4 and Nd:GdVO4 passively mode-locked lasers at 1064 nm were generated.Using the method of the ABCD matrix,we can calculate the length of the cavity.So we optimize the parameters of the laser cavity to get stable mode-locking laser.(VI)Employed the type of X-shape resonator with five mirrors,LD pumped different substrates bonding Nd:GdVO4/Nd:YVO4/Nd:GdVO4 crystal and Nd:YVO4/Nd:GdVO4/Nd:YVO4 crystal passively mode-locked lasers at 1064 nm were generated.The laser performances such as the average output powers of the two composite crystals were compared.Results showed that the Nd:GdVO4/Nd:YVO4/Nd:GdVO4 laser performance is better,and with the same condition its performance is superior to that of the same substrate bonding Nd:GdVO4/Nd:GdVO4/Nd:GdVO4 crystal.The innovation points of this thesis are as follows:(?)As far as I know,we firstly calculated the thermal focal lengths of the different substrates bonding crystals by regarding the segment crystals as thin lenses.We also stimulated the temperature distributions of the bonding Nd:GdVO4/Nd:GdVO4/Nd:GdVO4,Nd:GdVO4/Nd:YVO4/Nd:GdVO4,Nd:YVO4/Nd:GdVO4/Nd:YVO4 crystals by employing Matlab software and finite element method.(?)The passive mode-locking laser of composite Nd:GdVO4 with SESAM as saturable absorber was achieved and investigated for the first time.(?)LD pumped composite Nd:GdVO4/Nd:YVO4/Nd:GdVO4 and Nd:YVO4/Nd:GdVO4/Nd:YVO4 passively mode-locked lasers at 1064 nm were generated for the first time.The laser performance such as the average output power of the two composite crystals were compared.