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Study Of Single Longitudinal Mode And Injection Locking In Rapidly Tunable TEA CO2 Laser

Posted on:2011-02-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y H WangFull Text:PDF
GTID:1118330338489457Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
On account of the advantanges including narrow linewidth, high power, tunable, eye-safe, etc., single longitudinal mode (SLM) TEA CO2 laser is of special interest in areas such as optically pumped far-infrared lasers, molecular spectroscopy, velocimeters and remote sensing of the atmosphere. SLM TEA CO2 laser can be used in heterodyne differential absorption lidar (DIAL) system because of its excellent monochromaticity and coherency. Compared with direct detection CO2 DIAL, heterodyne detection DAIL has longer detection range and higher sensitivity. The velocity information can be acquired at the same time. Such kind of research has been conducted for a long period in many foreign institutes. In the heterodyne detection CO2 DIAL system, both power and frequency of the laser have to be stabilized. In view of this condition, the technologies to obtain SLM TEA CO2 laser and frequency locked laser have been investigated theoretically and experimentally in this dissertation.First of all, a six temperature vibrational-rotational model has been used to analyze the kinetic process of TEA CO2 laser. Output characteristics of the laser were investigated according to the model. The influences of gas pressure, gas mixture ratio, gas temperature, reflectivity of output coupler and cavity lengths on the output laser have been researched, respectively. The six temperature vibrational-rotational model will be contributed to the optimized design of TEA CO2 laser.A tunable TEA CO2 laser has been designed. The electrode style, preionization and discharge circuit of TEA CO2 laser were analyzed and calculated. A numerical model of the discharge circuit was established to simulate the discharge process of the laser. When the laser operated in single-transverse mode, 77 emission lines of the CO2 molecule rotational transition is obtained. The maximum energy of 350mJ and M2=1.21 are obtained when the laser operated in fundamental transverse mode.In order to obtain high power SLM laser and expand the tuning range, a multi-interferometeric resonator has been presented. Based on the principle of SLM oscillation obtained by using a three-mirror resonator, a numerical model of the interferometric resonator is investigated to optimize the laser for mode selection based on self-consistent wave method and a stochastic method. SLM operation has been theoretically predicted using the model. Experimentally, SLM TEA CO2 laser oscillation is realized using multi-interferometeric resonator. When the laser operated in SLM, 69 emission lines of the CO2 molecule rotational transition is obtained. Pulse output energy of 324mJ at 10.6μm has been obtained. In the same experiment conditions, it shows that this multi-interferometric resonator gives better performance in mode selection than other resonator based on multi-beam interference. Both the output energy of SLM laser and tuning range can be improved obviously using this configuration.To achieve rapid tuning in a stable SLM TEA laser, the injection locking technique of rapidly tunable TEA CO2 laser has been researched. Theoretically, considering vibrational kinetics of TEA CO2 laser and interaction between resonator modes, a numerical model has been developed to represent the kinetics of injection locked TEA CO2 laser by combined six-temperature model of vibrational kinetics with injected photon field equation. Output characteristics of the laser have been calculated and analyzed in different condition. Experimentally, a twisted mode cavity has been used to obtain SLM TEA CO2 laser with weak-gain. SLM output energy of 47mJ is obtained at 9.77μm. This method can solve the problem that stable SLM TEA CO2 laser of weak-gain is difficult to obtaine and it lays the foundation of injection locking. Then frequency locking of the TEA CO2 laser has been obtained. Mode matching between the seed laser and the pulse laser has been achieved by shortening built-up time of the pulse. The characteristics of output laser have been investigated both in the situation where laser frequency was locked and not. Finally, a novel rapid tuning mechanism has been presented to improve repetitive positioning accuracy when the laser achieved rapid tuning. Using this mechanism, the rapidly tunable output between frequency locked laser at 10.28μm and SLM laser at 9.77μm has been realized.
Keywords/Search Tags:TEA CO2 laser, single longitudinal mode, injection locked, heterodyne detection
PDF Full Text Request
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