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Improving On Thermal Effect In Gain Medium And Experimental Investigation Of All-solid-state High-Power Single-Frequency Lasers

Posted on:2015-11-30Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y J WangFull Text:PDF
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Laser Diode (LD) Pumped All-Solid-State Laser (DPSSL) has a variety of advantages, such as small size, high stability, and long lifetime. This type of lasers has been extensively applied in scientific research, industry manufacture, laser medicine and national defense construction, and so on. By means of mode-selection technology, we can compel DPSSLs to be operated in the state of single frequency (SL), which have low amplitude and phase noise, as well as long coherent length. Due to these favorable features, the SL lasers play important role in quantum information, quantum optics and cold atom physics. In the modern scientific reseach and application technology, different types of light sources with higher quality are required. The high power single frequency laser and the nonclassical light source with noise level below the shot noise limit (SNL) are urgently needed. We implemented the theoretical and experimental study in the two subjects.Firstly, in order to satisfy the applications of quantum optics in pumping Optical Parametric Oscillator (OPO) or Optical Parametric Amplifier (OPA), we constructed a double wavelengths Nd:YAP/LBO single frequency laser, in the cavity design of which the conditions of optimum intracavity double frequency is exploited.Secondly, the thermal effect problems in all solid state high power SL lasers are analysed in details. The schemes to overcome the thermal effect are presented. Finally, a stabe SL over 10W is obtained.At last, we achieved a compact nonclassical laser source, in which a small size 1080/540nm single frequency laser, a non-degenerate OPA (NOPA), and a Bell state detection system are all fixed in a breadboard. Meanwhile, a electronic locking system, a temperature controller, and the direct current (DC) power supply systems are also totally integrated together.The accomplished main works are listed as following:1. Application of low-doped level Nd:YVO4 crystal:Nd:YVO4 crystal has a high absorption coefficient for the pump wavelength of 808nm, which will induce a serious thermal effect (TE) in the crystal. The TE will decrease the output power and degrade the quality of the laser beam. To mitigate the TE, we selected a low Nd-doped cystal, in which the Nd-doped level was reduced from 0.3 at.% to 0.2 at.%. Then the output power of the single frequency 532nm laser is increased to 11.47 W.2. Design of ring resonator consisting of double concave and double convex mirrors:Based on analyzing the dependence of the intracavity second harmonic wave (SHW) conversion efficiency on the cavity parameters, we designed a double concave and double convex mirrors ring resonator and the cavity configuration is optimized, to enlarge the mode size of the fundamental wave in the laser crystal for improving the thermal effect and at the same time to reduce its waist size in the frequency doubler for increasing the SHW conversion efficiency. Using this design, we constructed a double wavelengths (1080nm/540nm) Nd:YAP/LBO laser with 4.5W (1.5W) single frequency output and two high power SL lasers at 532nm with 10W and 20W 532nm output, respectively.3. Self-compensation of astigmatisms:The π polarized beam generated by Nd:YVO4 crystal has the character of thermal lens astigmatism (TLA). It will make the stability ranges in the meridian and sagittal planes of the resonator to be splitted, which results in the output lasing unstable. To compensate the thermal lens astigmatisms, we put a Nd:YVO4 crystal into the resonator with c axis paralleling to the meridian plane. Then we optimized the parameters of the resonator to achieve the self-copmpensation between TLA and the astigmatism of the resonator. In this case, the stability and the beam quality of the high power SL lasers at 532nm are significantly improved.4. Appling the scheme of direct pump:To mitigate the thermal lens effect of Nd:YVO4 crystal, a pump source with 888nm wavelength, which implements the direct pumping between the gound state and the excited state, is used to decrease the quantum defect in the 1064nm lasing process. The pump scheme reduces the thermal effect of 7.5% compared with that using 808nm pump wavelength. Since the absorption property of the laser crystal at the 888nm wavelength does not depend on the polarization, thus the thermal effect in the crystal is further reduced also. In this case, a single frequency 532nm laser over 20W output is obtained.5. Finding the influence of boundary temperature on laser performance: Energy Transfer Upconversion (ETU) is related to the doping concentration of the gain medium. With the doping increasing, the ETU effect increases monotonously, as a consequence the thermal effect will become more serious. Via the experimental and theoretical analysis, we found that the ETU also depended on the boundary temperature of the gain medium. When the doping level of the Nd:YVO4 crystal is 0.8 at.%, if the boundary temperature of the crystal increases from 20℃ to 80℃, the output of the single frequency 532nm laser decreases from 25.3W to 13.6W. Therefore, in order to increase output power, the boundary temperature of the gain medium must be controlled to a lower level.6. Research and building of continuous-vaviable (CV) entanglement light generator:We integrated a small size 540/1080nm double wavelengths Nd:YAP/KTP single frequency laser, a NOPA operating below threshold, a Bell state detection system, a locking circuits, a temperature controller, the DC power supply system, and a detector together to construct a compact CV entanglement light generator. The generator can be stably operated for 30min with the quantum noise level of over 5dB below the SNL...
Keywords/Search Tags:Thermal effect of the gain medium, Improving of thermal effect, All-solid-state high power single frequency lasers, Intracavity doubling, EPR light source
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