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Research On Intracavity Optical Parametric Oscillator And Solid-state Lasers At New Wavelengths

Posted on:2012-10-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:W J SunFull Text:PDF
GTID:1118330335485264Subject:Optical Engineering
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Optical Parametric Oscillation (OPO) is an attractive method of frequency conversion. It uses the mixing characteristics of the nonlinear crystal and phase matching method to obtain broadband tunable output laser. OPOs usually focus on the following aspects:(1) The matured 1.06μm laser is used as the pump source to realize the eye-safe wavelength region. (2) The matured 1.06μm laser is used as the pump source to pump ZnGeP2 crystal and realize the 2μm region laser. Because this region has high ability to go through the atmosphere and smoke, so it has many important applications in laser radar, laser ranging, remote sensing and optical communications, etc. (3) By nonlinear frequency conversion technology, the mid-infrared 3-5μm region laser is realized. Because 3-5μm is an important atmospheric window, the laser under this region has very strong transmittance, which makes it feasible for wide applications in such field as radar system, spectral measurement, laser ranging, infrared remote sensing and other aspects. Mid-infrared OPO has been the hot research at home and abroad. It takes advantages of wide tunable region, high efficiency, compactness and high stability. And with the development of new high-quality mid-infrared nonlinear crystals, the mid-infrared OPO shows the much wider applications.Stimulated Raman scattering (SRS) is an attractive method of frequency conversion based on the third-order nonlinear optical effect. The wavelength of the scattered light is determined by the wavelength of the pumped light and the Raman shift of the Raman-active media. By selecting different pumping sources and Raman-active media, the laser spectrum reachable with SRS can extend from the ultraviolet to the near infrared. Compared with the conventional gases and liquids media, the solid-state Raman-active media offer high molecule density, high gain, favorable thermal and mechanical properties, and compatibility with the compact all solid-state laser technology. Hence they can find important applications in many fields such as national defence, medicine, traffic, information, industry and agriculture. So far, the researchers from USA, Russia, Australia and Taiwan are taking part actively in the field of the all-solid-state Raman lasers. Especially the scientists of Russia act as the leading role in the regime of Raman crystal growth and research on the solid state Raman lasers. China is renowned for the advanced crystal growth technology, and this provides favorable conditions to the study of all-solid-state Raman lasers in China.There are two parts in this dissertation. One is the theoretical and experimental studies on KTA intracavity optical parametric oscillator pumped by Nd:YAG laser. The other is the research on two kinds of new wavelength lasers. The main content of this dissertation is as follows:1. We analysis the three-wave interaction theory in optical parametric oscillation. We calculate the angle of phase-matching and the effective nonlinear coefficient of KTA crystal, and introduce the noncritical phase matching.2. By using Nd:YAG crystal as the laser gain medium (1064.2 nm), KTA as the nonlinear crystal, the diode-end-pumped acousto-optically (AO) Q-switched intracavity OPO (IOPO) is studied. The various characteristics are studied, e.g. spectrum, output power, conversion efficiency and beam quality. The signal wavelength and the idler wavelength in this case are determined to be 1535 nm and 3469 nm. The output powers and pulse widths are measured with different pump powers and different pulse repetition rates (PRRs). When the diode power is 14.93 W and the PRR is 40 kHz, an output mid-infrared idler power of 0.46 W is obtained, the total output power of 1.83 W, corresponding to an optical-to-optical (diode power to total power) conversion efficiency of 12.3%. Under the same condition, the pulse duration of idler wave is 4 ns, corresponding to the peak power of 2.9 kW. The beam quality factors (M2) of idler wave is about 12.3. Theoretical analyses are performed to study the output characteristics of the diode-end-pumped AO Q-switched Nd:YAG/KTA IOPO. By regarding the initial population inversion density (IPID) and the intracavity photon densities as Gaussian distributions, the rate-equation model is deduced. Thermal lens effect in the Nd:YAG crystal is also considered. The thermal focal lens of Nd:YAG crystal is calculated with different pump powers. The theoretical results are in good agreement with the experimental data, which confirms the applicability of the theoretical model.4. A high efficiency KTiOAsO4 (KTA) intracavity optical parametric oscillator (IOPO) pumped by a diode-side-pumped acousto-optically (AO) Q-switched two-rod Nd:YAG laser is demonstrated. The pump source is a diode-side-pumped two-rod Nd:YAG laser. A 90°quartz rotator is inserted between the two Nd:YAG modules to compensate the birefringence. The output powers including signal power and idler power, and pulse widths are measured with different pump powers and different pulse repetition rates (PRRs). When the diode power is 208 W and the PRR is 12.5 kHz, the highest output mid-infrared idler power of 3.4 W is obtained. When the diode power is 208 W and the PRR is 7.5 kHz, the highest output total power of 15.8 W is obtained, corresponding to an optical-to-optical conversion efficiency of 7.6%, which is the highest conversion efficiency in diode-side-pumped KTA IOPOs to our knowledge.5. A compact efficient Raman laser at 1103.2 nm is realized within a diode-end-pumped acousto-optically Q-switched 1064.2 nm Nd:YAG laser. A 46-mm-long BaWO4 crystal is used as the active medium and its 332 cm-1 Raman mode is employed to finish the conversion from 1064.2 nm fundamental laser to 1103.2 nm Raman laser. At an incident pump power of 7.55 W, the first-Stokes power of 1.23 W at 1103.2 nm is obtained at a repetition rate of 17 kHz, corresponding to a diode-to-Stokes conversion efficiency of 16.3%. The Raman beam quality factors (M2) in the two orthogonal directions are 2.0±0.2 and 1.8±0.2, respectively. The thermal focal length of the BaWO4 crystal is estimated.6. A flash-lamp pumped Nd:YAG laser emitting 1073.8 nm is demonstrated. A concave-plane cavity is employed, and Nd:YAG rod with a size of (?)6 mm×110 mm. With incident pump energy of 69.6 J and pulse repetition rate of 1 Hz, output pulse energy of up to 487 mJ is obtained. The main innovations of this dissertation are as follows:1. Diode-end-pumped AO Q-switched intracavity Nd:YAG/KTA mid-infrared OPO is optimal designed. When the diode power is 14.93 W and the PRR is 40 kHz, an output mid-infrared idler power of 0.46 W is obtained, the total output power of 1.83 W, corresponding to an optical-to-optical conversion efficiency of 12.3%. This is the highest efficiency reported for the diode-end-pumped AO Q-switched intracavity mid-infrared KTA OPOs.2. Diode-side-pumped acousto-optically (AO) Q-switched two-rod Nd:YAG mid-infrared KTA-IOPO is reported for the first time. The pump source is a diode-side-pumped two-rod Nd:YAG laser and a 90°quartz rotator is inserted between the two Nd:YAG modules to compensate the birefringence. All this design optimize the pump source.3. A high efficiency KTiOAsO4 (KTA) intracavity optical parametric oscillator (IOPO) pumped by a diode-side-pumped acousto-optically (AO) Q-switched two-rod Nd:YAG laser is demonstrated. The highest average output power of 12.7 W at 1.54μm and 3.1 W at 3.47μm are obtained at the pulse repetition rate (PRR) of 7.5 kHz under the diode power of 208 W, corresponding to an optical-to-optical conversion efficiency of up to 7.6%. This is the highest conversion efficiency in diode-side-pumped KTA IOPOs to our knowledge.4. Diode -end-pumped compact efficient Nd:YAG/BaWO4 Raman laser at 1103.2 nm based on the Raman shift of 332 cm-1 is reported for the first time. At an incident pump power of 7.55 W, the first-Stokes power of 1.23 W at 1103.2 nm is obtained at a repetition rate of 17 kHz, corresponding to a diode-to-Stokes conversion efficiency of 16.3%. The thermal focal length of the BaWO4 crystal is estimated. Diode -side-pumped Nd:YAG/BaWO4 Raman laser at 1103.2 nm is reported for the first time.5. A flash-lamp pumped Nd:YAG laser emitting 1073.8 nm is demonstrated for the first time. With incident pump energy of 69.6 J and pulse repetition rate of 1 Hz, output pulse energy of up to 487 mJ is obtained.
Keywords/Search Tags:optical parametric oscillators (OPOs), mid-infrared laser, nonlinear crystal, solid-state Raman lasers, KTiOAsO4 crystal, BaWO4 crystal
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