Nd:YVO_{4}, Nd:GdVO_{4}, BaWO_{4}, SrWO_{4} SolidState Raman Lasers  Posted on:20080105  Degree:Doctor  Type:Dissertation  Country:China  Candidate:F F Su  Full Text:PDF  GTID:1118360212994416  Subject:Optical Engineering  Abstract/Summary:  PDF Full Text Request  Stimulated Raman Scattering (SRS) is an effective method for frequency conversion. The obtained Raman laser wavelength is determined by the wavelength of the fundamental pump laser and the Raman shifts of the Ramanactive media. Ramanactive media include solids, liquids and gases. The lasers using liquid and gas Raman media have been studied for many decades. Compared with the traditional gas and liquid Raman media, solidstate Raman media offer high gain, high molecule density, good thermal and mechanical properties, and so on. Particularly, the lasers using crystal Raman media have the advantages of compactness, high efficiency, high stability. They have wide applications in such fildes as information, communication, measurement, military affairs, medical treatment, and so on.In recent years, solid Raman media and allsolidstate Raman lasers have attracted intensive research interests in the fields of laser materials and solidstate lasers. Scientists from Russia act as the leading role in the regime of Raman crystal growth and research on the solidstate Raman lasers. Researchers from America, Germany, Australia, etc. are taking part actively in the field of the allsolidstate Raman lasers. In the Chinese Mainland, the research groups from Shandong University, Shanghai Institute of Optics and Fine Mechanics, Fujian Institute of Research on the Structure of Matter are engaged in the research for solidstate Raman lasers.SRS can be realized in a variety of configurations, including singlepass Raman generation, extracavity or intracavity Raman resonators, or coupled resonator configurations. Several Raman crystals can be doped with laser iron such as Nd^{3+} to make them laser active, in this way, a single crystal can be used to generate the fundamental laser and to convert the wavelength through the SRS process simultaneously.The useful tools for analyzing the performances of lasers are the rate equations. The rate equations for the Qswitched Raman lasers can be obtained by adding a Raman loss term into the differential equation describing the fundamental photon density and adding a differential equation for the Raman photon density. The rate equations under the planewave approximation assume that the population inversion density and the intracavity photon density within the beam cross section only depend on time. They are relatively simple and can only reflect the basic characteristics of the Qswitched Raman lasers. To obtain more accurate theoretical results, the spatial distributions of resonating laser and pumping light must be taken into account in the rate equations. Intracavity Raman lasers that utilize the much higher intracavity power densities can lead to lowthreshold operation and high conversion efficiencies. LDpumped all solid state intracavity Raman lasers have many merits such as compactness, high efficiency and stability. Therefore, the intracavity solid state Raman lasers have attracted a great deal of attention in recent years.In this paper, by using Nd:YVO_{4} and Nd:GdVO_{4} as the Raman crystals, we study the LDpumped intracavity actively Qswitched and passively Qswitched Raman lasers theoretically and experimentally. By using BaWO_{4} and SrWO_{4} as the Raman crystals, we study the extracavity Raman lasers. The main contents of this dissertation are as follows:1. In the rate equations for the intracavity Qswitched Raman lasers, the intracavity fundamental photon density, Raman photon density and the initial populationinversion density of the gain medium are assumed to be Gaussian spatial distributions, and the thermal effect of the laser medium is considered. These rate equations have more accuracy.2. By using Nd:YVO_{4} crystal as the gain medium and Raman medim simultaneously, the diodepumped actively Qswitched selfRaman laser is studied in detail. The pulse energies and pulse widths of the first Stokes beams are investigated versus the pump power and pulse repetition frequencies. By numerically solving the rate equations, the obtained theoretical results are in good agreement with the experimental results.3. By using Nd:GdVO_{4} as the gain medium and Raman medim simultaneously, the efficient LDpumped actively Qswitched selfRaman Nd:GdVO_{4} laser at 1173nm is realized for the first time. At a pulse repetition rate of 30kHz, an average power up to 1.22W is obtained with a pump power of 9.6W, corresponding to a conversion efficiency of 12.7%. By numerically solving the rate equations, the obtained theoretical results are in good agreement with the experimental results.4. By using Nd:YAG as the gain medium, GdVO_{4} as the Raman crystal, the efficient LDpumped actively Qswitched Nd:YAG/GdVO_{4} intracavity Raman laser is realized for the first time. The pulse energies, average powers and pulse widths for different incident pump powers and pulse repetition rates are investigated.5. The rate equations for the passively Qswitched Raman lasers are obtained. In the rate equations, the intracavity fundamental photon density, Raman photon density and the initial populationinversion density of the gain medium are assumed to be Gaussian spatial distributions. These rate equations are normalized by introducing some synthetic parameters, and numerical calculations are carried out to illustrate the effects of the synthetic parameters on the performance of the passively Qswitched intracavity Raman lasers.6. By using the ccut Nd:GdVO_{4} as the selfRaman crystal, Cr^{4+}:YAG as the saturable absorbers, the efficient LDpumped passively (Qswitched Nd:GdVO_{4} intracavity selfRaman laser is realized. By using Nd:YAG as the laser crystal and GdVO_{4} as the Raman crystal, the efficient LDpumped passively Qswitched Nd:YAG/GdVO_{4} intracavity Raman laser was realized. In the rate equations, the Gaussian distributions of the intracavity photon densities of the fundamental and Raman lasers and the initial population inversion density were taken into account, these spacedependent rate equations are solved numerically, the obtained theoretical results are in agreement with the experimental results on the whole.7. By using BaWO_{4} as the Raman medium, the infrared nanosecond pulses from an actively Qswitched Nd:YAG laser as the pump source, the extracavity BaWO_{4} Raman laser is studied. The obtained maximum energy and conversion efficiency for the first Stokes pulses are 39.9mJ and 60.3%, respectivel, the obtained maximum energy and conversion efficiency for the second Stokes pulses are 22.6mJ and 34.9%, respectively. The extracavity SrWO_{4} Raman laser is also studied. The obtained maximum energy and conversion efficiency for the first Stokes pulses are 23.9mJ and 36.2%, respectively, the obtained maximum energy and conversion efficiency for the second Stokes pulses are 16.4mJ and 25.4%, respectively.The main innovations of this dissertation are as follows:1. In the rate equations for the actively Qswitched Raman lasers, the thermal effect of the laser medium is considered, the intracavity fundamental photon density, Raman photon density, the initial populationinversion density of the gain medium are assumed to be Gaussian spatial distributions. These rate equations can describe the performance of the intracavity actively Qswitched Raman lasers with good accuracy.2. The efficient actively Qswitched Nd:GdVO_{4} selfRaman laser at 1173nm is realized for the first time. At a pulse repetition rate of 30kHz, an average power up to 1.22W is obtained with the LD pump power of 9.6W, corresponding to a conversion efficiency of 12.7% .3. The efficient actively Qswitched Nd:YAG/GdVO_{4} intracavity Raman laser is realized for the first time. The relations between the output characteristics of the Raman laser and the pumped power with different pulse repetition rates are investigated. At a pulse repetition rate of 20kHz, an average power up to 1.35W was obtained with the LD pump power of 9.6W, corresponding to a conversion efficiency of 14.1%.4. By considering the transversal and longitudinal distributions of the laser fields inside the resonator, a new set of the rate equations for the passively Qswitched intracavity Raman laser is obtained. These rate equations are normalized by introducing some synthetic parameters, and numerical calculations are carried out to illustrate the effects of the synthetic parameters on the performance of the passively Qswitched intracavity Raman lasers.5. By using the infrared nanosecond pulses as the pump source, the high efficiency extracavity BaWO_{4} Raman laser is realized. The obtained maximum energy and conversion efficiency for the first Stokes pulse are 39.9mJ and 60.3%, respectively, the obtained maximum energy and conversion efficiency of the second Stokes pulse are 22.6mJ and 34.9%, respectively.  Keywords/Search Tags:  Solid state Raman laser, Stimulted Raman scattering, Intracavity Raman laser, Extracavity Raman laser, SelfRaman laser, Rate Equation, Nd:GdVO4 crystal, Nd:YVO4 crystal, BaWO4 crystal, SrWO4 crystal  PDF Full Text Request  Related items 
 
