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Experimental And Theoretical Investigation Of All-Solid-State, High-Power CW Lasers Of Single-Frequency Operation

Posted on:2010-10-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y H ZhengFull Text:PDF
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Lasers is the core of laser technology, which play an important role in these fields, such as advanced manufacturing, scientific and technical development, medical and national defense. Especially, single-frequency laser, which has some advantages of low-noise and long coherent-length, was widely used in nonlinear process, quantum optics, quantum information, cold-atom physics, optical measurement, spectrum et al. Many research works were under way. Until now, single longitudinal mode operation can be accomplished by inserting etalons into the cavity, shortening the optical resonator, twisted-mode cavity, with a birefringent filter and using a ring cavity configuration. However, only with a ring cavity configuration is the optimal mode-selecting method, which can be achieved by inserting optical diode into the cavity, then eliminating the spatial hole burning effect, obtaining the single longitudinal mode operation.With the development of science and technology, there have the higher requirements for the performance and parameter of single-frequency laser. There require high-power, low-noise single-frequency laser to pump Ti: sapphire laser and optical parameter oscillator (OPO); To meet the need of quantum optics and cold-atom physics, all kinds of wavelength lasers which have tuning properties are required to satisfy communication and energy level of all kinds of atoms; Frequency-stabilized, narrow-linewidth laser can meet the need of high-precision optical measurement, spectrum, frequency standard. So main research content of single frequency laser include the increase of output power, new mode-selecting and wavelength tuning techniques, spectrum range expanding and the improvement of laser property.We carried out a series of research job of spectrum range expanding, new mode-selecting and wavelength tuning techniques, and achieved some research findings as follows.1. A continuous fiber-coupled laser-diode end-pumped Nd:YVO4/KTP laser of single-frequency operation at 532nm. The ring laser resonator consists of four mirrors and a piece of frequency-doubling crystal KTP is placed between two concave mirrors. A simple method to increase the conversion efficiency of intracavity frequency doubling laser is proposed, in that elliptical Gaussian laser beam can slightly improve conversion efficiency when the walk-off plane is parallel to the sagittal surface in our experiment. We obtain 4.8W green laser of single-frequency operation by using the method, corresponding optical-optical conversion efficiency equals to 25.5%. In comparison with the results of 4.1W that the walk-off plane is perpendicular to the sagittal surface, the conversion efficiency has an increase of 3.7%, which make sure about the second-harmonic generation of elliptical Gaussian beam.2. When the ratio (γ) is less than a certain value, the nonlinear loss due to sum frequency generation (SFG) can be very small and it might be that the net gain can not be depleted by the nonlinear loss at some wavelengths, thus leading to multi-mode oscillation or mode-hopping. We analyzed theoretically the relation of the y value and the pump power to achieve the stable longitudinal-mode operation. The longitudinal-mode stability of a single-frequency intracavity frequency doubling laser was enhanced by increasing y value with an etalon inside the laser cavity. 4W of stable CW single frequency output at 532nm was obtained without mode-hopping in 6 hours and the power fluctuation is less than±1.2%. In contrast with the situation of no etalon inside the laser cavity, mode-hopping occurs at irregular intervals with the power fluctuation of±3.8% in 4 hours.3. We present a simple and effective way to prevent the oscillation of the fundamental-wave in non-phase-matched polarization direction. We cut a facet of Nd:YVO4 crystal in a wedge according to a calculated appropriate angle. In this case, the wedge birefringence crystal will act as a polarizing beam splitter, which forms an enough deviation between the transmission directions ofπ- andσ-polarization and thus efficiently avoids the oscillation of the non-phase-matchedσ-polarization mode of the fundamental wave in the laser resonator. Using the designed system, the single-frequency green laser at 532nm with the polarization degree of more than 500:1 and a stability of better than±0.3% for 3 hours was experimentally demonstrated.4. The wavelength of 1080nm emitted by Nd:YAP is able to realize typeⅡnon-critical phase-matching in an KTP crystal, which is easy to produce two-mode squeezed state and Einstein-Podolsky-Rosen (EPR). But the thermal effect of Nd:YAP crystal affects the increase of laser power seriously, by the methods of enlarging the fundamental mode waist and decreasing the intracavity power density we achieved 3W of 540nm and 1.1 W of 1080nm.5. We designed an approach to realize a broad-band and rapid tuning laser. The main features are a ring resonator employed in our experiment to enforce a single frequency laser, a LiNbO3 etalon (LE) to provide broad-band tuning, a LiNbO3 crystal (LC) to provide continuous tuning. Frequency tuning over the laser gain spectrum, covering many longitudinal modes, is fulfilled by controlling the voltage of the LE. Frequency control within a single longitudinal mode is obtained by adjusting the voltage of the LC which is used as an equipment of adjusting the optical path. Electronic tuning sets that are immovable were engaged instead of mechanical parts, which improved further robust and tuning speed of the laser. As a result, only one laser can we gain high output power, broad-band and high speed tuning at the same time. In our experiment, more than 480mW of output power has been obtained from a single-frequency tunable laser, which has a frequency tuning range of 17.2GHz and tuning speed of 10ns.The creative works are as follows:1. This is firstly demonstrated on the frequency-doubling of elliptical Gaussian beam in an intracavity frequency-doubling laser by using critical phase matching crystal.2. This is firstly analyzed that the ratio between the nonlinear spectral bandwidth and gain bandwidth affects the stability of longitudinal mode, by inserting the etalon into the cavity stable single-frequency laser was obtained, without mode-hopping in 6 hours.3. The wedge Nd:YVO4 crystal was used in a ring cavity laser for the first time, which does also act as a polarizing beam splitter. A single-frequency green laser with a stability of better than±0.3% for 3 hours was experimentally demonstrated.4. 3W of 540nm and 1.1W of 1080nm single-frequency laser was obtained experimentally at the same time. As far as I know, this is the maximum output power of single-frequency laser of 540nm.5. The etalon on the basic of the electro-optic crystal was designed and used in tunable laser for the first time. 480mW of output power, 17.2GHz of tuning range and 10ns of tuning speed were obtained at the same time.
Keywords/Search Tags:All-Solid-State, Laser, Single-frequency, Intracavity frequency-doubling, Ring cavity, Electro-optic tuning, Etalon, Wedge crystal
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