Dissertations / Theses on the topic 'Q Switched Nd: YAG'

碩士<br>國立中山大學<br>光電工程研究所<br>87<br>The timing jitter is a very serious problem in a passively Q-switched laser. However, most of the work of passively Q-switched laser concentrated on the shortening the pulsewidth, increasing the pulse energy or peak power. Little work has been done on the timing jitter for a passively Q-switched laser. In this study, a theoretical simulation is provided to explain the timing jitter and a new method is proposed to improve this problem. Our simulation result indicated that the spontaneous noise in the microwatt range significantly affects the repetition rate of passively Q-switched laser and creates large timing jitter. The phase of modulation signal is also found to be a crucial factor for reducing the timing jitter and can be improved up to 92%. A Nd3+:YVO4 microchip laser with wavelength of 1064 nm is employed as a modulation source to modulate the population of both ground and excited state of Cr4+:YAG simultaneously. A polarized beam-splitter(PBS) is used to direct the modulation beam onto the Cr4+:YAG crystal. A focus lens in front of the microchip laser is used for shaping the laser beam to match with the cavity mode. A function generator is used to provide the microchip laser a modulated pumping source. The timing jitter modulated with the microchip laser is then monitored by a 500 MHz digital scope. The experimental result has shown that the external modulation by a microchip laser proposed by us indeed improve the timing jitter up to 50%.

碩士<br>逢甲大學<br>光電物理研究所<br>91<br>The character of a passive Q-switched Nd:YAG laser system with a Cr4+:YAG saturable absorber is studied. The pulse has 1.8 kW peak power and 20 ns duration with a repetition rate of 5 kHz as the pump power being 2.8 W. When we increase the pump power, the period doubling route to chaos is found. A general period doubling route begins from period 1, but we had observed the period doubling route beginning from period 3. Besides, period 5 was also obtained in the experiments.

碩士<br>國立交通大學<br>理學院應用科技學程<br>106<br>The aim of this thesis is to study the relationship between orthogonal polarization and laser longitudinal modes in passively Q-switched (PQS) lasers. First, we change the crystal from isotropic into anisotropic by applying mechanical stress, and compare the temporal dynamics and spectrum in monolithic diffusion-bonded Nd:YAG/Cr4+:YAG PQS laser. Experimental results reveal that the period between two orthogonal polarizations in PQS laser is correlated with ratio of the lasing longitudinal mode numbers and we can realize multi-longitudinal-mode operation. We successfully established single longitudinal mode laser in each polarization by decreasing the length of Nd:YAG/Cr4+:YAG crystal. We expect the experimental finding can be applied in precision measurement and optical communication and so forth.

碩士<br>國立交通大學<br>理學院應用科技學程<br>103<br>To demonstrate an energy adjustable passively Q-switched laser, a diode laser pumped Nd:YAG crystal diffusion-boned with a wedged Cr4+:YAG crystal is utilized. By changing the transverse pump location of the laser diode on the laser crystal, the initial transmission of the saturable absorber can be flexibly adjusted to achieve the variation of output pulse energy. The experimental result for different crystal length and different pump area are also shown in the thesis. In addition, the multi-transverse-mode output is eliminated to maintain good beam quality by controlling the input power and pump location. For further applications, the 1064-nm PQS laser is utilized to generate a frequency-double 532-nm laser. Finally, the whole set of the green laser is modular in order to be used in actual industrial demand.

碩士<br>國立交通大學<br>理學院應用科技學程<br>99<br>We report on an analysis of the design guideline of a hemispherical resonator Nd:YVO4/Cr4+:YAG passively Q-Switched (PQS) laser by optimization of the mode matching condition and agreement with the good PQS criterion. Cr4+:YAG saturable absorbers with various initial transmission were used to investigate the performances of the laser configuration. Then we inject these high-peak-power PQS laser to realize the single-stage, linear-polarized fiber amplifier. With the seed laser of pulse repetition rate (PRR) of 50 kHz, the amplifier emits pulse energy of 178 and peak power of 37 kW under the pump power of 16 W. With the seed laser of PRR of 25 kHz, we can attain the amplifier with pulse energy of 192 and peak power of 113 kW under the pump power of 10 W which is restricted by the fiber facet damage.

博士<br>國立交通大學<br>電子物理系所<br>106<br>The aim of this thesis briefly introduces the historical development and conceptual understanding of the diode-pumped solid-state laser. We then focus on describing the characteristics of the Nd-doped crystals, and the practical issues for constructing Q-switched and mode-locked Nd:YVO4 dual-wavelength lasers are pointed out. Finally, we present some novel ideas for orthogonal polarizations of these Nd-doped crystal lasers in the future, and we hope that the works illustrated in this proposal can be usefully applied in a number of industrial and scientific fields.

碩士<br>國立交通大學<br>電子物理系所<br>93<br>All-solid-state Q-switched lasers at 1.3-μm wavelength are of practical importance for numerous application such as medical diagnostic, fiber sensing, distance measurements, intracavity optical parametric oscillator, intracavity Raman conversion. Because of thermal effects, CW laser can’t be used practically. If using Quantum Wells/barrier structures be absorbers for Nd:YVO4 lasers, it can produce a high peak power, high pulse energy, and stable Q-switching laser. Nowadays, the saturable absorbers for 1.3-μm lasers comprise V3+:YAG, Co2+:MgAl2O4, and SESAMs. However, the overall performance of the DBRs on InP substrates are hindered by disadvantage of small contrast of refractive indices. Despite that, the DBRs is merely an optional structure for the cavity design of the passively Q-switched lasers. In this work we present two kinds of barrier’s materials, InGaAsP QW/barrier and AlGaInAs QW/barrier structures. Using any of these respectively grown on a transparent InP substrate to be a SESA for Nd:YVO4 1.34-μm lasers. We study and compare with the two different SESAs as passively Q-switched lasers. Trying to find the physical characteristics of both and design a stable 1.34-μm laser.

碩士<br>逢甲大學<br>光電物理研究所<br>92<br>We study the nonlinear dynamic behavior in a passive Q-switched Nd:YAG laser system with a Cr4+:YAG saturable absorber. By operating in transverse-mode-degeneracy cavity, we find the doubling-route to chaos near the threshold. We find that the bifurcation accompanies with the low order of the transverse mode by analyzing the mode pattern variation. Therefore, we can confirm our mechanism should belong to multi-transverse mode competition, and the mechanism is different from the previous study. Besides, we also find the period-doubling route to chaos beginning from period 3、period 5 and period 7. By calculating correlation dimensions of the chaotic signals for the tradition route and the one beginning from period 3, the dimensions are 4.583 0.044 and 4.456 0.059, respectively. Thus, we think that the latter one is the periodic windows in a period-doubling route to chaos.

博士<br>國立交通大學<br>電子物理系所<br>107<br>Light beam polarization is a basic characteristic of laser radiation. Solid-state lasers usually generate linearly polarized or random polarized output. Orthogonally polarized laser sources have attracted intensive attention due to their wide applications in laser interferometry, holographic microscopy, differential absorption lidar, and precision measurement. This dissertation presents several optical experiments to investigate the orthogonally polarized states and longitudinal modes in diode-pumped Nd-doped solid-state lasers (DPSSLs) in continuous-wave (CW) and passively Q-switched (PQS) operation. Several studies have confirmed that the anisotropic and isotropic gain media can generate simultaneous emissions of two orthogonal polarizations. The orthogonally polarized laser can be generated by introducing the induced birefringence into an isotropic gain medium, such as Nd:YAG crystal. The induced birefringence that may come from the thermal stress or external force can lead to a frequency splitting between two orthogonally polarized modes. Moreover, the Nd-doped gain media are suitable to generate single- or multi-wavelength lasers in different transition level due to its abundant fluorescent lines. First of all, we utilize a monolithic Nd:YAG crystal to realize the self-mode-locked (SML) operation with orthogonal polarizations. The beat frequency between two orthogonally polarized states can be widely adjusted by controlling the water temperature. Next, we demonstrate a short linear cavity to explore the frequency splitting in the laser crystal by tuning the absorbed pump power from pump light. Furthermore, we put the monolithic SML laser into a cryogenic system to realize dual-wavelength operation. The relationship between the beat frequency and cooling temperature is further investigated. We also demonstrate the orthogonally polarized single-longitudinal-mode (SLM) and SML lasers by applying the mechanical stress on the Nd:YAG crystals with two crystal length. Moreover, we successfully design two types of coating specification for monolithic-coated Nd:YAG crystal to realize the single-wavelength or dual-wavelength lasers. Next, the synchronously dual SML operations at 946 nm and 1064 nm has been accomplished by physically combining the monolithic-coated Nd:YAG crystal to the Nd:YVO4 crystal as a composite gain medium. Finally, we explore the performance of orthogonally polarized PQS lasers. It has been found that the pulses of two orthogonally polarized states display the classical antiphase dynamics for two equal intensities.