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Study On Cerenkov Type Second Harmonic Theory And Performance Of All-solid-state Ion-implanted Waveguide Laser

Posted on:2012-05-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:G L DuFull Text:PDF
GTID:1118330335985263Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Laser-diode (LD) end-pumped all-solid-state Q-switched lasers which first appeared in 1980s have attracted significant attentions because of their low threshold power, high output beam quality, high efficiency, simplicity, compactness and good frequency stability. So they have a wide of applications in the fields of industry, medicine, optical communication, information storage, remote sensing, and so on. Optical waveguide has important applications in fields of waveguide lasers, waveguide frequency-doubling, optical amplifiers, optical switching devices and passive devices. People have been exploring the fabrication of fine performance optical waveguide methods. Several techniques have been employed to fabricate the waveguide, such as Ti diffusion and proton exchange. Ion implantation as an effective technology has aroused extensive concern to make optical waveguide. So far, there has been the use of ion implantation in the formation of a large number of waveguide structures in the optical crystal, glass, semiconductors, polymers and other materials.Ithium Niobate (LiNbO3) is a widely-used material in integrated nonlinear optics for its remarkable electro-optical, acousto-optical and nonlinear properties. It is widely used in surface wave filter, optical communication modulator, electro-optic switch, acousto-optic device, sensor, high density data storage etc. and becomes an important optical waveguide material as well as the basic and most important functional material in the field of optoelectronics.Compact and reliable short-wavelength light sources have a wide range of applications, such as high-density storage systems, image processing, efficient laser printers, medical laser, submarine optical communication, etc. As for Cerenkov second harmonic generation (CSHG), the harmonic radiation created by the nonlinear polarization radiates into the substrate at an angle that assures conversation of the k vector component parallel to the interface, automatically providing phase matching. So it greatly relaxes the requirements and can still be considered to be a very promising method to realize effective SHG.The field of waveguide lasers pumped by LD has created much interest during the last years and recently. The confinement of light in optical waveguides maintains a small spot size and hence a high intensity over lengths than would normally be forbidden by diffraction. If the waveguide is doped with an active ion, the enhancement of laser efficiency is allowed and, therefore, extremely low laser thresholds can be achieved.Therefore, there is of great significance to research about frequency-doubling and laser characteristics of LD-pumped ion-implanted optical waveguide.We have proposed a model analysis for calculating the conversion efficiency of the Cerenkov type second harmonic generation in ion-implanted LiNbO3 planar and channel waveguides. Useful formulas are derived, which express the SHG efficiency in terms of waveguide parameters. Numerical examples are plotted for LiNbO3 crystals.x-cut, y propagation Nd:YVO4 sample with a size of 3×3×10 mm3 was optically polished and cleaned before the ion implantation. The waveguide was formed by 3.0 MeV Si+ ion implantation at a dose of 1×1015 ions/cm2 at room temperature. The ion beam was electrically scanned to ensure a uniform implantation over the sample. In order to minimize the channeling effect, the sample was tilted by 7°off the beam direction. To remove the color centers induced by the implantation, the sample was annealed at 240℃for 60 min in air. The result of ion implantation is that the ordinary refractive index in the waveguide is higher than that of the substrate, while the extraordinary refractive index in the waveguide is lower than that of the substrate. In this dissertation, by using the fiber-coupled laser-diode as the pump source and Nd:YVO4 waveguide crystal as the gain medium, we have studied the performance of the actively Q-switched laser with acoustic-optic (AO) modulator, and passively Q-switched lasers with Cr4+:YAG as well as GaAs saturable absorbers, respectively.The main content of this dissertation is listed as follows:Ⅰ. Cerenkov type second harmonic generation in ion-implanted Lithium Niobate planar waveguides is theoretically analyzed. For a given waveguide depth the efficiency is very sensitive to the pump wavelength, and for a given pump wavelength the efficiency is also very sensitive to the waveguide depth. They are all oscillating periodically. Cerenkov angle decreases a little with the increasing of the ion-implanted depth. We discuss TE as well as TM mode in x-cut and z-cut LiNbO3 respectively, and give the specific mathematical formula for second harmonic generation conversion efficiency.Ⅱ. Cerenkov type second harmonic generation in ion-implanted Lithium Niobate channel waveguides is theoretically analyzed. We find that Cerenkov type second harmonic generation conversion efficiency vibrates periodically with the changes of pump wavelength and ion-implanted depth. Cerenkov angle decreases a little with the increasing of the ion-implanted depth. We discuss TE as well as TM mode in x-cut and z-cut LiNbO3 respectively, and give the specific mathematical formula for second harmonic generation conversion efficiency.Ⅲ. Continuous-wave laser oscillation at 1.064μm in Silicon ion-implanted Nd:YVO4 planar waveguide is researched. The output power versus absorbed pump power has been obtained. Compare with regular bulk laser, the threshold pump power for waveguide laser reduces and slope efficiency increases greatly due to its high-gain property. The threshold pump power is as low as 17.3 mW and the maximum laser output power of 125.2 mW has been obtained at an incident pump power of 191.2 mW. Meanwhile, waveguide fabrication, existing modes as well as the possibility of continuous-wave laser oscillation in waveguide layer are theoretically analyzed.Ⅳ. LD pumped actively Q-switched Silicon ion-implanted Nd:YVO4 waveguide laser with AO modulator has been realized. The dependences of the average output power and pulse width on the pump power have been measured. The shortest pulse duration of 7.4 ns is obtained at an absorbed pump power of 65 mW and a repetition rate of 10 kHz.Ⅴ. LD pumped passively Q-switched ion-implanted Nd:YVO4 planar waveguide laser with GaAs saturable absorber has been realized. With different output transmissions, the dependences of the average output power, pulse width, pulse repetition rate, single pulse energy, and peak power on the pump power have been measured. The threshold pump power is as low as 40 mW while the slope efficiency is up to 64.5% with an output transmission of 20%. The shortest pulse duration of 3.88 ns is obtained at an absorbed pump power of 78.8 mW.Ⅵ. LD pumped passively Q-switched ion-implanted Nd:YVO4 planar waveguide laser with Cr4+:YAG saturable absorber has been realized. The dependences of the average output power, pulse width, pulse reperition rate, single pulse energy and peak power on the pump power have been measured. The threshold pump power is as low as 47 mW. The maximum average output power of 21.5 mW has been obtained at an incident pump power of 70 mW. The shortest pulse duration is 54.8 ns while the highest pulse repetition rate is 416 kHz.The main innovations of this dissertation are as follows:Ⅰ. The dependence of Cerenkov type second harmonic generation in ion-implanted Lithium Niobate planar waveguides on the pump wavelength and waveguide parameters is firstly theoretically analyzed. The specific mathematical formula for second harmonic generation conversion efficiency is given.Ⅱ. The dependence of Cerenkov type second harmonic generation in ion-implanted Lithium Niobate channel waveguides on the pump wavelength and waveguide parameters is firstly theoretically analyzed. The specific mathematical formula for second harmonic generation conversion efficiency is given.Ⅲ. Continuous-wave laser oscillation at 1.064μm in Silicon ion-implanted Nd:YVO4 planar waveguide is demonstrated for the first time. The waveguide fabrication, existing modes as well as the possibility of continuous-wave laser oscillation in waveguide layer are theoretically studied.Ⅳ. LD pumped ion-implanted Nd:YVO4 planar waveguide lasers actively Q-switched with AO modulator, passively Q-switched with GaAs and Cr4+:YAG saturable absorber are demonstrated for the first time, respectively. The dependences of the average output power, pulse width, pulse reperition rate, single pulse energy and peak power on the absorbed pump power are researched.
Keywords/Search Tags:all-solid-state laser, waveguide laser, Cerenkov second harmonic generation, planner waveguide, channel waeguide, ion implantation, Q-switched
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