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Design And Characterization Of Semiconductor Saturable Absorber Mirror

Posted on:2011-05-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:J ZhangFull Text:PDF
GTID:1118360302990171Subject:Optics
Abstract/Summary:PDF Full Text Request
The main reason to apply Semiconductor Saturable Absorber Mirror (SESAM) is that it can be optimized independently of cavity design, allowing successful mode-locking to be achieved with a broad range of solid-state lasers and cavity designs. Because its bigger absorption cross-section and the resulting smaller saturation fluence can perfectly suppress Q-switch mode-locking instability, SESAM has been the ideal mode-locking device in solid state laser. The required characteristics of a SESAM can be ideally obtained with a broad range after the proper growth and design of semiconductor material, which made SESAM applicable in almost all solid state laser. And the characterization of SESAM is also becoming more and more important. In Europe and U.S.A, the design and growth of SESAM has been quite mature, but the research of SESAM in mainland is still in the primary stage.The main work in the thesis is the study of design of SESAM and the characterization of its ultrafast spectroscopy, or dynamic response. The details of the works are as follows:According to semiconductor physics and quantum mechanics, the function between absorber thickness and center wavelength is introduced; the definition of the dielectric function of absorber layer is given by Tauc-Lorentz model and Kramers-Kronig relation (KKR). And the dependences of electric field distribution, modulation depth, and reflection spectrum on inserted location of absorber layer in SESAM are also analyzed by simulation; based on experimental observation, damage mechanism of SESAM is studied by heat-imaging of SESAM in working ultrafast laser and the damage image on SESAM by high power ultrafast laser. The dependences of heat damage and stability of laser on the size of laser spot on SESAM are analyzed experimentally, which discloses that when laser spot size on SESAM increases, the damage possibility on it decreases, while the operation instability of laser increases at the same time. In order to guarantee the operation stability of ultrafast laser while protecting SESAM from being damaged by high power laser at the same time, the method of controlling the field intensity of standing wave near quantum well is studied by analyzing the dependences of electric field distribution, modulation depth, reflection spectrum, and etc. on the number of dielectric coatings on SESAM. The ultra-fast spectroscopy, or dynamic response of SESAM is obtained and analyzed by pump-probe setup. Two-photon absorption is observed when SESAM is pumped by ultrahigh power laser( energy density>1400μJ/cm2).The thesis is divided into 7 chapters. The brief introductions of every chapter are as follows:In chapter 1, the developments of mode-locking technology, SESAM mode-locked laser and SESAM design are recalled. The basic ultrafast processes in semiconductor exposed to ultrafast laser pulses and pump-probe setup for studying ultrafast process of SESAM are introduced.In chapter 2, the operating principle, band theory, structure types of SESAM are overviewed. The relationship between microscopic properties of SESAM and design criteria is is studied. The characterization of macroscopic characteristics especially the recovery time of some SESAM samples, and the functions of the characteristic parameters of SESAM are also introduced.In chapter 3, single-quantum-well low finesse antiresonant Fabry-Perot saturable absorber mirror is designed according to optical filming theory, band theory of semiconductor. The function between absorber thickness and oscillating wavelength is introduced as well as the definition of the dielectric function of absorber layer. The dependences of electric field distribution, modulation depth, and reflection spectrum on location of absorber layer in SESAM are also analyzed by simulation. The characteristics including the oscillating wavelength, modulation depth, electric field distribution derived from computer simulation matched with the required characteristics.In chapter 4, with the development of high power ultrafast laser passively mode-locked by a semiconductor saturable absorber mirror (SESAM), the damage threshold and degeneration mechanism of the SESAM become more and more important. The damage mechanism on surface of SESAM is studied by heat imaging of SESAM in working high power ultrafast laser and analyzing SESAM surface damaged by ultrafast laser. It can be concluded that the increasing of laser spot size can decrease the damage possibility on SESAM surface, but the study on the dependence of laser working stability on laser spot size disclose that the working stability of ultrafast laser decreases when increasing the laser spot size.In chapter 5, in order to guarantee the operation stability of SESAM mode-locked high power ultrafast laser while protecting SESAM from being damaged at the same time, the method of dielectric coating on SESAM surface is adopted. The simulation of the electric field distribution inside the SESAM shows that with a dielectric coating of two pairs of SiO2/Ta2O5 layers, the field enhancement in the absorber can be reduced to 50%, and the coated SESAM can also suppress the Q-switch instability of ultrafast laser.In chapter 6, when SESAM is exposed to laser, the dynamic response of it can directly influence the pulse shaping of ultrafast laser pulse. The dynamic response or recovery time of SESAM is measured by pump-probe setup, from which the femtosecond spectroscopy of SESAM under different pumping power, the femtosecond spectroscopy on different positions of one SESAM under same pumping power, the dependence of nonlinear reflectivity of SESAM on incident light energy density, and the femtosecond spectroscopy of SESAM under ultrahigh laser power are measured. When incident light power increases, the nonlinear changes of femtosecond spectroscopy can be observed. Two-photon absorption(TPA) can be observed in femtosecond spectroscopy of SESAM under ultrahigh incident light energy density.In 7th chapter, the author sums up all the content of this thesis and gives the creative work parts. In the end, some promising researches are presented from various fields.
Keywords/Search Tags:Semiconductor Saturable Absorber Mirror ( SESAM ), pump-probe, mode-locking, dielectric function, two-photon-absorption(TPA)
PDF Full Text Request
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