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Investigation On Dual-loss-modulated High Peak Power Single Mode-locking Pulsed Laser Characteristics Based On EOM And Saturable Absorber

Posted on:2019-06-01Degree:DoctorType:Dissertation
Country:ChinaCandidate:W J TangFull Text:PDF
GTID:1318330542496677Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
The pursuit of high-intensity laser is an important direction and interest field in laser technology research since laser was invented.The so-called ultra-short super-laser is a high-intensity laser with ultrashort pulse width.The study of ultra-short super-lasers has not only opened up a wide range of applications in the field of micro-machining and medicine,but has also been successfully applied to a variety of research areas,promoting the formation of many new subjects and breakthroughs.In order to obtain ultra-short lasers with high intensity,new laser technology has been expected by researchers.For a laser with certain energy,the shorter the pulse width,the higher the corresponding peak power and intensity of pulses.Therefore,the pulse width and peak power are two interrelated parameters of the laser.Looking at the development direction of pulsed lasers,the first is the continuous advancement of mode-locking technology,which promotes the development of lasers towards the ultra-short pulses direction;the second is the continuous increase of laser peak power,which provides a powerful tool for further study of ultra-fast and ultra-strong laser.However,for all solid-state continuous wave mode-locked pulsed lasers,compressing the pulse width often results in a large increase of the repetition frequency,which makes it difficult to improve the energy of a single mode-locked pulse.Thus,how to further increase the single pulse peak power of pulsed lasers is still a very important research topic.Based on the Q-switched mode-locking?QML?laser technology,a novel method of output low repetition rate subnanosecond mode-locking pulses was proposed in our paper,which can achieve a significant improve in pulse peak power and controllable operation of pulse repetition frequency.Using the active and passive dual-loss modulation technology,based on the mechanisms of active Q-switch and passive mode-locking with saturable absorber?SA?,the Q-switched envelope pulse duration can be greatly compressed until only one mode-locking pulse exists in it.The pulse energy of the entire Q-switched envelope can be concentrated on this single mode-locked pulse.This method is also called as single mode-locking pulse technology.Compared to the Q-switch,QML and CWML technologies based on single loss modulation,this method can further improve the pulse peak power,what's more,the repetition rate of the single mode-locking pulses is equal to the modulation frequency of active modulator.Based on this method,the coupling rate equations of the dual-loss modualtion single mode-locked laser was established,and the theoretical simulations about the oscillating condition of single mode-locking pulses was performed.The simulation results were basically in agreement with the experimental results.When choosing the SAs,besides the usual array of Cr4+:YAQ SESAM and CNTs,a variety of new 2D material SAs was used for single mode-locked lasers for the first time because of their excellent properties,such as large absorption bandwidth and simple fabrication.The specific research contents and innovation points of this thesis are summarized as follows:?1?Based on the dual-loss modulation mechanism of an electro-optic modulator?EOM?and a central semiconductor saturable absorption mirror?C-SESAM?,a high peak power subnanosecond single mode-locking Nd:Lu0.5Y0.5VO4/KTP intracavity frequency-doubled laser at 532 nm was successfully achieved.Under different electro-optic modulation frequency,the output characteristics of this dual-loss-modulation laser were studied.At 1 kHz modulation frequency,the minimum pulse width of 460 ps and the maximum single pulse peak power of 378.3 kW were obtained.According to the theory of fluctuation mechanism and rate equation theory,considering the Gaussian distribution approximation,the coupling rate equations can be concluded.The pulse energy,pulse width and pulse waveform are simulated.The experimental values are basically in accordance with the theoretical values.?2?Based on the electro-optical switch and the passively saturable absorber Cr4+:YAG,a dual-loss modulated high peak power subnanosecond single mode-locking Nd:Lu0.12Y0.85VO4/KTP intracavity frequency-doubled laser at 532 nm was successfully achieved.In the experiment,Cr4+:YAG crystals with three different small-signal transmittances were used as the passive modulation devices.Under different modulation frequencies,the dependence of laser output characteristics on the incident pump power was studied.At a modulation frequency of 1 kHz,a minimum pulse width of 349 ps and a maximum single pulse peak power of 1.063 MW were obtained.At the same time,considering the Gaussian distribution approximate,the coupling rate equations of the dual-loss modulation QML laser are given and numerical simulations are performed.The experimental values are basically in accordance with the theoretical values.?3?Based on one-dimensional nanomaterial carbon nanotubes?CNTs?with differents walls and electro-optical switch,a dual-loss modulated high peak power subnanosecond single mode-locking Nd:Lu0.15Y0.85VO4 laser at 1064 nm was successfully achieved for the first time.Single-wall,double-walled and multi-walled carbon nanotubes were used as passive saturable absorbers,respectively.The maximum peak power of 1.312 MW was obtained from the laser based on double-walled carbon nanotubes when the pump power reached 10.72 W.?4?As new type of SAs,2D materials have excellent saturable absorption properties,such as wide absorption wavebands,simple fabrication,and low cost.In order to further increase the maximum single-pulse peak power that can be obtained,three new two-dimensional materials?Graphene/WS2/BP?were used as passive saturable absorbers,to realize dual-loss modulation high peak power subnanoseconds single mode-locking Nd:Lu0.15Y0.85VO4 laser output,respectively.Finally,using EOM/BP as dual-loss modulation device,a peak power up to 3.89 MW was obtained for the first time.
Keywords/Search Tags:All Solid-state lasers, Dual-loss-modulation, Electro-optic modulator(EOM), Saturable absorber, High-peak-power, Subnanosecond, Q-switched mode-locking(QML), Nd:Lu0.15Y0.85VO4 crystal, Two-dimensional(2D)materials, Rate equations
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