Research On Passively Mode-locked Nd-doped Solid-state Laser With ReSe₂ Saturable Absorber

Ultrafast lasers play a significant role in a variety of applications ranging from optical communications to medical diagnostics and industrial materials processing.Furthermore,la-ser diode(LD)pumped solid state laser has attracted more and more attention due to its ad-vantages,which are characterized by the high output power,high beam quality and low cost.Recently,based on TMDs(transition metal dichalcogenides)as saturable absorber pas-sively Q-switched/mode-locked lasers can produce pulses with very narrow pulse width,high repetition rate and wide spectrum.ReSe₂,as a new type of 2-D TMDs,has the features of weak-layered dependence,broadband saturable absorption,and appropriate saturation inten-sity,which is beneficial to initiate robust Q-switching or mode-locking mechanism via non-linear saturable absorption.The main contents of this thesis are summarized as follows:Firstly,we achieved a stable ReSe₂ passively Q-switched Nd:YAG bulk laser near room temperature,which can generate near-repetition rate limit of microsecond pulse output at full depth modulation.A new kind of 2D transition metal dichalcogenide,ReSe₂,is exploited as an excellent saturable absorber at 1.06?m with extremely high rate of loss modulation.The microsecond pulse repetition rate of as high as 274 k Hz can be achievable under the pump power of 7.3 W,with the pulsewidth of 1.08?s and the pulse energy of 2.5?J.As the pump power varies from 4.4 to 7.3 W,the pulse repetition rate is tunable from 204 to 274 k Hz.The good stability in operation is evaluated with power fluctuation less than 1%.Secondly,in order to obtain pulse output with narrower pulse width and higher repetition rate,we adopted mode-locking operation.By using mode-locking theory and ABCD matrix theory,we decide to choose V-shaped cavity which compress the radius of resonator mode on laser crystal and saturable absorber efficiently.We report a ReSe₂ passively mode-locked composite YVO₄/Nd:YVO₄ laser at 1.06?m,which can stably generate pure continuous-wave mode-locking operation at watt-level output.By employing few-layered ReSe₂ as saturable absorber,the nanosecond mode-locked pulses at fundamental repetition rate of 90.37 MHz was obtained experimentally in a composite YVO₄/Nd:YVO₄ laser.The maximum output power in pure continuous-wave mode-locking operation was as high as 1.1 W.To the best of our knowledge,this is the first report of watt-level continuous-wave mode-locking output power in the TMDs saturable absorber mode-locked lasers.The high-power continuous-wave mode-locking laser source shows potential applications in time-resolved spectroscopy,tele-communication and detection.Thirdly,this work presents experimental results concerning a passively mode-locked in-tracavity frequency doubled Nd:YVO₄/LBO green laser with a ReSe₂ saturable absorber op-erated at the wavelength of 532 nm.A maximal output power of 240 m W was obtained at a pump power of 10.9 W,pulse width as well as repetition frequency were,3.5 ns and 87.51MHz,respectively.Moreover,by using KTP as a frequency-doubling crystal,adopting an in-tracavity frequency multiplication structure,maintaining the same V-folded cavity,a mode-locked green laser with average output power of 470 m W was obtained.The repetition is 87.13 MHz,which is in accordance with the theoretical calculations.