Research On Ultrafast Laser And Supercontinuum Generation Based On Novel Optical Functional Materials

Due to the ultra-short pulse duration and extremely high peak power of ultrafast laser,it has a wide range of applications in the fields of physics,biology,chemical control reaction,optical communication,medical treatment,“cold”ablation,ultra-fine fine processing,high density information storage and et.al.With the maturation and commercialization of high power laser diode（LD）,ultrashort pulse laser directly generated by LD-pumped rare earth doped gain medium has the advantages of high efficiency,low cost,stable performance and compact structure.It is a simple and effective technology to obtain ultrafast light source.The development of pulse modulator with wide band response and gain medium with wide spectrum characteristics is the key of ultrafast laser research.Generation of materials,generation of devices.The emergence of new optical functional materials brings new opportunities for ultrafast laser.The rare earth doped gain medium emits laser with corresponding wavelength through the energy level transition process.Limited by the energy level transition of doped ions,the output spectrum of the oscillator can only cover a limited range of wavelength and frequency.As the application of laser is expanding to more fields today,many new applications require ultra-wideband light sources operating in non-traditional bands.Photonic crystal fiber（PCF）is a flexible and efficient nonlinear medium with the characteristics of dispersion harmonization and high nonlinearity.The generation of supercontinuum based on ultrafast laser pumped PCF provides an effective technique for spectrum broadening.In this paper,the characteristics of 1-2μm band ultrafast laser pumped directly by LD are studied,and the theoretical simulation and experimental research of supercontinuum generation are carried out based on commercial large mode field PCF and self-developed high air filling rate PCF.The main research contents and innovation achievements are summarized as follows:1.Watt-level ultrafast laser based on graphdiyne mode-locker.A few layers of graphdiyne saturable absorber mirror（GDY-SAM）has been successfully prepared and applied to near-infrared all-solid-state ultrafast laser.The maximum average output power of 1.27 W is obtained in LD pumped Nd:YVO₄ continuous-wave mode-locked laser.In comparison experiments with commercial semiconductor saturable absorption mirror（SESAM）,GDY-SAM mode-locked laser is comparable to SESAM mode-locked laser in terms of mode-locked threshold,mode-locked stability and output spectral characteristics.In terms of average output power,GDY-SAM is superior to commercial SESAM.2.A hundred MHz nanosecond pulsed laser based on a single layer tungsten disulfide（WS₂）mode-locker.A high quality single layer WS₂ saturable absorber was prepared by chemical vapor deposition.Its nonlinear optical response was investigated.The single-layer WS₂ has a small modulation depth of 1.4%and a low saturable intensity of 68.6 k W/cm².Based on the unique nonlinear characteristics,single-layer WS₂ is used as a saturable absorber to realize stable continuous-wave mode-locked nanosecond pulse laser operation with a repetition rate of 93.1MHz.This work provides a new technical approach for the generation of high repetition frequency nanosecond pulses.3.LD pumped 2μm band passively mode-locked Tm:Sc₂Si O₅（Tm:SSO）ultra-fast laser.Using SESAM as the mode-locker,a stable Tm:SSO continuous-wave mode-locking laser is obtained in the water absorption peak band.The mode-locked laser operates at 1967.7 nm in the eye safe band,with an average output power of 207 m W and a pulse width of 16.5 ps.The pulse repetition rate is 81 MHz and the signal-to-noise ratio is up to 70 d B.These results demonstrate the great potential of Tm:SSO crystals for generating ultrafast lasers.4.LD pumped 2μm band passively mode-locked Tm,La:Ca F₂ ultrafast laser.Based on the disordered structure Tm,La:Ca F₂ crystal with wideband emission spectrum,the resonant cavity is optimized to achieve stable continuous-wave mode-locking operation.The central wavelength of the output laser is 1886.6nm,and the central frequency of the pulse is 96.6 MHz.The signal-to-noise ratio of more than 70 d B and the clean spectrum sequence further indicate that the mode-locking has good stability.5.High Energy supercontinuum generation by pumping large mode field PCF in normal dispersion region.Based on 1μm ultrafast laser,a large mode field PCF is pumped in the normal dispersion region.The spectrum broadening under different injection power and fiber lengths is investigated theoretically and experimentally.When the fiber length is 2.5 m and the injection pump power is 1 W,the spectrum is maximized.The supercontinuum covers the range of about1100 nm from 800 nm to 1900 nm.The average output power is 340 m W and the corresponding pulse energy is 0.46μJ.6.Wideband supercontinuum generation by pumping high air filling rate PCF in anomalous dispersion region.Three factors of pump optical repetition frequency,pump power and fiber length are studied.When the fiber length is 9 m,the pump repetition frequency is 758 k Hz,and the injected pump power is 195 m W,the broadband supercontinuum covers the spectral range from400 nm to 2100 nm,completely includes the visible band and the near infrared band and into the middle infrared band.In addition,two spectral peaks were detected in the ultraviolet band with central wavelengths of 379 nm and 353 nm,respectively.7.Theoretical simulation based on 2μm ultrafast light source and large mode field PCF.The soliton self-compression effect and spectral broadening phenomenon caused by pumping PCF in the anomalous dispersion region far away from the zero dispersion wavelength are investigated theoretically.The results show that the pulse width of the output terminal can be compressed to less than 10 fs after the initial pulse width of 300 fs is passed through the large mode field PCF with the length of 19.5 mm.In the process of soliton self-compression,the central wavelength of the spectrum is unchanged,and the wavelength of the spectrum is expanded to both sides.As the fiber length increases further,Raman solitons with stable transmission are generated under the influence of the Raman response,which continuously redshift to the edge of the fiber transmission window.The relevant conclusions provide a reliable theoretical basis for the next experimental research.