Ultrafast Fiber Laser Technology And Application Based On Pre-Chirp Management

Ultrafast technology based on fiber nonlinearity is a promising solution to increase the pulse peak power and realize wavelength conversion.In order to obtain high-quality output pulses and spectra,management of fiber nonlinearity is indispensable.Pre-chirp management,as a technique to control the nonlinear effects by pre-introducing chirp,has been widely used in ultrafast lasers,ultrafast spectroscopy,nonlinear microscopy and other fields.In this dissertation,we mainly study the novel ultrafast nonlinear technology combined with pre-chirp management.In terms of wavelength conversion,we proposed pre-chirp managed self-phase-modulation-enabled spectral selection(SESS)and developed a widely wavelength tunable femtosecond laser.Using the ultrafast fiber laser as a driving source,we implemented a multi-modal multiphoton microscope to successfully image various biological samples.In terms of energy scaling,we invented pre-chirp managed divided-pulse amplification(PCM-DPA).We systematically explored the influence of the thickness and number of birefringent plates on the combining efficiency,and proposed a new solution of composite birefringent plates.In terms of pulse compression,we developed pre-chirp managed adiabatic soliton compression(ASC)to effectively suppress the compressed pulse pedestal,which is demanded by high-field science.The main research contents and innovative results are summarized as follows:1.We proposed pre-chirp managed SESS,breaking through the bottleneck of traditional energy-tuned SESS in terms of output pulse energy and system robustness.Pre-chirp managed SESS not only greatly optimizes the energy utilization and wavelength conversion efficiency,but also reshapes the unfavorable input pulse shape into a bell-shaped profile suitable for spectral broadening.The excellent energy scalability of pre-chip managed SESS can produce wavelength tunable femtosecond pulses with megawatt-level peak power,which is well suited to drive multiphoton microscopy.2.Based on the pre-chirp managed SESS,we developed a high-performance femtosecond driving source with a wavelength tunable from 970 to 1200 nm.Driven by this source,our multiphoton microscope was successfully used to image various biological samples with two-photon fluorescence,three-photon fluorescence,second-harmonic generation and third-harmonic generation.We are the first to obtain four-modal imaging of clinical gastric tissue,revealing the significant application potential of multiphoton microscopy in clinical pathology.3.We proposed PCM-DPA to overcome the bottleneck of pulse energy and peak power limited by self-focusing.In PCM-DPA,we further developed a new concept of composite birefringent plates to solve the international problem of low combining efficiency caused by single material birefringent crystals.Our numerical analysis shows that PCM-DPA system based on composite birefringent plates can produce pulses with >100-μJ pulse energy,<50-fs duration,and >2-GW peak power,which is 40 times higher than that obtained by traditional pre-chirp managed amplification.4.We proposed pre-chirp managed ASC technique.Based on gas-filled pressuregradient hollow-core fiber,we can compress 125-μJ and 130-fs pulses at 2 μm into few-cycle pulses with a duration of 15 fs.Further analysis illustrates that pre-chirp managed ASC is in favor of compressing pulses centered at longer center wavelength.The resulting high-quality energetic few-cycle pulses will have important applications in high-field science.