Progress on Ultrafast Laser Coatings with Ultrabroadband High-Threshold and Dispersion Modulation(Invited)
Significance Superintense ultrafast laser pulses,characterized by their extremely short duration and high instantaneous power,generate extreme physical conditions,including ultrafast temporal scales,ultra-high energy densities,and ultra-strong electromagnetic fields.These pulses represent a cutting-edge scientific frontier with profound implications for fundamental science,life sciences,national defense,etc.Since the advent of lasers,researchers have strived to produce superintense ultrafast pulses with narrower pulse widths and higher peak powers.The development of mode-locking techniques,Ti-sapphire gain media,prism pairs,gratings,and other dispersion compensation techniques has made sub-100 fs pulses achievable.To further reduce femtosecond pulse widths,more precise dispersion compensation is required.Chirped mirrors have become essential for generating sub-10 fs pulses.In 2001,leveraging advanced chirped mirror technology,the Vienna University of Technology in Austria first generated and measured isolated attosecond pulses from femtosecond pulse lasers interacting with noble gas targets,marking the beginning of the attosecond era.In addition to efforts to shorten pulse widths,increasing peak pulse power has been a major goal.The advent of chirped pulse amplification(CPA)and optical parametric chirped pulse amplification(OPCPA)has enabled the production of petawatt(PW)-femtosecond(fs)pulses.Peak power has rapidly exceeded 4.2 PW-20 fs and even 10 PW-25 fs,creating unprecedented extreme physical conditions.As laser technology has evolved,ultrafast laser coating technology has evolved with it,and vice versa.Ultrafast laser coatings are crucial for guiding laser beams and managing dispersion within laser systems.Their performance metrics including reflectivity,bandwidth,dispersion control,and laser damage resistance significantly affect the performance of ultrafast laser pulses.This area continues to be a dynamic research focus.By employing gradual changes in optical thickness in layer structures,ultrafast laser coatings achieve wide bandwidth with high reflectivity while allowing the light of different wavelengths to propagate through different optical paths,thus providing precise dispersion compensation.This capability is critical for superintense ultrafast pulse technology.As ultrafast lasers approach petawatt and exawatt peak powers and pulse widths approach single optical cycle,the performance requirements for bandwidth,dispersion control,reflectivity,and damage thresholds become more stringent.Enhancing the overall performance of ultrafast laser coatings in these areas is vital for the generation of superintense ultrafast and attosecond pulses and is therefore a focal point of research.Progress We provide a comprehensive review of advances in ultrafast laser coatings,focusing on systems such as superintense ultrafast lasers and attosecond lasers.Our review addresses performance requirements related to damage thresholds,operational bandwidth,reflectivity,and dispersion control.We detail the fundamental design principles of ultrafast laser coatings that effectively balance these parameters.To address the challenge of dispersion oscillation in ultrafast laser coatings,we present detailed principles and methods for suppression.In response to the demand for broad bandwidth and high threshold in ultrafast laser coatings,we discuss theoretical design methods for improving broadband thresholds.We outline high-threshold deposition techniques,high-precision film thickness monitoring,and group delay dispersion(GDD)testing techniques for ultrafast laser thin films,providing a basis for their precise preparation and accurate performance testing.Regarding the damage characteristics of ultrafast laser coatings,we explore nonlinear optical effects under ultrashort pulses,describe the degradation patterns of coating performance before catastrophic damage,and discuss damage morphology,evolution processes,and phase damage mechanisms.Finally,we summarize the applications of ultrafast laser coatings in superintense ultrafast lasers,attosecond lasers,compression systems,and mid-infrared ultrafast laser systems.Conclusions and Prospects The advancement of ultrafast laser technology is creating new demands and challenges for ultrafast laser coatings,while advances in coating technology are driving the development of laser technology.Future research will focus on a comprehensive approach that includes theoretical design,precision manufacturing,damage characteristics,and system applications of ultrafast laser coatings.
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