Ultrabroadband high-power laser technology has opened a door to extreme optical sciences, such as frequency-comb metrology, attosecond science, and relativistic optics. Optical parametric chirped-pulse amplification (OPCPA) has become one of the key techniques of these emerging research areas employing the broad amplification bandwidth and wavelength tunability of optical parametric amplification (OPA). This proposal aims to develop a novel cavity-based parametric amplification technique that will allow octave-spanning gain bandwidth and near-quantum-limited conversion efficiency at ~100 MHz repetition rates, using ordinary pump sources and OPA media. This technique, referred to as cavity-enhanced optical parametric chirped-pulse amplification (C-OPCPA), recycles and passively reshapes pump pulses inside an external cavity to efficiently amplify seed pulses in a nonlinear medium. C-OPCPA employs the use of enhanced pump intensity to compensate for wave-vector mismatch, which, in the C-OPCPA geometry, can lead to efficient amplification at bandwidths of more than one octave.
Intellectual Merit: The proposed research will make significant contributions to the fundamental understanding of cavity dynamics with gain and nonlinear loss and develop a new method in order to achieve, for the first time, a highly efficient octave-spanning parametric amplifier at ~100 MHz repetition rate.
Broader Impact: C-OPCPA systems are very useful for many scientific and technological applications, such as frequency-comb amplification and attosecond metrology. The C-OPCPA system to be demonstrated can be scaled up to much higher average power and serve as a pump source for high-flux attosecond XUV pulse generation via high-harmonic generation. The project will also provide a teaching vehicle for graduate students, postdoctoral researchers, and visiting scientists.
Ultrafast ultrabroadband high-power laser technology has opened a door to extreme optical sciences, such as frequency-comb metrology, attosecond science, and relativistic optics. In fact, the 2005 Nobel prize was awarded to John Hall and Theodor Hänsch for their work in ultrfast optical frequency-combs. Additionaly, Paul Corkum and others have leveraged ultra-fast technology to image directly for the first time atomic orbitals. Optical parametric chirped-pulse amplification (OPCPA) has become one of the key techniques to these emerging research areas by taking advantages of the peak-power scalability from chirped-pulse amplification (CPA) technique and the broad amplification bandwidth and wavelength tunability from optical parametric amplification (OPA) technique. However, the bandwidth of current OPCPA technique is still limited to less than one octave and the conversion efficiency is relatively low (10-20% for signal). Another challenge with OPCPA is the high-repetition-rate operation, mainly limited by available pump sources (typically 10 Hz – 1 kHz). In the work enabled by this grant, we have developed a novel cavity-based parametric amplification technique that will allow octave-spanning gain bandwidth and near-quantum-limited conversion efficiency at ~100 MHz repetition rates. This technique, referred to as cavity-enhanced optical parametric chirped-pulse amplification (C-OPCPA), recycles and reshapes pump pulses inside an external cavity to efficiently amplify seed pulses in a nonlinear medium. This novel method will push the OPCPA technique to a new regime in terms of spectral bandwidth and repetition rate as well as efficiency, which are extremely useful for important several applications, such as direct frequency-comb amplification, high-flux attosecond pulse generation and attosecond metrology. The work presented here is a significant advance in our understanding of the C-OPCPA concept and performance potential. We have conducted comprehensive studies on the C-OPCPA system in both theoretical and experimental aspects. Specifically, on the theory side we report: Detailed theoretical modeling and simulation of the C-OPCPA operating principle. Modeling of the cavity locking dynamics and role of specific parameters including cavity-phase to achieve octave-spanning gain. New instability dynamics and how they can be avoided in a C-OPCPA system design. Simplifying graphical analysis which captures complex dynamics. On the experimental side we have constructed a first of its kind C-OPCPA system capable of amplifying at exceptionally high repetition rate with (80MHz) with minimal pump power (< 1-W) achieving more than 50% conversion efficiency and with a 3x improvement in bandwidth. This system dramatically out-performs comparable single pass OPCPA systems and illustrates the key concepts in C-OPCPA: that passive pulse shaping and impedance matching in C-OPCPA systems can extend the capabilities of nonlinear crystals well beyond material limitations from nonlinearity and dispersion. We report a detailed analysis of this exceptional experimental system performance: We detail the experimental apparatus and C-OPCPA system design. Perform a detailed comparison of conversion efficiency to a single pass amplifier to unravel the role of impedance matching in C-OPCPA performance. Demonstrate more than 3x bandwidth improvement of a C-OPCPA system in several configurations over single pass and provide a detailed experimental and numerical analysis furthering our understanding of core C-OPCPA operating principles. Analyze parasitic nonlinear processes and system issues that hinder system performance and address how to avoid/overcome these issues. The work presented here has made significant contributions to the fundamental understanding of cavity dynamics with gain and linear/nonlinear losses and represents a first step toward the development of a new method to achieve a highly efficient octave-spanning parametric amplifier at ~100 MHz repetition rates for the first time. Both experimental and theoretical studies were conducted bringing a balanced comprehensive understanding of this novel concept. The proposed approach has brought a new scientific and technological challenge to the conventional OPCPA technique and pushed parametric amplifiers to new regimes of operation. Broader Impact: C-OPCPA systems are very useful for many scientific and technological applications, such as frequency-comb amplification and attosecond metrology. The C-OPCPA system to be demonstrated can be scaled up to much higher average power and serve as a pump source for high-flux attosecond XUV pulse via high-harmonic generation. A similar cavity-based technique can also be applied to the inverse Compton scattering of electron bunches for high-flux hard X-ray generation. This project also has provided an excellent teaching vehicle for graduate students, postdoctoral researchers, and visiting scientists. Participants have carried out research at the current frontier in Ultrafast Optics. Our group has extensive collaborations and personnel exchange with other university research groups in this and related research areas. The results of this project directly influenced the graduate course of the PI in "Ultrafast Optics" and undergraduate course "Fundamentals of Photonics". We have a well-balanced group of researchers and students including women and minority students. We regularly engage undergraduate students in our research group through undergraduate research opportunity projects.
