Ultra-broadband Optical Parametric Chirped-pulse Research Articles

Generation of multi-octave spanning high-energy pulses by cascaded nonlinear processes in BBO.

We present the generation of optical pulses with a spectral range of 500-2400 nm and energies up to 10 µJ at 1 kHz repetition rate by cascaded second-order nonlinear interaction of few-cycle pulses in beta-barium borate (BBO). Numerical simulations with a 1D+time split-step model are performed to explain the experimental findings. The large bandwidth and smooth spectral amplitude of the resulting pulses make them an ideal seed for ultra-broadband optical parametric chirped pulse amplification and an attractive source for spectroscopic applications.

Design constraints of optical parametric chirped pulse amplification based on chirped quasi-phase-matching gratings.

Chirped quasi-phase-matching (QPM) gratings offer efficient, ultra-broadband optical parametric chirped pulse amplification (OPCPA) in the mid-infrared as well as other spectral regions. Only recently, however, has this potential begun to be realized [1]. In this paper, we study the design of chirped QPM-based OPCPA in detail, revealing several important constraints which must be accounted for in order to obtain broad-band, high-quality amplification. We determine these constraints in terms of the underlying saturated nonlinear processes, and explain how they were met when designing our mid-IR OPCPA system. The issues considered include gain and saturation based on the basic three-wave mixing equations; suppression of unwanted non-collinear gain-guided modes; minimizing and characterizing nonlinear losses associated with random duty cycle errors in the QPM grating; avoiding coincidentally-phase-matched nonlinear processes; and controlling the temporal/spectral characteristics of the saturated nonlinear interaction in order to maintain the chirped-pulse structure required for OPCPA. The issues considered place constraints both on the QPM devices as well as the OPCPA system. The resulting experimental guidelines are detailed. Our results represent the first comprehensive discussion of chirped QPM devices operated in strongly nonlinear regimes, and provide a roadmap for advancing and experimentally implementing OPCPA systems based on these devices.

Role of apodization in optical parametric amplifiers based on aperiodic quasi-phasematching gratings

We experimentally demonstrate and analyze two different techniques for apodizing the nonlinear coupling in aperiodically poled MgO:LiNbO(3) (APPLN) used in an ultrabroadband optical parametric chirped pulse amplifier (OPCPA). With an adiabatic increase of the nonlinear coupling, a smooth gain spectrum and spectral phase is preserved during amplification in such media. The two approaches we explore are poling period apodization (PPA) and duty cycle apodization (DCA). For the first implementation of the apodized APPLN amplifier we use a constant chirp-rate in the grating k-vector. The nonlinear coupling is apodized over 10% of the total length at each side of the APPLN chip. This allows us to achieve high-intensity output pulses with clean temporal structure.

Fully efficient adiabatic frequency conversion of broadband Ti:sapphire oscillator pulses

By adiabatic difference-frequency generation in an aperiodically poled nonlinear crystal-a nonlinear optical analog of rapid adiabatic passage in a two-level atomic system-we demonstrate the conversion of a 110 nm band from an octave-spanning Ti:sapphire oscillator to the infrared, spanning 1550 to 2450 nm, with near-100% internal conversion efficiency. The experiment proves the principle of complete Landau-Zener adiabatic transfer in nonlinear optical wave mixing. Our implementation is a practical approach to the seeding of high-energy ultrabroadband optical parametric chirped pulse amplifiers.

Conformal profile theory for performance scaling of ultrabroadband optical parametric chirped pulse amplification

We developed a theory of optimization of amplifier bandwidth and conversion efficiency in ultrabroadband optical parametric chirped pulse amplification based on the principle of making the optimal conversion length uniform in time through pulse shaping. Conformal profiles, ideal combinations of pump intensity, seed intensity, and wave-vector mismatch temporal profiles can be found analytically by use of the exact Jacobi elliptic function solutions for signal gain and pump depletion in optical parametric amplification. We derive and investigate these gain equations for the general purpose of aiding the design of optical parametric amplifiers. Using these analytics, through an extensive analysis of conformal profile methods, we find conformal profile pulse shaping can significantly boost amplifier bandwidth as well as conversion efficiency, allowing in some amplifiers a severalfold increase in obtainable peak power. Pump pulse shaping is found to be particularly effective and flexible.