Frequency converting pulses with bandwidths approaching an octave remains a daunting technical challenge. We show that by tailoring the frequency-dependent photon conversion position in a chirped quasi-phase matched crystal, it becomes possible to frequency shift ~10-fs, ~1 μJ pulses efficiently and uniformly, while intrinsically customizing their dispersion. We employed this technique to design frequency downshifters that apply zero group delay dispersion to a compressed input pulse. For example, we demonstrated conversion of an 11.1-fs, 680-820 nm pulse into an octave-spanning, 11.6-fs, 2-4 μm output pulse with 70% internal photon conversion. Within some constraints, it is also possible to apply custom dispersion of multiple order, or to pre- or post-compensate for other dispersive elements in an experiment. A general approach that also works for sum frequency generation, this technique thus provides significant flexibility in selecting frequency conversion pathways and designing a hyperspectral architecture with multi-color few- and single-cycle pulses.
Dispersion management is among the most challenging aspects of the design and realization of amplified laser systems possessing octave-spanning bandwidth and good compressed pulse quality. Here we demonstrate a new type of device for octave-spanning dispersion management. We combine the paradigm of chirped quasi-phase matching (QPM) for pulse shaping during frequency conversion with the robust, efficient, octave-spanning capability of an adiabatic frequency downconversion device. The result is a simple, monolithic device that can produce an octave-spanning infrared pulse with tailored dispersion – a technique that may be especially convenient for high-energy amplifier chains employing difference frequency generation and/or parametric amplification stages. The technique can also serve as a way to produce pulses of ~10 fs duration throughout the visible to mid-infrared spectrum for hyperspectral ultrafast spectroscopy. Adiabatic frequency conversion employs a slowly changing position-dependent poling frequency in a chirped QPM device to efficiently frequency shift photons over a wide bandwidth with a linear transfer function. In this work, we show that the frequency dependent localized conversion of the process allows tailoring of the total group-delay dispersion (GDD). We have demonstrated a first device with zero GDD, allowing efficient conversion of a few-cycle near-infrared input to a near-single-cycle mid-infrared output of the same duration (~12 fs, with bandwidth spanning 2.0-4.0 microns). We present additional designs for precise custom tailoring of the frequency-dependent group delay.
KEYWORDS: Quantum efficiency, Nonlinear optics, Picosecond phenomena, Signal processing, Harmonic generation, Energy efficiency, Crystal optics, Yttrium, System on a chip, Sum-frequency generation
We experimentally demonstrate a new technique for achieving efficient optical parametric amplification (OPA) which maintains the simplicity of conventional OPA implementation and works for common laser wavelengths using existing nonlinear media. This technique is achieved by simultaneously performing OPA and second harmonic generation at the idler wavelength. The dynamics of the two nonlinear processes hybridize, inhibiting back-conversion in the OPA and creating a long region of laser-like gain saturation. We show conversion of 2 μm picosecond pump pulses to 3.4 μm with 68% quantum efficiency, 44% internal pump to signal energy efficiency, and 48-dB gain in a bulk CSP crystal.
Second harmonic amplification - a hybridization of optical parametric amplification and second harmonic generation - is a route to ultra-efficient parametric amplification. Requiring the simultaneous phase matching of two parametric wave-mixing processes, it has limited frequency coverage in the collinear geometry in bulk media. Here we show that noncollinear birefringent phase matching can provide wide frequency tunability of second harmonic amplification across the near- and mid-infrared in the materials ZnGeP2, CdSiP2, LiNbO3, β - BaB2O4, and KD2PO4 in applications designed for accommodating high-energy picosecond pulses generated by solid state lasers. We discuss practical limitations including acceptance angle, phase-matching bandwidth, spatial walk off, and parasitic processes.
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