Abstract

The generation of light pulses with duration down to a few optical cycles is a major topic in ultrafast optics. The broad gain bandwidths of optical parametric amplifiers (OPAs) have been so far widely exploited for few-cycle pulse generation in the visible, while only limited work has been performed in the near- and mid-infrared spectral region. Near-IR short pulses are interesting for ultrafast spectroscopy as well as for high-harmonic generation and attosecond pulse synthesis, taking advantage of the extended energy cutoff afforded by the longer driving wavelength. The mid-IR spectral range (3-5 μm) overlaps with vibrational transitions of many molecular and solid-state systems, allowing measurement of vibrational dephasing and coherent control of chemical reactions. The OPA phase-matching bandwidth Δω depends on the group-velocity mismatch between signal and idler δ_si=1/v_gs-1/v_gi where v_gs and v_gi are the signal and idler group velocities respectively. To the first order one can write Δω∞1/δ_si, so that broadband gain is achieved when the group velocities of signal and idler are matched. This condition can occur in the following OPA schemes: (a) in a non-collinear OPA (NOPA), in which the projection of the idler group velocity along the signal direction is equal to the signal group velocity; (b) at degeneracy point ω_s − ω_i; (c) at some particular frequencies (ω_s≠ω_i) out of degeneracy. The characteristics of the non-linear materials are crucial to determine OPA scheme and phase-matching bandwidth [1].

© 2009 IEEE