Parametric amplification and frequency conversion

Cristian Manzoni

State-of-the-art femtosecond laser systems, based on Ti:sapphire or Yb:doped gain media, operate at fixed wavelengths (0.8 m for Ti:sapphire and 1 m for Yb). This contrasts with the requirements of many applications, which call for ultrashort light pulses broadly tunable from the mid-infrared to the ultraviolet. As there are no classical laser active media capable of providing gain over such a broad frequency range, frequency tunability must be achieved by a nonlinear optical effect, enabled by the high peak powers of femtosecond lasers. The most widespread solution exploits the second order nonlinear effect known as Optical Parametric Amplification (OPA). In an OPA energy is transferred, in a nonlinear crystal, from an high frequency and high intensity beam (the pump) to a lower frequency, lower intensity beam (the signal) which is thus amplified. The OPA process requires, for efficient energy conversion, momentum conservation (phase-matching). The OPA is thus an optical amplifier with continuously variable center frequency (determined by the phase-matching condition) and represents an easy way of tuning over a broad range the frequency of an otherwise fixed femtosecond laser system. If suitably designed, an OPA can simultaneously fulfill the phase-matching condition for a broad range of signal frequencies thus acting as a broadband amplifier, efficiently transferring energy from a narrowband pump pulse to a broadband signal pulse; it can therefore be used to dramatically shorten the duration of the pump pulse, generating tunable few-optical-cycle pulses. The tunability of the OPAs can be further extended in the UV and the IR spectral ranges by other broadband second-order processes, such as sum- and difference-frequency generation. In the talk we will discuss on the design principles and properties of femtosecond OPAs driven by pulsed laser sources, and we will introduce current and future challenges in parametric manipulation of ultrashort light pulses.

Dr. Cristian Manzoni got his PhD in Physics at Politecnico di Milano. Since 2010 he is at IFN-CNR, where he is now Senior Researcher. His research focuses on generation and characterization of few-cycle light pulses in the UV, visible and IR range for time-resolved spectroscopy. Recently, he also focused on hyperspectral imaging and microscopy in the visible and infrared spectral range, with applications in remote and environmental sensing, conservation science, security and medical imaging.