We address the use of optical parametric oscillator (OPO) to counteract phase diffusion, and demonstrate phase-noise reduction for coherent signals traveling through a suitably tuned OPO. In particular, we theoretically and experimentally show that there is a threshold value on the phase noise, above which OPO can be exploited to “squeeze” phase noise. The threshold depends on the energy of the input coherent state, and on the relevant parameters of the OPO, i.e., gain and input-output and crystal loss rates.

We present a conceptual design for a compact X-ray Source BriXS (Bright and compact X-ray Source). BriXS, the first stage of the Marix project, is an Inverse Compton Source (ICS) of X-ray based on superconducting cavities technology for the electron beam with energy recirculation and on a laser system in Fabry-Pérot cavity at a repetition rate of 100 MHz, producing 20–180 keV monochromatic X-Rays devoted mainly to medical applications. An energy recovery scheme based on a modified folded push-pull CW-SC twin Energy Recovery Linac (ERL) ensemble allows us to sustain an MW-class beam power with almost one hundred kW active power dissipation/consumption.

Single-cycle, high-power, high-repetition-rate THz pulse sources are becoming the cornerstone of several scientific and industrial applications. A promising and versatile method for high-power THz generation is optical rectification in nonlinear crystals pumped by powerful near-infrared ultrafast laser systems. In this context, ytterbium-based laser sources are particularly advantageous in terms of power scalability and technology establishment. However, as the repetition rate increases toward hundreds of MHz, the conversion efficiency typically decreases, as most laser systems do not reach sufficiently high average powers to correspondingly enhance the peak power to drive the nonlinear conversion process efficiently. An alternative approach to achieving a sufficiently high average power at a high repetition rate is based on passive enhancement cavities, which boost the pulse energy of standard watt-level ytterbium lasers by orders of magnitude. We present the first demonstration of optical rectification in a passive enhancement cavity at multi-kW levels, achieved by a 240-fold power enhancement. By irradiating a 50-μm thin lithium niobate plate with 1.9-kW average power inside the enhancement cavity, we generate milliwatt-level THz pulses with 2-THz bandwidth and 93-MHz repetition rate, mostly limited by the driving pulse duration. To the best of our knowledge, this represents the highest driving average power used for optical rectification. This methodology represents a promising new step toward high-repetition-rate and high average power single-cycle THz sources using widely available multi-watt level Yb lasers.