By exploiting nonlinear optical effects, a technology of unprecedented flexibility for the production of tunable coherent light has been developed. Referred to as optical parametric generation, it provides sources with spectral coverage extending all the way from the ultraviolet to the mid-infrared, and with temporal coverage extending over all time domains from the femtosecond pulse to the continuous wave. Such sources generate coherent light of outstanding optical quality and are now finding wide-ranging applications.

Characteristics of high-power, narrow-linewidth, continuous-wave (cw) green radiation obtained by simple single-pass second-harmonic-generation (SHG) of a cw ytterbium fiber laser at 1064 nm in the nonlinear crystals of PPKTP and MgO:sPPLT are studied and compared. Temperature tuning and SHG power scaling up to nearly 10 W for input fundamental power levels up to 30 W are performed. Various contributions to thermal effects in both crystals, limiting the SHG conversion efficiency, are studied. Optimal focusing conditions and thermal management schemes are investigated to maximize SHG performance in MgO:sPPLT. Stable green output power and high spatial beam quality with M(2)<1.33 and M(2)<1.34 is achieved in MgO:sPPLT and PPKTP, respectively.

We present studies of the optical properties of the new nonlinear material BiB3O6 for second harmonic generation from the visible to infrared. We have determined the phase-matching conditions and effective nonlinear coefficients in the three principal optical planes, acceptance bandwidths, spatial and temporal walkoff, group velocity dispersion and double phase-matching behaviour. We also report on experimental studies in this material, where efficient, high-average-power second harmonic generation of femtosecond pulses into the blue is demonstrated. Using 130-fs fundamental pulses at 76 MHz, single-pass second harmonic average powers as much as 830 mW at greater than 50% conversion efficiency have been generated over a tunable range of 375-435 nm. Using cross-correlation measurements in a 100-mum beta-BaB2O4 crystal second harmonic pulse durations of 220 fs are obtained. Our theoretical findings are verified by experimental data, where excellent agreement between the calculations and measurements is obtained. Direct comparison of BiB3O6 with beta-BaB2O4 also confirms improved performance of this new material for second harmonic generation of femtosecond pulses.

We review the physical properties, linear and nonlinear optical characteristics, and phase-matching configurations of BiB3O6 (BIBO), the first low-symmetry (monoclinic) inorganic nonlinear crystal that has found broad applications for frequency conversion of laser sources from the UV, across the visible, to the near-IR based on three-wave interactions. We describe in detail the most relevant optical properties that make this material an attractive candidate for nonlinear frequency conversion of laser light in general, and ultrafast femtosecond laser sources in particular. With special focus on ultrafast frequency conversion, characteristics such as group-velocity mismatch and spectral acceptance, parametric gain bandwidth, group-velocity dispersion, as well as angular acceptance and spatial walk-off are evaluated and optimum configurations for the attainment of maximum conversion efficiency, minimum pulse duration, and highest spatial beam quality are identified and compared with the most widely established alternative borate crystal, β-BaB2O4. Experimental results are presented on both parametric up-and down-conversion of femtosecond pulses, from the high-energy, low-repetition-rate (1 kHz) to the low-energy, high-repetitionrate (56-76 MHz) regime, demonstrating the unique versatility of BIBO for efficient frequency conversion of femtosecond pulses with broad tunability from 250 nm in the UV, throughout the visible, up to ∼ 3000 nm in the IR.Photograph of a femtosecond synchronously pumped optical parametric oscillator (SPOPO) based on BiB3O6 emitting in the yellow region of the spectrum. Pumped near 400 nm in the blue by the second harmonic of a Kerr-lens mode-locked Ti:sapphire laser, the SPOPO can generate femtosecond pulses across the full visible range of 480-710 nm, from the blue-green, through to yellow, orange and red.