Fig. 1. Schematic setup of the VIS-NOPO. The upper part of the sketch shows the pump laser and the third-harmonic-generation setup. A pump lens L (f=200  mm) focuses the third harmonic into the Brewster-cut BBO crystal (θ=39°; L=2  mm), which is surrounded by two curved DCMs (M1andM2: d=25.4  mm; ROC=−150  mm) with a spectral transmission window at 345 nm. Moreover, a BK7 substrate (uncoated, L=3  mm) is inserted into the cavity, which consists of six additional plane DCMs (M3−M8) and an output coupling mirror (OC) with 14% transmission from 480 to 720 nm.

Fig. 2. Tuning behavior of the VIS-NOPO. (a) Measured power spectral density (PSD) as a function of wavelength and cavity length/group delay. The green line indicates the calculated net intracavity GDD. (b) Measured pulse durations and output powers.

Fig. 3. (a) Normalized signal spectra for different cavity lengths. (b) Measured pulse durations (circles) and calculated Fourier limits (triangles). (c) Green line: calculated GDD.

Fig. 4. Measured slope efficiency and threshold of the signal at 530 nm. The solid red line illustrated a linear fit. Inset: signal beam profile at maximum output power.

Fig. 5. (a) Long-term stability measurement of the signal output power. (b) Phase noise PSD of signal and pump.