Control of frequency chirp in a PPKTP optical parametric oscillator with near Fourier-limited bandwidth

We use nonlinear optical processes to generate narrowband light from an optical parametric oscillator, yielding significantly improved frequency stability compared with dye lasers where the chirp arises principally from population inversion. We measure chirp using optical heterodyne detection and minimise it by phase matching, producing a near Fourier-transform limited bandwidth.