A spectral characterisation method for /spl chi//sup z/ gratings

Summary form only given. In a widely used technique for the characterisation of second-order nonlinear gratings the measurement of the quasi-phase-matching (QPM) curve for second-harmonic generation (SHG) is achieved by continuously varying either sample temperature or fundamental (F) wavelength. This curve reveals the information concerning the length and the regularity of the nonlinear grating. This technique exhibit some drawbacks, especially for long gratings. A temperature gradient, practically unavoidable over a long grating, leads to a chirp in the period or the need for very fine scan step in the tuning of the fundamental wavelength are some of these drawbacks. To overcome these constraints, we propose a method that does not need tuning of any parameter and involves short laser pulses and relatively long nonlinear gratings. The method is applied to the case of SHG of ultra-short pulses in QPM structures without depletion of the pump.