Full field characterization of complex objects illuminated by ultrashort pulse laser using delay-line sweeping off-axis interferometry

Measuring the complex field of ultrashort pulse lasers plays a fundamental role in light wavefront manipulation and nonlinear phenomena investigation; yet, it still constitutes a challenge for both full-field and high-resolution characterization due to the short coherent length. We proposed and implemented an off-axis interference system with a delay-line sweeping technique to overcome the fringe contrast degradation caused by the envelope mismatch between interfering pulses, resulting in an increased effective analysis area. The effectiveness of the proposed method was first demonstrated by measuring a complex field generated by a phase-only spatial light modulator, where a four-pixel binning technique was adopted for both amplitude and phase modulation; then it was used for the measurement of the second harmonic generation signal of a urea crystal sample. The experimental results show that the proposed method is capable of measuring complex fields having fine features within the full field. The proposed technique can be applied for strongly scattering medium refocusing and adaptive optics, where measuring the complex field of ultrashort pulse lasers is essential.