Ultra-short pulses are central to many technologies in telecommunication, laser micromachining and other industries. They are also extensively used in research in such fields as coherent control, non-linear spectroscopy.
The time profiles of femtosecond light pulses are usually retrieved by methods utilizing optical nonlinearities. Some drawbacks exist for these methods, which require significant signal powers and operate in limited spectral range, difficult due to phase matching issues. On the other hand, linear characterization methods require a coherent synchronized reference with an equivalent bandwidth, usually unavailable. Existing self-referenced linear methods are generally limited to relatively long (picosecond) pulses.
Here presented is a linear self-referenced ultra-short pulse characterization technique based on time domain localization of the spectral components of the pulse. Accurate timing of the spectral slices is achieved with standard commercially available detectors, despite the relatively slow response time, the time resolution ultimately limited by the signal to noise ratio is sufficient to reconstruct femtosecond pulses.
In this way the better of two worlds' linear detection and nonlinear optical methods are combined.
The invention demonstrates a linear referencing pulse characterization technique relaying on precise timing of spectral slices using a fast liner detector. It takes advantage of the fact that, depending on the signal to noise ratio, the timing jitter can be much smaller than the detector response time. For a train of identical pulses, the signal to noise ratio can be improved by averaging the relative delay over many pulses. The overall resolution then increases.Assuming that the detector response function is stable, it is thus possible to reconstruct the time profile of the pulse with precision limited only by the integration time and the stability of the characterized source. The principle of converting time accuracy into resolution of a time domain measurement is analogous to super-resolution microscopy techniques relying on precise spatial localization of individual fluorophores.