FROG Retrieval Algorithm

TECHNOLOGY| FROG Retrieval Algorithm

Fast analysis of FROG spectrograms

Using our proprietary algorithm, our VideoFROG software system can perform the phase retrieval in real time. Single-shot FROG geometries have allowed 30 Hz measurement rates to be obtained. Now you can tweak up your laser system systems while watching the phase, intensity, and duration of the pulses displayed on a computer screen. The ultrafast oscilloscope has arrived.

FROG is experimentally simple. A single pulse is split into two equal pulses, with one pulse used as the gate and the other pulse as the probe. The nonlinear medium can be as simple as a piece of optical quality quartz. The inset shows that a signal pulse is sliced out where the gate and probe overlap.

Our FROG Scan system works by step scanning an optical delay, and reading the spectrum at each delay using a mini-spectrometer. Because of the unique zero-backlash servo, data acquisition is fast rapid—it can be less than 300 ms. The resulting spectrogram provides immediate, qualitative information about the pulse. However, because VideoFROG seamlessly couples data acquisition with the inversion algorithm, true pulse measurement is achieved in real-time.

To obtain the our robust, real-time measurements, we use an algorithm developed by Dan Kane, CEO and founder of Mesa Photonics, called the Principal Component Generalized Projections algorithm (PCGP), that is very fast and easy to implement for common FROG geometries. This algorithm coupled with data acquisition in a multishot second harmonic generation (SHG) FROG device, is the basis of our FROG Scan femtosecond oscilloscope that displays the intensity and phase of the extracted pulse at rates of several Hertz.

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