The invention of the GRENOUILLE technique

Since the 1960’s, ultrashort laser pulses have been measured using autocorrelators. Unfortunately, autocorrelators are complex and expensive; they require frequent re-alignment; and they yield only rough measurements of the pulse length and give no information regarding the pulse phase (color vs. time) or its spatio-temporal distortions. But GRENOUILLE (GRating Eliminated No-nonsense Observation of Ultrashort Incident Laser Light E-fields) not only measures the precise pulse intensity vs. time and frequency, but it also yields the pulse phase vs. time and frequency, its spatial profile, and the two most important spatio-temporal distortions. It is also a simple, inexpensive, and compact device requiring no alignment.

GRENOUILLE is a simple version of Frequency-Resolved Optical Gating (FROG), a well-known and robust technique for measuring ultrashort pulses. GRENOUILLE uses a Fresnel biprism to split the pulse in two and recombine them (automatically aligned in space and time) in a thick second-harmonic-generation crystal. The thick crystal then gates one pulse with the other and also spectrally resolves the gated pulse, yielding a spectrogram of the pulse. Because spatio-temporal distortions in the pulse introduce characteristic distortions in the measured spectrogram, GRENOUILLE is also able to accurately measure the two most important such pulse distortions, spatial chirp and pulse-front tilt, which are present in most ultrashort pulses, but which have gone unmeasured for many years. GRENOUILLE can measure a single ultrashort pulse or a high-rep-rate train of them.

As a result, GRENOUILLE has been awarded an R&D100 award as one of the top 100 inventions of the year across all fields and over the entire world. And it has also been awarded Photonics Spectra magazine’s Circle of excellence award as one of the top 25 optics inventions of the year over the entire world.