The GRENOUILLE thick-crystal concept works beautifully for measuring pulses from ~20fs to ~1ps. But, in principle, it should work even better for measuring longer pulses. The catch is that the required Fresnel-biprism apex angle becomes too acute. As a result, total internal reflection occurs inside the biprism if it's oriented in one direction, and the beams overlap inside it if it's oriented in the other. What to do?
The answer is to make the crystal into a pentagon shape, so it acts like both the Fresnel biprism and the SHG crystal simultaneously! This works beautifully. And if GRENOUILLE isn't simple enough with its mere four optical elements, now it has only three!
We can help you build one of these simple devices!
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