Is there a definitive way to determine the delay between the fundamental (800 nm) and it's second harmonic (400 nm) generated by a type 1 BBO?
Our Ti-Sapphire laser generates 800 nm pulses at 30 fs, a Mach–Zehnder interferometer is constructed. One arm is made to pass through a type 1 beta-BBO of 100 microns, while the other is not disturbed. The delay between 800 and 800 nm was determined quite easily before the type-1 BBO was placed, but a delay is introduced between the 800 and 400 nm pulses in one arm due to the type-1 BBO. Is there any way to determine the delay between them?
PS: The THG generation method was not advisable since control of individual intensities was not guaranteed in the said method.
You can see the following research:
1. https://www.nature.com/articles/s41566-021-00841-8?proof=t%3B
2. https://arxiv.org/ftp/arxiv/papers/1211/1211.1436.pdf
3. Article Wavelength scaling of high harmonic generation for 267 nm, 4...
I don't understand the PS note. What does it mean ''control of individual intensities was not guaranteed''?
I do not quite understand your conclusion that type-I phase matching will give rise to a delay between fundamental and SHG as both pulses travel at identical phase velocities in the crystal. Of course, this does not mean that group velocities are identical, too, but as the SHG becomes most intense during the final stretch of the propagation I would not expect much of a measurable delay from that effect.
You can theoretically investigate this by setting up the coupled propagation equations for fundamental and SHG, including a group velocity mismatch. If you want to measure this then you can certainly try to set up an auto/cross correlator with a broadband nonlinearity, e.g., tightly focusing on a quartz substrate using surface SHG/SFG. However, you would unavoidably see dispersive effects due to beam splitters, lenses and air paths rather than the delay incurred during the original SHG process. There are ways around this, but this would be a rather challenging experiment for an effect that probably does not even exist.
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