Even if they were 400 dB? ;)
Seriously, optical materials are so linear that you really have to stand on one leg to get any SH signal to speak of.
If you have a gigawatt of peak power, you can do a lot of things, e.g. use topical disinfectant for SHG. Nitrofurazone (5-nitro 2-furaldehyde semicarbazone, Aldrich Catalog #73340) does a good job of making a little bit of visible from a whole lot of IR.
Cheers
Phil Hobbs
I bow to your superior knowledge, my only experience was years ago my kids had a tiny green laser pointer that ran off some button cells - the green was doubled IR. The DC input power cannot possibly have been more than 100-200 milliwatts. Whole thing was incredibly cheap and tiny.
piglet
maximum for a legal laser pointer is 5mW
Exactly! But PH was saying doubling required huge power, I doubt the kids toy lipstick sized pointer optical output was even a milli-watt but it showed optical doubling happens at sub-watt levels?
piglet
doesn't take much to make it not work,
On a sunny day (Wed, 26 Oct 2022 16:15:28 +0100) it happened piglet snipped-for-privacy@hotmail.com wrote in <tjbiug$2g6r6$ snipped-for-privacy@dont-email.me:
Most of your questions are answered here:
Nice thing to play with.
You cn test if your green laser is doubling (and uses high energy pulses) by swinging it against some wall and see it it produces a line of dots (swicthing frequency) But if it is younger than 10 years maybe it is just a green laser diode?
Yes, you can do that at surprisingly low power, but it takes focusing the beam down in just the right material, cut with the crystal axes just so.
The issues are: (1) the size of the elements in the nonlinear susceptibility tensor chi'' (normally very small except in special materials), and (b) getting the nonlinear electric polarization (*) to phase-match with a propagating wave at the second harmonic, which it normally doesn't.
A good material has large coefficients of chi-double-prime, which helps with the first, and enough birefringence, which makes the second possible.
The reason phase matching matters is that the growth of the second-harmonic wave is a coupled-modes problem--the fundamental beam causes a component of polarization at the second harmonic, and the SH beam grows from that, just like a microwave directional coupler.
The k vector of the SH _polarization_ is obviously exactly twice that of the fundamental beam, whereas the SH _beam's_ k vector is defined by the frequency and refractive index. (Normally the refractive index increases considerably towards short wavelengths, so this does not happen by accident.)
Cheers
Phil Hobbs
(*) This is dielectric polarization, the material response to the applied field, not polarization as in linear or circular or elliptical polarization of a propagating wave.
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