Re: Fields can be nonlinear

[John Gastineau <john@GASTINEAU.ORG>]

> John Gastineau wrote:
> > Any Nd:YAG laser that has a green output has a doubling crystal.
> > Essentially, think of a Taylor series expansion of the response of
> > the crystal to the intense electric field, and include the E^2 term.
>
> In my mind linearity or non-linearity applies to a relation
> between two physical quantities, such as V and I in an electric
> diode.
>
> What do you mean by the "response of the crystal"? In other
> words do x and y stand for in  the Taylor series expansion?

The y would be the electric field radiated by the KDP crystal, and the x the
electric field of the incident laser beam. x is large enough in a laser beam
to reach the non-linear regime.

> Does the term "crystal" refer to the lasing medium or to a
> device which receives IR light from the Nd:YAG laser and
> turns some  of it into visible light?

The Nd:YAG laser emits around 1 micron, in the near IR. The KDP doubling
crystal is a carefully-aligned device (oh-so-carefully, as I recall from grad
school) that is external to the laser. The KDP crystal takes in the 1u light
and emits a mixture of some 1u light (the unconverted, waste laser beam) and
the frequency doubled green light.

You can also add two frequencies to get the sum and difference frequencies.
This is useful in adding a tunable dye laser frequency to a powerful fixed
frequency of a solid or gas laser to get a tunable output in a new frequency
range.

> Ludwik Kowalski