Talk:Laser beam profiler

Summarize?

I haven't had a chance to read through this article, but I note that it seems to go into great detail on topics that have their own articles, without linking to them. Obviously links need to be added, but in addition it might be worth moving some of the detailed material into more specific articles such as Beam parameter product, Beam diameter, and Beam divergence, and pruning down the sections on those topics in this article.--Srleffler (talk) 01:24, 25 January 2008 (UTC)

The term "marginal distribution" is used a lot in this article, but I don't see a definition of it.--Srleffler (talk) 06:10, 27 January 2008 (UTC)

Knife Edge Technique - not possible with pulsed lasers

Slight question - I wasn't aware that the knife edge technique wasn't possible with pulsed lasers. What is the reason for this? Presumably if you are using a power meter or something to measure the intensity then unless it has a very sensitive time resolution, presumably it will average over several pulses, and as you measure the intensity at each movement of the knife edge it will be affected the same way.

I know this is a hand wavey argument, but i dont see why it can't work, and in any case it doesn't look like the beam profiling techniques are really referenced properly. In fact i'm going to try it tomorrow. Will report back.

• • slight note on the layout/style of this section - seems to me might be better to describe the two methods of profiling, then put the advantages/disadvantages in a box or table - because the advantages seem to be relative (if not mutually exclusive) - ie the advantage of knife edge is that it can be used for high powered lasers. Disadvantage of CCD is it can't. etc.

--Wideofthemark (talk) 17:27, 22 January 2009 (UTC)

The article presumes a scanning profiler, where the knife edge moves continuously (e.g. on a rotating disk or drum). The knife edge must not move significantly during the laser pulse. It should work if the pulses are very short, much less than the beam width divided by the speed of the knife edge, all divided by the resolution of your profile. --Srleffler (talk) 18:01, 23 January 2009 (UTC)

D4σ or second moment width

According to ISO 11146-3:2004, the beam width is not defined as

$D4\sigma =4\sigma =4{\sqrt {\frac {\int _{-\infty }^{\infty }\int _{-\infty }^{\infty }I(x,y)(x-{\bar {x}})^{2}\,dx\,dy}{\int _{-\infty }^{\infty }\int _{-\infty }^{\infty }I(x,y)\,dx\,dy}}}$.

Instead, the beam width along two directions is given by

$d_{\sigma x}=2{\sqrt {2}}\left(\langle x^{2}\rangle +\langle y^{2}\rangle +\gamma \left(\left(\langle x^{2}\rangle -\langle y^{2}\rangle \right)^{2}+4\langle xy\rangle ^{2}\right)^{1/2}\right)^{1/2}$

and

$d_{\sigma y}=2{\sqrt {2}}\left(\langle x^{2}\rangle +\langle y^{2}\rangle -\gamma \left(\left(\langle x^{2}\rangle -\langle y^{2}\rangle \right)^{2}+4\langle xy\rangle ^{2}\right)^{1/2}\right)^{1/2}$,

which incorporate also information about x-y-correlation $\langle xy\rangle$. For elliptic beams with semi-axes in x- or y-direction, both definitions are the same. A difference exists only for tilted beams (btw., this azimutal-angle is given by $\phi ={\frac {1}{2}}\arctan {\frac {2\langle xy\rangle }{\langle x^{2}\rangle -\langle y^{2}\rangle }}$).

Further necessary definitions:

$\gamma =\operatorname {sgn} \left(\langle x^{2}\rangle -\langle y^{2}\rangle \right)={\frac {\langle x^{2}\rangle -\langle y^{2}\rangle }{|\langle x^{2}\rangle -\langle y^{2}\rangle |}}$

$\langle f(x,y)\rangle ={\frac {1}{P}}\int {I(x,y)f(x,y)dxdy}$

$P=\int {I(x,y)dxdy}$

— Preceding unsigned comment added by Benji0mg (talk • contribs) 09:27, 18 April 2011 (UTC)

This seems like it would be good to add to the article. Since you seem to know a lot about it, why don't you add a new section on this additional definition of "beam width"? Don't replace the existing D4σ material, though, since that definition is also in use.--Srleffler (talk) 03:56, 19 April 2011 (UTC)

SHG as an application - A Mistake

"Therefore, to get efficient frequency conversion, the input beam waist must be as small as possible." This sentence is not true because of the Boyd-Kleinmann integral. A too small focus beam waist leads to a larger divergence of the light and thus a smaller interaction area with the crystal which indeed decreases the conversion efficiency, right? — Preceding unsigned comment added by 93.208.139.241 (talk • contribs) 15:17, 8 August 2021 (UTC)

Yes, "as small as possible" is misleading. I rephrased it.--Srleffler (talk) 19:56, 8 August 2021 (UTC)