Re: A new method for measuring the refractive index of micrometre-sized particles
- From: "Timo A. Nieminen" <timo@xxxxxxxxxxxxxxxxx>
- Date: Tue, 24 Oct 2006 05:44:50 +1000
On Mon, 23 Oct 2006, Andy Resnick wrote:
Timo A. Nieminen wrote:On Sat, 21 Oct 2006, mmeron@xxxxxxxxxxxxxxxxxx wrote:<snip>
In article <Yqf_g.246681$1i1.101002@attbi_s72>, Sam Wormley <swormley1@xxxxxxxxx> writes:
Microparticles feel the pinch (Oct 20)Timo, is this yours?
http://physicsweb.org/article/news/10/10/13
A new method for measuring the refractive index of micrometre-sized
particles has been developed at AustraliaEUR(TM)s University of
Queensland. The technique involves laser trapping in optical tweezers
and could lead to significant improvements in the study of a wide range
of microparticles including single biological cells, paint pigments and
smog (Phys Rev Lett 97 157402).
Yes indeed. I had this idea, iirc very early this year, that we could do this kind of thing - sometimes our meetings can actually be productive.
Interesting- and congratulations on the paper. How sensitive is the method to deviations in sphericity?
To small deviations, I doubt it's sensitive, unless you're at or very near a whispering gallery resonance. That's without crunching the numbers, but given that the microspheres we used aren't _exactly_ spherical, and it worked, it definitely isn't hypersensitive - for particles that look spherical, it won't be the largest source of error. The first time that we tried the method, we needed to find a (relative) refractive index for lysozyme crystals - the numbers we got from the literature were out by 10x - the perils of needing the difference between two similar numbers! These crystals aren't exactly spherical. In this particular case, because they're low contrast, I think the error in measuring the spring constant via Brownian motion due to the drag coefficient being different from the Stokes result is the biggest error, apart from the error due to measuring the size (which can be dealt with by repeated measurements on different particles, systematic errors aside).
That said, it might be a good idea to actually check the effect of nonsphericity someday, computationally. It wouldn't have fit into the PRL paper, but it could be good thesis filler for a student.
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
.
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- A new method for measuring the refractive index of micrometre-sized particles
- From: Sam Wormley
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- Re: A new method for measuring the refractive index of micrometre-sized particles
- From: Timo A. Nieminen
- Re: A new method for measuring the refractive index of micrometre-sized particles
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