Micro Thickness Measurement

Preferable than what?

Presumably you don't want to kill them before measurement?

I don't see how you would use a spectrophotometer to measure thickness. A spectrophotometer measures the transmission of light as a function of wavelength.

This might help:

http://iopscience.iop.org/0957-0233/7/12/006

I would consider simple optics for your measurement. Anything that has to make contact with a wing (micrometer, caliper, etc.) could easily damage a wing. Good luck getting a wing to hold still long enough for a measurement without killing the insect.

Laser measuring systems are capable of making non-contact measurements with this resolution. Keyence is one of many manufacturers of these systems, but they are not cheep

Look here

http://iopscience.iop.org/0957-0233/7/12/006

and here...http://download.springer.com/static/pdf/726/art%253A10.1007%252Fs11340-010-9411-x.pdf?auth66=1406730297_c9f3b090993c3e40ce09cc665ae91b8e&ext=.pdf

Not sure what "measures thickness upto 0.3 micrometer" means????

That's 1.18110236 × 10^-5 or one angstrom.

You'll never get there.

AFAIN laser resolution only goes down to 12.5 angstroms.

??? I make 0.3 micrometer (μm) = 300 nanometre (nm) = 3000 Angstrom

OOPS.

3000 Å is correct. Don't even know how I got the other result.

I hate it when people want me to work when I'm trying to CR4.

Why measure when you can Google?

These guys

http://www.plosone.org/article/authors/info%3Adoi%2F10.1371%2Fjournal.pone.0067893

... say that a dragonfly wing is about 3 µm thick.

The article describes the processes used to determine this. This article is actually sort of an interesting read. Amazing creature, the dragonfly.