Liquid Nitrogen Immersion Cryostat
I designed this liquid nitrogen immersion cryostat for infrared
spectroscopy of frozen samples, but it has also proven useful for
visible spectroscopy as well. Conventional (non-immersion)
spectroscopy position the sample in an evacuated region, which works
fine for solid phase samples or for liquid samples that can be
completely sealed. However, for liquids that need to be rapidly
frozen, or for sample holders that cannot be sealed (such as for Stark
effect spectroscopy), an immersion cryostat has proven to be a better
The cryostat is described in my paper in the Review of Scientific Instruments,
which can be downloaded from my Publications web page, or in Chapter 2
of my dissertation which is on the Dissertation web page. The
list of parts, some notes, and original drawings are available in this
pdf file: Drawings.pdf.
A few changes have been made added to my design since I had 2 cryostats
made in 2001. Tony Kanchanawong, in the Boxer group, designed a
window assembly for 4 windows, rather than the 2 that I used. I
don't have the machine drawings for it and I don't know if it was ever
built. Also, Janis Technologies will
now make an improved version of this cryostat by special order (contact
Pete Shields) for about $10,800. Here is a diagram of what they
are selling: JanisPict.pdf.
As far as I know, only one of these has been
sold. It is probably somewhat cheaper to make a custom one, and
if campus machine shops are subsidized.
While the cryostat is designed primarily for liquid nitrogen, it has
also been successfully used with liquid oxygen, which is useful
primarily for its different infrared absorption properties.
Following is a transmission spectrum through the cryostat with liquid
nitrogen and liquid oxygen, and no sample. Solid line: empty
dashes: liquid nitrogen filled, short dashes: liquid oxygen
filled. The cryostat windows were broadband anti-reflection
coated, for 5 microns, 2 mm thick Cleartran from Spectral Systems.
Note that it is hard to avoid absorption by water. With effort,
is possible to reduce the size of the water peak, but it always
increases every time the cap is opened, such as for sample
changing. I also designed a liquid helium insert for the cryostat
for 4K and colder research although I never built it. It's
described the downloadable pdf of parts listed above.