Hi

I think that ethylene material is very good (It's almost transparent to THz). Also teflon based material (thin layer).

regards

If you are referring to the standard band 0.3-3THz from antenna or ZnTe optical rectification sources, polyethylene is a very transparent material and you can find very easily Cuvettes or other biological containers from many resellers (e.g. Sigma-Aldrich).

Marco

Hi Stefania,

What is the size of your sample along with the sample holder size that you typically want? And may I know beam diameter of your THz wave?

Anyways, any plastic is good enough as THz waves easily pass through them. Or if you can get, look for HDPE cases if they are available. I use HDPE lenses to reduce THz beam diameters and they work really well. Hope this helps to some extent.

If you meant plastics then HDPE is typically good for THz. However, the thickness matters. There is a weak (~ 1-2 cm^-1) absorption feature at 2.1 THz, which will become apparent for very thick HDPE substrates. Polystyrene and Teflon are very good as well. But here, your bandwidth begins to matter because Teflon has a strong absorption near 6 THz (see e.g. J. Appl. Phys. 109, 043505-043510 (2011) ). The cyclic olefin copolymer called 'Topas' is very transparent out to 10THz. I would advise against PMMA (acrylic). You can also use fused silica or 'fused quartz', but not typical glasses. GE-124, which is a UV grade fused silica, is very good. Essentially you don't want ions in the glass. Quartz is a bad choice due to phonons.

If you meant solvents, it's best to use non-polar solvents like Hexane. Polar solvents will absorb THz. You may have to test individually the solvents you intent to use to see if there are any molecular vibrations present that would complicate your results.

Standard cell culture dishes are pretty transparent in the THz range. The problem will come from the H20 absorption in your culture media...if you plan to include media in the measurements.

Dear Stefania,

In my experience, we have had very good performance using polypropylene (see for instance http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-17-14-11730; sorry for the self-scitation!)

Another popular material is Topas, at least around 0.3-0.6 THz.

Best regards!

A 'good' sample holder maybe (1) transparent (2) opaque to THz radiation. One of the most transparent materials is crystalline quartz, the next best maybe HDPE but any contamination can add its spectrum to the data. An opaque material maybe anodized aluminium.

"Another popular material is Topas, at least around 0.3-0.6 THz."

Dear Miguel, what exactly is "Topas"?

Dear Jerzy,

According to the information found in research papers (I am not an expert in polymers), it is a cyclic olefin copolymer. Here is an example where the authors use it for low-loss bendable THz fibers: http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-17-10-8592

Regards!

Jerzy - I mentioned "Topas" above. It is a copolymer consisting of a cyclic olefin repeat unit and a polyethylene repeat unit (http://www.topas.com/) The material is resistive to many solvents, which is nice. It has very little THz absorption, which remains featureless, from 0.1 - 10THz (J. Appl. Phys. 109, 043505-043510 (2011)). Others have used it to take THz fibers, similar to polystyrene.

Alokmay - crystalline materials should be avoided due to phonons. Crystalline quartz is also birefringent, meaning the refractive index will not be the same for different polarizations. This means the orientation of your subrstate could potentially effect your results. Take home message: avoid crystalline quartz; use amorphous "fused quartz".

Thank you Paul & thank you Miguel !

Hi, I used THz to study ionic liquids. There, I used a 100 mm quartz cuvette. There are different grades of quartz, and it is important to specify "IR" quartz. It will extend the transmitted THz bandwidth from about 2 THz (normal quartz) towards 3 THz (IR quartz). That is close to the normal THz bandwidth for a usual standard THz setup. See ChemPhysChem12_145_2011. I used two cuvettes, one for containing the liquid, and one empty for reference. I had the best experience with IR-48 from NSG Precision Cells. They have two side tubes. I put the liquid in with a syringe carefully to avoid bubbles. I sealed with two homemade rubber stoppers. For room temperature measuremenst it should be straight forward, but a little more tricky for temperature measurements under vacuum in avoiding bubbles or liquid everywhere, but is doable. Hope this helps. Verner

Also see:

http://www.phluxi.com/P91-2-002.pdf

and:

Optical Materials Express, Vol. 3, Issue 2, pp. 260-269 (2013)

http://dx.doi.org/10.1364/OME.3.000260

Easiest material to get is kitchen wrap, made by polyethylene. It can avoid annoying fringes in spectra, usually seen using solid windows.

for the low end of the THz spectrum (below 2.2 THz I would recommend polyethylene. Polyethylene has a phonon mode at 2.26 THz. Another material to consider is Tsurupica which has a flatter absorption curve throughout the THz range and has the advantages of flat refraction in the THz range and the same refraction in the visible range. The other suggestions such as polystyrene, fused quartz, etc. are what I would consider the next set of solutions due to their higher absorption (and in most cases higher refractive indices). With a sufficiently powerful source and careful consideration of the THz optical properties all the presented solutions are practical.

Dear Stefania,

we use PTFE (Polytetrafluorethylen, "Teflon") as windows of our spectroscopy cell. It works well in the range from 0 - 1.4 THz.

Regards!

Hi,

I used HDPE as well as standard kitchen wrap made out of PE. Both worked fine. Although you need to be a little bit careful with kitchen wrap to avoid crinkles. Beside that Quartz would also be fine as Verner already mentioned. Be carefull with bubbles.

Best,

Andreas

Hello Stefania, the cell cultures is of course very specific sample, therefore it depends what you would like to achieve from your THz measurements, because cells contain high fraction of water. I would recommend to prepare a specially designed holder where your cells can be located between two thin windows transparent for THz radiation, with low refractive index. Hence no Silicon or Quartz windows but as proposed some colleagues above PE, HDPE or PTFE would be most suitable.

If it is a solid material then any metallic sample holder with a fixed iris will do. You have to keep in mind that the hole for transmission should be fixed in space while you need to measure the sample and afterwards the hole as calibration without changing the position of this hole in the transmission setup. You can buy sample holders for room temperature measurements from MicroTech instruments which distribute several THz spectrometers (frequency or time domain). If you plan to measure in a cryostat then I suggest to prepare a home made sample holder as we did in our lab.

If your sample are some sort of liquid solution then you can use a Quartz or Sapphire liquid cuvette (see for example http://www.oxford-instruments.com/products/cryogenic-environments/optical-cryostats-for-spectroscopy/cryostat-system-components/sample-holders-and-sample-rods).

Good luck

The materials for windows recommended in the other responses are good and should work well. Just one word of advice, cell cultures are dominated by water so the data you will get will be similarly dominated by water. Proteins and other macromolecules are relatively transparent compared to water. The absorbance of water can be reduced by freezing the sample though this is not always what you prefer to do. The other feature that is observed when working with cells is light scattering. This has to be considered when interpreting the data.

Sapphire is also birefringent, so I would similarly avoid using sapphire with THz where possible.

Also, keep in mind with any sort of aperture to be mindful of the frequency distribution of a THz beam. High frequencies focus tighter, lower frequencies are (spatially) on the outermost part of the beam (radially from the center). So low frequencies may be 'clipped' (attenuated) by an aperture that is too small.

Similar to Janek's suggestion, there are demountable liquid cells commercially available from Harrick that are good for solution samples if you prefer them to cuvettes. You can circulate the sample using a pump; though this can also be done with flow cell type cuvettes. They do have the advantage of adjustable path lengths, which is accomplished via a spacer between the two windows. As he suggests, depending on your THz system you may use fused silica windows or you may prefer one of the various plastic suggestions: Topas, Polystyrene, HDPE, polypropylene, PTFE, etc. High Resistivity silicon also has very low THz absorption and a "flat" spectral response, but high reflective losses due to the high refractive index. It is also more expensive than the other options.Some of these options (PTFE, HR-Si) are not transparent at optical wavelengths, which you may not prefer.

You may want to look at work by Ted Heilweil, Marcus Walther, etc on applying THz to biological samples for other useful tips that may be more specific to your particular samples and/or application.