Speaker
Description
Polyethylene is a highly transparent material in the terahertz (THz) region (1-200 cm$^{-1}$). This makes it ideal for lenses and windows, especially for cryostats. It is also often used as a binding medium in sample pellets to dilute trace amounts of optically thick samples.
One caveat for this extremely useful material, however, is an absorption at 73 cm$^{-1}$, often overlooked when utilising polyethylene for terahertz optics. This mode was first studied during the 1960’s [1,2] but has sparsely been mentioned in scientific literature since, most recently in 2019, being described as “elusive” [3].
To determine the effects of this absorption on terahertz optics we have quantified the intensity and frequency of this mode from 6-300 K for different sample thicknesses on the THz beamline at the Australaian Synchrotron. We have observed a large redshift of 6.7 cm$^{-1}$ (79.9-73.2 cm$^{-1}$) with heating over this temperature range, as well as significant reductions in the peak intensity. These results indicate that for thin samples (<2 mm) of polyethylene this mode is negligible at room temperature, however, at cryogenic temperatures this mode causes a notable drop in transmission, even for samples as thin as 0.5 mm. This warrants caution, especially when selecting cryostat windows and observing weak features near this mode.
[1] R. V. McKnight et al., “Far-infrared spectrum of polyethylene, and quartz-crystal plates”, J. Opt. Soc. Am., 54(1), 132-133, 1964.
[2] S. Krimm et al., “Assignment of the 71-cm-1 band in polyethylene”, J. Chem. Phys., 42(11), 4059-4060, 1965.
[3] K. Zhou et al., “Transmittance of high-density polyethylene from 0.1 THz to 15 THz”, Proc. SPIE 11196, Infrared, Millimeter-Wave, and Terahertz Technologies VI, 2019.
| Level of Expertise | Student |
|---|---|
| Condition of submission | Yes |
| Students Only - Are you interested in AINSE student funding | Yes |
| Do you wish to take part in the Student Poster Slam | No |
| Pronouns | He/Him |
| Presenter Gender | Man |
| Which facility did you use for your research | Australian Synchrotron |
