The ability of obtain relevant information at with high temporal resolution is critical for a large amount of the research conducted in the group. Much of this equipment is relatively specialised, but is also transportable (as opposed to being a build in part of a larger experimental apparatus) from experiment to experiment and can also be used off site if required.
The Doppler shift of light from a moving target can be used to determine the velocity of that surface. We have two different types of interferometry set up, VISAR and Het-V (or PDV), which differ in how they set up the interference fringes. VISAR splits the reflected light and delays one portion by slowing it down through a known length of glass, whereas Het-V compared the Doppler shifted light with un-shifted light, setting up a beat frequency (in our system the unshifted light is obtained from back reflectance at the end of the optical fibre going to the target). We have a single beam and a 3 beam VISAR system as well as a single beam and a dual beam Het-V system.
The group has investigated a number of method for measuring temperature changes on short timescales, and has a number of pieces of equipment either available or in development to make such measurements. A simple 3 channel pyrometer has been used in a couple of projects, as have fast acting thermocouples. A current on-going project is examining the possibility of fabricating temperature gauges from thinly deposited gold films.
Probing the evolution of chemical reaction on short timescales is a difficult task. In order to try and get some information on these events the group has two optical spectrometer setups. The first is a Princeton Instruments gated spectrometer that allows for high resolution visible spectra to be obtained. Owing to the high temporal resolution, the amount of light needed to obtain a suitable signal to noise ratio is quite high. If less light is available then we also have access to a highly image intensified spectrometer which can detect down to the level of single photon emission events. In addition to optical spectrometry we have recently developed a mass spectrometer system that is primarily used to sample gasses evolved during reactions on the dropweight apparatus.
The group has the capacity to operate a number of gauge systems including semiconductor strain gauges (that are normally used on the Hopkinson Bar), Manganin stress gauges and PVDF gauges. We have a variety of amplifiers, power systems and recording oscilloscopes and these allow us to field other types of gauges that might be specific to certain experiments.
High Speed Cameras
We have the capability of taking pictures from a few frames per second to 100 million per second (see Table below). The cameras complement each other, with different cameras being suitable for different applications. Many of the high-speed cameras currently available commercially are derived from cameras developed within the group. In addition, we have two cameras which can take streak photography records, and a single shot X-ray facility.
|Camera type||Make / Model||Speed / Performance|
|Ultra UHSi||Invisible Vision||2x108 s-1 (24 frames)|
|Image converter cameras||Hadland Imacon 790||107 s-1 (18 frames); also capable of streak|
|Hadland Imacon 792||107 s-1 (18 frames)|
|IMCO Ultranac||107 s-1 and streak. Choice of interframe and exposure times for individual frames (up to 24).|
|IMCO Ultra 8||108 s-1. Choice of interframe and exposure times for individual frames (8 frames)|