Wednesday, May 19, 2010
IR CCD arrays for spectroscopy?
The charge-coupled device, or CCD, was the gadget behind part of this past year's Nobel prize in physics. Far and away, the most common CCDs out there are based on silicon, and these devices are highly efficient from the visible out to the near-infrared, with efficiency really taking a major hit at wavelengths longer than about 1100 nm. One advantage of CCDs is that generally their total efficiency is high: an incident photon stands a good chance of producing some charge on a pixel, and that charge can be collected well, so that getting a "count" on a particular pixel requires only a couple of photons. It turns out that one can also get CCDs based on InGaAs, a semiconductor with a smaller band gap than Si, and therefore sensitive to longer wavelengths, typically from around 950 nm out to 1700 nm or so. I have been thinking about trying to get such a gadget for a few reasons, Raman spectroscopy in particular, and I would welcome reader recommendations. For our application we really would like something with CCD-like sensitivity (as opposed to a linear array of photodiodes, which is considerably cheaper, but requires on the order of 100 photons to produce a single "count"). Feedback would be greatly appreciated. I know that Princeton Instruments sells one gadget (though really for imaging rather than spectroscopy), and Newport appears (from press releases) to offer something with more pixels, though it doesn't show up on their website....
Posted by Douglas Natelson at 8:24 PM