Vacuum Ultraviolet Spectroscopy - Rob Morris

A variety of materials have spectral signatures in the vacuum ultraviolet (VUV) region of 10–200 nm. VUV spectroscopy is useful for biomedicine, semiconductor testing and other applications. Because the spectral response of standard silicon charge-coupled device (CCD) detectors drops off rapidly at wavelengths as long as 400 nm, and because oxygen and water absorb in the VUV spectral band, maintaining sufficient signal outside a vacuum is not possible. Nitrogen purging of the spectrometer helps to mitigate water and oxygen absorption in the VUV, but spectrometers with a vacuum purging feature require custom configuration and are too expensive and unwieldy for many common applications.

Testing the Maya2000 Pro Miniature Fibre Optic Spectrometer
The Maya2000 Pro Spectrometer (Figure 1) delivers high quantum efficiency and high dynamic range and is responsive in the deep UV (~185-300 nm). The Extra-Deep UV option extends spectral measurements to 153 nm. The spectrometer features a 101.6-mm focal length optical bench with a compact crossed Czerny-Turner design and a back-thinned CCD detector that offers superior UV and VUV performance. To minimise signal attenuation inside the optical path, the spectrometer bench is purged with nitrogen, achieving a robust signal for VUV experiments at wavelengths as low as 153 nm.

Experimental Conditions
To test performance, a Maya2000 Pro was configured with a high resolution, UVenhanced 2400g/mm holographic diffraction grating and a 5 μm slit. The backthinned detector (Hamamatsu S10420-1106) features a peak quantum efficiency of 75%, with UV quantum efficiencies as high as 50%. A custom magnesium fluoride (MgF2) glass window is placed over the detector for improved transmission over VUV wavelengths. The test sample for the experiment was a VUV deuterium lamp with a VUV-grade optical window, coupled directly to the spectrometer. We enclosed the source and spectrometer and purged the region with standard laboratory-grade nitrogen.