Ultraviolet (UV) spectral region spans 100-400 nm wavelength range. It comprises four sub-ranges UV-A, UV-B, UV-C and VUV (where the first “V” stands for vacuum) as shown in figure below. The energy of photons is inversely proportional to their wavelength; therefore, V-UV photons are the most energetic ones in the UV spectrum.

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Photons characterized by wavelengths of ~200 nm and below carry sufficient energy to break oxygen molecules and stimulate generation of ozone (O3). As a result, air (contains 21% of oxygen by mole fraction) efficiently absorbs wavelengths below 200 nm. In the past, vacuum was typically used as a medium for propagating such short wavelengths. For this reason, the 100-200 nm wavelength range is called Vacuum UV (VUV). However, in addition to vacuum, a number of gases, including nitrogen and all noble gases (He, Ne, Ar, Kr, Xe), transmit VUV photons up to, at least, 160 nm. The ability of nitrogen gas, in particular (nitrogen is cheap and versatile), to transmit VUV radiation allows for simple and cost-efficient solutions for…

Having devices and processing chambers operating at atmospheric pressures is extremely beneficial for research, manufacturing, and educational purposes. Such systems do not require expensive and bulky vacuum equipment and may be installed in basic laboratories and even office spaces. In the previous section it has been mentioned that nitrogen gas is one of the best media for transmitting VUV radiation. Pressurized nitrogen may be used to displace air from a relatively large volume of interest. For example, a properly designed nitrogen purging system, having a flow rate of ~10 liters/minute, is capable of displacing air volume of 10 cm x 10 cm x 10 cm (1 liter) in under 40 seconds. After the air is displaced, the flow rate may be reduced to significantly lower flow rates.