|
In this paper, a new method of calculating the diffraction efficiency for diffraction / refraction infrared hybrid system is
given. By using this method, an automatic measurement system is designed. This system covers the wavelength range of
1~3 μm, 3~5μm and 8~12μm. We use a blackbody as the energy source, put the lens which is to be measured above
a computer controlled turntable in order to gain different results in different filed of view. We also have several relay
lenses to cope with long or negative focal length. We use two types of detectors to deal with wavelength range of
1~3μm and 3~12μm .Both the detector and preamplifier are assembled together so we can easily change them for
different wavelength ranges. To improve the accuracy of the measurements, a new theory of measuring the main energy
is developed to minimize the negative impacts of other diffraction orders and the environment. We use an adjustable slit
cooperating with a two-axis stage to scan the focal point and by adjusting the width of the slit we can reduce the energy
of other diffraction orders and the environment that may come into our detector. During the experiment process we can
manually control the slit and two-axis stage to improve the efficiency and use our computer program to improve the
accuracy. The energy modulator and lock-in amplifier also help to improve the accuracy of our system. We designed two
standard lenses for the 3~5μm wavelength range. Both of them are made of the same material, have the same focal
length of 200mm and their shape is almost the same. The only difference between them is that one of them is pure
refraction piece which acts as a reference and the other one has a diffraction surface to achromatic aberration. The result
fits our theory well and the possible causes of the differences are discussed. This system has a practical meaning in the
quality evaluating of infrared hybrid system.
|
