Commercial interferometers

As an example of a modern commercial interferometer, the optical diagram of a Bruker IFS 66, is shown in Fig, 3.4-1. It allows working in the optical range from 40000 to 20 cm (250 nm to 500 im), to exchange different internal and external radiation sources and detectors, and to connect various accessories, such as a Raman module or an infrared or Raman microscope. 

For a Michelson interferometer, the rate of change of retardation is twice the mechanical velocity of the mirror. This parameter is often known as the optical velocity, V, and has the units of centimeters (retardation) per second. Some FT-IR vendors specify the velocity of the moving mirror in their interferometer in terms of its mechanical velocity and some in terms of its optical velocity. Note Users should make sure which of these two parameters is in fact specified.) Still others specify the optical velocity in terms of the corresponding modulation frequency of the laser interferogram although a few commercial interferometers no longer use HeNe lasers, we will denote the frequency of the laser interferogram as /neNe-... 

Because of the commercial availability of interferometers that have a repeatability around 1 nm peak-to-valley (P-V) at any pixel location in the detector, the discussion will be limited to the use of interferometric tests but the principles apply to any type of optical test device. Using this 1 nm repeatability as a benchmark, it will be easy to demonstrate where some of the other testing problems occur long before we hit the repeatability benchmark. 

There are few examples of mass produced MMW radars used for either commercial or military applications. An exception is the US Army s Longbow Apache attack helicopter that is equipped with the Northrop Grumman MMW Longbow radar. The Longbow fire control radar incorporates an integrated radar frequency interferometer for passive location... 

Advantages of Fourier transform infrared spectrometers are so great that it is nearly impossible to purchase a dispersive infrared spectrometer. Fourier transform visible and ultraviolet spectrometers are not commercially available, because of the requirement to sample the interferometer at intervals of S = l/(2Av). For visible spectroscopy, Av could be 25 000 cm 1 (corresponding to 400 nm), giving S = 0.2 im and a mirror movement of 0.1 xm between data points. Such fine control over significant ranges of mirror motion is not feasible. 

An interferometer can be used to very accurately measure the thermal expansion of solids. Although not utilized commercially to the level of dilatometry, NIST standard materials, which are in turn used to calibrate dilatometers, have had their expansion characteristics determined using interferometry. In fact, the formal definition of the meter is based on interferometric measurements. The operation of the device is based on the principle of interference of monochromatic light. The fundamental relations between wavelength and distance will first... 

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