Winston cone

In practice, the NEP of a room-temperature THz spectrometer is usually limited by fluctuations (shot-noise) in the ambient blackbody radiation. Usmg an optical bandwidth Av = 3 THz (limited by, for example, a polyethylene/diamond dust window), a field of view (at nomial incidence) 0 = 9 and a detecting diameter (using a so-called Winston cone, which condenses the incident radiation onto the detecting element) laboratory applications, the background-limited NEP of a bolometer is given by... 

The main problem of Far-Infrared ground based interferometers is the atmospheric attenuation at these frequencies. This effect can only be removed if the interferometer is space-based. However, water lines can be useful as a first instrument approach to calibrate the test-bed. Figure3.4 (left) shows the atmospheric attenuation and the Winston cone filtering in the 0-40 cm wavenumber range. 

Fig. 3.4 (Left) Atmospheric transmission (blue line) and cut-oflf wavenumber due to the Winston cone (green line). (Right) Spectra for different spatial baselines with a single slit (1 mm wide) source...

Spectrally, the MAL is a blackbody at 1800 K. The cut-on and cut-off wavenumbers are 5 cm and 33 cm respectively, and are defined by the Winston cone and the filters at the bolometer. All such relevant parameters are set in the SkySparams.xlsx file. In this case, as the testbed is set in a laboratory, the atmospheric transmission has also to be applied. 

Compound parabolic concentrator (CPC, also called Winston collector or Winston cone) [95-97] is a reflective nonimaging light concentrator intended to collect incident light from a spatial angle larger than that of imaging concentrators and to... 

Two parabolas pi, p2 can be seen in the figure, with their respective focal points in Fi, p2, and their axes being tzi, tza- The parabolas are cut at the line of their focal points and then mutually rotated so that the focal point of one of them coincides with the curve of the other parabola and the very edge of the exit opening. A 3D version of this stmcture is obtained as a body of revolution whose sides are parabolic segments satisfying the same condition. Thus a Winston cone is an ofif-axis parabola of revolution. 

The idea of the Fresnel reflector is to divide a curved reflector into segments and to move these segments to a single joint plane [132, 133]. Thus one is able to effectively reduce a 3D object to a thin (quasi-2D) object while keeping the identical optical path to that of the 3D object. For instance, if one starts a 3D body of revolution like, for instance, a parabolic reflective concentrator or a Winston cone, this body can be divided into a number of annular segments which are subsequently placed concentrically on a flat surface. This process is illustrated in Fig. 2.12a, where a curved body is cut into segments and placed on a surface. An incident beam reflects under the same angles as it would from the full 3D body. 

Two variations of the field lens concept are mentioned the immersion lens and the Winston cone. Both are designed to reduce the required detector area and, thereby, improve the signal-to-noise ratio. The immersion lens (Fig. 5.2.5) increases the speed of a condensing optic beyond that of a conventional field lens by coupling the detector directly to a material of a high refractive index. The immersion lens is the analog to the immersion objective of high-power microscopes. Instead of a... 

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