Collimating optics

Optical communication may give the design power efficiency that we would not otherwise be able to obtain. Optical transmission provides extremely high antenna gain and the received power only decays as the inverse of the distance squared [War 01, War 05], Optical systems can be made extremely tiny. Finally, it is very difficult to eavesdrop on collimated optical communication, which is a significant advantage for security and defense applications [War 05],... 

The fiber optic AOTF spectrometer is divided into several subsystems - collection optics, optical fiber, collimating optics, AOTF, detector system, driving electronics, and data acquisition. 

Collimating Optics Collimating optics is used to reduce the size of the beam inside the AOTF so that the diffraction efficiency of AOTF can be higher and the size of AOTF can be smaller. 

The collimated optics of the set-up demonstrated can be substituted by fibre cities. This type of equipment is shown in Fig. 4.11 using a bifurcated fibre and a diode array. Under these conditions white light has to be used to produce a reflection spectrum monitored by the diode array. However, white light causes undefined photochemical conditions. For this reason a third fibre arm is used, which guides monochromatic radiation to the sample. If the white radiation is blocked by a shutter, it may not disturb the monochromatic photoirradiation. Since modem diode arrays take spectra within a few milliseconds the time of measurement stays short compared to the total photochemical process time. This type of equipment can be used to monitor the photoprocess during irradiation of photoresists [101]. 

The fiber coupling problem is further exacerbated in applications where an optical isolator, which will be discussed in more detail in the next section, must be inserted between the laser and the fiber. Isolators are typically most effective for collimated light, which means that circularizing and collimating optics need to be placed between the laser and the isolator. Even with all this paraphernalia, it is stUl possible to achieve fiber-coupled slope efficiencies of 0.2 W/A. 

The major advantage of the d/0° system compared to the 07d is in radio-metric system efficiency. In Fig. 2, the amount of light that is collected from the lamp is a function of the /-number // ) of the collimating optics. Those familiar with photography understand that f/ expresses the light gathering power of a camera lens. Lower values off/ are required for slower speed film. 

To achieve a much higher spectral resolution two Fabry-Perot etalons can be rotated into the collimated optical path between the fore-optic and the grating. 

C27 is an visible YSO with a collimated optical jet and a luminosity of 400-500 Lq. Figure 2 shows a spectrum of the CO 2-0 bandhead in... 

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