Diode optical

Instrumentation for UV-vis process analysis falls into four categories scanning instruments, diode-array instruments, photometers, and fiber-optic diode-array and CCD instruments. The former two are more typically encountered in at-line or near-line applications, whereas the latter two are better suited to actual on-line analyses. 

The measurements by ultraviolet analyzers can utilize (1) single-beam (2) split-beam (3) dual-beam, single-detector (4) dual-beam, dual-detector (5) flicker photometer (6) photodiode and (7) retroreflector designs. The standard errors of these measurements are 2% FS, whereas it is 1% FS for the fiber-optic diode-array designs. These analyzers can handle process pressures up to 50 barg (750 psig) and temperatures up to 450°C (800°F). 

These methods of obtaining complete ultraviolet-visible spectra can be very time-consuming. However, rapid scanning spectrophotometers based on optical diode array detectors are now eormnereially available and are capable of recording complete spectra in very short time intervals (1 second or less). They can therefore be used to obtain spectra of separated components without stopping eluent flow or to detect at several wavelengths simultaneously. 

Figure 3. Schematic drawing of the experimental set-up for the C02-Iaser heating experiments in a DAC 1=C02 laser, 2 = Si mirror, 3=ZnSe lens, 4=diamond cell, 5=reflecting objective, 6=monochromator, 7 = CCD detector, 8=PC, 9 and 12 = beam splitter, 10 = optical diode, 11 = regulating unit, 13 = ocular, 14=power supply of the CO2 laser. The dashed and dotted line shows the path of the C02-laser beam, the dash lines show the visible light path, and the solid ones depict electrical connections.

Figure 4.11 CW dye Laser with ring-resonator configuration, exhibiting unidirectional beam drculation (using an optical diode device). HR high-reflecting mirrors OC output coupler...

Fig. 5.18a,b. Optical diode consisting of a Faraday rotator, a birefringent crystal, and Brewster windows. Tilting of the polarization vector for the forward (a) and backward (b) directions... 

Fig. 5.78a,b. Two possible resonator designs for cw color-center lasers (a) folded linear resonator with astigmatic compensation and (b) ring resonator with optical diode for enforcing only one direction of the traveling laser wave and tuning elements (birefringent filter and etalon) [5.145]... 

In order to avoid laser waves propagating in both directions through the ring resonator, losses must be higher for one direction than for the other. This can be achieved with an optical diode [5.32]. This diode essentially consists of a birefringent crystal and a Faraday rotator (Fig. 5.18), which turns the bifringent rotation back to the input polarization for the wave incident in one direction but increases the rotation for the other direction. 

External passive resonators may become advantageous when the absorption cell cannot be placed directly inside the active laser resonator. However, there also exist some drawbacks the cavity length has to be changed synchronously with the tunable-laser wavelength in order to keep the external cavity always in resonance. Furthermore, one has to take care to prevent optical feedback from the passive to the active cavity, which would cause a coupling of both cavities with resulting instabilities. This feedback can be avoided by an optical diode (Sect. 5.2.7). 

T.F Johnston Design and performance of broadband optical diode to enforce one direction travelling wave operation of a ring laser. IEEE J. QE-16, 483... 

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