Coupling, into fibres

The SKN18 glass for henzil crystal cored fibre has chromatic dispersion of 0.018 in the 0.532ym to 1.06l+um wavelength range and this is sufficient for the SH to couple into the radiation field. The SH radiation in this case exits from the fibre core at an angle, a, given by... 

All of these factors need to be considered against the cost, the robustness, and the amount of light available to couple into the fibre from the NIR process analyser. 

PDT was performed by a KTP pumped dye laser (Laser Sonic) or a diode laser emitting at 652 nm (Diomed IW). Light was delivered by bare fibres coupled into a modified balloon system (Lajat/Patrice), by a spherical distributor or by a 20 mm long cylinder for interstitial treatment (Medlight Switzerland). The power density varied from 2500 mW s (KTP-dye) to 870 mW s (diode laser). For interstitial... 

Fig. 5.61 Effect of a filter on the effective NA of fight coupled into an optical fibre...

Optical fibres are convenient for sending light from one place to another. Once the light is coupled into one end of a fibre it arrives at the other, regardless of how the fibre is bent or moved. Optical fibres come in three versions - multimode fibres, gradient-index fibres, and single-mode fibres (Fig. 7.21). 

The light from the source, in this case a laser diode, is transferred to the fibre input cross section by a transfer lens system. The first lens is the laser collimator, with a focal length, fl, which is normally a few mm. If the collimated beam is focused into a fibre by a lens of a longer focal length, 12, all aberrations in the laser beam profile are magnified by a factor M = 12 / fl. This requires a fibre of a eorrespondingly large diameter. However, the NA of the beam coupled into the fibre, and eonsequently the pulse dispersion in the fibre, is reduced by the same ratio. 

If a lens of short foeal length is used, e.g. a seeond laser diode collimator, magnification of the aberrations is avoided. Now the laser ean be coupled into a thin fibre. However, the NA is large, and so is the pulse dispersion. An example is shown in Fig. 7.23. Pulses from a 650 nm, 45 ps diode laser were sent through a 1 mm fibre of 2 m length. The pulse shape shown left is for an NA of 0.3, the right pulse shape is for an NA of < 0.1. 

SO as to push apart the adjacent turns in a heterochiral coil (Figure 13.7a) or draw closer together the adjacent turns in a homochiral coil (Figure 13.7b). Further evidence to support coupling between fibre torsion and coil tensile actuation is the near equivalence of work density in both modes 2.1 kj kg torsional work capacity was measured in twisted nylon-6,6 fibre and 2.5 kjkg was measured when the same fibre was formed into a coil and operated in the tensile contraction mode. 

Principles and Characteristics As mentioned already (Section 3.5.2) solid-phase microextraction involves the use of a micro-fibre which is exposed to the analyte(s) for a prespecified time. GC-MS is an ideal detector after SPME extraction/injection for both qualitative and quantitative analysis. For SPME-GC analysis, the fibre is forced into the chromatography capillary injector, where the entire extraction is desorbed. A high linear flow-rate of the carrier gas along the fibre is essential to ensure complete desorption of the analytes. Because no solvent is injected, and the analytes are rapidly desorbed on to the column, minimum detection limits are improved and resolution is maintained. Online coupling of conventional fibre-based SPME coupled with GC is now becoming routine. Automated SPME takes the sample directly from bottle to gas chromatograph. Split/splitless, on-column and PTV injection are compatible with SPME. SPME can also be used very effectively for sample introduction to fast GC systems, provided that a dedicated injector is used for this purpose [69,70],... 

Elastomeric fibres based upon both polyester-urethane and polyether-urethane structures followed. The early work by Bayer led to the use of highly polar solvents such as dimethyl formamide. Formation of fibres by reactive spinning, where the isocyanate-ended polymer is extruded into an aqueous solution of a chain-coupling agent, was described in 1949 [75] and by dry-spinning a solution of the chain-coupled polymer in 1951 [76], However, Bayer did not immediately use their technology to produce commercial fibres [77],... 

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