Optical laser sensor

The principle of optical triangulation has been known since the time of the early Greeks, and indeed optical triangulation has been used for hundreds of years in applications such as surveying, camera auto-focus and even smart-bombs. With the advent of low-cost, compact electro-optic components such as lateral-effect photodetectors, diode lasers and micro-optics, laser-based triangulation sensors can now be employed for applications that were, heretofore, considered uninspectable. 

Applications exploiting porous silica to encapsulate sensor molecules, enzymes and many other compounds are developing rapidly. Nowadays, sol-gel technology is being used in various fields of modem technology, as for example the basis for optodes, integrated systems, fiber optics, lasers, and new materials. 

By way of introduction, these two sections are preceded by the lecture of Prof. Townes on the birth of laser and maser and by a retrospective vision of optical chemical sensors of Prof. Wolfbeis. 

It is especially fitting that this Course on Optical Chemical Sensors should be the occasion to recollect the early days of the laser and honor those whose vision and brilliance opened up such a rich and productive area of science. Laser-based chemical sensors serve as valuable research tools while at the same time they have found many practical applications - in this sense, they offer a representative snapshot of the entire field of masers and... 

An NIR biosensor coupled with an NIR fluorescent sandwich immunoassay has been developed. 109 The capture antibody was immobilized on the distal end of an optical fiber sensor. The probe was incubated in the corresponding antigen with consecutive incubation in an NIR-labeled sandwich antibody. The resulting NIR-labeled antibody sandwich was excited with the NIR beam of a laser diode, and a fluorescent signal that was directly proportional to the bound antigen was emitted. The sensitivity of the technique increased with increasing amounts of immobilized receptor. There are several factors involved in the preparation of the sandwich type biosensor. A schematic preparation of the sandwich optical fiber is shown in Figure 7.14. 

T. Okazaki, T. Imasaka, and N. Ishibashi, Optical-fiber sensor based on the second-harmonic emission of a near-infrared semiconductor laser as light source, Anal Chim Acta 209, 327-331 (1988). 

Baer, D. S., M. E. Newfield, N. Gopaul, and R. K. Hanson. 1994. Mnltiplexed diode laser sensor system for simultaneous H2O, O2 and temperatnre measnrements. Optic Letters 19(22) 1900-2. 

Figure 24.8 Experimental schematic of the multiplexed diode-laser sensor system used to measure CO, CO2, CH4, and H2O absorption by sampling hot combustion gases 1 ECDL 1.49-1.58 pm 2 optical isolator 3 — fiber coupler 4 — 1x2 fiber splitter 5 — etalon 6 — InGaAs detector 7 — DEB 1.65 pm 8 — 2 x 1 fiber combiner 9 optical fiber 10 fiber pitch 11 — concave mirror 12 — multipass...

Multiplexed diode laser sensors have also been applied for measurements of gas temperature, velocity, and H2O partial pressures in hypervelocity air flows at the Calspan University of Buffalo Research Center s (CUBRC) Large Energy National Shock Tunnel (LENS Tunnel) in Buffalo, New York [12]. The sensors were developed to provide quantitative characterization of the facility operation and, in particular, the freestream flow properties as a function of time. The measurements were recorded using a hardened probe, which contained critical optical components and photodetectors, that was installed directly into the hypersonic shock-tunnel near the nozzle exit to minimize complications due to boundary layers and facility vibration. 

Tunable diode-laser sensors offer considerable promise for combustion research and development and also for process sensing and control applications. These devices are rugged and relatively easy to operate and they have been demonstrated to yield simple and quantitative measurements of species, temperature, and velocity, where line-of-sight measurements are useful or preferred. These techniques will grow in use as costs of laser sources and fiber-optic components decrease and access to more wavelength regions improves. 

Optical and laser technologies also offer the prospect for improvements in fluorescence and phosphorescence determinations. An important development is the use of fluorescence and phosphorescence with optical fiber sensors. 

Demas et al. described optical oxygen sensors using analogous osmium(II) complexes that have intense red absorptions and that can be excited with low-cost, high-intensity red diode lasers [25]. The osmium(II) complexes are probably more photochemically robust than ruthenium(II) complexes because of the larger energy gap between emitting state and the photochemically destructive upper d-d state. In Table 2, the photochemical and photophysical properties of osmium(II) tris(l,4-diphenyl-l,10-phenanthroline) (Os(dpp)3+) and osmium(II) tris(l,10-phenanthroline) (Os(phen)3+) are indicated as examples of osmium(II) complexes. The luminescence lifetimes of Os(dpp)3+ and Os(phen)3+ are 4.6 and 6.0 ns in dichloromethane solution,... 

Because of expected electrical, electrochemical, optical, chemo-sensor, and other properties of the ball-type Pcs, several metallo and metal-free ball-type Pcs with different linkers have been reported. Metallo and metal free ball-type Pcs containing four calyx[4]arene units as linkers have been synthesized, Fig. 1 [37], The structures of compounds 1-3 were confirmed by UV-vis, IR, 1II-NMR, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and elemental analysis. Because of their unique structure and versatile complexation properties [38], calixarenes were found to be one type of interesting compounds to be incorporated into Pc. The cone conformation of the t-butylcalix[4]arene direct... 

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