Broadband detection

C. Direct Broadband Detection Using Infrared Focal Plane Arrays... 

Figure 5 Transient IR difference spectrum of [Ru(dceb)(bpy)2]+2 in room temperature dichloromethane 35 ps after 532 nm excitation showing the parent CO stretch bleach and red-shifted CO stretch excited state absorption. The data points were obtained by direct broadband detection with a HgCdTe (MCT) 256 x 256 focal plane array system.

McFadden, P. (2002). Broadband detection Holmes on a chip. Science 297 2075-6. 

The low power of THz sources coupled with relatively high thermal background has necessitated highly sensitive detection systems. In this respect, broadband detection based on thermal absorption is commonly used to detect low THz signal. The drawback of these detectors, however, is the fact that they require cooling units, to reduce thermal background. For pulsed THz detection, in THz time domain systems, coherent detectors are required. 

Sensors and detectors include the development and application of techniques and methods for sensing targeted chemicals or for broadband detection of many chemicals in vivo and in the environment. 

Abstract. We present a novel instrument combining femtosecond pump-probe spectroscopy with broadband detection and confocal microscopy. The system has 200-fs temporal resolution and 300-nm spatial resolution. We apply the instrument to map excited state dynamics in thin films of polyfluorene-polymethylethacrylate blends. 

Slow-passage ODMR signals frequently are observed by the continuous wave method in which the optical effect is monitored using broadband detection. On the other hand, if the triplet state decay constants are sufficiently large, the microwave power may be amplitude modulated at an audio frequency which results in modulated phosphorescence when the microwave frequency is at resonance. The phosphorescence is then monitored with narrow-band phase-sensitive detection, for a great improvement in the signal/noise ratio. The latter detection method is frequently used to produce a magnetic resonance-induced phosphorescence spectrum by a technique referred to as phosphorescence-microwave double resonance (PMDR). The microwave frequency is fixed at resonance,... 

The solution to this problem appears to lie in the use of narrow-band optical excitation using dye lasers (Szabo, 1970). Several workers have shown the power of optical-site selection spectroscopy (Eberly et al., 1974 Abram et al, 1974 Dinse et al, 1976,1978). The resulting emission spectrum is often dramatically sharper than that obtained with broad band excitation. Using this method, Dinse et al (1976,1978) have observed sharp ( 1 MHz) zf ODMR transitions of several triplets in different organic glasses. It was also indicated that insofar as ODMR linewidths are concerned, very narrow band selective detection ( 1 cm ) is equivalent to broadband detection combined with selection laser excitation. 

In the case of piezoelectric or PZT sensors, the sensors are usually operated in resonance, i. e. the signals are recorded in a small frequency range due to the frequency characteristics of the sensor to enhance the detection of AE signals. Very damped sensors are operated outside their resonance frequencies allowing a broadband detection, although they are usually less sensitive to wave motions. 

Like broadband analysis, narrowband analysis also monitors the overall energy, but for a user-selected band of frequency components. The ability to select specific groups of frequencies, or narrowbands, increases the usefulness of the data. Using this technique can drastically reduce the manpower required to monitor machine-trains and improve the accuracy of detecting incipient problems. 

Two types of radiation sources are used in IR sensing. Common sources are thermal broadband emitters. The second type are laser sources, mostly semiconductor lasers. The application of (monochromatic) laser sources trades the ability of multi-component detection against higher sensitivity for pre-defined target analytes. Hence, laser sources are primarily suitable for sensitive sensing in well-defined, stable systems, also because spectrally interfering substances can neither be detected as such nor compensated. 

This chapter provides an overview of the basic principles and designs of such sensors. A chemical sensor to detect trace explosives and a broadband fiber optic electric-field sensor are presented as practical examples. The polymers used for the trace explosive sensor are unpoled and have chromophores randomly orientated in the polymer hosts. The electric field sensor uses a poled polymer with chromophores preferentially aligned through electrical poling, and the microring resonator is directly coupled to the core of optical fiber. 

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