| An acousto-optic tunable filter (AOTF) is electronically tunable spectral bandpass filter, which is based on the principle of acousto-optic interaction in an anisotropic medium. Generally, the AOTF is composed of an anisotropic crystal and an array of piezoelectric transducer, which is bonded onto the anisotropic crystal. The piezoelectric transducer is in conjunction with a RF generator, from which a RF signal is generated and applied to the transducer which, in turn, generates an acoustic wave propagating through the anisotropic crystal. The propagating acoustic wave produce a periodic moving grating, which will diffract incident white light into two orthogonally polarized beams. When a specific radio frequency (RF) is applied to the filter, only a very narrow band of optical frequencies can approximately satisfy the phase matching condition and be diffracted. The wavelength of the diffracted light is selected by tuning of the RF applied to the crystal and can be changed by changing the frequency. The wavelength of the diffracted light can be turned over large optical regions by simple changing the frequency of the applied RF.The electronic tunability of the AOTF provides it with the most compelling advantages such as all-solid-state, compact, no moving parts, fast scanning ability, wide spectral tuning range and high throughout over the more conventional spectroscopic devices that are mechanically tuned to change wavelength. The scanning speed of the AOTF is determined by the speed of the acoustic wave in the crystal, which is on the order of microseconds (μs). In practice, the access time will be longer if limited by electronic switching speed and the settling times of RF generator. Frequency selection may be random access, a sequence of predetermined frequencies, or a linear scan. Not only monochromatic but also polychromatic light can be diffracted from the AOTF when more than one RF signals are simultaneously applied to the AOTF. So, the AOTF can be used as a polychromator, for example, multidimensional fluorimeter. Principles and applications of AOTF are introduced in Chapter 1. In recent years, surface plasmon resonance (SPR) biosensors have been extensively applied to the analysis of biomolecular interactions in real time without labeling. With these sensors, biomolecular interactions are detected via a change in the refractive index or layer thickness at the sensor surface. SPR biosensors have also been applied to determine reaction kinetic and affinity constants for molecular interactions and the active concentration of biomolecules in solution. Most commercial SPR biosensing devices are based on angular modulation. In contrast, the wavelength modulation SPR biosensor is based on the measurement of changes in the resonant wavelength induced by SPR. The latest developments in application of SPR technology with an emphasis on wavelength modulation SPR sensor are reviewed in Chapter 3.The SPR sensors based on angle and wavelength modulation have the approximately the same resolution. Compared to the angle modulation, the wavelength modulation method has more potential for sensor miniaturization and analysis to remote location. A novel AOTF-SPR instrument based on wavelength modulation were designed and installed. The AOTF-SPR sensor is designed on the basis of fixing angle of incidence and measuring the change of resonant wavelength. A halogen tungsten lamp is used as the light source and photomultiplier tube (PMT) is used as detector. The most obvious characteristics is to use AOTF as wavelength selector. The AOTF-SPR setup is described in Chapter 3. In this paper, the AOTF used consists of an anisotropic TeO2 crystal and the piezoelectric transducer is LiNbO3. The piezoelectric transducer is in conjunction with the voltage controlled oscillator (VCO). A direct voltage signal from 0v to 5v is supplied to the VCO of AOTF by digital to analog converter controlled by computer. Then, the signal corresponding to RF is produced and transmitted to the LiNbO3 piezoelectric transducer w...
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