Nonlinear optical signals

In the degenerate four wave mixing (DFWM) experiment the third-order susceptibility 3)(-tt>,tt>,-CL>,CL>) with degenerate frequencies can be determined [22]. This nonlinear susceptibility is directly proportional to the nonlinear refractive index n2, which is used to describe optically induced refractive index changes. An advantage of this technique is the possibility to record the temporal shape of the third-order nonlinear optical signal. 

Figure 25. Pictorial representation of the calculation of exciton population and relaxation induced by pulsed laser excitation and the resulting linear and nonlinear optical signals. See text for details.

Simple jellium-model concepts also helped to understand the potential dependence of a nonlinear optical signal from the electrochemical interface - the second harmonic generation [146, 147], and of the frequency of surface plasmon resonance [148, 149]. In both cases, the effect of field-induced adsorption of anions at positive charges of the electrodes was rationalized. An application of the inverted Lang model [107] revealed the... 

For this reaction an organometallic photoinitiator was used that absorbs at 532 nm. Photocrosslinking of the oriented polymer can be used to produce a patterned material that exhibits a stable second-order nonlinear optics signal that lasts for several weeks at 100 °C. Addition of phenol is necessary to prevent thermal crosslinking. 

SSHG measurements have also been performed at ion-selective membrane electrodes (ISE) in presence of the cations Li", and Na dissolved in the aqueous phase and several ionophores like dibenzo-24-crown-8 in a poly(vinyl chloride) (PVC) membrane [49]. In these experiments, the nonlinear optical signal has been observed as a function of the analyte concentration in the aqueous phase and has been ascribed to the oriented cation-ionophore complexes at the aqueous phase/liquid membrane. Langmuir isotherms were built from the data and the results suggested that a saturation of the interface was achieved at high analyte concentration. 

Wu et al. [11] have proposed the use of Kerr lens deflection to separate clearly the fifth-order contribution to the nonlinear optical signal from lower order processes. The principle of this technique is shown in Fig. 4. The sample is placed slightly away from focus to create a small spatial displacement d between the axes of pulse 1 and pulse 2 at the center of the sample. The spatial components of the interacting field amplitudes are [11]... 

Current discussions of potential applications of nonlinear optical signal processing in computers (7), both general and special purpose, and in communications for functions such as switching, amplifying, and multiplexing are primarily focussed on devices for the manipulation of laser beams in thin transparent films. With particular reference to bistable optical devices, the fundamental physical mechanisms which provide limits on speed, power dissipation, and size of optical switching elements have been discussed (8). 

Problem 6.5. An electromagnetic wave hits a metal surface and generates a second-order nonlinear optical signal. What is the typical thickness of the surface layer that contributes to the signal and which physical effect is of the main importance in determining this length scale ... 

Problem 6.5. The second-order nonlinear optical signal from a metal surface is determined by Friedel oscillations, which have a typical wavelength of Ap n/kp with kp the Fermi wavevector. One finds typical wavelengths of the order of 0.5 to 1 nm. 

A valuable handbook describing the many uses of nonlinear optics for spectroscopy. The focus of the book is a unified treatment of and methods for modelling the signal. 

Nonlinear optical properties are of interest due to their potential usefulness for unique optical devices. Some of these applications are frequency-doubling devices, optical signal processing, and optical computers. 

Nonlinear Optical Devices. A transparent, optically active, sol—gel-derived organic—inorganic glass has been synthesized (68). This hybrid consists of a 2,4-dinitroaminophenylpropyl-triethoxysilane covalently bound to a siUcon alkoxide-derived siUca network. This hybrid exhibits a strong electric field-induced second harmonic signal and showed no signs of crystallization. 

Small probed regions down to 1-2 pm are possible using microscope lenses. Lasers can supply as much pump power as needed to compensate for weaker signals, but a limit is reached when sample heating or nonlinear optically induced processes become significant. 

The complex amplitude of the signal field at the output of the crystal is amplified by a factor g with respect to the input field, g is always larger than one so that there is always coherent amplification of the signal field one speaks of parametric amplification. Nonlinear optics provides an amplification different from the amplification occurring in a medium which present population inversion. For a t)q)ical value of the nonlinear coefficient of 1 pm/V, a pump of... 

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