Wave frequency, light

The capillary wave frequency is detected by an optical heterodyne technique. The laser beam, quasi-elastically scattered by the capillary wave at the liquid-liquid interface, is accompanied by a Doppler shift. The scattered beam is optically mixed with the diffracted beam from the diffraction grating to generate an optical beat in the mixed light. The beat frequency obtained here is the same as the Doppler shift, i.e., the capillary wave frequency. By selecting the order of the mixed diffracted beam, we can change the wavelength of the observed capillary wave according to Eq. (11). 

For example, the light emitted by a faint source may be chopped by means of a chopper producing a square wave-shaped light signal on an optical detector (see Fig. 10.8). Other spurious optical signals which are not modulated at the frequency of the chopper, as we... 

The motion of atoms in the lattice can be depicted as a wave propagation (phonon). By dispersion we mean the variation in the wave frequency as reciprocal space is traversed. The propagation of sound waves is similar to the translation of all atoms of the unit cell in the same direction hence the set of translational modes is commonly defined as an acoustic branch. The remaining vibrational modes are defined as optical branches, because they are capable of interaction with light (see McMillan, 1985, and Tossell and Vaughan, 1992, for more exhaustive explanations). 

The following relationship exists between the wave frequency, v, and wavelength, X frequency times wavelength = velocity. Velocity refers to the speed of electromagnetic radiation waves in a vacuum. It is a constant (2.998 x 10 m/s), sometimes called the speed of light, c. 

In real fluids, low-frequency light-scattering reveals a central Rayleigh peak, due to heat diffusion, and two symmetrically displaced Brillouin peaks, due to sound waves, such that... 

As we have seen, the energy of a photon is proportional to its wave frequency nf which is obtained by dividing the velocity of light C, by the wave length /. 

Heterodyne detection detects radiation (radio waves or light) of angular frequency cos and amplitude Escos(a)st + [Pg.644]

Fig. 5. Typical power spectrum of the optically mixed light intensity. O/W, ripplon (capillary wave) frequency at nitrobenzene-water interface W/A, ripplon frequency at water-air interface. (Reprinted from [76] with permission. Copyright The Japan Society of Analytical Chemistry).

Figure 9.1 Energy, frequency, wavelength and wavenumber ranges of electromagnetic waves. Frequency range of molecular vibrations is in infrared region close to visible light. (Reproduced from A. Fadini and F-M. Schnepel, Vibrational Spectroscopy Methods and Applications, Elbs Horwood, Chichester, 1989.)...

In addition to behaving as a wave, visible light (and other types of electromagnetic radiation) exhibits the properties of particles such as mass and acceleration (Einstein s observation that energy has mass, or E = me2, applies to the photon.) When light interacts with matter, it does so in discrete packets of energy called photons. The energy e of a photon is proportional to the frequency of the radiation. 

The number of waves of light that pass a point in one second is its frequency, v (nu). If the wavelength is long, the frequency is low. If the wavelength is short, the frequency is high. 

---