Radiation zero-point

The unique feature in spontaneous Raman spectroscopy (SR) is that field 2 is not an incident field but (at room temperature and at optical frequencies) it is resonantly drawn into action from the zero-point field of the ubiquitous blackbody (bb) radiation. Its active frequency is spontaneously selected (from the infinite colours available in the blackbody) by the resonance with the Raman transition at co - 0I2 r material. The effective bb field mtensity may be obtained from its energy density per unit circular frequency, the... 

Unlike the typical laser source, the zero-point blackbody field is spectrally white , providing all colours, CO2, that seek out all co - CO2 = coj resonances available in a given sample. Thus all possible Raman lines can be seen with a single incident source at tOp Such multiplex capability is now found in the Class II spectroscopies where broadband excitation is obtained either by using modeless lasers, or a femtosecond pulse, which on first principles must be spectrally broad [32]. Another distinction between a coherent laser source and the blackbody radiation is that the zero-point field is spatially isotropic. By perfonuing the simple wavevector algebra for SR, we find that the scattered radiation is isotropic as well. This concept of spatial incoherence will be used to explain a certain stimulated Raman scattering event in a subsequent section. 

Figure 9.50(a) illustrates the ionization process in a UPS experiment. In this type of experiment the incident radiation always has much more energy than is necessary to ionize the molecule M into either the zero-point level or a vibrationally excited level of M. The excess energy is then removed as kinetic energy of the photoelectron. 

Finally, in the quantum approximation the radiation is no longer treated classically (i.e., using Maxwell s equation), and so both radiation and matter are described by quantum methods. For most of the features in the spectra of solids, this approach is not necessary and it will not be invoked. However, this approximation also leads to important aspects, such as zero-point fluctuations, which are relevant in the theory of lasers and Optical Parametic Oscillators (Chapter 3). 

This, as it were, rapidly varying dipole, produced by the zero-point motion, gives rise to an electric field and this polarizes the other atom in which a dipole is induced in phase with the first this interacts with the instantaneous dipole. The zero-point motion is thus, as it were, accompanied by a synchronized electric field but there is no radiation because the atom is in the ground state and the zero-point energy cannot be transformed into radiation. 

Dunitz wrote of these equations Debye s paper, published only a few months after the discovery of X-ray diffraction by crystals, is remarkable for the physical intuition it showed at a time when almost nothing was known about the structure of solids at the atomic level. Ewald described how The temperature displacements of the atoms in a lattice are of the order of magnitude of the atomic distances The result is a factor of exponential form whose exponent contains besides the temperature the order of interference only [h,k,l, hence sin 9/M]. The importance of Debye s work, as stressed by Ewald,was in paving the way for the first immediate experimental proof of the existence of zero-point energy, and therewith of the quantum statistical foundation of Planck s theory of black-body radiation. ... 

There are two ways in which molecular vibrations affect non-linear optical properties. The first, which is well understood, is zero-point-vibrational averaging of the calculated electronic properties. This need not delay us long. The second comes about from the effect that the electromagnetic radiation has on the vibrational motions themselves and this leads to the vibrational polarizabilities and hyperpolarizabilities which are the exact counterparts of the electronic ones which stem from the effect that the radiation has on the electronic motions. This phenomenon is now receiving long overdue attention and will be the main subject of this section. A more extensive review is available elsewhere [2]. 

The observed bands are more than twenty times broader than the bandwidth of the laser radiation (-5-15 cm i). The increased width could be caused by vibrational hot-bands, but these should be largely eliminated in the spectra because the ions are collisionally cooled prior to interaction with the laser pulse. However, the zero-point motion of the central proton on the extremely flat PES likely extends over an unusually large area, leading to the exploration of a much larger part of... 

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