Doppler shift frequency

So far, a modulator device has been described, not a filter. This can be used on a monochromatic (for example laser) input beam to vary the Doppler-shifted frequency or direction or intensity of an output beam as a function of input RF frequency and power. In order to understand how an AOTF device goes further than this, it is necessary to look at the effect of Bragg regime diffraction and the impact of the anisotropy of the AOTF crystal medium. 

This technique involves the creation of a two-dimensional image of skin perfusion. It operates by emitting laser light on to the skin tissue, which upon partial absorption and diffuse scattering, is then reflected with doppler shifted frequencies from blood cells and with unshifted frequencies from stationary tissue. It is a popular method, as it is easy to use and non-invasive, however subjects must refrain from smoking for 4 h prior to measurements and no caffeine intake is permitted 1 h prior to measurements.26... 

Fig. 5. Diagrams contributing to the AC Stark-shifts and mixing of the I1S1/2- and 2S i/2-levels of a hydrogen-like atom under the action of two laser waves of the frequency u>l, counter-propagating in the direction nz. As seen by an atom in its rest frame moving with the velocity v = vn relative to the laboratory system, appropriate Doppler-shifted frequencies are determined as 0)1,2 = wl(1 vn-n /c) / 1 — (v/c)2...

High resolution studies by conventional spectroscopy are genuinely hampered by Doppler-broadening of the rotation-vibration lines in the low pressure regime. Individual Doppler-shifted frequencies contribute to the (normalized) Doppler-broadened line shape, due to the distribution of molecular velocities along the direction of observation... 

Figure 5-11 indicates that, for turbulent flow, the energy of the signal is concentrated about the Doppler-shift frequency and therefore closely resembles a single-tone signal. The zero-crossing counting mechanism will work and yield the Doppler frequency that is proportional to flow velocity. 

Laser Doppler anemometry A velocity measurement device using the principle of Doppler shifted frequency of laser Hght by particles moving with the fluid. 

The linewidths of spontaneous and stimulated Raman lines depend on the linewidth of the pump laser. For narrow linewidths, however, the width of the stimulated Raman lines becomes smaller than that of the spontaneous lines, which are Doppler-broadened by the thermal motion of the scattering molecules. A Stokes photon hco, which is scattered into an angle 0 against the incident laser beam by a molecule moving with the velocity v, has a Doppler-shifted frequency... 

In this section, a basic state at rest is assumed alternatively, if a constant mean flow m in the x direction were assumed, the frequency a would be changed to a Doppler-shifted frequency cr — kw as in previous sections. 

The rate of radiation from dipolar emitters moving with high velocities is appreciably reduced compared to the rate of ordinary electric-dipole radiation at Doppler-shifted frequencies. This reduction is due to the magnetization arising in a dipolar emitter moving relative to the detector, which is revealed by a nonrelativistic treatment. Additional corrections to the emission rate are encountered at relativistic velocities. The nature of all these corrections is discussed below. They are then included in the analysis of spontaneous and stimulated emission from relativistic channeled particles (electrons and positrons) in a crystal, as a model example. In this system, the particle propagates relativistically in the... 

Here q is the photon wavevector and e its polarization. The initial photon occupation number n and the matrix element for vacuum excitation (coupling element) determine the emission rate at the Doppler-shifted frequency 0). The imperative question is what is the appropriate coupling element to be used in Eq. (3) ... 

The important point is that the inhomogeneous phase relaxation, which occurs between r = 0 and t = 2T because of the random Doppler-shifted frequencies of atoms with different velocities, does not prevent a complete restoration of the initial phases by the tt-pulse. If the velocity of a single atom does not change within the time 27, the different phase development of each... 

Laser-Doppler velocimetry requires a light signal that oscillates at the Doppler shift frequency. This is usually obtained by subtracting the illuminating wave frequency... 

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