Untitled - IRS

GLOSSAR 263
the Brownian motion these particles move preferentially along the field lines. This directed
movement is measured in the same manner as is the Brownian motion by PCS and from
the mean velocity the charge is obtained when the hydrodynamic diameter is known from
a measurement without electric field. It is worthwhile noting a different view of the PCS
measurement. A particle which moves with v only a few cm s −1 causes a Doppler shift of the
sacttered light of the order of v/c ∼ 10 −10 . The signal of the photon counter can be looked at
as the superposition of the incident and the frequency shifted light, which causes a beating
of the order of νLightv/c ∼ 10 000Hz. Hence PCS could be named high precision Doppler
spectroscopy. (Eq. (1.0)) [p. 13]
Phasenanpassung Phase matching. In a birefringent crystal ordinary and extraordinary beam have
different indices of refraction nO and nA. nA depends on the angle θP between crystal optical
axis and beam direction while nO does not. It is hence possible to match the indices of
refraction of two beams of different wavelengths by tuning θP . Both light waves then travel
with constant phase. Hence, this process is called phase matching. (Eq. (4.36)) [p. 112]
Photon flux density Number of photons per second per unit area. Symbol φ. (Eq. (7.12)) [p. 201]
Piezo receiver Microphone based on the piezoelectric effect. A piezo-crystal generates a voltage
which is linearly proportional to the applied pressure. (Eq. (4.12)) [p. 93]
Polarisierbarkeit, elektrische Polarizability, electric. When an electric field acts on a medium, a net
force acts on the charge carriers in the medium and they try to follow the electric filed lines
and separate into opposite directions. This is called polarization of a medium and after the
charge separation the body carries a polarization. The electric field can be static or periodic
in time. The polarizability quantifies the efficiency of separating charges and depends on
material and on the frequency of the electric field. (Eq. (3.3)) [p. 45]
Power density Energy per second per unit area. Symbol I. (Eq. (7.12)) [p. 201]
Poyntingvektor Poynting vector: � S = c
4π E ×H and | � S |= ɛ0cE 2 . | � S | represents the amount of energy
which crosses per second a unit area normal to the directions of E and H (Eq. (3.5)) [p. 45]
Räumliche Kohärenz Spatial coherence. The term spatial coherence is used to describe partial coherence
arising from the finite size of an incoherent source. Hence, for the equipath position
for the addition of two beams, a coherence interval is defined as the separation of
two points such that the absolute difference in path length is some prechosen value, e.g.
λ/4. (Eq. (2.67)) [p. 36]
Schmalbandigkeit Narrow spectral bandwidth (unit Hz or cm −1 ). Typically GHz for fixed frequency
ns- Lasers, Up to eV for ultra short Pulse Lasers and down to less than 1 Hz for cw
lasers (Eq. (1.0)) [p. 11]
Schwarzkörperstrahlung Blackbody radiation. Continuous electromagnetic radiation spectra of a
body with absorptivity = 1 (ideal absorber/radiator) and defined temperature. Due to the
quantum nature of light emission the b.r. spectra exhibits a maximum at λ = 0.2898 cm K −1
(Wien’s law). (Eq. (2.0)) [p. 15]
Spektrale Breite Spectral width of light. There is no true monochromatic light, but rather it comrises
fractions of different wavelength. The spectral width is the difference between longest