Biophotonics_Concepts_to_Applications

If the negative sign is selected forδ, then the electricfield vector is given by

E¼E 0 ½excosðxtkzÞþeysinðxtkzފ ð 2 : 19 Þ

NowErotates counterclockwise and the wave isleft circularly polarized.

2.3 Quantized Photon Energy and Momentum

The wave theory of light adequately accounts for all phenomena involving the
transmission of light. However, in dealing with the interaction of light and matter,
such as occurs in the emission and absorption of light, one needs to invoke the
quantum theory of light, which indicates that optical radiation has particle as well as
wave properties. The particle nature arises from the observation that light energy is
always emitted or absorbed in discrete (quantized) units calledphotons. The photon
energy depends only on the frequencyν. This frequency, in turn, must be measured
by observing a wave property of light.

Phase difference

Direction

of wave

propagation

between Exand Ey

Ex

x

y

z

zref

Ex

Circle traced

out by E in a

travelling wave

Ex

Ey

Ey

E

E

(t=0)

(t = π/ 2 ω)

π|

2

Fig. 2.7 Addition of two equal-amplitude linearly polarized waves with a relative phase
differenced¼p= 2 þ2mpresults in a right circularly polarized wave

2.2 Polarization 35