a) Reference wave b) Amplitude Reduced object amplitude C Phase Retarded object phase Figure 7-2 Effects of amplitude and phase objects on the waveform of light.(a)Reference ray with characteristic amplitude,wavelength,and phase.(b)A pure amplitude object absorbs energy and reduces the amplitude,but does not alter the phase,of an emergent ray.(c)A pure phase object alters velocity and shifts the phase,but not the amplitude,of an emergent ray. ·Change of amplitude 。 Change of phase and/or wavelength Invisible to human eyes eg.bright field,dark field ·Phase change-> ·Visible to human eyes amplitude change eg.polarized light,phase contrast,DIC 4• Change of amplitude and/or wavelength • eg. bright field, dark field • Visible to human eyes • Change of phase • Invisible to human eyes • Phase change -> amplitude change • eg. polarized light, phase contrast, DIC 4