Biophotonics_Concepts_to_Applications

After this wave passes through the optical coupler, the returning waves are

Er¼Er0exp½iðkzrxtފ ð 10 : 2 Þ

from the reference arm and

Es¼Es0exp½iðkzsxtފ ð 10 : 3 Þ

from the sample arm. Here zrand zsare the path lengths from the optical coupler to
the reference mirror and to a specific depth in the sample, respectively. The
monochromatic wave amplitudes Er0from the mirror and Es0from the sample are
quite different, because only a small amount of light returns from the sample,
whereas the mirror reflects most of the light incident on it. The total electricfield
Etotalat the detector in Fig.10.3is given by the sum of the two returning waves as

Etotal¼Er0exp½iðkzrxtފ þEs0exp½iðkzsxtފ ð 10 : 4 Þ

The intensity IDat the detector of the light beams coming from the two arms of
the interferometer is given by the square of the electricfield amplitude

Cornea

(n = 1.376)

Retina

Incoming light

Lens

(n = 1.406)

Aqueous humor

(n = 1.336) Vitreous humor

(n = 1.336)

A-line scan

Retina

Anterior lensPosterior lens

Cornea

Reflectance peaks

Peak locations

Fig. 10.5 Reflectance peaks for an A-line scan of the eye

296 10 Optical Imaging Procedures