Question

block? ght to illuminate structures 20.14 A diagnostic device uses a bright red laser light to illuminatest just under the surface of the skin. Light from the laser passes first through the air. and then the skin, to scatter off the sub- Fi cutaneous structures that are to be im- aged. The scattered light passes back pl through the skin and into an optical de- vice which forms an image of the scat- tered light on a CCD array. The laser light 3: used has a wavelength of 633.0 nm in a sh vacuum. The refractive indices of air, the th glass used in the imaging optics, and skin le are 1.008, 1.700, and 1.381 respectively. m (Use c = 2.998 x 108 m s-l for this ques. CD tion.) (a) What is the frequency the frequency of the red (a light when it passes through each (L material? (b) What is the way he wavelength of the red

Answer 1

given
lamda = 633.0 nm = 633.0*10^-9 m
n_air = 1.008
n_glass = 1.700
n_skin = 1.381
c = 2.998*10^8 m/s

a) frequency of the light, f = c/lamda

= 2.998*10^8/(633.0*10^-9)

= 4.736*10^14 Hz

frequency is remains same in all the materials.

b) wavelength of the light in air,

lamda_air = lamda/n_air

= 633.0/1.008

= 628.0 nm

lamda_glass = lamda/n_glass

= 633.0/1.700

= 372.4 nm

lamda_skin = lamda/n_skin

= 633.0/1.381

= 458.4 nm

c) speed of light in air,

v_air = c/n_air

= 2.998*10^8/1.008

= 2.974*10^8 m/s

v_glass = c/n_glass

= 2.998*10^8/1.7

= 1.764*10^8 m/s

v_skin = c/n_skin

= 2.998*10^8/1.381

= 2.171*10^8 m/s