Demo #1: Fishtank Optics - MIT OpenCourseWare

Demo #1: Fishtank Optics

02/15/2012

2.71/2.710 Optics

Mechanical Engineering

MIT

Matt Klug

1

Demo #1: Fishtank Optics

Setup:

Fishtank

4 lbs of Sugar (Sucrose)

Air Water

Mirror

Refraction: na sina = nw sinw

Simple Refraction

Waveguiding inside higher index medium

Air Concentration Gradient

Dispersion in Water

Air to Water Water to Air

Air to Water, (a = 45?)

Source: Engel et alA,ppAlppl .Opt. (1998).

Water

a

a

w w

TIR

w w

n a

sin

2

=

n w

sin

w-crit

Critical Angle for Total Internal Reflection w > wcritical then ray reflected, not refracted

w-crit

=

sin -1

n a n w

sin-1 1 1.33

48?

GRadientIndex (GRIN) Medium:

Increasing Time Csucrose(z)

Scaling Analysis:

L = D ; D = 0.6 10-9 m2 / s

if L = 10cm; = L2 = 193 days D

if = 3 days; L = 1.24 cm

This content is excluded from our Creative Commons license. For more information, see .

Color Red Green Violet

[nm] 650 532 405

nwater() 1.331 1.338 1.345

w (deg) 22.06 21.94 21.82

Dispersion not readily observable in demo. Lack precision and beams spread.

Diffusivity of Sucrose in Water

Time for Sucrose to Diffuse to Surface

Extent of Sucrose Diffusion from Bottom

2

Concentration gradient exists only very close to tank bottom!

Vertical Dirqxection, z

Index of Refraction, n

Source: Handbook of Chemistry & Physics, 64. edition, CRC, 1984.

Demo #1: Fishtank Optics

GRadientIndex (GRIN) Medium:

What do we observe?

Light will bend due to local

index gradient, n(z)

z

Surface

n(z) 0

10

Reflection will occur off

GRIN in Quadratic Index Profile

mirrors located on tank floor

20

30

40

Floor

50

25

20

15

10

5

0

x

Horizontal Direction, x

Would a GRIN be helpful in a difficult situation?

n vs. Sucrose Concentration

1.52 1.50 y = 7E06x2 + 0.0014x + 1.3334 1.48 1.46

1.44

1.42

1.40

1.38

1.36 1.34 1.32

0 20 40 60 80 100 Sugar Concentration, (% Mass in Water)

? CRC Press. All rights reserved. This content is excluded from our Creative Commons license. For more information, see .

Image of Dr. Evil removed due to copyright restrictions.

Would Austin avoid impending doombylaser in a GRIN medium?

Better off with high tensile strength dental floss: Laser light would bend the same as the shark's sight. If the shark sees Austin, it can toast him with a "frickin' laser beam".

3

MIT OpenCourseWare

2.71 / 2.710 Optics

Spring 2014 For information about citing these materials or our Terms of Use, visit: .

4

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download