introduction to photonics lecture 4 optical instruments(1) (1)

8/10/2019 Introduction to Photonics Lecture 4 Optical Instruments(1) (1)

1/35

Introduction to Photonics

Lecture 4: Optical InstrumentsSeptember 15, 2014

Eyes Magnifying glasses Microscopes

Telescopes

Lunar Laser Communications Demonstrationon LADEE spacecraft


2/35

Magnifying Glass

2

What type of lens is this?


3/35

Eyes

Mosaic sensory image; many small field-of-view points like looking through abundle of tubes

Divides and digitizes scene so no real

image on retinal screen Synthesis occurs in nervous system

3

Compound eyeInsects (horsefly, dragonfly, ant),crayfish

Single centered lens systemVertebrates, some mollusks,

some spiders Positive double-lens system Casts real image on light-sensitive

surface (retina)

Why do we not see sell well under water?


4/35

Human Eye

4

Retina contains many light sensitive rods and cones on its surface

Rods are extremely sensitive but cannotdistinguish color

Cones not as sensitive but distinguish color Macula has more cones than rods

Fovea centralis, at center of macula, denselypacked so sharpest image

Eye constantly moving to focus light here

Human vision wavelength range sensitivity:390-780 nm Crystalline lens absorbs UV

Some studies claim: 310-1050 nm


5/35

Blind Spot

5

X 1 2


6/35

Fine Focusing (Accommodation)

=

=+

21

0

11)1(

1

111

R Rn

f

f ss i

6

Mammals vary lens curvature Crystalline lens changes curvature for fine

focusing (accommodation) Muscle contracts and relaxes to vary the

focal length while keeping s i constant

Near point is closest point on which eyecan focus

Fish move lens with respect to retina Mollusks expand/contract entire eye

Birds change curvature of cornea


7/35

Near Point/Far Point

Near point ( d 0 ): closest point on which the eye can focus (~25 cm butvaries with age)

Far point: most distant point that can be brought to a focus on the retinaFor the normal eye the far point is located at infinity, which is everywherebeyond about 5 m.

7


8/35

Vision Problems

8


9/35

9

Eyeglasses

Dioptric powerD

of lens = 1 /f Units 1 m -1 = 1 D (diopter)

Focal length for two thin lenses in contact Power of any thin lens is sum of powers of

its surfaces 21 DDD

D

+=

+=

=

=

=+

21

21

21

0

111

11)1(

11)1(

1

111

f f f

R Rn

R Rn

f

f ss

l

l

i


10/35

Correcting for Nearsightedness

Nearsightedness is corrected by negative (diverging)

lens with a focal length equal to the far-point distance

Virtual image of the object at infinity

2 / 1 / 1 / 1 / 1 / 1 0 +=+= iss f

Short far point

10

Suppose an eye has a far point of 2 m (as opposed to 5 m)

The myopia will be corrected if the spectacle lens images distantobjects in closer than 2 m negative lens to diverge rays

D5.0m2 = = D f

Use lens to cast nearby (between near and far points)images of objects


11/35

Correcting for FarsightednessLong near point

Farsightedness is corrected by positive (converging)lens with a focal length equal to the far-point distance

A converging lens with positive power will effectivelymove a close object out beyond the near point where

the eye works properly

Want that an object at 25 cm (good near point)has its image at 125cm, so can see it normally

D f f

2.331.031.0 / 1)25.1 /(1)25.0 /(1 / 1

+==

=+=

Dm

Example: suppose an eye has a near point of 125 cm(as opposed to 25 cm)

11


12/35

The Magnifying Lens

00 ss

y y M iiT ==

Transverse magnification

Desirable if image is magnified and erect Magnifying lens: the object is less than one

focal length from the lens

The image is virtual and magnified

12


13/35

The Magnifying PowerMagnifying power (angular magnification):ratio of size of retinal image seen through instrumentto size seen by unaided eye at normal distance (near point)

u

a MP

=

f h

h

a

u

/ '

cm25 /

=

f

m MP cm25

=

Largest possible angle

:0d Near point: the closestpoint on which theeye can focus (25 cm)

:a

Aided vision viewing angle

:u Un-aided vision viewing angle

13


14/35

Magnifying Glass

14

What type of lens is this?


15/35


16/35


17/35

Basic ConceptsModern compound microscopes * feature a two-stagemagnifying design built around separate lens systems:the objective and the eyepiece (commonly termed an

ocular ), mounted at opposite ends of a tube, known as thebody tube .

The objective is composed of several lens elements thattogether form a magnified real image (the intermediateimage ) of the specimen being examined.

The intermediate image is further magnified by theeyepiece . The user is able to observe a greatly enlargedvirtual image of the specimen by peering through theeyepieces.

The total magnification of a microscope is determined bymultiplying the individual magnifications of the objectiveand eyepiece.

*This invention isattributed to the Janssenbrothers in theNetherlands and Galileoin Italy, 1600 circa

18


18/35

Microscope II

ob

iT f

sss

M ==

0

Transverse magnification of the objective

Overall instrument magnificationeyob

T f cm

f s

MP M M 25

==

19


19/35

Magnifying power (angular magnification)

ocob

o

u

a f L

f d

MP ==

:0d Near point: the closestpoint on which theeye can focus (25 cm)

: L Tube length

20

Microscope III


20/35

Contemporary Microscope

7: Light source

8: Diaphragm andcondenser * lens

*A condenser is a lens that serves to concentrate light from the illumination source that is in turnfocused through the object and magnified by the objective lens.

2, 3: Objectives

1: Ocular lens (eyepiece)

9: Sample holder stage

4, 5: Focus wheels to movethe stage (fine and coarseadjustments)

21

6: Sample


21/35

A Look Inside

Optical path in a typical (real) microscope

22


22/35

Evolution of Microscopes

23


23/35

Specialized Microscopy Techniques

Darkfield Microscopy

Differential Interference Contrast (DIC) microscopy

Polarized Light Microscopy

Confocal Microscopy

Near-Field Scanning Optical Microscopy

Fluorescence Microscopy

Learn more at: http://micro.magnet.fsu.edu/primer/techniques/index.html

24


24/35

The Telescope

Image of a refractingtelescope from theCincinnati Observatory

in 1848

25


25/35

Types of TelescopesThree primary types of optical telescope:1. Refractors (Dioptrics) which use lenses2. Reflectors (Catoptrics) which use mirrors3. Combined Lens-Mirror Systems (Catadioptrics) which use lenses and mirrors in

combination; (Maksutov telescope and the Schmidt camera)

The basic scheme is that the primary light-gathering element the objective (1)(the convex lens or concave mirror used to gather the incoming light), focusesthat light from the distant object (4) to a focal plane where it forms a real image

(5). This image may be recorded or viewed through an eyepiece (2) which actslike a magnifying glass. The eye (3) then sees an inverted magnified virtual

image (6) of the object.

26


26/35

The Refractive Telescope - Galilean

oc

ob

oc

ob

D D

f f

MP ==

oc f ob f

ob Doc D

Angular magnification

27


27/35

Types of Reflecting Telescopes

28

All use concave paraboloidalprimary mirror to collect light

Planar secondary mirror

Convex ellipsoidalsecondary mirror

Convex hyperboloidalsecondary mirror


28/35

Newtonian Telescope

A replica of Newton's secondreflecting telescope that hepresented to the Royal Society in1672.

First invented by the British scientist Sir Isaac Newton (16431727), using a concave primarymirror and a flat diagonal secondary mirror

Newtonian telescope's simple design makes them very popular with amateur telescope makers.

29


29/35

Reflecting Telescope - Newtonian

The large curved mirror by itself would form an image I, but the small mirrorcreates an image of the image, I. The relationship between I and I is exactly

the same as it would be if I was an actual object rather than an image.

30


30/35

Gregorian Telescope

The Gregorian telescope is a type of reflecting telescope designed by Scottish mathematicianand astronomer James Gregory in the 17th century, and first built in 1673 by Robert Hooke.

The Gregorian telescope consists of two concave mirrors ; the primary mirror (aconcave paraboloid ) collects the light and brings it to a focus before the secondarymirror (a concave ellipsoid ) where it is reflected back through a hole in the centre of

the primary.

Primary mirror

Can be viewedwith the aid of the eyepiece(or camera, detector).

This design of telescope renders an upright image,making it useful for terrestrial observations.

31


31/35

Cassegrain ReflectorThe Cassegrain reflector is a combination of a primary concave mirror and a secondary

convex mirror, often used in optical telescopes and radio antennas.

The classic Cassegrain configuration uses a parabolic reflector as the primarywhile the secondary mirror is convex hyperbolic ( increases effective focal length).

There are lots of specific variations to this geometry,including: SchmidtCassegrain, MaksutovCassegrain,ArgunovCassegrain, KlevtsovCassegrain, etc

32


32/35

Cassegrain in Action

A Cassegrain radio antenna the 70meter dish at JPL's Goldstone antenna

complex. In this case the final focus is infront of the primary mirror.

Cassegrain designs are also utilized in satellite communications earth stationantennas and radio telescopes, ranging in size from 6.3 metres to 70 metres.

The Raisting Satellite Earth Station is thelargest satellite communications facility inGermany (radioastronomy).

33


33/35

Hubble space telescope

http://hubblesite.org/

The Hubble Space Telescope (HST)

34


34/35


Spacecraft: 13 mWeight: 11,600 kgOrbit: 599 km by 591 kmPeriod: 96 minutes

35

2.4m diameter hyperboloidal primary mirror


35/35


Spacecraft: 13 mWeight: 11,600 kgOrbit: 599 km by 591 kmPeriod: 96 minutes

One of Hubble's most famous images, Pillarsof Creation shows stars forming in the EagleNebula

36

introduction to photonics lecture 4 optical instruments(1) (1)

Documents