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Microwave%20Optics

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In Pasco experiment, alpha(incident angle) was 0. Fabry-Perot Interferometer ... www.mathworld.wolfram.com. www.hyperphysics.phy-astr.gsu.edu/hbase ... – PowerPoint PPT presentation

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Title: Microwave%20Optics


1
Microwave Optics
  • Adam Parry
  • Mark Curtis
  • Sam Meek
  • Santosh Shah

Acknowledgements Fred, Geoff, Lise and Phil
Junior Lab 2002
2
History of Microwave Optics
  • WW2 in England Sir John Randall and Dr. H. A.
    Boot developed magnetron
  • Produced microwaves
  • Used in radar detection
  • Percy Spencer tested the magnetron at Raytheon
  • Noticed that it melted his candy bar
  • Also tested with popcorn
  • Designed metal box to contain
  • microwaves
  • Radar Range
  • First home model - 1295

3
How to Make Microwaves
  • Magnetron
  • Oldest, still used in microwave ovens
  • Accelerates charges in a magnetic field
  • Klystron
  • Smaller and lighter than Magnetron
  • Creates oscillations by bunching electrons
  • Gunn Diode
  • Solid State Microwave Emitter
  • Drives a cavity using negative resistance

4
Equipment Used
receiver
transmitter
5
Intensity vs. Distance
Shows that the intensity is related to the
inverse square of the distance between the
transmitter and the receiver
6
Reflection
  • Angle of incidence equals angle of reflection

7
Measuring Wavelengths of Standing Waves
  • Two methods were used
  • A) Transmitter and probe
  • B) Transmitter and receiver
  • Our data
  • Method A
  • Initial probe pos 46.12cm
  • Traversed 10 antinodes
  • Final probe pos 32.02cm
  • ? 2(46.12-32.02)/10
  • ? 2.82cm
  • Method B
  • Initial T pos 20cm
  • Initial R pos 68.15cm
  • Traversed 10 minima
  • Final R pos 53.7cm
  • ? 2.89cm

8
Refraction Through a Prism
  • Used wax lens to collimate beam
  • No prism max 179o
  • Empty prism max 177o
  • Empty prism absorbs only small amount
  • Prism w/ pellets max 173o
  • Measured angles of prism w/ protractor
  • q1 22 /- 1o
  • q2 28 /- 2o
  • Used these to determine n for pellets
  • n 1.25 /- 0.1

9
(No Transcript)
10
Polarization
  • Microwaves used are vertically polarized
  • Intensity depends on angle of receiver
  • Vertical and horizontal slats block parallel
    components of electric field

11
Single Slit Interference
  • Used 7 cm and 13 cm slit widths
  • This equation assumes that we are near the
    Fraunhofer (far-field) limit

12
Single Slit Diffraction 7cm
Not in the Fraunhofer limit, so actual minima are
a few degrees off from expected minima
13
Single Slit Diffraction 13cm
14
Double Slit Diffraction
  • Diffraction pattern due to the interference of
    waves from
  • a double slit
  • Intensity decreases with distance y
  • Minima occur at d sin? m?
  • Maxima occur at d sin? (m .5) ?

15
Double Slit Diffraction
16
Lloyds Mirror
  • Interferometer One portion of wave travels in
    one path, the other in a different path
  • Reflector reflects part of the wave, the other
    part is transmitted straight through.

17
Lloyds Mirror
Condition for Maximum
Trial 1
Trial 2
  • D1 50 cm
  • H17.5 cm
  • H2 13.6 cm
  • ? 2.52 cm
  • D1 45 cm
  • H16.5 cm
  • H2 12.3 cm
  • ? 2.36 cm

18
Fabry-Perot Interferometer
  • Incident light on a pair of partial reflectors
  • Electromagnetic waves in phase if
  • In Pasco experiment, alpha(incident angle) was 0.

19
Fabry-Perot Interferometer
  • d1 distance between reflectors for max reading
  • d1 31cm
  • d2 distance between reflectors after 10 minima
    traversed
  • d2 45.5cm
  • lambda 2(d2 d1)/10 2.9cm
  • Repeated the process
  • d1 39cm
  • d2 25cm
  • lambda 2.8cm

20
Michelson Interferometer
  • Studies interference between two split beams
    that are brought
  • back together.

21
Michelson Interferometer
Constructive Interference occurs when
22
Michelson Interferometer
  • Split a single wave into two parts
  • Brought back together to create interference
    pattern
  • A,B reflectors
  • C partial reflector
  • Path 1 through C reflects off A back to C
    Receiver
  • Path 2 Reflects off C to B through C
    Receiver
  • Same basic idea as Fabry-Perot
  • X1 A pos for max reading 46.5cm
  • X2 A pos after moving away from PR 10 minima
    32.5cm
  • Same equation for lambda is used
  • Lambda 2.8cm

23
Brewsters Angle
  • Angle at which wave incident upon dielectric
    medium is completely transmitted
  • Two Cases
  • Transverse Electric
  • Transverse Magnetic

Equipment Setup
24
TE Case
S polarization
  • Electric Field transverse to boundary
  • Using Maxwells Equations (?1 ?2 1)

Transverse Electric Case at oblique incidence
NO BREWSTERS ANGLE
25
TM Case
  • Electric Field Parallel to Boundary
  • Using Maxwells Equations (?1 ?2 1)

P polarization
Transverse Magnetic Case at oblique incidence
26
Brewsters Angle
  • Plotting reflection and transmission(for
    reasonable n1 and n2)

27
Brewsters Angle (our results)
Setting the T and R for vertical polarization, we
found the maximum reflection for several
angles of incident. We then did the same for the
horizontal polarization and plotted I vs.
theta We were unable to detect Brewsters Angle
in our experiment.
28
Bragg Diffraction
  • Study of Interference patterns of microwave
    transmissions in a crystal
  • Two Experiments
  • Pasco ( d 0.4 cm, ? 2.85 cm)
  • Unilab (d 4 cm, ? 2.85 cm).

Condition for constructive interference
29
Bragg Diffraction (Pasco)
30
Bragg Diffraction(Unilab)
  • Maxima Obtained

Maxima Predicted
Wax lenses were used to collimate the beam
31
Frustrated Total Internal Reflection
  • Two prisms filled with oil
  • Air in between
  • Study of transmittance with prism separation
  • Presence of second prism disturbs total
    internal reflection.

Transmitter
Detector
32
Frustrated Total Internal Reflection
33
Optical Activity Analogue
  • E-field induces current in springs
  • Current is rotated by the curve of the springs
  • E-field reemitted at a different polarization
  • Red block (right-handed springs) rotates
    polarization 25o
  • Black block (left-handed springs) rotates
    polarization 25o

34
References
  • www.joecartoon.com
  • www.mathworld.wolfram.com
  • www.hyperphysics.phy-astr.gsu.edu/hbase
  • www.pha.jhu.edu/broholm/I30/node5.html
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