Microwave%20Optics

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Microwave Optics

• Adam Parry
• Mark Curtis
• Sam Meek
• Santosh Shah

Acknowledgements Fred, Geoff, Lise and Phil
Junior Lab 2002
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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

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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

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Equipment Used
receiver
transmitter
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Intensity vs. Distance
Shows that the intensity is related to the
inverse square of the distance between the
transmitter and the receiver
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Reflection

• Angle of incidence equals angle of reflection

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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

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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

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Polarization

• Microwaves used are vertically polarized
• Intensity depends on angle of receiver
• Vertical and horizontal slats block parallel
  components of electric field

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Single Slit Interference

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

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Single Slit Diffraction 7cm
Not in the Fraunhofer limit, so actual minima are
a few degrees off from expected minima
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Single Slit Diffraction 13cm
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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) ?

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Double Slit Diffraction
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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.

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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

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Fabry-Perot Interferometer

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

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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

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Michelson Interferometer

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

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Michelson Interferometer
Constructive Interference occurs when
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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

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Brewsters Angle

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

Equipment Setup
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TE Case
S polarization

• Electric Field transverse to boundary
• Using Maxwells Equations (?1 ?2 1)

Transverse Electric Case at oblique incidence
NO BREWSTERS ANGLE
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TM Case

• Electric Field Parallel to Boundary
• Using Maxwells Equations (?1 ?2 1)

P polarization
Transverse Magnetic Case at oblique incidence
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Brewsters Angle

• Plotting reflection and transmission(for
  reasonable n1 and n2)

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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.
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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
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Bragg Diffraction (Pasco)
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Bragg Diffraction(Unilab)

• Maxima Obtained

Maxima Predicted
Wax lenses were used to collimate the beam
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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
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Frustrated Total Internal Reflection
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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

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References

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