Title: Microwave%20Optics
1Microwave Optics
- Adam Parry
- Mark Curtis
- Sam Meek
- Santosh Shah
Acknowledgements Fred, Geoff, Lise and Phil
Junior Lab 2002
2History 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
3How 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
4Equipment Used
receiver
transmitter
5Intensity vs. Distance
Shows that the intensity is related to the
inverse square of the distance between the
transmitter and the receiver
6Reflection
- Angle of incidence equals angle of reflection
7Measuring 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
8Refraction 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)
10Polarization
- Microwaves used are vertically polarized
- Intensity depends on angle of receiver
- Vertical and horizontal slats block parallel
components of electric field
11Single Slit Interference
- Used 7 cm and 13 cm slit widths
-
- This equation assumes that we are near the
Fraunhofer (far-field) limit -
12Single Slit Diffraction 7cm
Not in the Fraunhofer limit, so actual minima are
a few degrees off from expected minima
13Single Slit Diffraction 13cm
14Double 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) ?
15Double Slit Diffraction
16Lloyds 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.
17Lloyds 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
18Fabry-Perot Interferometer
- Incident light on a pair of partial reflectors
- Electromagnetic waves in phase if
- In Pasco experiment, alpha(incident angle) was 0.
19Fabry-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
20Michelson Interferometer
- Studies interference between two split beams
that are brought - back together.
21Michelson Interferometer
Constructive Interference occurs when
22Michelson 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
23Brewsters Angle
- Angle at which wave incident upon dielectric
medium is completely transmitted - Two Cases
- Transverse Electric
- Transverse Magnetic
Equipment Setup
24TE Case
S polarization
- Electric Field transverse to boundary
- Using Maxwells Equations (?1 ?2 1)
Transverse Electric Case at oblique incidence
NO BREWSTERS ANGLE
25TM Case
- Electric Field Parallel to Boundary
- Using Maxwells Equations (?1 ?2 1)
P polarization
Transverse Magnetic Case at oblique incidence
26Brewsters Angle
- Plotting reflection and transmission(for
reasonable n1 and n2)
27Brewsters 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.
28Bragg 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
29Bragg Diffraction (Pasco)
30Bragg Diffraction(Unilab)
Maxima Predicted
Wax lenses were used to collimate the beam
31Frustrated 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
32Frustrated Total Internal Reflection
33Optical 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
34References
- www.joecartoon.com
- www.mathworld.wolfram.com
- www.hyperphysics.phy-astr.gsu.edu/hbase
- www.pha.jhu.edu/broholm/I30/node5.html