1. Adam Parry Mark Curtis Sam Meek Santosh Shah
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 M S qI qR
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*( )/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 = /- 0.1

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 sinθ = mλ
Maxima occur at d sinθ = (m + .5) λ

15. Double Slit Diffraction
Mirror
Extension S M

16. Lloyd’s 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. Lloyd’s Mirror D1= 50 cm H1=7.5 cm H2= 13.6 cm = 2.52 cm D1= 45 cm
Condition for Maximum:
Trial 1
Trial 2
D1= 50 cm
H1=7.5 cm
H2= 13.6 cm
= 2.52 cm
D1= 45 cm
H1=6.5 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 S M
reflectors

23. Brewster’s Angle
Angle at which wave incident upon dielectric medium is completely transmitted
Two Cases
Transverse Electric
Transverse Magnetic
Equipment
Setup

24. Transverse Electric Case at
TE Case
S polarization
Electric Field transverse to boundary
Using Maxwell’s Equations (1 = 2 =1)
Transverse Electric Case at
oblique incidence
NO BREWSTER’S ANGLE

25. Transverse Magnetic Case at
TM Case
Electric Field Parallel to Boundary
Using Maxwell’s Equations (1 = 2 =1)
P polarization
Transverse Magnetic Case at
oblique incidence

26. Brewster’s Angle
Plotting reflection and transmission(for reasonable n1 and n2)

27. Brewster’s 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 Brewster’s Angle in our experiment.

28. Bragg Diffraction
Study of Interference patterns of microwave transmissions in a crystal
Two Experiments
Pasco ( d = 0.4 cm, λ = 2.85 cm)
Unilab (d = 4 cm, λ = 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