Farha Islam - Research Journal
----------------------------------------------------------------------------
February 19th, 2009 - Laser Diffraction and CD track spacing
DIAGRAM HERE
*This setup shows infringing of laser (basically the superimposing of
out of phase and in-phase wave fronts)
*A similar setup was used by Michelson and Morley to prove that
nonexistence of "luminiferous aether"
*If a glass (eyeglass lens) is held in front of the laser beam, the
wave infringing becomes spherical.
*Gas is less dense if heated and index is closer to 1. If a heated rod
is held close to the laser infringing is not bad. But if the heated
rod is held a little lower, the heated air rises and causes turbulence
and there is extreme infringement.
(Side Note- Beam Splitter looks like a "prism" but it's actually two
triangles or a cube cut in its side diagonal (not major diagonal) and
the two triangles placed with minor gap in between. Splitter splits
beam into horizontal and vertical)
*Hugghens - experimented and concluded that when light passes through
slits, it comes back and the interference is visible.
*Young's Experiment:
1) DIAGRAM HERE (page 8 diagrams) constructive interference when the bright spots formed without any "splitting"
2) DIAGRAM HERE (page 8 diagrams) - for first order
3)DIAGRAM HERE (page 8 diagrams) - for second order
*Young's Experiment (Continued)
Constructive Interference - whole l difference
Destructive Interference - Fraction l difference
DIAGRAM 1 HERE (page 9 diagrams) d= slit/gap distance
DIAGRAM 2 HERE (page 9 diagrams) Dd = n l Young's Formula
n l = sinf = Dd nl = dsinf ~ df
d d
*Don't need n b/c n= # of slit spots*
(Copy the rest by hand!!!)
----------------------------------------------------------------------------
February 17th, 2009 - ??
A. We did a mini-experiment about mirrors - relating mirror length to
its properties and images.
Full length mirror - even if the height of the mirror isn't equal to
viewer's height- can be used to see the entire image of the viewer's
body. To prove this we followed the simple protocol below:
1. Stare straight to see your eyes.
2. Look down to see your toes or a full body reflection
1. Increase distance between viewer and mirror
2. Repeat and see if you can still see your toes or a full body reflection
Thus, as long as mirror is half the viewer's height, head to toe will be visible in the image.
A viewer can stand far from a mirror and see his/her full body. If he/she approaches mirror - which must be half the viewer's height- viewer can still see
fully body length by looking up and down.
B. Refraction - light moves from one medium to another
Snell's Law and Fermat's Principle are crucial for understanding refraction.
DIAGRAM HERE
C. Fermat's Principle - light will go from medium "a" to "b" in the shortest possible time.
Analogy of crossing a river
DIAGRAM HERE
D. Using lens to burn initials into paper
A. 1ft distance from a 60 watt light bulb. A photo-detector measured 0.5mAmp
B. The photo-detector measured sunlight to give 3.6mAmp
C. The dimension of the photo-detector used is 3.6mm (length) *it's a square photo-detector*
*Luminous flux contributes to the rate at which a given lens can gather and focus energy. Luminous flux is dependent on the area on which light is
gathered. Hence, a big lens gathers and focuses light over larger area, thus a higher luminous flux and faster rate of gathering and focusing energy.
E. What is Light
a. Light is electromagnetic field. Energy propagating through space.
b. Light Ray- is obstruction- a ling showing direction of light in space
c. Light is a wave but light ray shows direction of light waves.
d. Polarized Light - the electric and magnetic fields point in the same direction
e. Light Rays are approximation of the way light behaves or points
Electromagnetic field and Magnetic Field
a. Electromagnetic Field
i. Generated by charge that's accelerating in orbitals or moving in general
ii. Can have dipoles
iii. Denoted by E
Magnetic field
i. Can't have monopole
ii. Doesn't have any point of source
iii. Denoted by B
Electric Field and Magnetic Field are perpendicular to each other in an x, y, z axis.
G. Light and its properties:
*Photo is presented only when light is emitted or absorbed.
E=hf=hC/l and lf= C/n where n is the index
*Speed of light varies based of index of material in which light travels
*Relation between speeds of light in the material corresponding to the index
Glass: n = 3/2 v= 2/3 C
Water: n = 4/3 v= 3/4 C
Air: n = 0.999 v= C
*Charges traveling on a straight line (aka wire) generate electromagnetic waves.
H. Polarized Light
a. Polarized light is the electric and magnetic fields point in the same direction
b. When un-polarized light is shined on Polarizer, Polarizer picks light electric field that has same direction or slot as the polarizer.
c. Polarizer refers to how electric field is going
d. Sound and water are transverse or scalar waves -waves that do not point at a particular direction
e. Light- unlike sound and water DOES point at a direction
Carolina's project will be about - How to focus light small enough to recall data of a CD?
----------------------------------------------------------------------------
February 12th, 2009 - CD player and Blu-Ray Discs
A. Disk Player:
Disk player has a laser and lens, though we think lenses focus light to a point, it actually focuses to a minimum diameter- not a point.
This minimum diameter is called a waist.
When focal length matches the track of a CD, the CD is "read"
CD must be placed at the waist of the beam- the concentrated spot of light. If CD isn't placed at the waist, all the light would spread out in all direction.
(Objects can be burned using magnifying glass because objects are placed in short focal point and magnifying glass has large diameter, hence more light
gathers over an area and more light is focused)
B. Retroreflectors:
Light shined to an object will go back to the source.
Eye is retroreflector. [When photos are taken with flash, tepetum reflects light]
This was proven in an experiment using crystal ball.
C. Types of Lasers:
Red laser - 632 nanometer
Purple laser - 404 nanometer
Argon (Blue) Laser - 488 nanometer
The wavelength of semiconductor lasers is determined by the material: Arsenide (causes Red Laser) and Nitrite (Causes Blue Laser)
D. Frequency Doublers
A device that produces an output signals frequency that is twice the frequency of the input signal.
E. Gravitational Laser was mentioned. So I will have to look up information about this type of laser. Sounded pretty cool so it should be interesting to
learn about.
----------------------------------------------------------------------------
February 5th, 2009 - Feedback systems
Feedback systems regulate and equilibrate to maintain certain value of
an instrument.
Feedback in computer:
1. If A>B - make A smaller
2. If A<B - make B bigger
3. If A=B - do nothing
Similar programming in thermostats, cruise control, laser temperature.
For thermostats A and B are high and low temperatures.
For cruise control A and B are the max and min speeds.
For laser temperature A and B are max and min lengths or expansion of laser tube.
Feedback in Thermostat:
1. TemperatureHouse > TemperatureThermostat - Do nothing
2. TemperatureHouse < TemperatureThermostat - Turn on heat
You can set Temperature of the house and vary it for seasons
Feedback of laser heating - a feedback system regulates how much a
laser is heated based on the expansion of laser's tube due to heating.
----------------------------------------------------------------------------
February 3rd, 2009 - Schrodinger Uncertainty talk- Dr. Marburger
I attended a talk but understood very little. However, the speaker
mentioned the play "Copenhagen" by M. Frayn - which I want to look
into.
I also looked into possible topics:
1. Why does a zoetrope form a sequence of images?
2. Why does zinc oxide LEDs provide less expensive and efficient light?
3. How does a lateral inhibition influence visual distinction?
4. Why do gender neutral images give opposite gender after image?
5. (Jan '05) How are lasers used in breath markers?
6. (April '06- page 13) How can magnification be established without lenses?
7. (April '07- page 25) What and how are lasers used in forensics?
8. (April '07- page 25) How are 3-D images created?
----------------------------------------------------------------------------
January 29th, 2009 - Introduction to Laser Teaching Center
Today Dr. No� showed me and Carolina (my WISE rotation partner) around
the lab. We learned about his system of teaching us new concepts via
colloquy.
For starter we talked about previous projects (Microbank,
Mirage ...). Then we talked about reflecting telescopes that uses a parabolic
mirror rather than a spherical mirror.
Today was the first day in the lab and I learned about parabolic and
spherical mirrors. The way in which parabolic mirrors reflect is that
light hits the mirror and all of it reflects to a same point. This
parabolic shape of the sphere plays an important role on the Mirage
toy. The rest of the conversation was more about mirrors: rotating
liquid mirror, telescope parts and mirrors.
Forms of parabolic mirrors can include rotating liquid mirror.
http://www.zemax.com/kb/content_images/customers/tocci2/tocci1.gif
Also note: always send emails as .txt files !!