
                       LABS FOR THE CLASS ROOM LASER

DEMOS:   The tyndall effect.
                       Darken the room and show the scattering of the beam
                              with chalk dust.
                        It s neat, too, to shoot the beam through the water
                              in a aquarium.  Splash it up a bit for bubbles.  
                         Change the angles of incidence to show refraction
                               and total reflection.
                

                                  LASER LAB

Beam Divergence


Topic:

     Beam divergence and convergence by lenses.


Purpose:

     To measure the effects of the laser's narrow beam on the optics 
of converging and diverging lenses.


Procedure:

     Use the -4mm and the +80mm lenses separated by 8cm to produce 
a collimated beam.  Check it with a piece of graph paper.

     Direct this collimated beam at a +15mm lens and move a piece of 
graph paper back and forth to find the principal focus, where the ray 
is converging, and where the ray is diverging.

     Diagram the path of a ray as it passes through a converging lens 
and a diverging lens.


Observations & Diagrams:


Conclusions:

------------------------------------------------------------
                        LASER LAB
                     Beam Intensity


Topic:

     Beam Intensity.

Purpose:

     To note how the intensity of the laser beam varies with distance.


Procedure:

     Hold a piece of glossy white paper close in front of
          the beam and note its intensity.

     Then move the paper away by one meter increments as far as you 
can, continuing to note the changes in in- tensity.


Observations:



Conclusions:

------------------------------------------------------------

                                 LASER LAB
   Topic:

     Color


Purpose:

     To determine the transmission of laser light through different 
colored filters.


Procedure:

     Send a beam of white light through a prism and note the 
spectrum.

     Send the laser beam through the prism and note the results.

     Now send the laser beam through different color filters and note 
the results.

Observations:


Conclusions:

------------------------------------------------------------

                             LASER LAB
                            Diffraction

Topic:

     Diffraction gratings.

Purpose:

     To investigate the patterns and detail of three diffraction 
gratings and calculate the distance of separation of the slits.

Procedure:

     Aim the beam at a screen 3 meters away.

     Use the 25 lines/mm grating, and observe the pattern.

     Then use the 50 lines/mm grating and observe

     Try the 100 lines/mm grating and observe.

     Compare the fine detail of the bright fringes with those of the 
double slit experiment.

     Compare the detail of the different gratings.

     Calculate the distance between slits by placing the screen 5 
meters from the laser and using the
formula,  l = d sin 0  where l is the wavelength of light (6.328 X 10-
7meter), d is distance between the slits, and sin 0 is the distance 
between two adjacent fringes divided by the dist. between the 
grating and the screen.

Observations:



Calculations:


Conclusions:
-----------------------------------------------------------

                                     LASER LAB
                                    Divergence


Topic:

     Divergence of a laser beam.


Purpose:

     To measure the spread-out of a laser beam.


Procedure:

     Measure the diameter of the beam's spot on a white card at one 
meter intervals to as far as possible. Outside, send the beam along 
close to the ground in the direction of the sun with a cardboard sun 
shield.

     Make a graph plotting the beam diameter versus distance and 
draw a straight line through the points.

     Calculate the angular divergence of the beam by dividing the 
change in beam diameter by the distance from the laser.  The 
quotient will be the angle measured in radians.  Multiply this value 
by 1000 to obtain the beam divergence angle in units of milliradians.



Observations:



Conclusions:

----------------------------------------------------------

                                    LASER LAB
                                   Double Slit


Topic:

     Double slit diffraction.

Purpose:

     To produce and observe the diffraction patterns of a double slit 
on the laser beam.

Procedure:

     Use the double slit slide to produce a diffraction pattern on a 
screen 1 meter away.

     Notice the difference between this pattern and that produced by a 
single slit. (Several interference fringes within the diffraction 
maxima).

     Try again with other slits on the slide.

     Sketch the diffraction pattern and the interference fringes.

     Using the formula  l = d sin 0, calculate the exact distance, d, 
between each slit on the slide.  l for the laser is 632 X 10-9 m,  sin 
0 is the distance between two adjacent interference fringes on the 
screen divided by the distance between the diffraction slide and the 
screen.

     Tell how this formula might be used to measure the distance to 
stars.

Observations:


Calculations:


Conclusions:
------------------------------------------------------------

                                       LASER LAB
                                    Filter Opticks


Topic:

     Fiber Optics and Light Pipes.


Purpose:

     To investigate the total reflection inside a trans- parent light 
conductor.


Procedure:

     Aim the laser beam into a lucite curved rod at various angles and 
observe the conduction of light around the bends and through the rod.

     Place a mirror at a 45o angle in the bottom of a large can with a 
5mm hole drilled in its bottom side. Fill the can with water and 
direct the laser beam down through the water at the mirror so that 
it reflects out through the hole as water pours our. Note the 
conductivity of the light through the stream of water.



Observations:


Conclusions:

---------------------------------------------------------

                                       LASER LAB
                                       Filtering



Topic:

     Special filtering.


Purpose:

     To remove the mottled appearance of the enlarged laser beam 
which is caused by specks of dust and minor irregularities in the 
laser optics.  These cause diffraction patterns that appear in the 
laser output as unwanted "noise".

Procedure:

     Mount a +15mm lens and a 100um pinhole in the laser beam.

     Place the pinhole about 15mm from the lens (at the focal point).

     Adjust it to give a clean beam.




Observations:


Conclusions:

------------------------------------------------------------

                                     LASER LAB
                                       Glass


Topic:

     The index of refraction of glass.


Purpose:

     To measure the index of refraction of glass.


Procedure:

     Tape a glass plate onto a piece of graph paper mounted onto a 
support.

     Rotate it so that the laser beam enters the edge of the plate at 
about 30o.

     On the graph paper mark the place where the beam enters and 
where it leaves the glass.

     Measure the angles of incidence and refraction.

     Calculate:  n = sin i/sin r,  Snell's Law.

     Repeat the above at different angles.


Observations:



Calculations:



Conclusions:

-----------------------------------------------------------

                                    LASER LAB
                                    Hologram



Topic:

     Observing Holograms


Purpose:

     To see the effect of the laser light on holograms and to notice 
the three dimensional effects thereon.


Procedure:

    Spread the laser beam by placing the diverging lens (-4mm) over 
the laser aperture.

     Place the hologram in the laser beam about one meter from the 
laser.

     Adjust it so that the diameter of the beam is about 7cm so that 
it illuminates most of the hologram.

     Look through the hologram at about a 45 degree angle. (It is safe 
to look into the laser beam when it is spread out this much).

     Move your head around at various angles and notice how the scene 
moves in different perspectives.

     View the hologram through a 1 cm hole in a card and notice that 
the entire scene is still there.  Each part of the hologram contains 
complete information for viewing.

     While looking at the scene through the hologram, reach out and 
try to touch various portions of the objects that you see.  Notice the 
illusion of depth perception as your hand moves further away or 
closer to you to reach the various objects.


     Holding the hologram in the laser beam, lower your head and look 
at the area about 20cm above the laser aperture.  A second image 
should come into view at this location.  Describe this image and 
compare it with the first one.


Observations:

------------------------------------------------------------


                                      LASER LAB
                                 Index of Refraction


Topic:

     Index of refraction for liquids.

Purpose:

     To use the laser to find the ratio of the sine of the angle of 
incidence to the sine of the angle of refraction.

Procedure:

     Fill a 3000ml beaker half-full of water.  Using a protractor, 
measure several angles of incidence and their angles of refraction.

   Calculate the index of refraction in each case and compare the 
results.

     The formula is  n = sin i/sin r.

     Repeat the above with an aqueous solution of sugar and compare 
results.

     Observe the gradual bending of light that occurs when a laser 
beam is transmitted through a solution in which the optical density 
is not constant, using sugar and water in a fish tank.

     Relate the last observation to the bending of sunlight as it enters 
the earth's atmosphere.


Observations:



Calculations:


Conclusions:
------------------------------------------------------------


                                         LASER LAB
                                       Interference

Topic:

     Thin film interference.


Purpose:

     To observe the phenomenon of interference of light passed 
through a thin film, and to relate it to soap bubble and oil slick 
patterns.


Procedure:

     Make an air wedge with two glass plates with a piece of paper 
for a shim at one end.

     Place the air wedge in the beam which is aimed at the screen.

     Enlarge the beam from the wedge with a -4mm lens.

     Note the patterns thus produce.

     Explain how the interference patterns can be formed with soap 
bubbles and oil slicks.




Observations:


Conclusions:

----------------------------------------------------------


                                        LASER LAB
                                       Knife Edge


Topic:

     Foucault knife-edge test.


Purpose:

     To detect aberration of light caused by imperfections in a lens.


Procedure:

     Mount a diverging lens and a converging lens before the laser to 
give a collimated beam.

     Mount a +15mm lens in the collimated beam.

     Observe that this lens converges the light to a fine point after 
which the light diverges onto a screen

     Insert a razor blade into the laser beam at the cross-over point.  
If the lens is perfect, the spot on the screen should darken uniformly 
as the razor cuts the beam.

     Try other lenses to test their quality.


Observations:


Conclusions:
------------------------------------------------------------


                                      LASER LAB
                                    Make Hologram



Topic:

     Making a hologram.


Purpose:

     To make a reflection hologram.


Procedure:

     In the dark or under green light, squeeze the film tightly between 
two glass plates and clamp them together.

     With blocks of wood, squeeze the film tightly between the glass 
plates for at least 10 seconds to remove any air bubbles.

     Place the film sandwich with the emulsion side toward the 
subject (the emulsion side feels sticky when touched by moist 
finger). (The subject goes on the side opposite the laser.)

     Place the subject close to the side of the film which is opposite 
the laser (the emulsion side).

     Allow the laser to warm up before making exposures (15 min).  
Use a shutter card to control the exposure.

     Expose the film for the required amount of time.

     Develop until the film turns as dark as it will get (2-5 minutes).

     Wash in large volume of water for 5 minutes.

     Dry with a photographic squeegee or hang dry.


Observations:

     When it is completely dry observe it by laser light and by 
sunlight.

------------------------------------------------------------


                                     LASER LAB
                                  Ophthalomology


Topic:

     Ophthalmology.


Purpose:

     To observe the grainy interference patterns of an enlarged laser 
beam as its coherent light is focused on the retina of the eye.

     Check for myopia (nearsightedness).

     Check for hyperopia (farsightedness).



Procedure:

     Aim the laser beam on a white paper 3 meters away. Expand the 
beam with the +15mm lens.

     Observe the illuminated area for small dots.

     Move your head slowly from side ot side while observing the spot. 
If you are farsighted or normal, the spots will appear to move in the 
same direction as your head due to the focusing behind the retina. If 
you are nearsighted, the spots will appear to move in the opposite 
direction due to the focusing in front of the retina.

     Observe the parallax described above by holding your fingers 
apart a few centimeters in front of your eyes while looking at a 
distant object and moving your head back and forth.

     Simulate myopia by holding a +80mm lens in front of your eyes 
and watching the movement of the dots.

     Simulate hyperopia by observing the spots with a -46mm lens.

     If you wear eyeglasses, check the above with and with- out them.


Observations:



Conclusions:

------------------------------------------------------------


                                     LASER LAB
                                   Polarization


Topic:

     Polarization.


Purpose:

     To investigate the polarization of white light and laser light.


Procedure:

     Shine white light through a single polarizing filter and note 
results.  See if rotating the filter makes any difference.

     Shine white light through two polarizing filters and rotate one of 
them, noting results.

     Now do the above with laser light, and note results. Notice 
especially if rotating a single filter has any effect.


Observations

Conclusions:

------------------------------------------------------------


                                       LASER LAB
                                         Prism

Topic:

     Index of Refraction of a Prism.


Purpose:

     To study the twice refracted beam of the laser as it passes 
through a prism.


Procedure:

     Mount the prism on a vertical mount.

     Measure the apex angle of the prism.

    Slowly rotate the prism while observing the amount of deviation 
between the emerging laser beam and the original beam direction.

    Record the value of the minimum angle of deviation which was 
observed while rotating the prism.

    Use this formula to calculate the index of refraction of the prism:

     n =  sin 1/2 (A + 0)
             sin 1/2 A


Observations:


Calculations:

Conclusions:

-------------------------------------------------------

                                  LASER LAB
                                 Reflection


Topic:

     Interference by multiple internal reflections in glass.


Purpose:

     To investigate the nature of interference of the part of the beam 
which is reflected from the surface of a glass plate with that which 
is internally reflected from the rear of the plate.


Procedure:

     Place the -4mm and the +80mm lenses between the laser and a 
glossy white screen about 1 meter away. Make a spot on a screen 
adjusted to about 15cm diameter.

     Place a microscope slide in the beam at an angle of 90o with the 
beam.

     Observe the interference patterns as the plate is moved.

     Observe that the second set of patterns is in reverse order.



Observations:


Conclusions:

------------------------------------------------------------

                                    LASER LAB
                                 Reflection Law


Topic:

     The Law of Reflection



Purpose:

     To investigate several types of laser beam reflections.



Procedure:

   Use a piece of paper to monitor reflections from several types of 
substances including a plane mirror, a convex mirror, a concave 
mirror, rough
          surfaces, etc.

     Using a glass plate, observe the phenomenon of partial reflection 
and transmission.  Note the relative intensities of the rays.

     Shine the beam into a beaker of water and notice reflections at 
both the points of entry and exit.

     Aim the laser at the center of a wall across the room, place a 
mirror on the wall at the point of attack, measure the angles of 
incidence and reflection. Then change the angle of incidence several 
times, and measure the new angles of reflection.

    Try the angles again with the elevation of the laser beam changed.


Observations:


Conclusions:
------------------------------------------------------------

                           LASER LAB

                                     Refraction

Topic:

     Diffraction and Index of Refraction.



Purpose:

     Compare the refraction of the beam in air with that in water.


Procedure:

     Aim the beam into an empty fish tank so the beam is normal to 
the surface of the glass.

     Tape a diffraction grating to the glass where the beam enters the 
tank.

     Measure the angle that the beam makes between the central 
maximum and the first order maximum to the left or the right of the 
central point.

     Fill the tank with water and notice the changes.



Observations:


Conclusions:

---------------------------------------------------------

                                     LASER LAB
                                    Single Slit


Topic:

     Single slit diffraction.


Purpose:

     To cause and observe the bending and interference of light when 
it passes a sharp edge or through a narrow slit.

Procedure:

     Point the laser at a glossy white paper screen about 3 meters 
away.

     Slide the edge of a razor part way into the beam and observe the 
patterns on the screen.

     Notice that there is no sharp shadow but a diffraction pattern.

     Now make a slit with two razor blades and make note of what 
happens as the slit distance is varied.



Observations:


Conclusions:
------------------------------------------------------------

                                  LASER LAB

                                 Scattering


Topic:    The Scattering of Light.


Purpose:  To discover how light is scattered by small particles.


Procedure:

     Shoot the laser beam through the following media:

          Chalk dust in air

          Air bubbles in water

          Ice cube (crystal imperfections)

          Milk in water

     Make notes on the different scattering effects:




Observations:



Conclusions:
-------------------------------------------------------------
--


                                  LASER LAB
                                  Small Hole


Topic:

     Diffraction from small holes.


Purpose:

     To observe the interference patterns of the laser beam as it 
passes through small holes and calculate the size of the holes.


Procedure:

     Use the small hole slide, and direct the laser beam through the 
holes onto the screen about 1 meter away.

     Make a tiny hole in a piece of aluminum foil with the point of a 
needle and repeat the above.

     Compare the patterns for the different sized holes.

     Calculate the size of the holes using the formula,
          d = l (x/L)   where d is the diameter of the pinhole, x is the 
radius of the Airy disk (the bullseye),  L is the distance from the 
pinhole to the screen, and l is the wavelength of the light (6.23  X  
10-7meter).

Observations:


Calculations:


Conclusions:

