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: *** HERE ENDETH THE DEMOS ***