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Lasers

Lasers. Instrument Resolution. If observing two distant objects, the diffraction patterns could overlap as shown. Without diffraction, there would be two bright spots on the screen. Resolving Power. The wavelength (  ) and the opening size ( D ) determine the resolving power.

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Lasers

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  1. Lasers

  2. Instrument Resolution • If observing two distant objects, the diffraction patterns could overlap as shown. • Without diffraction, there would be two bright spots on the screen.

  3. Resolving Power • The wavelength () and the opening size (D) determine the resolving power. •  is the limiting angle between the two resolved objects measured in radians. • Longer wavelengths require a larger aperture (D) to resolve distant objects. • Because radio waves are long waves, radio telescopes are very large to accommodate the need for a large aperture.

  4. Instrument Resolution • Imagine the opening is the pupil of your eye and the two sources are adjacent red and green pixels on your television screen. • What will you see? • How would it change if your pupil opening was larger? • How would it change if you were closer? • How would it change if the pixels were farther apart?

  5. Coherent Light • Light bulb filaments emit light of many different wavelengths and phases. • Hot filaments emit incoherent light. • Like water waves on a pond during the rain • Lasers produce a narrow beam of coherent light. • Laser light is not produced by a hot filament.

  6. Laser • LASER is an acronym. • Light Amplification by Stimulated Emission of Radiation • Lasers use light, electrical energy, or chemical energy to produce coherent light. • The active medium can be a solid, liquid, or gas. • The medium determines the wavelength of the light.

  7. Producing Light with a Laser (Step 1) • Energy is added to the medium. • When absorbing the energy, atoms move into higher energy states. • Excited atoms release this energy as light or some other EM radiation when they return to lower energy states.

  8. Producing Light with a Laser (Step 2) • Light emitted by one atom can induce adjacent atoms to emit light with the same properties (wavelength and phase). • The process continues, and light intensity begins to increase. • Called stimulated emission

  9. Producing Light with a Laser (Step 3) • Mirrors at the ends reflect the light back into the medium, and intensity continues to increase. • The mirror on the right is not fully reflective. Thus, some light passes through once the intensity is great enough. • The light is monochromatic and in phase (coherent).

  10. Laser Click below to watch the Visual Concept. Visual Concept

  11. Applications of Lasers • Measuring distance is possible because the beam does not spread out very much. • Mirrors left on the moon are used to reflect laser light back to Earth to determine the distance. • Accurate to within a few centimeters • Able to measure the rise and fall of Earth’s crust

  12. Applications of Lasers • Medical uses • Certain lasers that pass though the cornea and lens can be used to treat tears in the retina or to seal bleeding vessels in the retina. • Lasers can be used for incisions. • This cauterizes the wound while cutting to reduce bleeding. • Laser light can pass through optical fibers and treat internal problems without massive surgery.

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