Podcast
Questions and Answers
What defines two waves as coherent?
What defines two waves as coherent?
- They have the same frequency and wavelength with a constant phase difference. (correct)
- They have varying amplitudes.
- They propagate in different directions.
- They have different frequencies.
Temporal coherence measures the correlation of a wave's phase at different spatial points.
Temporal coherence measures the correlation of a wave's phase at different spatial points.
False (B)
What does a high temporal coherence indicate about a light source?
What does a high temporal coherence indicate about a light source?
It indicates that the light source is close to monochromatic.
________ coherence refers to the correlation of the light wave's phase at different points along the direction of propagation.
________ coherence refers to the correlation of the light wave's phase at different points along the direction of propagation.
Match the following types of coherence with their descriptions:
Match the following types of coherence with their descriptions:
What is the primary characteristic of a monochromatic light source?
What is the primary characteristic of a monochromatic light source?
Spatial coherence is a measure of how uniform the phase of a wavefront is at different points along the direction of propagation.
Spatial coherence is a measure of how uniform the phase of a wavefront is at different points along the direction of propagation.
What does spatial incoherence indicate about a light wave's phase?
What does spatial incoherence indicate about a light wave's phase?
The formula for coherence length is given by Lc = _____
The formula for coherence length is given by Lc = _____
Match the following terms with their correct descriptions:
Match the following terms with their correct descriptions:
Which of the following properties describes how a laser emits light at a single wavelength?
Which of the following properties describes how a laser emits light at a single wavelength?
A laser beam has a high divergence compared to a normal flashlight.
A laser beam has a high divergence compared to a normal flashlight.
What is the term for a laser's ability to maintain a fixed phase relationship over distance?
What is the term for a laser's ability to maintain a fixed phase relationship over distance?
A laser beam can travel significant distances with minimal __________.
A laser beam can travel significant distances with minimal __________.
Which of the following is NOT a property of lasers?
Which of the following is NOT a property of lasers?
All lasers produce perfectly monochromatic light.
All lasers produce perfectly monochromatic light.
What is the typical divergence of a normal flashlight?
What is the typical divergence of a normal flashlight?
Flashcards
Coherence (LASER)
Coherence (LASER)
A measure of the correlation between the phases of a wave at different points in space and time. Two waves are coherent if they have the same frequency and wavelength and a constant phase difference.
Spatial Coherence
Spatial Coherence
Correlation of light wave's phase at different points across the wavefront (i.e., in a plane perpendicular to the light's direction of travel).
Temporal Coherence
Temporal Coherence
Correlation of light wave's phase at different points along the direction of propagation.
Temporal Coherence Length
Temporal Coherence Length
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Monochromatic
Monochromatic
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Coherence Time (Ï„c)
Coherence Time (Ï„c)
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Coherence Length (Lc)
Coherence Length (Lc)
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Laser: Highly Intense
Laser: Highly Intense
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What is the key characteristic that distinguishes the light emitted by a LASER from regular light?
What is the key characteristic that distinguishes the light emitted by a LASER from regular light?
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What is the difference between ideal and practical monochromaticity in the context of lasers?
What is the difference between ideal and practical monochromaticity in the context of lasers?
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How monochromatic is laser light compared to ordinary light?
How monochromatic is laser light compared to ordinary light?
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What does it mean for a LASER to be highly directional?
What does it mean for a LASER to be highly directional?
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What does 'divergence' refer to in the context of a LASER?
What does 'divergence' refer to in the context of a LASER?
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How does the divergence of a laser beam compare to a flashlight?
How does the divergence of a laser beam compare to a flashlight?
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What is the concept of Stimulated Emission?
What is the concept of Stimulated Emission?
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What was the first commercial LASER?
What was the first commercial LASER?
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Study Notes
Coherence of Waves
- Two waves are considered coherent if they maintain a constant phase relationship over time
- Temporal coherence measures how long a wave's phase remains correlated at different spatial points.
- High temporal coherence indicates that a light source emits light with a narrow bandwidth and that the light waves have a long coherence length.
- Spatial coherence refers to the correlation of a light wave's phase at different points along the direction of propagation.
- A high spatial coherence indicates that a light wave's phase is uniform and consistent across the wavefront
- Spatial incoherence means that the phase of the light wave is not uniform and varies across the wavefront.
- The formula for coherence length is given by Lc = c/Δν, where Lc is the coherence length, c is the speed of light, and Δν is the bandwidth of the light source.
Monochromatic Light Sources
- The primary characteristic of a monochromatic light source is that it emits light at a single wavelength.
Properties of Lasers
- Monochromaticity: Lasers emit light at a single wavelength, making them highly monochromatic.
- Spatial Coherence: Laser beams exhibit high spatial coherence, meaning the wavefront has uniform phase across its entire width
- Temporal Coherence: Laser beams maintain a fixed phase relationship over distance, demonstrating high temporal coherence.
- Low Divergence: Laser beams travel significant distances with minimal spreading or divergence
- Directional Emission: Lasers emit light in a highly directional, narrow beam, unlike a typical flashlight which emits light in a broader cone.
- Note that not all lasers produce perfectly monochromatic light, while most lasers exhibit high monochromaticity, some have a slightly broader bandwidth.
- The divergence of a typical flashlight is around 10 degrees.
- Laser properties summary: High monochromaticity, high spatial coherence, high temporal coherence, low divergence, and directional emission.
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