# 27: Wave Optics


• 27.0: Introduction to Wave Optics
• 27.1: The Wave Aspect of Light- Interference
• 27.2: Huygens's Principle - Diffraction
An accurate technique for determining how and where waves propagate is given by Huygens’s principle: Every point on a wavefront is a source of wavelets that spread out in the forward direction at the same speed as the wave itself. The new wavefront is a line tangent to all of the wavelets. Diffraction is the bending of a wave around the edges of an opening or other obstacle.
• 27.3: Young’s Double Slit Experiment
Young’s double slit experiment gave definitive proof of the wave character of light. An interference pattern is obtained by the superposition of light from two slits. There is constructive interference and destructive interference depending on the angle of probing.
• 27.4: Multiple Slit Diffraction
A diffraction grating is a large collection of evenly spaced parallel slits that produces an interference pattern similar to but sharper than that of a double slit. There is constructive interference for a diffraction grating when $$d\sin{\theta} = m \lambda \left( for m = 0,1,-1,2,-2,...\right)$$, where $$d$$ is the distance between slits in the grating, $$\lambda$$ is the wavelength of light, and $$m$$ is the order of the maximum.
• 27.5: Single Slit Diffraction
A single slit produces an interference pattern characterized by a broad central maximum with narrower and dimmer maxima to the sides. There is destructive interference for a single slit when $$D \sin{\theta} = m \lambda,~ \left(for~m = 1, -1, 2, -2, 3, ...\right)$$ where $$D$$ is the slit width, $$\lambda$$ is the light's wavelength, $$\theta$$ is the angle relative to the original direction of the light, and $$m$$ is the order of the minimum. Note that there is no $$m = 0$$ minimum.
• 27.6: Limits of Resolution- The Rayleigh Criterion
Diffraction limits resolution. For a circular aperture, lens, or mirror, the Rayleigh criterion states that two images are just resolvable when the center of the diffraction pattern of one is directly over the first minimum of the diffraction pattern of the other. This occurs for two point objects separated by the angle $$\theta = 1.22 \frac{\lambda}{D}$$, where $$\lambda$$ is the wavelength of light (or other electromagnetic radiation) and $$D$$ is the diameter of the aperture, lens, mirror, et
• 27.7: Thin Film Interference
The bright colors seen in an oil slick floating on water or in a sunlit soap bubble are caused by interference. The brightest colors are those that interfere constructively. This interference is between light reflected from different surfaces of a thin film; this effect is known as thin film interference. Interference effects are most prominent when light interacts with something having a size similar to its wavelength. A thin film is one having a thickness smaller than a few times the wavelengt
• 27.8: Polarization
Polarization is the attribute that a wave’s oscillations have a definite direction relative to the direction of propagation of the wave. (This is not the same type of polarization as that discussed for the separation of charges.) Waves having such a direction are said to be polarized. For an EM wave, we define the direction of polarization to be the direction parallel to the electric field. Thus we can think of the electric field arrows as showing the direction of polarization.
• 27.9: Microscopy Enhanced by the Wave Characteristics of Light
Physics research underpins the advancement of developments in microscopy. As we gain knowledge of the wave nature of electromagnetic waves and methods to analyze and interpret signals, new microscopes that enable us to “see” more are being developed. It is the evolution and newer generation of microscopes that are described in this section.
• 27.E: Vision and Optical Instruments (Exercise)

Thumbnail: Physical optics is used to explain effects such as diffraction; this photo shows diffraction from a single pinhole. (CC-SA-BY-3.0; Wisky).

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