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Interactive Tutorials

Microscope Light Sources

Arc Lamp Instability

Illumination sources based on plasma discharge (arc lamps) require a considerable period after ignition to reach thermal equilibrium, a factor that can affect temporal, spatial, and spectral stability. This tutorial examines several of the origins of arc lamp instability, including wander, flare, and flutter.

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Halogen Regenerative Cycle

In the halogen regenerative cycle, which operates in tungsten halogen incandescent lamps, vaporized tungsten reacts with hydrogen bromide to form gaseous halides that are subsequently re-deposited onto cooler areas of the filament rather than being slowly accumulated on the inner walls of the envelope. This interactive tutorial demonstrates how halogens combine with tungsten and oxygen to complete the halogen regenerative cycle in incandescent tungsten halogen lamps.

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Coherence of Light

One of the important parameters of illumination sources is their coherence, which is somewhat related to brightness due to the fact that extremely bright light sources are more likely to be highly coherent. This tutorial examines how incoherent light emitted by an arc lamp can be passed through a slit and filter to increase coherence and narrow the wavelength band.

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Elliptical Reflectors

Advanced light sources suitable for use in high-performance fluorescence microscopy couple metal halide arc lamps with elliptical collection mirrors and high-speed filter wheels for rapidly shifting the output wavelength. These sources also provide fiber optics or liquid light guides for coupling the output to the microscope optical train. This interactive tutorial explores how careful positioning of the arc with respect to elliptical reflector focal points is critical to the formation of a focused beam at the input of a liquid light guide.

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Mercury Lamphouses

High pressure mercury plasma arc-discharge lamps are highly reliable, produce very high flux densities, and have historically been widely used in fluorescence microscopy. This interactive tutorial examines advanced mercury arc lamphouses that are capable of automatic bulb alignment and intensity control.

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Light-Emitting Diode Operation

Among the most promising of emerging technologies for illumination in optical microscopy is the light-emitting diode (LED). These versatile semiconductor devices possess all of the desirable features that incandescent (tungsten-halogen) and arc lamps lack, and are now efficient enough to be powered by low-voltage batteries or relatively inexpensive switchable power supplies. This interactive tutorial explores how two dissimilar doped semiconductors can produce light when a voltage is applied to the junction region between the materials.

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LED Illumination for Microscopy

Among the most promising of emerging technologies for illumination in optical microscopy is the light-emitting diode (LED). These versatile semiconductor devices possess all of the desirable features that incandescent (tungsten halogen) and arc lamps lack, and are now efficient enough to be powered by low-voltage batteries or relatively inexpensive switchable power supplies. The interactive tutorial featured in this section explores the ZEISS Colibri LED illumination system for widefield fluorescence microscopy.

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