Montshire Minute: Holography

Originally aired during the week of November 16, 1998

Monday

That new electron microscope at the museum isn't really there. Oh, you can see it all right. In fact, you can look right into its eyepiece - or the place where the eyepiece seems to be - and see a magnified image of a microchip. But the chip is not really there, either! Great exhibit, huh!? Let me explain. The electron microscope is a hologram, and it is one of 20 images on view as part of Montshire's Light Dreams exhibit that opens November 20. The significance of the microscope as an art object relates to experiments by London scientist Dennis Gabor back in the 1940s. While Gabor was searching for a way to produce better electron microscope resolution, he accidentally created the first hologram. It was one of those happy accidents in science, and since then, artists have used the optical properties of laser technology to create exquisite three-dimensional light "sculptures."

Tuesday

With Light Dreams, a new holography exhibit now on display at Montshire, we're talking about the nature of light and color on the program this week. When he wasn't inventing the calculus or making discoveries about gravity and motion, Sir Isacc Newton somehow found the time to demonstrate how white light is made up of a whole spectrum of colors. How did he do this? He let a narrow beam of sunlight pass through a small hole in a window shutter. By holding a triangular glass prism against the beam, the light was projected on the wall as a "rainbow" of colors. This happened, Newton decided, because light is refracted, or bent, as it passes through a prism. Each color has a slightly different wavelength - waves of red light are about one and a half times as long as waves of blue light.

Wednesday

Holograms are pictures recorded with laser light to create images so real they seem to float in space. In photography, a camera lens is used to focus an image onto the film. In holography, waves of laser light are bounced off a subject and recorded on a special plate. The completed film is lit from a certain angle by a small bright light (sometimes a simple light bulb) which projects the three-dimensional image to the viewer's eye. You can make a hologram yourself - all you need is a laser beam, a beam splitter, a piece of holographic film . . . come to think of it, I guess it's not one of those "try it at home" projects. You'll have to come to Montshire's new holography visiting exhibit Light Dreams to see what I mean. These works of art show many basic principles of light, lasers, and optics while exciting the eye and imagination with 3-D images of incredible depth and beauty.

Thursday

When you look at a hologram, what you see depends on the angle at which you are looking. The same is true when we're looking at a rainbow. We can think of raindrops as small natural prisms. When sunlight shines into an individual raindrop, the light hits the inside wall of the drop and then reflects back out of it. The many colors combined within the sunlight are dispersed on their way out, as the little drop splits the light into separate colors by acting as a prism. If the drop is at a 42 degree angle from the horizon, we see the red light in the spectrum. At a slightly different angle, 40 degrees, we see blue. The other rainbow colors, which travel in different wavelengths, come from drops that are between these two ends of the spectrum. Many other things in nature catch natural sunlight in the same way: fish scales, soap bubbles peacock feathers, or dragonfly wings.

Friday

Our eyes pick up only a small part of the electromagnetic spectrum. Visible light (the light our eyes perceive) is divided into seven basic colors: red, orange, yellow, green, blue, indigo and violet. Red has the longest wavelength, violet the shortest. Of course, we can see many small variations in hue between these seven colors. An object's color depends on how its surface reflects light. But how we perceive color is really a combination of the physics of light, the physiology of our eyes and brain, and . . . psychology! For instance, that shiny red apple in the fruit bowl looks kind of grayish at night, when there's not a strong light source. Our eyes and brain tend to still call the apple "red", because past experience tell us that apples should be red. You can make yout own observations about color when you see Montshire's new holography exhibit Light Dreams.