We can only see light within an extremely limited range. That range is about 400 to 700 nanometers and is called the visible light range. The other light ranges that we cannot normally see contain vast quantities of hidden information. At Hamamatsu Photonics we are developing systems capable of detecting and imaging a wide spectrum of light up to the X-ray and infrared ray ranges.

Light is a stream of particles called photons. Our everyday environment is filled to overflowing with photons. About 200 trillion photons rain down on us at an average indoor brightness (200 to 400 lux). That figure drops to 1/1000th of a lux for starlight on a moonless night and declines even further in the region called extremely low light levels where the brightness of light is less than one billionth of a lux and is completely impossible to see with the naked eye. In this region there are only a few photons each second per one square millimeter. The signal received from one photon is so small that it cannot be captured by the typical high sensitivity camera. Photon counting imaging is a technique for visualizing an image in extremely low light levels, by detecting individual photons and their positions and then by integrating the detected signals.

The streak camera is a device for measuring ultra high-speed (ultra-short) phenomenon. Unlike the ordinary camera that captures actual images, the streak camera captures the state within the extremely short time that the light intensity changes. The principle of the streak camera is simple. Light input in the form of a slit is converted into electrons on the photoelectric surface called "photocathode". These electrons are then swept at high speed (from top to bottom) and reconverted back into a light image on the phosphor screen. The changes in the input light intensity over time can in this way be observed as variations in image brightness that change from top to bottom. Hamamatsu Photonics developed and marketed an advanced streak camera with a time resolution down to 200 femtoseconds.

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