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Name: Unknown
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993
Question:
I have before me a Radio Shack Archer (cat no. 276-099) INFRARED SENSOR. The sensor is used to identify and locate near-infrared radiation emanating from either LED or laser sources. When a source, such as a remote control device, is shined onto the card, it has a visible light emission. How can a lower energy IR source activate a higher energy visible light emission? Is not this a violation of conservation of energy? It says that the sensor must be charged by short exposure to daylight or fluorescent light prior to use. Why? What is the material, and can it be made for less than $7/cm^2?

Question #2. -- On the recent Space Shuttle mission, they shot a stream of electrons into the atmosphere below them to stimulate an aurora. Where did the protons go (it would be difficult to attach a long wire to ground)?


Replies:
The simplest answer is that the energy of the emitted visible light comes from the power supply of the circuit and the infrared light simply supplies charge carriers to the circuit. I do not know the details of this device or why it is so cheap, but I will give a brief explanation. This is a semiconductor device. A semiconductor has an energy gap within which no electron can move or exist with that energy. If there are impurity atoms put into the material there can be localized energy levels in the gap that will hold electrons until something can exit them into the conduction band at the top of the gap. Once the electrons are in the conduction band at the top, they will flow to a boundary where they can be made to cascade to the bottom of the band and create visible light. The charging of the device is essentially exciting enough electrons in to the impurity band where they remain trapped until an infrared photon can excite them into the conduction band.

Question 2. -- The protons stay on the ship and its electrostatic energy becomes larger, making it harder to shoot more electrons off and ultimately causing other electrons in the plasma of space to be attracted to the ship.

Sam Bowen


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