IR Sensors and Electron Beams
Date: Around 1993
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)?
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.
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Update: June 2012