18WuD2x

photograph reception • photon 531
photograph reception 1. The use of FACSIMILE to
print photographs transmitted in analog form via
wire or radio. 2. The use of a computer, equipped
with a modem and graphics software, to display
and/or store photographs transmitted in digital
form via wire or radio.
photograph transmission 1. The use of FACSIM-
ILE to scan and send photographs in analog form
via wire or radio. 2. The use of a computer,
equipped with a modem and video camera or optical
scanner, to digitize and send photographs
via wire or radio.
photoionization The ejection of electrons from
atoms or molecules by the action of infrared, visible
light, or ultraviolet radiation.
photoisolator See OPTOELECTRONIC COUPLER.
photojunction cell A photocell consisting of a semiconductor
pn junction. The cell is useful mainly
for its photoconductivity, although infrared, visible
light, or ultraviolet energy striking the junction
produces a small amount of photovoltaic action.
photokinesis Light-induced motion, as in a RA-
DIOMETER.
photolithographic process A method of producing
integrated circuits and printed circuits by photographing
(often at considerable reduction) an
enlarged pattern of the circuit on a suitable lightsensitized
surface of metal or semiconductor, and
chemically etching away unwanted portions of
the surface.
photolysis See PHOTODECOMPOSITION.
photomagnetic effect Light-sensitive magnetic
susceptibility in some materials.
photomap A photo taken of terrain from a high altitude
and usually overlaid with a reference grid.
photomask In PHOTOFABRICATION, the transparent
film or template on which the etching pattern
is drawn.
photometer An instrument used to compare the
luminous intensity of two light sources.
photometric measurement of power See PHOTO-
ELECTRIC WATTMETER.
photometry The science of visible-light measurement.
The response of the human eye is used as
the basis for preferred sensors (those used with
photometric instruments, which have spectral
sensitivity curves resembling those of the eye).
Compare RADIOMETRY.
photomosaic In a television camera tube, the flat
photocathode screen on which the image is projected
by the lens system and scanning electron
beam. The surface of the screen is covered with
tiny light-sensitive droplets. Also see DISSECTOR
TUBE, ICONOSCOPE, and ORTHICON.
photomultiplier tube A type of PHOTOTUBE that
delivers high output current for a given light intensity
by utilizing the secondary emission of electrons.
The initial light-sensitive cathode emits
electrons; these strike a specially placed metal
plate with a force that dislodges more electrons.
These electrons, together with the initial emission,
Relative perceived brightness for
light source of constant intensity
0
200 300 400 500 600 700 800
Photomosaic
Incident
electron
beam
Violet Indigo
Electron gun
Blue
Green
Wavelength (nm)
photometry
photomosaic
Yellow Orange Red
Light
Focusing
lens
Returned, modulated
electron beam
Anode
Output
are reflected to a second plate, where they dislodge
still more electrons. This process continues
from deflection plate to deflection plate through
the tube. The final plate deflects the accumulated
electrons to the anode (collector electrode).
photon A quantum of radiant energy whose energy
constant W (in joules) is equal to hf, where h is
the PLANCK CONSTANT and f is the frequency in
Hertz.