Environmental Engineering Reference
In-Depth Information
FIgure 23.8
Radiation.symbol.used.as.a.warning.of.its.presence.
that. maximum. has. been. reached,. a. worker. can. have. no. more. exposure.. The. gen-
erally. used. number. is. 5. rems. per. year.. This. is. ifty. times. higher. than. the. U.S..
Environmental.Protection.Agency.recommends.for.the.public.on.a.yearly.basis..The.
average.public.exposure.is.supposed.be.no.more.than.0.1.rems.per.year..Five.rems.
has.been.employed.for.many.years.and.seems.to.provide.reasonable.protection.for.
workers..Exposure.to.radiation.should.be.considered.serious.because.overexposure.
can.lead.to.serious.health.problems.or.even.death.
lAsers
The. term. “laser”. is. an. acronym. for. Light. Ampliication. by. Stimulated. Emission.
of.Radiation..Light.can.be.produced.by.atomic.processes.that.generate.laser.light..
A.laser.consists.of.an.optical.cavity,.a.pumping.system,.and.an.appropriate.lasing.
medium..It.is.a.form.of.nonionizing.radiation.
The. optical. cavity. contains. the. media. to. be. excited. and. mirrors. to. redirect. the.
produced. photons. back. along. the. same. general. path.. The. pumping. system. uses.
.photons.from.another.source,.such.as.a.xenon.gas.lash.tube.(optical.pumping),.to.
transfer.energy.to.the.media..It.may.use.electrical.discharge.within.the.pure.gas.or.
gas.mixture.media.(collision.pumping),.or.it.may.rely.on.the.binding.energy.released.
in.chemical.reactions.to.raise.the.media.to.the.metastable.or.lasing.state..The.laser.
medium.can.be.a.solid.(state),.gas,.dye.(in.liquid),.or.semiconductor..Lasers.are.com-
monly.designated.by.the.type.of.lasing.material.employed.
Solid-state.lasers.have.lasing.material.distributed.in.a.solid.matrix.[e.g.,.the.ruby.
or.neodymium-YAG.(yttrium.aluminum.garnet).laser]..The.neodymium-YAG.laser.
emits.infrared.light.at.1.064.micrometers,.while.gas.lasers.[helium.and.helium-neon.
(HeNe). are. the. most. common. gas. lasers]. have. a. primary. output. of. a. visible. red.
light..CO
2
.lasers.emit.energy.in.the.far-infrared,.10.6.micrometers,.and.are.used.for.
cutting.hard.materials..Excimer.lasers.(the.name.is.derived.from.the.terms.excited.
and.dimers).use.reactive.gases.such.as.chlorine.and.luorine.mixed.with.inert.gases.
such.as.argon,.krypton,.or.xenon..When.electrically.stimulated,.a.pseudomolecule.
or.dimer.is.produced.and.when.lased.it.produces.light.in.the.ultraviolet.range..Dye.
lasers.use.complex.organic.dyes.like.rhodamine.6G.in.liquid.solution.or.suspension.
as.lasing.media..They.are.tunable.over.a.broad.range.of.wavelengths..Semiconductor.
lasers,.sometimes.called.diode.lasers,.are.solid-state.lasers..These.electronic.devices.
are. generally. very. small. and. use. low. power.. They. may. be. built. into. larger. arrays.
(e.g.,.the.writing.source.in.some.laser.printers.or.compact.disk.players).
