7 37
Solution
ix
a
1290시이쇼
490r
Amaxi
3
b Am
250i
c Amar
2
0.64Mm
1 16Mm
임이 2 32Mm
76
olution
Similarities
emit a photon of the same energy E
hv
Differences
Spontaneous emission occurs when a species loses all partof
fluorescence phosphorescence radia
ton This
intheform
energy
of
and occur in anydirection incoherentradiation
its excess
process is random
Stimulated emission occurs when excited species interacts with externally produce
photons thathave energies matching thetradition nagy Then photons are produce
emission and coherent radiation is the result
by
77
dation
A fourlevel laser hastheadvantagethat population inversion is achieved more easily than
with a threelevel system It isonly necessaryto maintain a numberofexcitedthat exceeds
thenumber in an intermediate energy levelthat is higher in energy thantheground state
Ifthe lifetime oftheintermediate state is brief a relativelyfewexcited species is requiredforpopulation
inversion
87
luton
the width in wavelength units oftheband transmitted bythefilterwhen measured atonehalfthe
peakheight
7 167
lotion
F fd
f f numberispeed fi focallengthoflens d diameter
15 6cm 5 2 Cm
3
7 207
solution
pn junction
device operated under reverse bias conditions Photons striking
thedepletion layer create electronset and holesctl that can be attracted
across thejunction giving rise to a current proportional to
the fluxof ph.tns
7217
olution
a spec
troscope optical instrument for visual identification of spectra It is a device
a dispersing element and an eyepiece that can be
with an entrance
moved along the focal plane
b spectrograph a device with an entrance slit a dispersing element and a large
slit
aperture ext thatallows a widerangeof wavelengths to strike a multichannel detector in thefocalplan
c spectrophotometer
chroma
aninstrumentwitha monochromator poly
tor and photodetectorarranged
toallowtheratio oftwobeams tobeobtained