CHEM 524 -- Course Outline (Sect. 2)
FOR A PDF VERSION OF 2002 NOTES WITH
EMBEDDED FIGURES CLICK HERE
II. Light Sources (Assignment -- alternate
reading: Reference list from Oriel
hand out )
Conventional-incandescent
and discharge -- incoherent, all directions, no phase
vs. laser –
coherent (frequency and phase well defined, directional)
All Electro-magnetic
(E-M) radiation has orthogonal oscillating E and B fields Figure S-0:
Polarization indicates orientation of E and B fields
A. Black body sources follow Planck result qualitatively (See table S-1)
1. Black-body ideal: emission-absorption equilibrium,
T-characterize, standard reference is a heated cavity
whose emissivity is fairly flat (Oriel example)
--source has constant energy density (ref.
Text: Fig 4-1) See Figure S-1
and it shifts in intensity and
frequency with increasing temperature
Planck: ------ Stefan-Boltzmann: ----
Wien:
, 
, 
Higher
temperature—maximum moves to vis-uv, intensity increase at all l
Real sources
--correct for emissivity (e<1), transmittance (ref.Text:
Fig 4-3)
–
Comparison of ceramic sources Fig.16 (ceramic vs. IR emitter), fig.17
–
–
-- gray body attemp. T
-- See FigureS-2,
Figure 4 - dischargesources, uv-vis Figure 2 -
incandescent, vis-IR sources
2. Incandescent sources -- Continuum (in l), continuous (in time), irradiance comparison
- EXAMPLES (Text Table 4-2, Fig 4-5, 4-4) -
- Ceramic
coated wire-(Oriel models linked)
-cheap, (low Tc~1000K)
- SiC Glower (Glowbar)- higher power, cooling required (Tc~1300-1500K)
- -- good for FTIR – cross-section like
aperture (round)
- -- Compare to Nerst: Figure S-3,
- Nernst
Glower- expensive, fragile, high temperature (Tc~1500
- 2000 K)
- --Lifetime inverse relate to Temperature
Compare to Glowbar: Figure S-3,
- --special circuit (negative coefficient of
resistance),
- --good for dispersive, tall thin
cross-section, high resolution
- C-Rod – cheap source,
expensive housing, cooling, big power (KW), (Tc~2500 K)
- -- need inert atmosphere, good for IR with
salt window (TAK group built)
- W-I lamp – inexpensive, wide variety of designs and
powers (Tc~3000 K)
- -- good for near
IR, vis (typical for commercial
vis. Absorption spectrometers)
- --compare to black body and to
SiC (Oriel catalog)
Figure 3 - Nerst vs. Glowbar, Figure 5 - Discharge vs. Glowbar, Slides—compare Oriel sources irradiance and emissivity
B. Discharge sources , Compare to Black Body: compare, discharge and incandescence
(poor version with D2 lamp as well—Figure S_9) also see, Figure S-4, Figure S-5,
1.Continuum—high
pressure. PTI comparison
- C-arc–old, stability problem, no window
- Xe-arc
(include Xe-Hg and Hg) (Ar
arc)– popular, quartz envelope (T~6000K)
- --Hg - makes intense uv, vis lines, good to
stimulate fluorescence
- --Xe - common for CD, fluorescence, good near IR, but
structured
- --Ar – good for vuv, not common
- H2/D2
discharge lamp –low power, good
in uv, 370-180 (envelope) nm
2.Line
sources– low pressure discharge- get
atomic/ion lines
- Na – lamp [a ]D
determination, ORD
- Hg – lamp–few uv-vis lines (254nm
max)–germicidal / fluorescence excite
- Hollow cathode–AA source, select analyte
- Electrodeless discharge–more intense–atomic
emission
3.Standards
- Intensity -- W-I and others (NIST calibrate)
- Frequency -- atomic: Hg (simple), hollow
cathode: Fe/Th (vis), Ne (red)
C. Synchrotron – different
mechanism
- unique virtues: tunable, collimated,
polarized, intense (high frequency pulses)
- – especially useful for uv, vuv , x-ray
- --in IR especially promising for microscopy, high power density
- experiment and operator must go to the source,
especially inconvenient
Homework –
part of #1, link here
Link to slides
shown in lecture
Web sites for lamps:
Physics Today Buyers Guide (L section-pick your lamp for vendors)
http://www.aip.org/ptbg/browseP.jsp?alpha=L
Oriel Corporation, (purchased by Newport),Lamps section:
http://www.oriel.com/netcat/VolumeIII/Descrippage/lamps.htm
Hamamatsu Lamps:
http://sales.hamamatsu.com/en/products/electron-tube-division/light-sources.php
PTI fluorescence specialists:
http://www.pti-nj.com/obb.html
Eurosep supplier of lamps
http://www.eurosep.com/Dep_light/light4.htm
Perkin-Elmer Lamps (include CERMAX lamps, succeed EIMAC, under short arc
Xe)(site not working! Pdf available)
optoelectronics.perkinelmer.com/content/RelatedLinks/cermaxguide.pdf
http://optoelectronics.perkinelmer.com/Catalog/Category.aspx?CategoryName=Cermax+Xenon+Lighting
Ushio America, large selection--go to Products, then Scientific-Medical
Solar Light Co.
http://www.solar.com/sources.htm
Cairn Research
http://www.cairnweb.com/menus/menustub_product.html
Other Sites of possible interest:
Analytical encyclopedia and spectroscopy pages--on-line course in analyticalchemistry
http://elchem.kaist.ac.kr/vt/index.htm
Spectrum page
http://elchem.kaist.ac.kr/vt/chem-ed/light/em-spec.htm
Lamp page
http://elchem.kaist.ac.kr/vt/chem-ed/optics/sources/lamps.htm- blackbody