CHEM 524 -- Course Outline (Sect. 2)

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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-characterizes shape,

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 (warning: old eqn. wrong)

Planck (distribution): Stefan-Boltzmann (integrated inten.): Wien ( max):

B = (2hc2/5)(ehc/kT – 1)-1, ∫Bd = T4, max = (2.897x106)/T

Higher temperature—maximum moves to vis-uv, intensity increase at all 

Real sources --correct for emissivity (<1), transmittance (ref.Text: Fig 4-3)

Comparison of ceramic sources Fig.16 (ceramic vs. IR emitter), fig.17

(Above top-left, Oriel Ceramic (6575) verses IR emitter (6363)-coated metal)

–

-- gray body attemp. T -- See FigureS-2,

Figure 4 – dischargesources, uv-visFigure 2 - incandescent, vis-IR sources

2. Incandescent sources -- Continuum (in ), continuous (in time),irradiance comparison

Note: QTH—quartz/halogen W lamp, SiC like glowbar, blackbody is theory

EXAMPLES(Text Table 4-2, Fig 4-5, 4-4) –

  • Ceramic coated wire-(Oriel models linked) -cheap, (low Tc~1000K)
  • Above pictures: 6363, 6575, 6580 and 6581 Infrared Elements.from Oriel

Model / Element Type / Voltage
(V) / Operating Current (A) / Typical Power (W) / Nominal Radiating Area / Total Area / Color Temp
(K) / Average Life / Price
6363 / IR Emitter / 12.0 / 12.0 / ~140 / 6.4 x 17.5 mm / 6.4 x 104 mm / 1000 - 1050 / 1 year / $232.00
6575 / Ceramic Element / 2.5 to 3.5 / 6.8 to 8.2 / 22 / 3 x 10 mm / 3 x 15 mm / 1600 - 2000 / 600 h / $556.00
6580 / Low Cost Element / 5.0 / 1.8 / 9 / 3.6 x 3.6 mm / 7 x 3.7 mm / 1100 - 1150 / 3 years / $284.00
6581 / Miniature Element / 8,0 / 0.1 / 0,8 / 100 µm dia.x 7 mm long / 100 µm dia. x 7 mm long / ≥1000 / 1 year / $362.00
80030 / SiC Element / 12.0 / 1.8 to 2.4 / 24 / 3.8 x 5 mm / 3.8 x 12.7 mm / ~1273 / 2000 h / $252.00

Classic (generic) IR models:

SiC Glower (Glowbar)- higher power, cooling required (Tc~1300-1500K)

  • -- good for FTIR – cross-section like aperture (round)
  • Compare Nerst to Glowbar: Figure S-3,better ~4 , worse 5-14  -- W-glower below is bare filament

Nernst Glower- expensive, fragile, difficult connect,but can have high temperature (Tc~1500 - 2000 K)

  • --Lifetime inverse relate to Temperature, Efficiencycompare to Glowbar: Figure S-3,
  • --special circuit (negative coefficient of resistance), also heater to start conducting
  • --good for high resolution dispersive, illuminate slit withtall, thin cross-section

Nerst schematicQuartz halogen scheme -- Text S-6

C-Rod– cheap source, expensive housing, cooling, big power (KW), but very high color T (Tc~2500 K)

  • -- need inert atmosphere, good for IR with salt window (TAK group built)
  • Front view – electrodes above/below Side view-exploded front plate/window

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) [see efficiency curves above]

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 []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


6035 Hg(Ar) Lamp in 6058 Fiber Optic Accessory. Generic hollow cathode lamp
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)

Oriel Corporation, (purchased by Newport),Lamps section:

Hamamatsu Lamps:

PTI fluorescence specialists:

Eurosep supplier of lamps

Perkin-Elmer Lamps (include CERMAX lamps, succeed EIMAC, under short arc Xe)(site not working! Pdf available)

optoelectronics.perkinelmer.com/content/RelatedLinks/cermaxguide.pdf

Ushio America, large selection--go to Products, then Scientific-Medical

Solar Light Co.

Cairn Research

Other Sites of possible interest:

Analytical encyclopedia and spectroscopy pages--on-line course in analyticalchemistry

Spectrum page

Lamp page

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