Pencil Style Calibration Lamps

Pencil style mercury and rare gas sources are used to calibrate the wavelength of spectroscopic instruments such as monochromators, spectrographs, and spectral radiometers. Narrow intense lines from the excitation of a number of rare gases and metal vapors are produced. Also a complete range of accessories from mounts and holders to fiber optic adapters and aperture shields are offered.

The key features of pencil style calibration lamps are:

  • Compact and simple tools for calibrating spectral instruments
  • Narrow, discrete UV to IR wavelengths
  • Excellent stability
  • Supported by mounting and fiber optic accessories for efficient coupling

Spectral Calibration Lamp mounted to MS125™ Spectrograph, using the 77251 Lamp Mount. A diode array detector is on the output of the MS125™.

Figure 1. Spectral Calibration Lamp mounted to MS125™ Spectrograph, using the 77251 Lamp Mount. A diode array detector is on the output of the MS125™.

Lamp Selection

Six lamps are offered by Oriel Instruments and one can select the lamp suitable to his particular application using Table 1 as a guide. The single gas lamps Xe, Ar, Ne and Kr have distinct lines; the Hg(Ar) and He(Ne) share the mercury lines, but also have distinct differences

Mercury (Argon) Lamp

The 6035 Hg(Ar) lamp is sensitive to temperature. For the mercury vapor o dominate the discharge there is a need for a 2-minute warm up then 30 minutes for complete stabilization. The average intensity is remarkably constant and reproducible after the thermal conditions stabilize.

The key features of the mercury argon lamp are:

  • Preferred lamp for calibration, using mercury line spectrum
  • Temperature insensitive
  • Average intensity is constant and reproducible
  • Longer life
  • Preferred lamp for calibration using Mercury line spectrum

Mercury (Neon) Lamp

The 6034 Hg(Ne) Lamp is temperature dependent. The output is very much like the Hg(Ar) lamp that is the characteristic mercury line spectrum. Forced air cooling (i.e. from a muffin fan) of the lamp adds the neon lines to the output. This spectrum has a large number of useful calibration lines in the longer VIS and NIR regions as seen in Table 1.

The key features of the mercury neon lamp are:

  • Emits additional lines in the VIS-NIR
  • Temperature dependent

Table 1. Usable Wavelengths of Spectral Calibration Lamps

Lamp Type (Model No.)
Hg(Ar) (6035) Hg(Ne) (6034) Xenon (6033) Argon (6030) Neon (6032) Krypton (6031)
Wavelength (nm)
184.9 253.65 418.0 294.3 585.25 427.4
187.1 296.73 419.3 415.9 594.48 432.0
194.2 302.15 433.1 420.1 607.43 435.5
253.65 312.57 439.6 427.7 609.62 457.7
265.4 313.151 444.8 476.5 614.31 461.9
284.8 313.181 446.2 488.0 616.36 465.9
302.2 365.02 473.4 696.54 621.73 473.9
312.571 404.66 480.7 738.40 626.65 476.6
313.151 435.84 483.0 750.39 630.48 483.2
313.181 546.07 508.1 751.47 633.44 557.0
320.8 576.96 529.2 763.51 638.30 587.1
326.4 579.07 531.4 772.381 640.111 758.74
345.2 614.31* 554.0 772.421 640.221 760.15
365.02 638.30* 541.9 794.82 650.65 769.45
404.66 640.111* 547.2 801.48 653.29 769.45
435.84 640.221* 597.7 811.53 659.901 785.48
546.07 650.65* 603.6 826.45 660.291 805.95
576.96 703.24* 605.1 840.82 667.83 810.44
579.07 1013.98 609.8 842.46 671.70 811.29
615.0 1128.74 659.5 912.3 692.95 819.00
1014.0 1357.02** 680.5 922.4 703.24 826.32
1357.0 1367.35** 699.1 965.8 717.39 829.81
1692.0 1529.58 823.2 1047.1 724.52 829.81
1707.3 1688.15** 828.0 1331.3 743.89 850.9
1711.0 1692.02** 834.7 1336.7 783.9 877.7
  1694.20** 840.9 1371.8 792.7 829.9
  1707.28** 881.9 1694.0 793.7 975.2
  1710.99** 895.2   794.3 1363.4
  1732.94** 980.0   808.2 1442.7
  1813.04** 992.3   811.9 1523.9
  1970.02** 1262.3   812.9 1533.4
    1365.7   813.6 1678.51
    1473.3   825.9 1689.04
    1541.8   826.6 1689.68
    1672.8   826.7 1693.58
    1732.5   830.0 1816.73
    2026.2   836.6  
    2482.4   837.8  
    2626.9   841.7  
    2651.0   841.8  
        846.3  
        848.8  
        849.9  
        854.5  
        857.1  
        859.1  
        863.5  
        864.7  
        865.4  
        865.6  
        867.9  
        868.2  
        870.4  
        877.2  
        878.0  
        873.4  
        885.4  
        920.7  
        930.1  
        932.7  
        942.5  
        948.7  
        953.4  
        1056.2  
        1079.8  
        1084.5  
        1114.3  

Note:
1 Adjacent lines will remain unresolved on many spectroscopic systems.
* These are neon lines brought out by forced air cooling.
** These lines are very weak, but forced air cooling makes them more useful.

Construction of the Lamp

These are termed as pencil lamps especially because of their size and shape. They are made of double bore quartz tubing with two electrodes at one end sealed into a phenolic handle. They can be held with simple laboratory clamps, operate them in any position, and insert them into restricted openings to illuminate enclosed areas. A 1ft (305mm) long cord with male connector is attached to the end of the handle for connection to the power supply.

Power Supplies:AC Vs DC

Different power supplies are offered for different needs:

AC Supplies

If only one or two line lamps are being operated and output variations are not a concern then use AC supply. This mode of operation also prolongs the life of the lamps.

DC Supplies

DC supply is used if you are calibrating multichannel detectors, such as our InstaSpec™ PDAs or CCDs, or if you are using various lamps, as these supplies run all our Spectral Line Lamps (AC supplies are lamp specific). Figure 2 compares the output stability between the AC and DC supplies.

Output intensity variation of 6034 Hg(Ar) Lamp when operated by 6047 AC Power Supply (top) and 6060 DC Power Supply (bottom).

Figure 2. Output intensity variation of 6034 Hg(Ar) Lamp when operated by 6047 AC Power Supply (top) and 6060 DC Power Supply (bottom).

Output spectrum of 6035 Hg(Ar) Lamp, run at 18 mA, measured with MS257™ 1/4 m Monochromator with 50 ^m slits.

Figure 3. Output spectrum of 6035 Hg(Ar) Lamp, run at 18 mA, measured with MS257™ 1/4 m Monochromator with 50 ^m slits.

Output spectrum of 6034 Hg(Ne) Lamp, run at 18 mA, measured with MIR 8000™ FT-IR with CaF2 beam splitter and InGaAs Detector.

Figure 4. Output spectrum of 6034 Hg(Ne) Lamp, run at 18 mA, measured with MIR 8000™ FT-IR with CaF2 beam splitter and InGaAs Detector.

Observed Signal

The curves obtained illustrate the relative signal strength observed at various wavelengths. The signal can differ very significantly from these curves due to the spectral throughput of the optical system, e.g. monochromator and its grating, or FT-IR and its beam splitter, and the spectral responsivity of the detector being convolved with the spectral properties of the incident light to produce that signal. The differences are quite insignificant or it may be quite drastic based on the exact experimental conditions.

Output spectrum of 6033 Xenon Lamp, run at 6 mA, measured with MIR 8000™ FT-IR with CaF2 beam splitter and InGaAs Detector.

Figure 5. Output spectrum of 6033 Xenon Lamp, run at 6 mA, measured with MIR 8000™ FT-IR with CaF2 beam splitter and InGaAs Detector.

Output spectrum of 6030 Argon Lamp, run at 10 mA, measured with MIR 8000™ FT-IR with CaF2 beam splitter and InGaAs Detector.

Figure 6. Output spectrum of 6030 Argon Lamp, run at 10 mA, measured with MIR 8000™ FT-IR with CaF2 beam splitter and InGaAs Detector.

Output spectrum of 6032 Neon Lamp, run at 6 mA, measured with MIR 8000™ FT-IR with CaF2 beam splitter and InGaAs Detector.

Figure 7. Output spectrum of 6032 Neon Lamp, run at 6 mA, measured with MIR 8000™ FT-IR with CaF2 beam splitter and InGaAs Detector.

Output spectrum of 6031 Krypton Lamp, run at 10 mA, measured with MIR 8000™ FT-IR with CaF2 beam splitter and InGaAs Detector

Figure 8. Output spectrum of 6031 Krypton Lamp, run at 10 mA, measured with MIR 8000™ FT-IR with CaF2 beam splitter and InGaAs Detector

Accessories

The following accessories facilitate the coupling of these lamps to Oriel’s instruments.

  • Spectral Calibration Lamp Mount
  • Fiber Optic Accessory
  • Rod Mounted Lamp Holder

Filters

Filters are offered by Oriel Instruments that fit over the lamp to block a specific wavelength region as shown in Figure 8.

The following models are offered:

  • 6041 Short Wave Filter: this filter absorbs the visible lines.
  • 6042 Long Wave Conversion Filter: this model attenuates the 253.7 nm Hg line and fluoresces in the 300 -400 nm region.
  • 6057 Glass Safety Filter: this filter protects you from the lamp’s intense UV lines. It completely absorbs the 253.7 nm Hg line and attenuates the 312.6 nm line.

Aperture Shields

The listed shields fit over the lamps to limit the radiation area. Three aperture sizes are offered:

  • 6038 Pinhole Shield: 0.040 inch (1 mm) diameter
  • 6039 Small Aperture Shield: 0.313 x 0.375 inches (8 x 9.5 mm)
  • 6040 Large Aperture Shield: 0.188 x 1.50 inches (4.8 x 38 mm)

NIST-Oriel Joint Research on Pencil Style Calibration Lamps

The wavelengths emitted by the pencil lamps are normally considered to be absolute since the elements in the lamps generate their narrow, reproducible spectral lines by a well understood and documented excitation and emission process. However, conditions in these pencil style lamps are not truly ideal as is seen from signs such as a low level continuum in the Hg(Ar) lamps. To study these lamps further, Oriel entered into a Cooperative Research and Development Agreement with scientists at the National Institute of Standards and Technology (NIST). The results of this CRADA were published in Applied Optics. This agreement laid the foundation for a study of Hg(Ar) pencil style lamps. All lamps for the study were powered at 15mA by the 6060 regulated DC power supply.

Wavelength Accuracy

NIST scientists measured the wavelength location of prominent Hg lines with a Fourier Transform Spectrometer (FTS). The FTS is capable of 0.001nm or better resolution throughout the primary Hg(Ar) spectral range. Table 2 shows the average wavelengths emitted by the Hg(Ar) pencil lamps, as measured with the FTS, along with published values for prominent Hg lines. These lamps accurately matched published mercury spectra to within ± 0.002 nm.

Table 2. Average wavelengths emitted by Hg(Ar) pencil lamps

Published2 Wavelength (nm) Measured* Position (nm) Irradiance at 25 cm** (MW cm-2) Absolute Variation*** (%) Relative Variation*** (%)
253.652 253.6521 74.0 8.2 9.9
296.728 296.7283 0.65 7.3 3.0
312.567 312.5674 0.71 6.5 2.7
365.015 365.0158 1.35 5.5 1.6
404.656 404.6565 1.12 6.9 2.0
435.833 435.8335 2.55 5.8 0.0
546.074 546.0750 2.56 5.9 1.2
576.960 576.9610 0.28 9.2 3.9
579.065 579.0670 0.30 9.2 3.8

Note:
1 Per Reader, Sansonetti, and Bridges, Wavelengths of Spectral Lines in Mercury Pencil Lamps and Irradiances of Spectral Lines in Mercury Pencil Lamps, Applied Optics, Vol. 35, No.1 Jan, 1996.
2 Per Reader, et al, Wavelengths and Transition Probabilities of Atoms and Atomic Ions, NSRDS-National Bureau of Standards #68, 1980.
* Wavelength Uncertainty 0.0001 nm.
** Operated at 15 mA using the 6060 Regulated DC Power Supply.
*** One sigma level.

Spectral Irradiance

The NIST scientists used a 1m plane grating spectrometer to measure the irradiance from these prominent Hg(Ar) lines. Although there are wide variations (near 10%) in the absolute irradiance from each line, due to lamp-to-lamp differences and aging; the irradiance ratios of the lines in any one lamp are remarkably consistent. With the notable exception of the 253nm peak, these lines may be used for a relative irradiance calibration to accuracies better than 5%. Pencil style spectral calibration lamps are by no means a substitute for Oriel’s carefully calibrated broadband sources, however, they are an economical means of obtaining good relative irradiance calibrations.

About Oriel Instruments

Oriel Instruments, a Newport Corporation brand, was founded in 1969 and quickly gained a reputation as an innovative supplier of products for the making and measuring of light. Today, the Oriel brand represents leading instruments, such as light sources covering a broad range from UV to IR, pulsed or continuous, and low to high power.

Oriel also offers monochromators and spectrographs as well as flexible FT-IR spectrometers, which make it easy for users across many industries to build instruments for specific applications. Oriel is also a leader in the area of Photovoltaics with its offering of solar simulators that allow you to simulate hours of solar radiation in minutes. Oriel continues to bring innovative products and solutions to Newport customers around the world.

This information has been sourced, reviewed and adapted from materials provided by Oriel Instruments.

For more information on this source, please visit Oriel Instruments.

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