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f ¥ : *°«w NIST SPECIAL PUBLICATION 260-133

U.S. DEPARTMENT OF COMMERCE/Technology Administration

National Institute of Standards and Technology

Standard Reference Materials:

Acetylene 12 C2H2 Absorption Reference for

1510—1540 nm Wavelength Calibration

SRM 2517

QC

100

.1157 NO. 260-133

Sarah L. Gilbert and William C. Swann
rhc National Institute of Standards and Technology was established in 1988 by Congress to "assist industry in the development of technology . . . needed to improve product quality, to modernize manufacturing processes,

to ensure product reliability . . . and to facilitate rapid commercialization ... of products based on new scientific discoveries." NIST, originally founded as the National Bureau of Standards in 1901, works to strengthen U.S. industry's competitiveness; advance science and engineering; and improve public health, safety, and the environment. One

of the agency's basic functions is to develop, maintain, and retain custody of the national standards of measurement, and provide the means and methods for comparing standards used in science, engineering, manufacturing, commerce, industry, and education with the standards adopted or recognized by the Federal Government. As an agency of the U.S. Commerce Department's Technology Administration, NIST conducts basic and

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'At Boulder. CO 80303.

J Some elements at Boulder. CO.
NIST Special Publication 260-133

Standard Reference Materials:

Acetylene 12 C2H2 Absorption Reference for

1510-1540 nm Wavelength Calibration

SRM 2517

Sarah L. Gilbert William C. Swann

Electronics and Electrical Engineering Laboratory

National Institute of Standards and Technology

Boulder, CO 80303

U.S. DEPARTMENT OF COMMERCE, William M. Daley, Secretary

TECHNOLOGY ADMINISTRATION, Gary R. Bachula, Acting Under Secretary for Technology NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Raymond G. Kammer, Director Issued January 1998
National Institute of Standards and Technology Special Publication 260-133

Natl. Inst. Stand. Technol. Spec. Publ. 260-133, 34 pages (Jan. 1998)

CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1998

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
Foreword

Standard Reference Materials (SRMs) as defined by the National Institute of Standards and

Technology (NIST) are well-characterized materials, produced in quantity and certified for one or more physical or chemical properties. They are used to assure the accuracy and compatibility of measurements throughout the Nation. SRMs are widely used as primary standards in many

diverse fields in science, industry, and technology, both within the United States and throughout

the world. They are also used extensively in the fields of environmental and clinical analysis. In many applications, traceability of quality control and measurement processes to the national measurement system is carried out through the mechanism and use of SRMs. For many of the

Nation's scientists and technologists, it is therefore of more than passing interest to know the

details of the measurements made at NIST in arriving at the certified values of the SRMs

produced. The NIST Special Publication 260 Series is a series of papers reserved for this purpose. The 260 Series is dedicated to the dissemination of information on different phases of the

preparation, measurement, certification, and use of NIST SRMs. In general, much more detail

will be found in these papers than is generally allowed, or desirable, in scientific journal articles. This enables the user to assess the validity and accuracy of the measurement processes employed, to judge the statistical analysis, and to learn details of techniques and methods

utilized for work entailing greatest care and accuracy. These papers also should provide

sufficient additional information so SRMs can be utilized in new applications in diverse fields not foreseen at the time the SRM was originally issued.

Inquiries concerning the technical content of this paper should be directed to the author(s). Other questions concerned with the availability, delivery, price, and so forth, will receive prompt

attention from: Standard Reference Materials Program

Bldg. 202, Rm. 204

National Institute of Standards and Technology

Gaithersburg, MD 20899

Telephone: (301) 975-6776

FAX: (301) 948-3730

e-mail: srminfo@nist.gov, or www: http://ts. nist.gov/srm

Thomas E. Gills, Chief Standard Reference Materials Program

iii
OTHER NIST PUBLICATIONS IN THIS SERIES

Trahey, N.M., ed., NIST Standard Reference

Materials Catalog 1995-96, NIST Spec.Publ. 260(1995 Ed.). PB95-232518/AS

Michaelis, R.E., and Wyman, L.L., Standard Reference Materials: Preparation of White Cast

Iron Spectrochemical Standards, NBS Misc.

Publ. 260-1 (June 1964). COM74-1 1061**

Michaelis, R.E., Wyman, L.L., andFlitsch, R., Standard Reference Materials: Preparation of NBS Copper-Base Spectrochemical Standards, NBS Misc. Publ. 260-2 (October 1964). COM74-11063**

Michaelis, R.E., Yakowitz, H., and Moore, G.A., Standard Reference Materials: Metal lographic

Characterization of an NBS Spectrometric

Low-Alloy Steel Standard, NBS Misc. Publ. 260-3 (October 1964). COM74-1 1060**

Hague, J.L., Mears, T.W., and Michaelis, R.E., Standard Reference Materials: Sources of

Information, Publ. 260-4 (February 1965). COM74-11059**

Alvarez, R., and Flitsch, R., Standard Reference

Materials: Accuracy of SolutionX-Ray

Spectrometric Analysis of Copper-Base Alloys, NBS Misc. Publ. 260-5 (February 1965). PB168068**

Shultz, J. I., Standard Reference Materials: Methods

for the Chemical Analysis of White Cast Iron Standards, NBS Misc. Publ. 260-6 (July 1965). COM74-11068**

Bell, R.K., Standard Reference Materials: Methods

for the Chemical Analysis of NBS Copper-Base

Spectrochemical Standards, NBS Misc. Publ. 260-7 (October 1965). COM74-1 1067** Richmond, M.S., Standard Reference Materials: Analysis of Uranium Concentrates at the National Bureau of Standards, NBS Misc. Publ. 260-8 (December 1965). COM74-1 1066**

Anspach, S.C., Cavallo, L.M., Garfinkel, S.B., et al., Standard Reference Materials: Half Lives of

Materials Used in the Preparation of Standard Reference Materials of Nineteen Radioactive Nuclides Issued by the National Bureau of

Standards, NBS Misc. Publ. 260-9 (November

1965). COM74-1 1065**

Yakowitz, H., Vieth, D.L., Heinrich, K.F.J., et al., Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric Standards II: Cartridge Brass and LowAlloy

Steel, NBS Misc. Publ. 260-10 (December

1965). COM74-11064**

Napolitano, A., and Hawkins, E.G., Standard Reference Materials: Viscosity of Standard

Lead-Silica Glass, NBS Misc. Publ. 260-1 1** (November 1966). Yakowitz, H., Vieth, D.L., and Michaelis, R.E., Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric Standards III: White Cast Iron and Stainless Steel Powder Compact, NBS Misc. Publ. 260-12 (September 1966). Spijkerman, J.J., Snediker, D.K., Ruegg, F.C., et al., Standard Reference Materials: Mossbauer

Spectroscopy Standard for the Chemical Shift of

Iron Compounds, NBS Misc. Publ. 260-13**

(July 1967). Menis, O., and Sterling, J.T., Standard Reference

Materials: Determination of Oxygen in Ferrous

Materials (SRMs 1090, 1091, 1092), NBS Misc.

Publ. 260-14** (September 1966).

Passaglia, E. and Shouse, P.J., Standard Reference

Materials: Recommended Method of Use of

Standard Light-Sensitive Paper for Calibrating Carbon Arcs Used in TestingTestiles for Colorfastness to Light, NBS Spec.Publ. 260-15

(July 1967). Superseded by SP 260-41. Yakowitz, H., Michaelis, R.E., and Vieth, D.L., Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric Standards IV: Preparation and Microprobe

Characterization of W-20% Mo Alloy Fabricated by Powder Metallurgical Methods, NBS Spec.

Publ. 260-16 (January 1969). COM74-1 1062**

Catanzaro, E.J., Champion, C.E., Garner, E.L., et al., Standard Reference Materials: Boric Acid;

Isotopic, and Assay Standard Reference

Materials, NBS Spec.Publ. 260-17 (February

1970). PB189457**

iv
Geller, S.B., Mantek, P.A., and Cleveland, N.G.,

Calibration of NBS Secondary Standards Magnetic Tape Computer Amplitude Reference Amplitude Measurement "Process A" NBS

Spec. Publ. 260-18 (November 1969). Superseded by SP 260-29.

Paule, R.C., and Mandel, J., Standard Reference

Materials: Analysis oflnterlaboratory Measurements on the Vapor Pressure of Gold

(Certification of SRM 745). NBS Spec.Publ. 260-19 (January 1970). PB 190071**

260-20: Unassigned

Paule, R.C., and Mandel, J., Standard Reference

Materials: Analysis oflnterlaboratory Measurements on the Vapor Pressures of Cadmium and Silver, NBS Spec. Publ. 260-21

(January 1971). COM74-1 1359**

Yakowitz, H., Fiori, C.E., and Michaelis, R.E., Standard Reference Materials: Homogeneity

Characterization of Fe-3 Si Alloy, NBS Spec.

Publ. 260-22 (February 1971). COM74-1 1357**

Napolitano, A., and Hawkins, E.G., Standard Reference Materials: Viscosity of a Standard

Borosilicate Glass, NBS Spec.Publ. 260-23 (December 1970). COM7 1-001 57**

Sappenfield, K.M., Marinenko, G., and Hague, J.L., Standard Reference Materials: Comparison of Redox Standards, NBS Spec. Publ. 260-24

(January 1972). COM72-50058**

Hicho, G.E., Yakowitz, H., Rasberry, S.D., et al., Standard Reference Materials: A Standard Reference Material Containing Nominally Four

Percent Austenite, NBS Spec. Publ. 260-25

(February 1971). COM74-1 1356**

Martin, J.F., Standard Reference Materials: NBS-U.S. Steel Corp. Joint Program for Determining Oxygen and Nitrogen in Steel, NBS

Spec. Publ. 260-26 (February 1971). PB

81176620**

Garner, E.L., Machlan, L.A., and Shields, W.R.,

Standard Reference Materials: Uranium Isotopic Standard Reference Materials, NBS Spec.Publ. 260-27 (April 1971). COM74-1 1358**

Heinrich, K.F.J. , Myklebust, R.L., Rasberry, S.D., et

al., Standard Reference Materials: Preparation and Evaluation of SRMs 481 and 482

Gold-Silver and Gold-Copper Alloys for Microanalysis, NBS Spec.Publ. 260-28 (August

1971). COM71-50365**

Geller, S.B., Standard Reference Materials: Calibration of NBS Secondary Standard Magnetic Tape (Computer Amplitude Reference) Using the Reference Tape Amplitude Measurement "Process AModel 2," NBS Spec.

Publ. 260-29 (June 1971). COM7 1-50282**

Supersedes Measurement System in SP 260-18. Gorozhanina, R.S., Freedman, A.Y., and Shaievitch, A.B., (translated by M.C.Selby), Standard Reference Materials: Standard Samples Issued in the USSR (A Translation from the Russian), NBS Spec. Publ. 260-30 (June 1971). COM71-50283**

Hust, J.G., and Sparks, L.L., Standard Reference

Materials: Thermal Conductivity of Electrolytic Iron SRM 734 from 4 to 300 K, NBS Spec. Publ. 260-31 (November 1971). COM7 1-50563** Mavrodineanu, R., and Lazar, J.W., Standard Reference Materials: Standard QuartzCuvettes

for High Accuracy Spectrophotometry, NBS

Spec. Publ. 260-32 (December

1973).COM74-50018**

Wagner, H.L., Standard Reference Materials: Comparison of Original and Supplemental SRM

705, Narrow Molecular Weight Distribution Polystyrene, NBS Spec.Publ. 260-33 (May

1972) . COM72-50526**

Sparks, L.L., and Hust, J.G., Standard Reference

Material: Thermoelectric Voltage of Silver-28 Atomic Percent Gold Thermocouple Wire, SRM

733, Verses Common Thermocouple Materials (Between Liquid Helium and Ice Fixed Points), NBS Spec. Publ. 260-34 (April 1972). COM72-

50371**

Sparks, L.L., and Hust, J.G., Standard Reference

Materials: Thermal Conductivity ofAustenitic

Stainless Steel, SRM 735 from 5 to 280 K, NBS

Spec. Publ. 260-35 (April 1972). COM72-50368**

V
Cali, J. P., Mandel, J., Moore, L.J., et al., Standard Reference Materials: A Reference Method for the Determination of Calcium in Serum NBS

SRM 915, NBS Spec. Publ. 260-36 (May 1972). COM72-50527**

Shultz, J.I., Bell, R.K., Rains, T.C., et al., Standard Reference Materials: Methods of Analysis of NBS Clay Standards, NBS Spec. Publ. 260-37

(June 1972). COM72-50692**

Richard, J.C., and Hsia, J.J., Standard Reference

Materials: Preparation and Calibration of

Standards of Spectral Specular Reflectance, NBS

Spec. Publ. 260-38 (May 1972). COM72-

50528**

Clark, A.F., Denson, V.A., Hust, J.G., et al., Standard Reference Materials: The Eddy Current Decay Method for Resistivity Characterization of

High-Purity Metals, NBS Spec. Publ. 260-39 (May 1972). COM72-50529**

McAdie, H.G., Garn, P.D., and Menis, O., Standard Reference Materials: Selection of Differential Thermal Analysis Temperature Standards Through a Cooperative Study (SRMs 758, 759,

760), NBS Spec. Publ. 260-40 (August 1972) COM72-50776**

Wood. L.A., and Shouse, P.J., Standard Reference

Materials: Use of Standard Light-Sensitive Paper

for Calibrating Carbon Arcs Used in Testing

Textiles forColorfastness to Light, NBS Spec.

Publ. 260-41 (August 1972). COM72-50775**

Wagner, H.L., and Verdier, P.H., eds., Standard Reference Materials: The Characterization of

Linear Polyethylene, SRM 1475, NBS Spec.

Publ. 260-42 (September 1972). COM72-50944**

Yakowitz, H., Ruff, A.W., and Michaelis, R.E., Standard Reference Materials: Preparation and Homogeneity Characterization of anAustenitic Iron-Chromium-Nickel Alloy, NBS Spec. Publ. 260-43 (November 1972). COM73-50760**

Schooley, J.F., Soulen, R.J., Jr., and Evans, G.A.,

Jr., Standard Reference Materials: Preparation and Use of Superconductive Fixed Point Devices, SRM 767, NBS Spec. Publ. 260-44 (December 1972). COM73-50037**

Greifer, B., Maienthal, E.J., Rains, T.C., et al., Standard Reference Materials: Development of NBS SRM 1579 Powdered Lead-Based Paint, NBS Spec. Publ. 260-45 (March 1973). COM73-50226**

Hust, J.G., and Giarratano, P.J., Standard Reference

Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials: Austenitic Stainless Steel, SRMs 735 and 798, from 4 to 1200 K, NBS Spec. Publ. 260-46 (March 1975). COM75-10339**

Hust, J.G., Standard Reference Materials: Electrical Resistivity of Electrolytic Iron, SRM 797, and

Austenitic Stainless Steel, SRM 798, from 5 to 280 K, NBS Spec. Publ. 260-47 (February

1974). COM74-50176**

Mangum, B.W., and Wise, J.A., Standard Reference

Materials: Description and Use of Precision Thermometers for the Clinical Laboratory, SRM

933 and SRM 934, NBS Spec. Publ. 260-48 (May 1974). Superseded by NIST Spec. Publ. 260-113. COM74-50533**

Carpenter, B.S., and Reimer, G.M., Standard Reference Materials: Calibrated Glass Standards

for Fission Track Use, NBS Spec. Publ. 260-49 (November 1974). COM74-51 185**

Hust, J.G., and Giarratano, P.J., Standard Reference

Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials:

Electrolytic Iron, SRMs 734 and 797 from 4 to 1000 K, NBS Spec. Publ. 260-50 (June 1975). COM75-10698**

Mavrodineanu, R., and Baldwin, J.R., Standard Reference Materials: Glass Filters As a SRM for Spectrophotometry-Selection, Preparation,

Certification, and Use-SRM 930 NBS Spec.

Publ. 260-51 (November 1975). COM75-10339**

Hust, J.G., and Giarratano, P.J., Standard Reference

Materials: Thermal Conductivity and Electrical Resistivity SRMs 730 and 799, from 4 to 3000

K, NBS Spec. Publ. 260-52 (September 1975). COM75-11193**

Durst, R.A., Standard Reference Materials: Standardization of pH Measurements, NBS

Spec. Publ. 260-53 (December 1978). Superseded by SP 260-53 Rev. 1988 Edition. PB882 17427**

vi
Burke, R.W., and Mavrodineanu, R., Standard Reference Materials: Certification and Use of

Acidic Potassium Dichromate Solutions as an

Ultraviolet Absorbance Standard, NBS Spec.

Publ. 260-54 (August 1977). PB272168**

Ditmars, D.A., Cezairliyan, A.Jshihara, S., et al., Standard Reference Materials: Enthalpy and

Heat Capacity; Molybdenum SRM 781, from

273 to 2800 K, NBS Spec. Publ. 260-55 (September 1977). PB272127**

Powell, R.L., Sparks, L.L., andHust, J.G., Standard Reference Materials: Standard Thermocouple

Material, Pt-67: SRM 1967, NBS Spec. Publ. 260-56 (February 1978). PB277172**

Cali, J.P., and Plebanski, T., Standard Reference

Materials: Guide to United States Reference

Materials, NBS Spec. Publ. 260-57 (February

1978). PB277173**

Barnes, J.D., and Martin, G.M., Standard Reference

Materials: Polyester Film for Oxygen Gas

Transmission Measurements SRM 1470, NBS

Spec. Publ. 260-58 (June 1979). PB297098**

Chang, T., and Kahn, A.H., Standard Reference

Materials: Electron Paramagnetic Resonance

Intensity Standard: SRM 2601; Description and

Use, NBS Spec. Publ. 260-59 (August 1978). PB292097**

Velapoldi, R.A.,Paule, R.C., Schaffer, R., et al., Standard Reference Materials: A Reference Method for the Determination of Sodium in Serum, NBS Spec. Publ. 260-60 (August 1978). PB286944**

Verdier, P.H., and Wagner, H.L., Standard Reference Materials: The Characterization of

Linear Polyethylene (SRMs 1482, 1483, 1484), NBS Spec. Publ. 260-61 (December 1978). PB289899**

Soulen, R.J., and Dove, R.B., Standard Reference

Materials: Temperature Reference Standard for Use Below 0.5 K (SRM 768), NBS Spec. Publ. 260-62 (April 1979). PB294245**

Velapoldi, R.A., Paule, R.C., Schaffer, R., et al., Standard Reference Materials: A Reference Method for the Determination of Potassium in Serum, NBS Spec. Publ. 260-63 (May 1979). PB297207**

Velapoldi, R.A., andMielenz, K.D., Standard Reference Materials: A Fluorescence SRM

Quinine Sulfate Dihydrate (SRM 936), NBS

Spec. Publ. 260-64 (January 1980). PB80132046**

Marinenko, R.B., Heinrich, K.F.J. , andRuegg, F.C., Standard Reference Materials: Micro-Homogeneity Studies of NBS SRM, NBS

Research Materials, and Other Related Samples, NBS Spec. Publ. 260-65 (September 1979). PB300461**

Venable, W.H., Jr., andEckerle, K.L., Standard Reference Materials: Didymium Glass Filters for Calibrating the Wavelength Scale of

Spectrophotometers (SRMs 2009, 2010, 2013,

2014). NBS Spec. Publ. 260-66 (October 1979). PB801 04961**

Velapoldi, R.A., Paule, R.C., Schaffer; R., et al., Standard Reference Materials: A Reference Method for the Determination of Chloride in Serum, NBS Spec. Publ. 260-67 (November

1979). PB80110117**

Mavrodineanu, R., and Baldwin, J.R., Standard Reference Materials: Metal-On-Quartz Filters as a SRM for Spectrophotometry SRM 203 1, NBS

Spec. Publ. 260-68 (April 1980). PB80 197486**

Velapoldi, R.A., Paule, R.C., Schaffer, R., et al., Standard Reference Materials: A Reference Method for the Determination of Lithium in Serum, NBS Spec. Publ. 260-69 (July 1980). PB80209117**

Marinenko, R.B., Biancaniello, F.,Boyer, P.A., et

al., Standard Reference Matffials: Preparation and Characterization of an Iron-Chromium-Nickel Alloy for Microanalysis: SRM 479a, NBS Spec. Publ. 260-70 (May

1981). SN003-003-02328-1*

Seward, R.W., and Mavrodineanu, R., Standard Reference Materials: Summary of the Clinical Laboratory Standards Issued by the National Bureau of Standards, NBS Spec. Publ. 260-71 (November 1981). PB82135161**

Reeder, D.J., Coxon, B., Enagonio, D., et al., Standard Reference Materials: SRM 900, Antiepilepsy Drug Level Assay Standard, NBS Spec.

Publ. 260-72 (June 1981). PB81220758

vii
Interrante, C.G., andHicho, G.E., Standard Reference Materials: A Standard Reference

Materia] Containing Nominally Fifteen Percent

Austenite (SRM 486), NBS Spec.Publ. 260-73

(January 1982). PB82215559**

Marinenko, R.B., Standard Reference Materials: Preparation and Characterization of K4 1 1 and K-412 Mineral Glasses for Microanalysis: SRM

470, NBS Spec. Publ. 260-74 (April 1982). PB82221300**

Weidner, V.R., and Hsia, J.J., Standard Reference

Materials: Preparation and Calibration of First Surface Aluminum Mirror Specular Reflectance

Standards (SRM 2003a), NBS Spec.Publ. 260-75 (May 1982). PB82221367**

Hicho, G.E., and Eaton, E.E., Standard Reference

Materials: A Standard Reference Material Containing Nominally Five PercentAustenite (SRM 485a), NBS Spec. Publ. 260-76 (August

1982). PB831 15568**

Furukawa, G.T., Riddle, J.L.,Bigge, W.G., et al., Standard Reference Materials: Application of Some Metal SRMs as Thermometric Fixed

Points, NBS Spec. Publ. 260-77 (August 1982). PB831 17325**

Hicho, G.E., and Eaton, E.E., Standard Reference

Materials: Standard Reference Material Containing Nominally Thirty PercentAustenite (SRM 487), NBS Spec. Publ. 260-78 (September

1982). PB831 15576** Richmond, J.C., Hsia, J.J., Weidner, V.R., et al., Standard Reference Materials: Second Surface Mirror Standards ofSpecular Spectral Reflectance (SRMs 2023, 2024, 2025), NBS

Spec. Publ. 260-79 (October 1982). PB84203447**

Schaffer, R., Mandel, J., Sun, T., et al., Standard Reference Materials: Evaluation by an ID/MS

Method of the AACC Reference Method for Serum Glucose, NBS Spec. Publ. 260-80

(October 1982). PB842 16894**

Burke, R.W., and Mavrodineanu, R., Standard Reference Materials: Accuracy in Analytical Spectrophotometry, NBS Spec.Publ. 260-81

(April 1983). PB83214536**

Weidner, V.R., Standard Reference Materials: White Opal Glass Diffuse Spectral Reflectance Standards for the Visible Spectrum (SRMs 201

5

and 2016), NBS Spec. Publ. 260-82 (April 1983). PB83220723**

Bowers, G.N., Jr., Alvarez, R., Cali, J.P., et al., Standard Reference Materials: The Measurement

of the Catalytic (Activity) Concentration of Seven Enzymes in NBS Human Serum (SRM

909), NBS Spec. Publ. 260-83 (June 1983). PB83239509**

Gills, T.E., Seward, R.W., Collins, R.J., et al., Standard Reference Materials: Sampling,

Materials Handling, Processing, and Packaging

of NBS Sulfur in Coal SRMs 2682, 2683, 2684, and 2685, NBS Spec. Publ. 260-84 (August

1983). PB84109552**

Swyt, D.A., Standard Reference Materials: A Look

at Techniques for the Dimensional Calibration of Standard Microscopic Particles, NBS Spec.Publ. 260-85 (September 1983). PB841 12648**

Hicho, G.E., and Eaton, E.E., Standard Reference

Materials: A SRM Containing Two and One-Half Percent Austenite, SRM 488, NBS

Spec. Publ. 260-86 (December 1983). PB84143296** Mangum, B.W., Standard Reference Materials: SRM

1969: Rubidium Triple-Point - A Temperature

Reference Standard Near 39.30° C, NBS Spec.

Publ. 260-87 (December 1983). PB84149996**

Gladney, E.S., Burns, C.E., Perrin, D.R., et al., Standard Reference Materials: 1982 Compilation of Elemental Concentration Data for NBS

Biological, Geological, and Environmental

Standard Reference Materials, NBS Spec.Publ. 260-88 (March 1984). PB842 18338**

Hust, J.G., Standard Reference Materials: AFineGrained, Isotropic Graphite for Use as NBS

Thermophysical PropertyRMs from 5 to 2500 K, NBS Spec. Publ. 260-89 (September 1984). PB851 12886**

Hust, J.G., and Lankford, A.B., Standard Reference

Materials: Update of Thermal Conductivity and

Electrical Resistivity of Electrolytic Iron, Tungsten, and Stainless Steel, NBS Spec.Publ. 260-90 (September 1 984). PB85 1 1 5 8 1 4*

viii
Goodrich, L.F., Vecchia, D.F., Pittman, E.S., et al., Standard Reference Materials: Critical Current Measurements on anNbTi Superconducting Wire SRM, NBS Spec.Publ. 260-91 (September

1984). PB85 118594**

Carpenter, B.S., Standard Reference Materials: Calibrated Glass Standards for Fission Track Use

(Supplement to NBS Spec. Publ. 260-49), NBS

Spec. Publ. 260-92 (September 1984). PB851 13025**

Ehrstein, J.R., Standard Reference Materials: Preparation and Certification of SRM for Calibration of Spreading Resistance Probes, NBS Spec. Publ. 260-93 (January 1985). PB85177921**

Gills, T.E., Koch, W.F., Stolz, J.W., et al., Standard Reference Materials: Methods and Procedures Used at the National Bureau of Standards to Certify Sulfur in CoalSRMs for Sulfur Content,

Calorific Value, Ash Content, NBS Spec.Publ. 260-94 (December 1984). PB85 165900**

Mulholland, G.W., Hartman, A.W., Hembree, G.G.,

et al, Standard Reference Materials: Development of a 1mm Diameter Particle Size Standard, SRM 1690, NBS Spec. Publ. 260-95 (May 1985). PB95-232518/AS**

Carpenter, B.S., Gramlich, J.W., Greenberg, R.R., et

al., Standard Reference Materials: Uranium-235

Isotopic Abundance Standard Reference

Materials for Gamma Spectrometry Measurements, NBS Spec.Publ. 260-96

(September 1986). PB87 108544**

Mavrodineanu, R., and Gills, T.E., Standard Reference Materials: Summary of the Coal, Ore,

Mineral, Rock, and Refactory Standards Issued by the National Bureau of Standards, NBS Spec.

Publ. 260-97 (September 1985). PB861 10830**

Hust, J.G., Standard Reference Materials: Glass

Fiberboard SRM for Thermal Resistance, NBS

Spec. Publ. 260-98 (August 1985). SN003-003-02674-3*

Callanan, J.E., Sullivan, S.A., and Vecchia, D.F., Standard Reference Materials: Feasibility Study

for the Development of Standards Using

Differential Scanning Calorimetry, NBS Spec.

Publ. 260-99 (August 1985). PB86 106747**

Taylor, J.K., Trahey, N.M., ed., Standard Reference

Materials: Handbook for SRM Users, NBS Spec.

Publ. 260-100 (February 1993). PB93 183796** Mangum, B.W., Standard Reference Materials: SRM

1970, Succinonitrile Triple-Point Standard: A

Temperature Reference Standard Near 58.08° C, NBS Spec. Publ. 260-101 (March 1986). PB86197100**

Weidner, V.R., Mavrodineanu, R., Mielenz, K.D., et

al., Standard Reference Materials: Holmium

Oxide Solution Wavelength Standard from 240

to 640 nm - SRM 2034, NBS Spec. Publ. 260-102 (July 1986). PB86245727**

Hust, J.G., Standard Reference Materials: Glass

Fiberblanket SRM for Thermal Resistance, NBS

Spec. Publ. 260-103 (September 1985). PB86109949**

Mavrodineanu, R., and Alvarez, R., Standard Reference Materials: Summary of the Biological and Botanical Standards Issued by the National Bureau of Standards, NBS Spec.Publ. 260-104 (November 1985). PB86155561**

Mavrodineanu, R., andRasberry, S.D., Standard Reference Materials: Summary of the Environmental Research, Analysis, and Control Standards Issued by the National Bureau of

Standards, NBS Spec. Publ. 260-105 (March

1986) . PB86204005**

Koch, W.F., ed., Standard Reference Materials: Methods and Procedures Used at the National Bureau of Standards to Prepare, Analyze, and

Certify SRM 2694, Simulated Rainwater, and Recommendations for Use, NBS Spec.Publ. 260-106 (July 1986). PB86247483**

Hartman, A.W., and McKenzie, R.L., Standard Reference Materials: SRM 1965, Microsphere

Slide (10 |im Polystyrene Spheres), NIST Spec.

Publ. 260-107 (November 1988). PB89153704**

Mavrodineanu, R., and Gills, T.E., Standard Reference Materials: Summary of Gas Cylinder and Permeation Tube Standard Reference

Materials Issued by the National Bureau of

Standards, NBS Spec. Publ. 260-108 (May

1987) . PB87209953**

ix
Candela, G.A., Chandler-Horowitz, D.,Novotny,

D.B., et al., Standard Reference Materials: Preparation and Certification of an

Ellipsometrically Derived Thickness and

Refractive Index Standard of a Silicon Dioxide

Film (SRM 2530), NIST Spec. Publ. 260-109

(October 1988). PB89133573**

Kirby, R.K., and Kanare, H.M., Standard Reference

Materials: Portland Cement Chemical

Composition Standards (Blending, Packaging, and Testing), NBS Spec. Publ. 260-1 10 (February 1988). PB88193347**

Gladney, E.S., OMalley, B.T., Roelandts, I., et al., Standard Reference Materials: Compilation of

Elemental Concentration Data for NBS Clinical, Biological, Geological, and Environmental

Standard Reference Materials, NBS Spec. Publ. 260-111 (November 1987). PB88156708**

Marinenko, R.B., Blackburn, D.H., and Bodkin,

J.B., Standard Reference Materials: Glasses for Microanalysis: SRMs 1871-1875, NIST Spec.

Publ. 260-1 12 (February 1990). PB90215807** Mangum, B.W., and Wise, J.A., Standard Reference

Materials: Description and Use of a Precision Thermometer for the Clinical Laboratory, SRM

934, NIST Spec. Publ. 260-1 13 (June 1990). PB90257643**

Vezzetti, C.F., Varner, R.N., and Potzick, J.E., Standard Reference Materials: BrightChromium

Linewidth Standard, SRM 476, for Calibration of

Optical Microscope Linewidth Measuring

Systems, NIST Spec. Publ. 260-1 14 (January

1991). PB91 167163**

Williamson, M.P., Willman, N.E., and Grubb, D.S., Standard Reference Materials: Calibration of NIST SRM 3201 for 0.5 in. (12.65 mm) Serial Serpentine Magnetic Tape Cartridge, NIST Spec.

Publ. 260-1 15 (February 1991). PB91 187542**

Mavrodineanu, R., Burke, R.W., Baldwin, J.R., et

al., Standard Reference Materials: Glass Filters as a Standard Reference Material for Spectrophotometry-Selection, Preparation,

Certification and Use of SRM 930 and SRM

1930, NIST Spec. Publ. 260-1 16 (March 1994). PB94-188844/AS**

Vezzetti, C.F., Varner, R.N., and Potzick, J.E., Standard Reference Materials: Anti- reflecting-Chromium Linewidth Standard, SRM

475, for Calibration of Optical Microscope

Linewidth Measuring Systems, NIST Spec. Publ. 260-1 17 (January 1992). PB92-149798**

Williamson, M.P., Standard Reference Materials: Calibration of NIST Standard Reference Material 3202 for 18-Track, Parallel, and 36-Track,

Parallel Serpentine, 12.65 mm (0.5 in), 1491 cpmm (37871 cpi), Magnetic Tape Cartridge, NIST Spec. Publ. 260-1 18 (July 1992). PB92-

226281**

Vezzetti, C.F., Varner, R.N., and Potzick, Standard Reference Materials: Antireflecting-Chromium Linewidth Standard, SRM 473, for Calibration of

Optical Microscope Linewidth Measuring

System, NIST Spec. Publ. 260-1 19 (September

1992) Caskey, G.W., Philips, S.D., Borchardt, et al., Standard Reference Materials: A Users' Guide to NIST SRM 2084: CMM Probe Performance

Standard, NIST Spec. Publ. 260-120 (1994) Rennex, B.G., Standard Reference Materials:

Certification of a Standard Reference Material

for the Determination of Interstitial Oxygen

Concentration in Semiconductor Silicon by

Infrared Spectrophotometry, NIST Spec. Publ. 260-121 (1994) PB95-125076/AS

Gupta, D., Wang, L., Hanssen, L.M., Hsai, J.J., and

Datla, R.U., Polystyrene Films for Calibrating

the Wavelength Scale of Infrared Spectrophotometer (SRM 1921). NIST Spec.

Publ. 260-122 (1995) PB95-226866/AS

Development of Technology and the Manufacture of

Spectrometric SRMs for Naval Brasses (MC62

M63). NIST Spec. Publ. 260-123 (IN PREP).

Strouse, G.F., SRM 1744: Aluminum

Freezing Point Standard. NIST Spec. Publ. 260- 124 (1995) SN003-003-03342-1

Schiller, S.B, Standard Reference Materials:

Statistical Aspects of the Certification of Chemical Batch SRMs. NIST Spec. Publ. 260-

125 (1996) PB96-210877/AS

x
Guenther, F.R., Dorko, W.D., Miller, W.R., et al., Standard Reference Materials: The NIST

Traceable Reference Material Program for Gas

Standards, NIST Spec.Publ. 260-126 (1996) PB96-210786/AS

Strouse, G.F., and Ahmet, A.T., Standard Reference

Material 1747: Tin Freezing-Point Cell and

Standard Reference Material 1748: Zinc

Freezing-Point Cell. NIST Spec.Publ. 260-127

SN003-003-03488-6.

Zhang, Z.M., Gentile, T.R., Migdall, A.L., and

Datla, R.U., Transmission Filters with Measured

Optical Density at 1 064 nm Wavelength-SRMs

2046, 2047, 2048, 2049, 2050, and 2051. SRM

Spec. Publ. 260-128 (IN PREP).

Potzick, J.E., Antireflecting-Chromium Linewidth

Standard, Standard Reference Material 473, for Calibration of Optical MicroscopeLinewidth

Measuring Systems, NIST Spec.Publ. 260-129

(1997) SN003-003-03447-9.

Zarr, R.R., Standard Reference Materials: Glass

Fiberboard, Standard Reference Material 1450c,

for Thermal Resistance from 280K to 340K, NIST Spec. Publ. 260-130 (1997) PB97-

177166/AS.

Ehrstein, J.R., andCroarkin, M.C., The Certification of 100 mm Diameter Silicon Resistivity SRMs

2541 through 2547 Using Dual-Configuration

Four-Point Probe Measurements. NIST Spec.

Publ. 260-131.

Strouse, G.G., Standard Reference Material 1745: Indium Freezing Point Standard and Standard Reference Material 2232: Indium DSC Melting

Point Standard, NIST Spec.Publ. 260-132 (IN PREP).

*Send order with remittance to: Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325. Remittance from

foreign countries should include an additional one fourth of the purchase price for postage. **May be ordered from: National Technical

Information Services (NTIS), Springfield, VA

22161. For information phone (703-487-4650) To Place an Order with PB# phone (800-553- 6847)

NIST SPECIAL PUBLICATION 260-133

Standard Reference Materials: Acetylene 12C2H2 Absorption Reference for 1510-1540 nm Wavelength Calibration - SRM 2517

Sarah L. Gilbert and William C. Swann

Optoelectronics Division

Electronics and Electrical Engineering Laboratory

National Institute of Standards and Technology

Boulder, CO 80303

ABSTRACT

Standard Reference Material (SRM) 2517 is an optical-fiber-coupled absorption cell containing

acetylene (

12C2H2) gas. It is intended for use in calibrating the wavelength scale of wavelength

measuring instruments in the 1500 nm region. About 50 accurately measured absorption lines of

the R and P branch of the Vi + v3 rotational-vibrational band of 12C2H2 are located between 1510- 1540 nm. We have measured the pressure-induced shift of the lines and certify the SRM

wavelengths with an expanded uncertainty (coverage factor k = 2) of ± 0.0006 nm. This

publication describes the SRM, the NIST measurement procedure, and the uncertainty determination for SRM certification.

Keywords: absorption; acetylene; molecular spectroscopy; optical fiber communication; Standard Reference Material; wavelength calibration; wavelength division multiplexing; wavelength

reference; WDM

1
1. Introduction Wavelength references are needed in the 1500 nm region to support future wavelength division multiplexed (WDM) optical fiber communication systems. In a WDM system, many wavelength

channels are sent down the same fiber, thereby increasing the bandwidth of the system by the number of channels. If one channel's wavelength were to shift, crosstalk could occur between it and a neighboring channel. Wavelength references are needed to calibrate instruments that measure and set the wavelengths of the channels. The NIST Optoelectronics Division has received numerous inquiries about wavelength calibration

in the 1500 nm region. Most applications involve calibrating a commercial optical spectrum

analyzer (OSA) which is based on the dispersion of light by a diffraction grating. An OSA

typically has a resolution of 0.1 nm; the highest resolution currently available is 0.05 nm. Most

users are interested in calibrating these instruments to an uncertainty between 0.1 and 0.01 nm. Many users are also interested in calibrating the wavelength scan linearity of their instruments. A

calibration service did not seem practical for these instruments; they are large and fragile, and the

optical elements can shift during shipment, causing a loss of wavelength calibration. The NIST

solution is to produce Standard Reference Material (SRM) cells containing gases which have

accurately measured absorption lines in this wavelength region. Fundamental molecular

absorptions provide references which are very stable under changing environmental conditions such as temperature and pressure variations, or the presence of electric and magnetic fields. These SRMs can also be used to calibrate the wavelength readout of tunable lasers and check the accuracy of wavelength meters.

There are very few wavelength references available in the 1500 nm region. There is only one gas

laser reference line: the 1523 nm helium-neon laser. The only atomic absorption lines in this region are between excited states and thus require initial excitation by a laser or electric discharge. Another possibility is frequency doubling 1500-1560 nm light to probe atomic transitions in the 750-780 nm region. This requires fairly complicated and expensive apparatus. Molecular

transitions in the 1500 nm region are combination or overtone bands that can be probed directly. We have chosen to use the absorption lines of acetylene (this SRM) and hydrogen cyanide (SRM

2519) for references in the 1500 nm region for the following reasons:

(1) Molecular lines are simple to access, since this involves simply passing light through a cell containing the gas and observing the absorption spectrum.

(2) These molecules have strong absorption bands in this region.

(3) The combined spectra of the two gases cover the communications band, from 1510 to 1565 nm.

(4) The spectra are uncomplicated; thus it is not difficult to identify the lines. (5) The wavelengths of the prominent lines have been measured with an uncertainty of less than 0.001 nm.

(6) There are many reference lines with spacings ranging from 0.4 to 0.9 nm, providing for scan

linearity calibration as well as single-point wavelength calibration. 2
(7) A cell containing the gas can be easily pigtailed with optical fiber, so that it is compatible with the sources and measurement instruments used by the optical fiber communications

industry.

(8) The gas cell design allows for versatile calibration capability; it can be used with a variety of

sources (LED, amplified spontaneous emission, white light, laser, etc.) to calibrate any wavelength measuring instrument in this region.

2. SRM 2517 description

This SRM is based on the fundamental absorptions of light by acetylene (

12C2H2). The spectrum of this molecule in the 1500 nm region is shown in Fig. 1. The lines are the R and P branches of

the Vi + v3 rotational-vibrational band of 12C2H2 . Figure 2 shows a schematic diagram of our

apparatus for measuring the spectrum in Fig. 1. Light from an LED source (about 80 nm

bandwidth) is coupled to an acetylene absorption cell using single-mode optical fiber. The light exiting the fiber is collimated by a lens, passes through the absorption cell, and is coupled into another section of single-mode fiber. This fiber is connected to a commercial optical spectrum

analyzer. The resulting spectrum is the emission spectrum from the LED with narrow depressions due to the absorption of the light by the molecules. The spectrum in Fig. 1 has been normalized

to the LED spectrum. We have also recorded the spectrum using a tunable laser as the light source. In this case the transmission through the cell was monitored by a detector as the laser's wavelength was tuned. The vacuum wavelengths of the acetylene Vi + v3 lines have been measured with an uncertainty of

less than 0.0001 nm [1]. Table 1 lists the literature values for the wavelengths from 1513 to 1541 nm. We have compared these values with other experimental measurements in the literature [2,3] and find agreement within 0.0002 nm, which is within the expanded uncertainty of Refs. 2 and 3. Our measurements of six lines (below) also agree within our 0.0015 nm wavelength meter

uncertainty.

3. SRM design

The SRM design is essentially that shown schematically in Fig. 2; an absorption cell is pigtailed with single-mode optical fiber. The input and output ports are FC/PC fiber bulkhead connectors on the outside of the instrument box. Users supply their own light source and detection; this enables flexibility since some users may want to calibrate optical spectrum analyzers using a broadband light source, and others may want to check the calibration of tunable lasers or wavelength meters using a narrowband source. The absorption cell material is Pyrex glass; the windows are fused to the cell. The cell is first evacuated and leak-checked, and then filled with high purity gas (99.96%

12C2H2). It is then

tipped off using a torch, providing an all-glass seal. The cell is securely mounted in an aluminum

holder. The fiber-coupled collimators are also mounted on this holder using commercially

available aligners. FC/PC connectors on the other ends of the optical fibers connect to bulkhead

connectors mounted on the instrument box which houses the cell holder.

3
We chose a pressure of 27 kPa (200 Torr) so that the lines would be pressure-broadened by less than 0.05 nm and thus provide a large signal, without significant loss of resolution, when used

with instruments with this resolution. At this pressure, a slight shift of each line (pressure shift) is possible due to energy level shifts caused by the interaction of the molecules during elastic collisions [4]. An upper limit for the pressure shift of 200 kHz/Torr (1.5 kHz/Pa) has been

reported for one acetylene line at low pressure [5]. We have measured the pressure shift of

several lines, as described in section 4.1.

4. Line center uncertainty For this Standard Reference Material, the stability of the wavelength of each absorption line is a

critical characteristic. The choice of fundamental molecular absorption lines makes the SRM

insensitive to most changes in environmental conditions. The symmetric isotopic species of

acetylene (

12C2H2 and 13C2H2) are particularly insensitive to changes because they have no

permanent dipole moment. Thus, pressure broadening, pressure shift, and Stark shift are expected

to be small. For the desired SRM certification uncertainty of about 0.001 nm, the only line shift mechanism which could potentially contribute at this level is the shift due to pressure (collisions between molecules). Other factors associated with line fitting could cause apparent shifts of lines. In section 4. 1 we discuss our measurement of the pressure shift.

4. 1 Pressure shift measurement A schematic diagram of our pressure shift measurement apparatus in shown in Fig. 3. Light from

a tunable diode laser is sent through two absorption cells simultaneously, and the transmission through each cell is monitored by a detector. One cell contains acetylene gas at low pressure

(8.0 ± 0.8 kPa; about 60 Torr) and the other contains a relatively high pressure of 54 + 5 kPa

(about 400 Torr). The pressure uncertainty quoted is the expanded uncertainty using a coverage

factor k = 2. A wavelength meter with an uncertainty of 1 part in 10

6 (0.0015 nm) monitors the wavelength of the laser. A computer scans the wavelength of the laser in approximately 0.001 nm

steps and records the two detectors and wavelength meter readings.

Figure 4 shows the spectrum obtained of line P5. The pressure broadening in the high-pressure

cell is obvious. We are interested in the relative shift between the line centers in the low-pressure and high-pressure cells. Six lines were recorded using this technique. The measured quantity, the transmitted power IT, is related to the absorption coefficient a and the absorption path length L by

It = I<>exp(-aL), (1) where I0 is the incident power. We first normalized the data to I0 and then took the natural logarithm to obtain aL. The low pressure lines were fitted to a Voigt profile [6] using the least- squares method of a commercial fitting program. Due to the dominance of pressure broadening in the high pressure cell, these lines were fitted to a Lorentzian profile. Several factors complicated

the fitting procedure: overlap with nearby lines, background slopes, interference fringes on the cell transmission spectra, and uncertainty in the wavelength of each point. Our approach to minimizing and measuring the effects of these contributions is discussed below.

4
4.1.1 Overlap with nearby lines Wings of nearby lines can skew the shape of the line being measured and shift its apparent center. There are a number of weak lines throughout the spectrum which are due to hot bands (transitions that are not out of the ground vibrational state) [7]. To account for the weak nearby lines, we did

a multiple-line fit to the low pressure cell spectrum (Fig. 5a - spectrum inverted) and then used

the line locations and strengths obtained in this fit as input to a multiple-line fit of the high

pressure cell spectrum (Fig. 5b). A multiple-line fit is simply a fit to a sum of lines instead of a

single line. For the spectra shown in Figs. 5a and 5b, the multiple-line fit consisted of the main

line near 1528.6 nm and three weak lines at longer wavelengths. After modeling the weak lines, we subtracted them from the data to obtain a spectrum that contained only the main line. This modified spectrum could then be fit more accurately with the appropriate error bars. We

estimated the uncertainty in this process by visibly changing the center wavelength parameter of

the nearest line and refitting the data with this parameter fixed. This resulted in a negligible shift of the main line for the low pressure cell data and a maximum shift of ± 0.0002 nm for the high

pressure cell data. Assuming a rectangular distribution with upper and lower limits of ± 0.0002 nm about the mean value, this corresponds to a standard uncertainty (estimated standard

deviation) u of 0.0001 nm (=0.0002/^3).

4.1.2 Background slope A background slope on the spectrum can shift the apparent center of a line, particularly for the wide lines of the high pressure cell. We have identified two sources of background slope: (1) wavelength dependence of the fiber couplers and other optical components, and (2) change in the

laser power. Since the magnitudes of the background slopes were small, we chose to fit the data without removing the slopes. Slight residual slopes in the data could be seen in the fit residual

plots. By fitting the data again with the slope removed, we calculate that the maximum shift due

to any residual slope is negligible for the low pressure cell data and ± 0.0002 nm for the high

pressure cell data. Assuming a rectangular distribution with upper and lower limits of ± 0.0002 nm about the mean value, this corresponds to a standard uncertainty u of 0.0001 nm.

4. 1 .3 Interference fringes Interference fringes due to reflections of the laser light can be a problem. We spent considerable time reducing these effects. The windows of the cells were mounted at a 10° angle with respect

to the laser beam path. We selected low back-reflection fiber-pigtailed lenses and terminated the

fibers (at the detectors) with angled fiber connectors. These measures reduced the interference

fringe amplitude considerably. The amplitudes of the remaining fringes were less than 0.2%. We

modeled the effect of the fringes by simulating lines with and without the modulation and fitting the simulated data to obtain the line centers. Using the worst-case scenario for the phase of the modulation relative to the line center, we calculate a maximum apparent line shift of ±0.00001 nm for the low pressure cell data and ±0.0004 nm for the high pressure cell data. Assuming a rectangular distribution with upper and lower limits of ± 0.0004 nm about the mean

value, this corresponds to a standard uncertainty u of 0.0002 nm for the high pressure cell data.

5
4. 1 .4 Wavelength uncertainty Since the transmissions through the low and high pressure cells were measured simultaneously,

the accuracy of the wavelength meter was adequate for this measurement. However, its limited resolution (0.001 nm) did add noise to the data. This, in turn, complicated the fitting since there was noise in both y (transmitted intensity) and x (wavelength), and our fitting program could accommodate uncertainty in y only. Since the transmission is a complicated function of

wavelength, uncertainty of the wavelength has the largest effect where the transmission slope is the greatest. Our approach to estimating the uncertainty in each data point was to first fit the data with a Lorentzian lineshape [8]. We then took the derivative of this function with respect to wavelength and from that derived a virtual uncertainty in the transmission T due to this wavelength dependence:

We then combined this uncertainty with the uncertainty due to intensity variation (measured

experimentally) for the overall estimate of uncertainty for each transmission measurement point.

5. Uncertainty determination We measured the pressure shifts for six different lines, choosing lines at a variety of locations in the spectrum. This ensured that our data would be sensitive to any variations in the pressure shift, if the shift varied with line number. We obtained reduced residual-sum-of-squares (x

2

) values ranging from 0.9 to 2.6 for the fitting of six lines. From the fit residual plots, we could discern the

slight slopes and sinusoidal modulation described above; fitting and removing these slopes and

modulations reduced the %

2 values to 0.8 - 1.1. As discussed above, we used the line center values obtained from fitting without the slopes and modulations removed, since we do not think it was justified to arbitrarily remove these effects. Instead, we used the residual plots to estimate

the uncertainty in the line centers. The magnitudes of the slopes and modulations in the residual

plots were consistent with background data taken with the cells removed from the measurement

apparatus. The uncertainty budget for the relative line center determinations is given in Table 2 and the

uncertainty source type [9] (A or B) is indicated. The largest source of uncertainty is the apparent shift due to interference fringes. Table 3 lists the shifts measured for six lines. Since it is possible that the pressure shifts for the different lines are slightly different, we use the average of

the pressure shifts measured, and combine the individual shift standard uncertainty uc(A) with the standard deviation of the six line shifts u(six) using the a root-sum-of-squares (RSS) method to obtain the overall line shift standard uncertainty of 0.0005 nm.

Unless otherwise stated, the uncertainties given below are all expanded uncertainties using a coverage factor k = 2. Our result is a pressure shift of 0.0015 ± 0.0010 nm for a pressure

difference of 46 ± 5 kPa (345 ± 40 Torr); yielding (+ 3.2 + 2.2) x 10"5 nm/kPa [(+ 4.3 ± 2.9) x

10-6 nm/Torr], or - 4. 1 ± 2.8 MHz/kPa (- 0.55 ± 0.37 MHz/Toit).

(2)

6
For the 21 ±1 kPa (200 ± 50 Torr) pressure used in the SRM units, the pressure shift is + 0.0009 ± 0.0006 nm. Table 4 lists the certified wavelengths for the SRM units. We obtain

these wavelengths by adding the pressure shift to the literature values given in Table 1

6. SRM 2517 certificate The certificate for SRM 2517 is presented in Appendix A. It includes the certified wavelength

values for the Vi + v3 band of 12C2H2 ranging from R25 to P25 (1513-1541 nm), a scan of the band, and instructions for storage, handling, and use of the SRM.

7. Acknowledgment

The authors gratefully acknowledge the help of C. Wang for useful discussions and suggestions on uncertainty analysis, D. Franzen and R. Fox for careful reading of the SRM documentation, and R. Gettings for coordinating the certification and issuance of SRM 2517.

8. References

[1] K. Nakagawa, M. de Labachelerie, Y. Awaji, and M. Kourogi, "Accurate optical frequency

atlas of the 1.5-jim bands of acetylene," J. Opt. Soc. Am. B 13, 2708-2714 (1996).

[2] T. Yoshida and H. Sasada, "Near-infrared spectroscopy with a wavemeter," J. Molec.

Spectrosc. 153, 208-210 (1992).

[3] G. Guelachvili and K. N. Rao, Handbook of Infrared Standards II (Academic Press, San

Diego, CA, 1993), pp. 564-568.

[4] Demtroder, Laser Spectroscopy, second edition (Springer-Verlag Berlin Heidelberg New

York 1996), pp. 71-82.

[5] Y. Sakai, S. Sudo, and T. Ikegami, "Frequency Stabilization of Laser Diodes Using 1.51 —

1.55 [im Absorption Lines of 12C2H2 and 13 C2H2," IEEE J. Quantum Electron. 28, 75-81

(1992).

[6] A Voigt profile is a convolution of Lorentzian and Gaussian profiles; it results when there is a combination of Gaussian broadening (due to Doppler broadening, for example) and

Lorentzian line shape (due to natural linewidth or collision line broadening, for example). See W. Demtroder, Laser Spectroscopy, second edition (Springer-Verlag Berlin Heidelberg

New York 1996), pp. 70-71.

[7] A. Baldacci, S. Ghersetti, and K.N. Rao, "Interpretation of the Acetylene Spectrum at 1.5 urn," J. Mol. Spectrosc. 68, 183-194 (1977).

7
Due to the complexity of a Voigt profile, a Lorentzian profile was used to estimate the

virtual uncertainty in transmission caused by wavelength uncertainty. A Lorentzian profile

is a reasonable approximation to the lineshape; the lines are predominantly Lorentzian due

to pressure broadening.

B. N. Taylor and C. E. Kuyatt, "Guidelines for Evaluating and Expressing the Uncertainty ofNIST Measurement Results," Natl. Inst. Stand. Technol. Tech. Note 1297 (Jan. 1993).

8
Table 1. Vacuum Wavelengths of Acetylene 12 C2H2 Lines The wavelengths were calculated using the experimentally determined molecular constants from

Ref. 1, and were compared with less accurate measurements (Refs. 2 and 3). The wavelength

uncertainty estimate given in Ref. 1 is 1 x 10"6 nm (one standard uncertainty).

Branch wavelength

(nm) P Branch wavelength(nm)

25 1513.1999 1 1525.7598

24 1513.5830 2 1526.3138

23 1513.9725 3 1526.8742

22 1514.3682 4 1527.4410

21 1514.7702 5 1528.0142

20 1515.1785 6 1528.5938

19 1515.5930 7 1529.1798

18 1516.0139 8 1529.7722

17 1516.4411 9 1530.3710

16 1516.8746 10 1530.9762

15 1517.3144 11 1531.5878

14 1517.7605 12 1532.2059

13 1518.2129 13 1532.8303

12 1518.6716 14 1533.4613

11 1519.1367 15 1534.0986

10 1519.6081 16 1534.7424

9 1520.0858 17 1535.3927

8 1520.5699 18 1536.0493

7 1521.0603 19 1536.7125

6 1521.5570 20 1537.3821

5 1522.0601 21 1538.0582

4 1522.5696 22 1538.7407

3 1523.0854 23 1539.4298

2 1523.6075 24 1540.1253

1 1524.1360 25 1540.8273

9
Table 2. Uncertainty Budget

Uncertainty budget for determination of relative line centers for the low pressure and high

pressure cells. The combined standard uncertainties are root-sum-of-squares (RSS) of the standard uncertainties due to the sources listed. The absolute accuracy of the wavelength meter is not included since we are concerned only with the relative line centers.

Source of uncertainty

Nearby line contribution Background slope

Interference fringes

Fit statistical uncertainty

Uncertainty

type [9] Standard

uncertainty (nm)

8 kPa (low) cell < 0.00001 < 0.00001 < 0.00001

0.0001

Standard

uncertainty (nm)

54 kPa (high) cell 0.0001 0.0001 0.0002

0.0001 Combined standard

uncertainty uc (low) = 0. 000 1 uc (high) = 0. 0003

10
Table 3. Pressure Shift Measurement

Measured center wavelengths and shifts for six lines of

12 C2H2 . The individual line shift standard

uncertainty uc (A) is the RSS combined uncertainty of uc(low) and uc(high) from Table 2. The

lines in the high pressure cell are shifted by an average of + 0.0015 nm relative to the lines in the low pressure cell.

Line Measured Measured Shift (nm) Shift standard

center X (nm)

8 kPa (low) cell center % (nm)54 kPa (high) cell [A = high - low]

uncertainty uc(A) (nm)

R18 1516.0130 1516.0150 + 0.0020 0.0003

P3 1526.8738 1526.8749 + 0.0011 0.0003

P5 1528.0136 1528.0154 + 0.0018 0.0003

P6 1528.5934 1528.5950 + 0.0016 0.0003

P14 1533.4604 1533.4619 + 0.0015 0.0003

P25 1540.8270 1540.8278

Average shift

+ 0.0008 + 0.00150.0003

Standard deviation of six lines, u(six) 0.0004 nm

Shift overall combined standard

uncertainty [(u(six)f + (wc(A))

2

]

1/2 0. 0005 nm

11
Table 4 Certified Wavelengths for SRM 2517

Literature values from Ref. 1 adjusted for the pressure shift due to the 27 kPa (200 Torr) cell pressure. These vacuum wavelengths of the Vi + v3 band 12 C2H2 are certified with an expanded

uncertainty of ± 0.0006 nm (coverage factor k = 2).

Branch wavelength P Branch wavelength

(nm) (nm)

25 1513.2007 1 1525.7607

24 1513.5839 2 1526.3147

23 1513.9733 3 1526.8751

22 1514.3690 4 1527.4419

21 1514.7710 5 1528.0151

20 1515.1793 6 1528.5946

19 1515.5939 7 1529.1806

18 1516.0148 8 1529.7730

17 1516.4419 9 1530.3718

16 1516.8754 10 1530.9770

15 1517.3152 11 1531.5886

14 1517.7613 12 1532.2067

13 1518.2138 13 1532.8312

12 1518.6725 14 1533.4621

11 1519.1376 15 1534.0995

10 1519.6090 16 1534.7433

9 1520.0867 17 1535.3935

8 1520.5707 18 1536.0502

7 1521.0611 19 1536.7134

6 1521.5579 20 1537.3830

5 1522.0610 21 1538.0590

4 1522.5704 22 1538.7416

3 1523.0862 23 1539.4306

2 1523.6084 24 1540.1261

1 1524.1369 25 1540.8281

12
Figure 1. Acetylene (

12C2H2) spectrum taken by passing LED light through an absorption cell and recording the spectrum of the transmitted light using an optical spectrum analyzer with

0.05 nm resolution. This spectrum has been divided by the LED spectrum.

13
AcGtylGnG

Collating AbsorPtion Cel1

IS ^gs^^^^^^px^^

Optical

Fiber

Tilt Alignment

(with lock screws)

Aluminum Frame

light source in Fiber

Connector

output to optical

spectrum analyzer

or detector

Figure 2. Schematic of fiber-pigtailed cell holder.

14
Tunable Diode Laser

GPIB Bus

Wavelength Meter

Controller

High Pressure—Cell

Low Pressure—Cell

ch ch

Optical Power Meter

Figure 3. Schematic of the pressure-shift measurement apparatus.

15
25

I I I I I 1527.8 1527.9 1528.0 1528.1 1528.2 Wavelength (nm)

Figure 4. Scan over line P5 showing transmission through low pressure and high pressure cells.

16
1528.4 1528.5 1528.6 1528.7 1528.8 Wavelength (nm)

1528.4 1528.5 1528.6 1528.7 Wavelength (nm)

Figure 5. (a) Multiple line fit of line P6, low pressure cell. Of all the lines measured, P6 had the most significant contribution from nearby lines, (b) Multiple line fit of line P6, high pressure cell.

17

APPENDIX A

^ ^National (Snsttiuis nf JStattJmrirs & ©eclrnnlngg

Certificate

Standard Reference Material 2517

Wavelength Reference Absorption Cell - Acetylene (

Serial No.:

This Standard Reference Material (SRM) is intended for use in calibrating the wavelength scale of wavelength measuring equipment in the spectral region from 1513 nm to 1541 nm. SRM 2517 is an optical-fiber-coupled absorption cell containing acetylene (

12C2 H2) gas. Acetylene has more than 50 accurately measured absorption

lines in the 1500 nm wavelength region.

Certified Wavelength Values: The vacuum wavelengths of absorption lines in the R and P branch of the v, +v3 rotational -vibrational band of 12 C2H2 have been measured previously to high accuracy by several independent

research groups [1,2]. These literature values for the vacuum wavelengths were adjusted for the pressure shift due to the collisions between acetylene molecules at the 27 kPa (200 Torr) pressure within the SRM cell to obtain

the certified wavelength values for this SRM. Details of the measurement procedure and data analysis for the determination of the pressure shift can be found in reference [3]. A spectrum of the absorption band is shown in Figure 1 and certified wavelength values are given in Table 1 . Figure 2 shows a higher resolution scan near line P9. The wavelengths of the lines listed in Table 1 are certified with an expanded uncertainty of + 0.0006 nm

(coverage factor k = 2).

Expiration of Certification: The certification of this SRM is indefinite within the measurement uncertainties

specified, provided the SRM is handled, stored, and used in accordance with the instructions given in this certificate. Measurement Conditions and Procedure: The long term stability of acetylene and the use of fundamental

molecular absorption lines render the SRM insensitive to changes in environmental conditions. The purpose of the

certification procedure is to verify that the unit contains the correct pressure of I2 C2 H2 gas and has no significant contaminants that produce additional absorption lines. Measurements were made using a 0.05 nm resolution

optical spectrum analyzer. Spectra s imil ar to those shown in Figures 1 and 2 were taken of each SRM unit and compared with measurements of reference absorption cells maintained at NIST.

Storage and Handling: The protective caps provided for the FC/PC fiber connectors should be replaced when

the SRM is not in use. This SRM is intended to be used in a laboratory environment near ambient room

temperature (22 °C ± 5 °C). Optical alignment is critical; the user should avoid exposing the unit to large temperature variations, temperature cycling, or mechanical shock, as these may cause the optical alignment to degrade. Optical misalignment affects the throughput of the SRM but will not shift the centers of the absorption

lines. A more serious, but less likely problem is cell breakage or leakage. The unit should be replaced if the linewidths or depths differ significanUy from those shown in Figures 1 and 2 (when measured using comparable

resolution). Development of the SRM and supporting measurements were performed by S.L. Gilbert and W.C. Swann of the NIST Optoelectronics Division.

Gaithersburg, MD 20899 Thomas E. Gills, Chief

Certificate Issue Date: 20 October 1997 Standard Reference Materials Program

SRM 2517 Page 1 of 6
Statistical consultation was provided by CM. Wang of the NIST Statistical Engineering Division. The support aspects involved in the preparation, certification, and issuance of this SRM were coordinated through

the Standard Reference Materials Program by R.J. Gettings.

Table 1. Certified Wavelengths for SRM 2517

Literature values from Reference [1] adjusted for the pressure shift due to the 27 kPa (200 Torr) cell pressure. These vacuum wavelengths of the v, + v3 band of I2 C2H2 are certified with an expanded uncertainty of + 0.0006 nm (coverage factor k = 2).

R Branch nm P Branch nm

25 1513.2007 1 1525.7607 24 1513.5839 2 1526.3147

23 1513.9733 3 1526.8751 22 1514.3690 4 1527.4419

21 1514.7710 5 1528.0151 20 1515.1793 6 1528.5946

19 1515.5939 7 1529.1806

18 1516.0148 8 1529.7730

17 1516.4419 9 1530.3718

16 1516.8754 10 1530.9770

15 1517.3152 11 1531.5886

14 1517.7613 12 1532.2067

13 1518.2138 13 1532.8312

12 1518.6725 14 1533.4621

11 1519.1376 15 1534.0995

10 1519.6090 16 1534.7433

9 1520.0867 17 1535.3935

8 1520.5707 18 1536.0502

7 1521.0611 19 1536.7134

6 1521.5579 20 1537.3830

5 1522.0610 21 1538.0590 4 1522.5704 22 1538.7416

3 1523.0862 23 1539.4306

2 1523.6084 24 1540.1261

1 1524.1369 25 1540.8281

SRM 2517 Page 2 of 6
INSTRUCTIONS FOR USE

General Considerations: The SRM can be used to calibrate a wavelength measuring instrument in the 1510 nm

to 1540 nm region. The wavelength calibration is vacuum wavelength; if the user requires the wavelength in air, the appropriate correction for the index of refraction of air must be applied (see Reference [4]). Depending on

what type of instrument is being calibrated, a broadband source or a tunable narrowband source may be used. Use With a Broadband Source: A broadband source in the 1500 nm region (such as a light emitting diode, white light, or amplified spontaneous emission source) is useful when calibrating a low resolution instrument such

as a diffraction grating based optical spectrum analyzer or monochrometer. A schematic for this type of

calibration is shown in Figure 3(a). Light from the broadband source is coupled into the SRM and the output

(transmission through the SRM) is connected to the instrument that is being calibrated. The absorption lines of

acetylene appear as dips in the spectrum of the light source (see Figure 1). Use With a Narrowband Source: The SRM can be used to calibrate the wavelength scale of a tunable narrowband source in this region (such as a diode laser or fiber laser). Alternatively, a tunable source and the SRM can be used to check the calibration of a wavelength meter, as shown in Figure 3(b). The laser is tuned over one or more of the acetylene absorption lines. The transmission through the SRM is monitored by a

detector; the transmitted power passes through a minimum at the center of an absorption line. Suggested Procedure for Low-Accuracy Requirements; Calibration Uncertainty 5: 0.1 nm: Connect the light source (either broadband or narrowband, as discussed above) to one of the fiber connectors on the SRM unit using

a single-mode optical fiber terminated with a clean FC/PC connector. After identifying the absorption lines by comparing to the spectrum in Figure 1, find the center or the minimum point of a line listed in Table 1. If the instrument has variable resolution, it is best to use a resolution of < 0.2 nm. For this level of accuracy, the procedure used to find the line center can be quite simple: setting a cursor to the line center or minimum by eye is sufficient. If using a tunable source, simply tune it to the transmission minimum of the line, using tuning steps of < 0.01 nm. Calibrate the instrument to the wavelength of this line (from Table 1) using the calibration procedure

specified by the instrument manufacturer. The instrument's linearity can be checked by repeating the procedure

for a different absorption line and comparing it to the value listed in Table 1

Suggested Procedure for Moderate-Accuracy Requirements; Calibration Uncertainty in the Approximate Range of 0.01 nm to 0.1 nm: Connect the light source (either broadband or narrowband, as discussed above) to one

of the fiber connectors on the SRM unit using a single-mode optical fiber terminated with a clean FC/PC connector.

If the source power varies significantly with wavelength, divide the SRM transmission spectrum by the source spectrum to obtain a normalized trace. After identifying the absorption lines by comparing to the spectrum in Figure

1, make a high resolution scan of a line listed in Table 1. If the instrument has variable resolution, it is best to use a

resolution of < 0.1 nm with a data point density of at least one point every 0.005 nm. Find the wavelength readings on both sides of the line where the absorption is 50 % of the maximum; the line center is half-way between these two

wavelength readings. Repeat this procedure five times and take the average of the five measurements for the line center. Calibrate the instrument to the center wavelength of this line (from Table 1) using the calibration procedure

specified by the instrument manufacturer. The instrument's linearity can be checked by repeating the procedure for a

different absorption line and comparing it to the value listed in Table 1. Suggested Procedure for High-Accuracy Requirements; Calibration Uncertainty £ 0.01 nm: [Note: due

to the presence of weak nearby lines, background slope, and interference fringes, this SRM is not recommended

for a calibration with an uncertainty of less than 0.001 nm.] Connect the light source (either broadband or narrowband, as discussed above) to one of the fiber connectors on the SRM unit using a single-mode optical

fiber terminated with a clean FC/PC connector. Divide the SRM transmission spectrum by the source spectrum to obtain a normalized trace. After identifying the absorption lines by comparing to the spectrum in Figure 1, make a high resolution scan of a line listed in Table 1. If the instrument has variable resolution, it is best to use a resolution of < 0.1 nm with a data point density of at least one point every 0.001 nm. Using a

fitting technique such as the least squares technique, fit the absorption data to the appropriate lineshape (Lorentzian if the line shape is dominated by the molecular absorption profile, Lorentzian convoluted with the instrument's filter characteristics if the instrument contributes significantly to the profile). Details of line

fitting procedure and potential errors sources can be found in Reference [3]. Calibrate the instrument to the center wavelength of this line (from Table 1) using the calibration procedure specified by the instrument manufacturer. The instrument's linearity can be checked by repeating the procedure for a different absorption

line and comparing it to the value listed in Table 1.

SRM 2517 Page 3 of 6
1.0

0.8 -

CDO

czCDg 0.6

"O

CD £ 0.4 CD£

0.2

0.0 ' 1 '

' 1

1

R Branch

11 g 7 mm

P Branch

-I I I I I I I I 1 I I 1 1 !_ 1510 1515 1520 1525 1530 Wavelength (nm)

1535 1540 1545

Figure 1. Acetylene (

12 C2 H2) spectrum taken by passing LED light through an absorption cell and recording the spectrum of the transmitted light using an optical spectrum analyzer with 0.05 nm resolution. This spectrum has been divided by the LED spectrum.

SRM 2517 Page 4 of 6
Wavelength (nm)

Figure 2. The P8, P9, and P10 lines from Figure 1 on an expanded wavelength scale to show lineshape.

SRM 2517 Page 5 of 6
Broadband

Source

SRM

Unit

(a)

Tunable

Narrowband

Source

SRM

Unit Detector

Wavelength

Meter

(b)

Figure 3. (a) Schematic of technique when using the SRM and a broadband source to calibrate an optical spectrum analyzer, (b) Schematic of technique when using the SRM and a narrowband source to calibrate a

tunable laser or a wavelength meter. The wavelength meter is not required for a laser calibration.

REFERENCES

[1] Nakagawa, K., Labachelerie, M., Awaji, Y., and Kourogi, M., "Accurate Optical Frequency Atlas of the 1.5-um Bands of Acetylene," J. Opt. Soc. Am. B 13, pp. 2708-2714, (1996).

[2] Yoshida, T. and Sasada, H., "Near-Infrared Spectroscopy with a Wavemeter," J. Molec. Spectrosc. 153, pp. 208-210 (1992); Guelachvili, G. and Rao, K.N., Handbook of Infrared Standards II, Academic Press, San

Diego, CA, pp. 564-568 (1993).

[3] Gilbert, S.L., and Swann, W.C., "Standard Reference Materials: Acetylene 12 C2 H2 Absorption Reference

for 1510-1540 nm Wavelength Calibration - SRM 2517," NIST Special Publication 260-133 (1997). In Press.

[4] Edlen, B., "The Refractive Index of Air," Metrologia, 2, p. 12, (1966); CRC Handbook of Chemistry and

Physics 77th Ed., pp. 10-266, (1996).

ft is the responsibility of users of this SRM to assure that the certificate in their possession is current. This can be accomplished by contacting the SRM Program at (301) 975-6776 (select "Certificates''), Fax (301) 926^751, e- mail srminfo@nist.gov, or via of the Internet http://ts.nist.gov/srm.

SRM 2517 Page 6 of 6
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