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Gas Absorption Line Finder (≤2.9 µm)TDLAS Line Selection

Click a gas tag to see its common absorption lines and strong bands below 2.9 µm (nm and wavenumber side by side, with references). In-stock models cover part of the range; the rest is within our roadmap and available as custom builds.

λ ↔ Wavenumber quick converter (HITRAN indexes in cm⁻¹)
⇄
wavenumber = 10⁷ / λ(nm). More units in the wavelength converter
Filter by gas · click to view its line map (12 gases)
All O₂ OxygenHF Hydrogen fluorideH₂O Water vaporNH₃ AmmoniaC₂H₂ AcetyleneCO Carbon monoxideCO₂ Carbon dioxideH₂S Hydrogen sulfideC₂H₄ EthyleneCH₄ MethaneC₂H₆ EthaneHCl Hydrogen chloride
760.44 760.89 761.32 763.84 764.29 759.7 nm 765.0 nm O₂ Oxygen · 760 nm · A-band (stick height = relative strength, orange = recommended)
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
760.44 13150.28 ●●○ R branch
760.89 13142.50 ●●○ R branch · Recommended
761.32 13135.08 ●●○ R branch
763.84 13091.75 ●●○ P branch · also used
764.29 13084.04 ●●○ P branch

References: O₂ A-band line parameters (J Mol Spectrosc)

1272.9 1278.2 1284 1271.6 nm 1285.3 nm HF Hydrogen fluoride · 1.28 µm · first overtone (stick height = relative strength, orange = recommended)
2400–2520 nm · 2.5 µm fundamental: fundamental band, ~2 orders stronger (dedicated 2476 nm DFBs exist) — custom on request
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
1272.9 7856.08 ●●○ R(2)
1278.2 7823.50 ●●● R(1) · Recommended
1284 7788.16 ●●○ R(0)

References: HF detection at 2476 nm (EQ Photonics) · Li-battery runaway HF sensing (J Power Sources)

1389.06 1391.67 1392.53 1396.37 1397.75 1388.0 nm 1398.8 nm H₂O Water vapor · 1.39 µm (stick height = relative strength, orange = recommended)
1854 1853.6 nm 1854.4 nm H₂O Water vapor · 1.85 µm strong band (stick height = relative strength, orange = recommended)
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
1389.06 7199.11 ●●○
1391.67 7185.61 ●●●
1392.53 7181.17 ●●● Recommended · 7181.16 cm⁻¹
1396.37 7161.43 ●●○
1397.75 7154.36 ●●● also used
1854 5393.74 ●●● 1.85 µm band, stronger (industrial moisture)

References: TDLAS hygrometer white paper (Baker Hughes)

1510 1512.24 1513.86 1515.97 1522.5 1508.6 nm 1523.9 nm NH₃ Ammonia · 1.51 µm (stick height = relative strength, orange = recommended)
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
1510 6622.52 ●●○
1512.24 6612.71 ●●● Recommended · 6612.7 cm⁻¹
1513.86 6605.63 ●●○
1515.97 6596.44 ●●○
1522.5 6568.14 ●○○

References: NH₃/CO₂/H₂O absorption near 1512 nm (Opto-Electron Eng)

1519.1 1520.1 1521.1 1518.5 nm 1521.7 nm C₂H₂ Acetylene · 1.52 µm · R branch (common in DGA schemes) (stick height = relative strength, orange = recommended)
1528.01 1529.18 1530.37 1531.59 1532.83 1527.2 nm 1533.6 nm C₂H₂ Acetylene · 1.53 µm · P branch (stick height = relative strength, orange = recommended)
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
1519.1 6582.85 ●●○ R(9)
1520.1 6578.51 ●●● R(7) · dissolved-C₂H₂ schemes ≈1520
1521.1 6574.19 ●●● R(5)
1528.01 6544.46 ●●○ P(5)
1529.18 6539.45 ●●● P(7)
1530.37 6534.37 ●●● P(9) · Recommended
1531.59 6529.16 ●●● P(11)
1532.83 6523.88 ●●○ P(13)

References: NIST SRM 2517a acetylene wavelength reference · Tracing C₂H₂ dissolved in transformer oil (Sci Rep)

1567.99 1567.28 1566.64 1565.98 1565.35 1564.7 nm 1568.6 nm CO Carbon monoxide · 1.57 µm · second overtone (3ν) (stick height = relative strength, orange = recommended)
2333.7 2333.3 nm 2334.1 nm CO Carbon monoxide · 2.33 µm strong band (2-0) (stick height = relative strength, orange = recommended)
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
1567.99 6377.59 ●●○ R(4)
1567.28 6380.48 ●●○ R(5)
1566.64 6383.09 ●●○ R(6) · Recommended, clear of H₂O/CO₂
1565.98 6385.78 ●●○ R(7)
1565.35 6388.35 ●●○ R(8)
2333.7 4285.04 ●●● R(6) · 4285.01 cm⁻¹, ~500× stronger — custom on request

References: Telecom-band CO detection (Appl Opt) · 2.3 µm CO combustion sensing

1571.24 1571.63 1572.02 1572.41 1572.81 1570.7 nm 1573.3 nm CO₂ Carbon dioxide · 1.57 µm (30013) (stick height = relative strength, orange = recommended)
2004 2051 1999.8 nm 2055.2 nm CO₂ Carbon dioxide · 2 µm strong band (stick height = relative strength, orange = recommended)
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
1571.24 6364.40 ●○○ R branch
1571.63 6362.82 ●○○
1572.02 6361.24 ●●○ Recommended · 6361.25 cm⁻¹ (column sensing)
1572.41 6359.66 ●○○
1572.81 6358.05 ●○○
2004 4990.02 ●●● 2 µm band, ~30× stronger
2051 4875.67 ●●● 2 µm DIAL workhorse — custom on request

References: 1572 nm frequency locking (NASA) · CO₂-TDLAS at 2 µm (Meas Sci Technol)

1573.9 1578.13 1582.13 1590.58 1572.2 nm 1592.3 nm H₂S Hydrogen sulfide · 1.58 µm (stick height = relative strength, orange = recommended)
2500–2700 nm · 2.6 µm fundamental: ν₁/ν₃ fundamentals, ~2 orders stronger — custom on request
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
1573.9 6353.64 ●●○ also seen (≈6353.5 cm⁻¹)
1578.13 6336.61 ●●● Recommended · 6336.62 cm⁻¹
1582.13 6320.59 ●●○
1590.58 6287.01 ●●○ also used · 6287.01 cm⁻¹, away from CO₂

References: 1578 nm WMS detection (Chin Phys B) · ppb-level QEPAS at 1590.6 nm (Photoacoustics)

1620 1626 1630 1618.8 nm 1631.2 nm C₂H₄ Ethylene · 1.62 µm · ν₅+ν₉ band (stick height = relative strength, orange = recommended)
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
1620 6172.84 ●●○ also used
1626 6150.06 ●●● Recommended · strong-peak region (1626–1626.6)
1630 6134.97 ●●○ also used (vendor SKU wavelength)

References: Ethylene multiline WMS-2f/1f (Sci Rep) · Ethylene TDLAS at 1626 nm (Photonic Sensors)

1665.3 1653.72 1650.96 1648.22 1645.56 1643.6 nm 1667.3 nm CH₄ Methane · 1.65 µm (2ν₃) (stick height = relative strength, orange = recommended)
2290–2370 nm · 2.3 µm combination band: combination band, ~10× stronger — custom on request
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
1665.3 6004.92 ●●● Q branch (dense)
1653.72 6046.97 ●●● R(3) · Recommended · 6046.95 cm⁻¹
1650.96 6057.08 ●●● R(4)
1648.22 6067.15 ●●○ R(5)
1645.56 6076.96 ●●○ R(6)

References: Wavelength locking at 1653.72 nm (Sensors)

1684.3 1683.9 nm 1684.7 nm C₂H₆ Ethane · 1.68 µm (stick height = relative strength, orange = recommended)
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
1684.3 5937.18 ●●● Recommended (several strong lines in 1684–1687.5)

References: CH₄/C₂H₆ dual-gas TDLAS (Anal Chem)

1752.55 1747.27 1742.38 1737.87 1733.7 1731.8 nm 1754.5 nm HCl Hydrogen chloride · 1.74 µm · first overtone (stick height = relative strength, orange = recommended)
Line (nm)Wavenumber (cm⁻¹)Rel. strengthNote
1752.55 5705.97 ●●○ R(1)
1747.27 5723.21 ●●○ R(2)
1742.38 5739.28 ●●● R(3) · Recommended · 5739.25 cm⁻¹
1737.87 5754.17 ●●○ R(4)
1733.7 5768.01 ●○○ R(5)

References: HCl TDLAS in combustion (ACS Omega)

Recommended lines below 2.9 µm and matched models (typical positions — consult HITRAN for quantitative selection)
GasFormulaRecommended line (nm)Wavenumber (cm⁻¹)BandTypical applicationMatched model
Oxygen O₂ 760.89 13142.50 A-band Combustion control / medical O₂ DFB-B14-0760-O2 RFQ →
Hydrogen fluoride HF 1278.2 7823.50 2-0 Al smelting / Li-battery runaway / etch exhaust custom Custom RFQ →
Water vapor H₂O 1392.53 7181.17 ν₁+ν₃ Humidity / dew point custom Custom RFQ →
Ammonia NH₃ 1512.2 6612.88 2ν₁ DeNOx slip / agriculture DFB-T08-1512-NH3 RFQ →
Acetylene C₂H₂ 1530.37 6534.37 ν₁+ν₃ Transformer DGA / λ reference custom Custom RFQ →
Carbon monoxide CO 1566.64 6383.09 3ν Mining / metallurgy process gas DFB-B14-1566-CO RFQ →
Carbon dioxide CO₂ 1572.02 6361.24 30013←00001 Carbon monitoring / breath custom Custom RFQ →
Hydrogen sulfide H₂S 1578.13 6336.61 2ν Petrochemical / gas sweetening custom Custom RFQ →
Ethylene C₂H₄ 1626 6150.06 ν₅+ν₉ Coal-fire early warning / fruit ripening / transformer DGA custom Custom RFQ →
Methane CH₄ 1653.72 6046.97 2ν₃ Pipeline leak / mine safety DFB-B14-1653-CH4 RFQ →
Ethane C₂H₆ 1684.3 5937.18 2ν Natural-gas speciation / leak attribution custom Custom RFQ →
Hydrogen chloride HCl 1742.38 5739.28 2ν Incineration / semiconductor custom Custom RFQ →
700 800 1250 1450 1650 1800 nm NIR recommended lines (solid = in-stock model, dashed = custom; 2–2.9 µm strong bands in the per-gas panels) O₂ HF H₂O NH₃ C₂H₂ CO CO₂ H₂S C₂H₄ CH₄ C₂H₆ HCl

TDLAS in three sentences

Tunable diode laser absorption spectroscopy sweeps a single-longitudinal-mode DFB laser repeatedly across one isolated absorption line of the target gas, and extracts ppm- to ppb-level concentrations with wavelength modulation and 2f harmonic detection. Single-line detection works because the laser linewidth is far narrower than the gas line (≈3–5 GHz at atmospheric pressure) — a DFB's MHz-class linewidth has margin to spare.

Three rules for line selection

Enough line strength: the same gas varies enormously between bands — CO at 2.33 µm (2-0) is ~500× stronger than at 1.57 µm (3ν), CO₂ at 2 µm ~30× stronger than at 1.57 µm; telecom-band devices are cheap and mature, longer wavelengths buy detection limit. Avoid interference: prefer lines clear of H₂O/CO₂ background (CH₄ 1653.72 and CO 1566.64 are chosen for this; the H₂S 1578-vs-1590 trade-off is the same logic). Device maturity: the 1.3–1.7 µm supply chain is the most mature; wavelengths up to 2.9 µm are within our roadmap — beyond the in-stock models (including the 2 µm / 2.3 µm strong bands), ask us for a custom evaluation.

Transformer-oil DGA in one place: of the seven DGA marker gases, all but H₂ (no IR activity — needs electrochemical/GC methods) are measurable by NIR TDLAS: CO, CO₂, CH₄, C₂H₂, C₂H₄ and C₂H₆ — the per-gas panels on this page give exactly the line combinations used in multi-gas DGA schemes (C₂H₂ on the R branch ≈1520 to stay clear of CH₄/C₂H₄ interference).

※ Line positions are compiled from HITRAN2020 and the literature cited in each panel; relative strengths are 3-level indicative. For quantitative selection (line strength, broadening, isotopes, interference) refer to HITRAN online.

Related Products
Gas-sensing DFB series In-stock wavelengths → PD-GAS-CAL Calibration detector for a complete chain →

Related tools: DFB tuning calculator · Wavelength / wavenumber

※ Formulas on this page assume ideal models; all device parameters shown are typical values — refer to the datasheet and the serialized factory test report shipped with each unit. For selection support, contact sales@lncetek.com.