Abstract

In an accompanying paper [Appl. Opt. 40, 783–793 (2001)], we predict the existence of background signals from a frequency-doubled wavelength-modulated diode-laser system. We now demonstrate and characterize various nf harmonics of such background signals from a system producing light in the 422-nm region by use of a single-pass KNbO3 crystal with respect to the modulation amplitude, the laser center frequency, and the crystal temperature. It is demonstrated that 2f detection is plagued by considerably larger amounts of background signal than is detection at other higher, even harmonics. This result implies that 4f or 6f detection is often to be preferred in comparison with 2f detection when frequency-doubled wavelength-modulation spectrometry (WMS) is to be used. This preference is illustrated by the detection of Ca in an acetylene–air flame. It is also shown that the background signals have a much stronger dependence on the modulation amplitude than do the analytical signals. This difference implies that the optimum detectability for frequency-doubled WMS is often reached for modulation amplitudes lower than those normally used. An analysis of the effect of a finite temperature stability of the doubling crystal on the drift of the background signals as well as on the detectability is included. The results verify the theoretical description given in our accompanying paper.

© 2001 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |
  • |

  1. D. T. Cassidy, J. Reid, “Atmospheric pressure monitoring of trace gases using tunable diode lasers,” Appl. Opt. 21, 1185–1190 (1982).
    [CrossRef] [PubMed]
  2. J. A. Silver, “Frequency-modulation spectroscopy for trace species detection: theory and comparison among experimental methods,” Appl. Opt. 31, 707–717 (1992).
    [CrossRef] [PubMed]
  3. D. S. Bomse, A. C. Stanton, J. A. Silver, “Frequency-modulation and wavelength-modulation spectroscopies: comparison of experimental methods using a lead-salt diode laser,” Appl. Opt. 31, 718–731 (1992).
    [CrossRef] [PubMed]
  4. K. Niemax, H. Groll, C. Schnürer-Patschan, “Element analysis by diode laser spectroscopy,” Spectrochim. Acta Rev. 15, 349–377 (1993).
  5. G. Groll, C. Schnürer-Patschan, Y. Kuritsyn, K. Niemax, “Wavelength modulation diode laser atomic absorption spectrometry in analytical flames,” Spectrochim. Acta Part B 49, 1463–1472 (1994).
    [CrossRef]
  6. P. Werle, “Spectroscopic trace gas analysis using semiconductor diode lasers,” Spectrochim. Acta Part A 52, 805–822 (1997).
    [CrossRef]
  7. V. Liger, A. Zybin, Y. Kuritsyn, K. Niemax, “Diode-laser atomic-absorption spectrometry by the double-beam–double-modulation technique,” Spectrochim. Acta Part B 52, 1125–1138 (1997).
    [CrossRef]
  8. P. Kluczynski, O. Axner, “Theoretical description based on Fourier analysis of wavelength-modulation spectrometry in terms of analytical and background signals,” Appl. Opt. 38, 5803–5815 (1999).
    [CrossRef]
  9. P. Kluczynski, Å. M. Lindberg, O. Axner, “Background signals in wavelength-modulation spectrometry by use of frequency-doubled diode-laser light. I. Theory,” Appl. Opt. 40, 783–793 (2001).
    [CrossRef]
  10. X. Zhu, D. T. Cassidy, “Modulation spectroscopy with a semiconductor diode laser by injection-current modulation,” J. Opt. Soc. Am. B 14, 1945–1950 (1997).
    [CrossRef]
  11. P. Kluczynski, Å. M. Lindberg, O. Axner, “Characterization of background signals in wavelength-modulation spectrometry in terms of a Fourier based theoretical formalism,” Appl. Opt. 40, 770–782 (2001).
    [CrossRef]
  12. H. Groll, G. Schaldach, H. Berndt, K. Niemax, “Measurement of Cr(iii)/Cr(vi) species by wavelength modulation diode laser flame atomic absorption spectrometry,” Spectrochim. Acta Part B 50, 1293–1298 (1995).
    [CrossRef]
  13. A. Zybin, C. Schnürer-Patschan, K. Niemax, “Simultaneous multielement analysis in a commercial graphite furnace by diode laser induced fluorescence,” Spectrochim. Acta Part B 47, 1519–1524 (1992).
    [CrossRef]
  14. K. A. Peterson, D. B. Oh, “Diode laser-based tunable ultraviolet sources for combustion diagnostics,” in Laser Applications to Chemical and Environmental Analysis, Trends in Optic and Photonics Series Vol. 36, T. Li, ed. (Optical Society of America, Washington, D.C., 1997), p. 126.
  15. P. Kluczynski, “Second-harmonic generation of 850-nm cw laser diode radiation in KNbO3,” Masters thesis (Department of Experimental Physics, Umeå Univ., Umeå, Sweden, 1997).
  16. The reason for these etalon background signals is that the optical system consists of a multitude of surfaces between which several weak optical etalons can inadvertently be formed. Because a slight change in the alignment of the system will alter the shape as well as the size of these etalon-dominated background signals, two consecutive 4f and 6f spectra will therefore not, in general, look exactly the same. The nf background signals from etalons were characterized previously (see Ref. 11) and are therefore not considered further in this paper.
  17. O. Axner, P. Kluczynski, Å. M. Lindberg, “A general noncomplex analytical expression for the n:th Fourier component of a wavelength-modulated Lorentzian line-shape function,” J. Quant. Spectrosc. Radiat. Transfer 68, 299–317 (2001).
    [CrossRef]
  18. Although the Doppler broadening, which gives rise to a Gaussian line broadening, in many instances can rival (and even dominate) the collision–lifetime broadening, which gives rise to a Lorentzian line profile, in this study, we chose to describe the analytical signal as a pure Lorentzian profile. The main reason for our choice is that the use of a Lorentzian profile simplifies the SBR analysis in this study considerably. There are several reasons for this simplification: First, the previously developed theoretical formulation makes use of various Fourier components of the line-shape function. There exist convenient analytical expressions for a Lorentzian profile, whereas no comparable expressions have yet been found for the Gaussian or the Voigt functions. Second, there is only a small difference in the WM signal shape from the Lorentzian- and the Gaussian-shaped profiles. Third, the main aim of the SBR analysis is to investigate the behavior of the various nf harmonics of the background signal under various conditions. For the purpose of a comparison of various types of background signal to an analytical signal, we are of the opinion that a Lorentzian description of the analyte therefore serves the purpose of this study sufficiently well.
  19. Y. Uematsu, “Nonlinear optical properties of KNbO3 single crystal in the orthorhombic phase,” Jpn. J. App. Phys. 13, 1362–1368 (1974).
    [CrossRef]
  20. P. Günter, “Near-infrared noncritically phase-matched second-harmonic generation in KNbO3,” Appl. Phys. Lett. 34, 650–652 (1979).
    [CrossRef]

2001 (3)

1999 (1)

1997 (3)

X. Zhu, D. T. Cassidy, “Modulation spectroscopy with a semiconductor diode laser by injection-current modulation,” J. Opt. Soc. Am. B 14, 1945–1950 (1997).
[CrossRef]

P. Werle, “Spectroscopic trace gas analysis using semiconductor diode lasers,” Spectrochim. Acta Part A 52, 805–822 (1997).
[CrossRef]

V. Liger, A. Zybin, Y. Kuritsyn, K. Niemax, “Diode-laser atomic-absorption spectrometry by the double-beam–double-modulation technique,” Spectrochim. Acta Part B 52, 1125–1138 (1997).
[CrossRef]

1995 (1)

H. Groll, G. Schaldach, H. Berndt, K. Niemax, “Measurement of Cr(iii)/Cr(vi) species by wavelength modulation diode laser flame atomic absorption spectrometry,” Spectrochim. Acta Part B 50, 1293–1298 (1995).
[CrossRef]

1994 (1)

G. Groll, C. Schnürer-Patschan, Y. Kuritsyn, K. Niemax, “Wavelength modulation diode laser atomic absorption spectrometry in analytical flames,” Spectrochim. Acta Part B 49, 1463–1472 (1994).
[CrossRef]

1993 (1)

K. Niemax, H. Groll, C. Schnürer-Patschan, “Element analysis by diode laser spectroscopy,” Spectrochim. Acta Rev. 15, 349–377 (1993).

1992 (3)

1982 (1)

1979 (1)

P. Günter, “Near-infrared noncritically phase-matched second-harmonic generation in KNbO3,” Appl. Phys. Lett. 34, 650–652 (1979).
[CrossRef]

1974 (1)

Y. Uematsu, “Nonlinear optical properties of KNbO3 single crystal in the orthorhombic phase,” Jpn. J. App. Phys. 13, 1362–1368 (1974).
[CrossRef]

Axner, O.

Berndt, H.

H. Groll, G. Schaldach, H. Berndt, K. Niemax, “Measurement of Cr(iii)/Cr(vi) species by wavelength modulation diode laser flame atomic absorption spectrometry,” Spectrochim. Acta Part B 50, 1293–1298 (1995).
[CrossRef]

Bomse, D. S.

Cassidy, D. T.

Groll, G.

G. Groll, C. Schnürer-Patschan, Y. Kuritsyn, K. Niemax, “Wavelength modulation diode laser atomic absorption spectrometry in analytical flames,” Spectrochim. Acta Part B 49, 1463–1472 (1994).
[CrossRef]

Groll, H.

H. Groll, G. Schaldach, H. Berndt, K. Niemax, “Measurement of Cr(iii)/Cr(vi) species by wavelength modulation diode laser flame atomic absorption spectrometry,” Spectrochim. Acta Part B 50, 1293–1298 (1995).
[CrossRef]

K. Niemax, H. Groll, C. Schnürer-Patschan, “Element analysis by diode laser spectroscopy,” Spectrochim. Acta Rev. 15, 349–377 (1993).

Günter, P.

P. Günter, “Near-infrared noncritically phase-matched second-harmonic generation in KNbO3,” Appl. Phys. Lett. 34, 650–652 (1979).
[CrossRef]

Kluczynski, P.

Kuritsyn, Y.

V. Liger, A. Zybin, Y. Kuritsyn, K. Niemax, “Diode-laser atomic-absorption spectrometry by the double-beam–double-modulation technique,” Spectrochim. Acta Part B 52, 1125–1138 (1997).
[CrossRef]

G. Groll, C. Schnürer-Patschan, Y. Kuritsyn, K. Niemax, “Wavelength modulation diode laser atomic absorption spectrometry in analytical flames,” Spectrochim. Acta Part B 49, 1463–1472 (1994).
[CrossRef]

Liger, V.

V. Liger, A. Zybin, Y. Kuritsyn, K. Niemax, “Diode-laser atomic-absorption spectrometry by the double-beam–double-modulation technique,” Spectrochim. Acta Part B 52, 1125–1138 (1997).
[CrossRef]

Lindberg, Å. M.

Niemax, K.

V. Liger, A. Zybin, Y. Kuritsyn, K. Niemax, “Diode-laser atomic-absorption spectrometry by the double-beam–double-modulation technique,” Spectrochim. Acta Part B 52, 1125–1138 (1997).
[CrossRef]

H. Groll, G. Schaldach, H. Berndt, K. Niemax, “Measurement of Cr(iii)/Cr(vi) species by wavelength modulation diode laser flame atomic absorption spectrometry,” Spectrochim. Acta Part B 50, 1293–1298 (1995).
[CrossRef]

G. Groll, C. Schnürer-Patschan, Y. Kuritsyn, K. Niemax, “Wavelength modulation diode laser atomic absorption spectrometry in analytical flames,” Spectrochim. Acta Part B 49, 1463–1472 (1994).
[CrossRef]

K. Niemax, H. Groll, C. Schnürer-Patschan, “Element analysis by diode laser spectroscopy,” Spectrochim. Acta Rev. 15, 349–377 (1993).

A. Zybin, C. Schnürer-Patschan, K. Niemax, “Simultaneous multielement analysis in a commercial graphite furnace by diode laser induced fluorescence,” Spectrochim. Acta Part B 47, 1519–1524 (1992).
[CrossRef]

Oh, D. B.

K. A. Peterson, D. B. Oh, “Diode laser-based tunable ultraviolet sources for combustion diagnostics,” in Laser Applications to Chemical and Environmental Analysis, Trends in Optic and Photonics Series Vol. 36, T. Li, ed. (Optical Society of America, Washington, D.C., 1997), p. 126.

Peterson, K. A.

K. A. Peterson, D. B. Oh, “Diode laser-based tunable ultraviolet sources for combustion diagnostics,” in Laser Applications to Chemical and Environmental Analysis, Trends in Optic and Photonics Series Vol. 36, T. Li, ed. (Optical Society of America, Washington, D.C., 1997), p. 126.

Reid, J.

Schaldach, G.

H. Groll, G. Schaldach, H. Berndt, K. Niemax, “Measurement of Cr(iii)/Cr(vi) species by wavelength modulation diode laser flame atomic absorption spectrometry,” Spectrochim. Acta Part B 50, 1293–1298 (1995).
[CrossRef]

Schnürer-Patschan, C.

G. Groll, C. Schnürer-Patschan, Y. Kuritsyn, K. Niemax, “Wavelength modulation diode laser atomic absorption spectrometry in analytical flames,” Spectrochim. Acta Part B 49, 1463–1472 (1994).
[CrossRef]

K. Niemax, H. Groll, C. Schnürer-Patschan, “Element analysis by diode laser spectroscopy,” Spectrochim. Acta Rev. 15, 349–377 (1993).

A. Zybin, C. Schnürer-Patschan, K. Niemax, “Simultaneous multielement analysis in a commercial graphite furnace by diode laser induced fluorescence,” Spectrochim. Acta Part B 47, 1519–1524 (1992).
[CrossRef]

Silver, J. A.

Stanton, A. C.

Uematsu, Y.

Y. Uematsu, “Nonlinear optical properties of KNbO3 single crystal in the orthorhombic phase,” Jpn. J. App. Phys. 13, 1362–1368 (1974).
[CrossRef]

Werle, P.

P. Werle, “Spectroscopic trace gas analysis using semiconductor diode lasers,” Spectrochim. Acta Part A 52, 805–822 (1997).
[CrossRef]

Zhu, X.

Zybin, A.

V. Liger, A. Zybin, Y. Kuritsyn, K. Niemax, “Diode-laser atomic-absorption spectrometry by the double-beam–double-modulation technique,” Spectrochim. Acta Part B 52, 1125–1138 (1997).
[CrossRef]

A. Zybin, C. Schnürer-Patschan, K. Niemax, “Simultaneous multielement analysis in a commercial graphite furnace by diode laser induced fluorescence,” Spectrochim. Acta Part B 47, 1519–1524 (1992).
[CrossRef]

Appl. Opt. (6)

Appl. Phys. Lett. (1)

P. Günter, “Near-infrared noncritically phase-matched second-harmonic generation in KNbO3,” Appl. Phys. Lett. 34, 650–652 (1979).
[CrossRef]

J. Opt. Soc. Am. B (1)

J. Quant. Spectrosc. Radiat. Transfer (1)

O. Axner, P. Kluczynski, Å. M. Lindberg, “A general noncomplex analytical expression for the n:th Fourier component of a wavelength-modulated Lorentzian line-shape function,” J. Quant. Spectrosc. Radiat. Transfer 68, 299–317 (2001).
[CrossRef]

Jpn. J. App. Phys. (1)

Y. Uematsu, “Nonlinear optical properties of KNbO3 single crystal in the orthorhombic phase,” Jpn. J. App. Phys. 13, 1362–1368 (1974).
[CrossRef]

Spectrochim. Acta Part A (1)

P. Werle, “Spectroscopic trace gas analysis using semiconductor diode lasers,” Spectrochim. Acta Part A 52, 805–822 (1997).
[CrossRef]

Spectrochim. Acta Part B (4)

V. Liger, A. Zybin, Y. Kuritsyn, K. Niemax, “Diode-laser atomic-absorption spectrometry by the double-beam–double-modulation technique,” Spectrochim. Acta Part B 52, 1125–1138 (1997).
[CrossRef]

H. Groll, G. Schaldach, H. Berndt, K. Niemax, “Measurement of Cr(iii)/Cr(vi) species by wavelength modulation diode laser flame atomic absorption spectrometry,” Spectrochim. Acta Part B 50, 1293–1298 (1995).
[CrossRef]

A. Zybin, C. Schnürer-Patschan, K. Niemax, “Simultaneous multielement analysis in a commercial graphite furnace by diode laser induced fluorescence,” Spectrochim. Acta Part B 47, 1519–1524 (1992).
[CrossRef]

G. Groll, C. Schnürer-Patschan, Y. Kuritsyn, K. Niemax, “Wavelength modulation diode laser atomic absorption spectrometry in analytical flames,” Spectrochim. Acta Part B 49, 1463–1472 (1994).
[CrossRef]

Spectrochim. Acta Rev. (1)

K. Niemax, H. Groll, C. Schnürer-Patschan, “Element analysis by diode laser spectroscopy,” Spectrochim. Acta Rev. 15, 349–377 (1993).

Other (4)

Although the Doppler broadening, which gives rise to a Gaussian line broadening, in many instances can rival (and even dominate) the collision–lifetime broadening, which gives rise to a Lorentzian line profile, in this study, we chose to describe the analytical signal as a pure Lorentzian profile. The main reason for our choice is that the use of a Lorentzian profile simplifies the SBR analysis in this study considerably. There are several reasons for this simplification: First, the previously developed theoretical formulation makes use of various Fourier components of the line-shape function. There exist convenient analytical expressions for a Lorentzian profile, whereas no comparable expressions have yet been found for the Gaussian or the Voigt functions. Second, there is only a small difference in the WM signal shape from the Lorentzian- and the Gaussian-shaped profiles. Third, the main aim of the SBR analysis is to investigate the behavior of the various nf harmonics of the background signal under various conditions. For the purpose of a comparison of various types of background signal to an analytical signal, we are of the opinion that a Lorentzian description of the analyte therefore serves the purpose of this study sufficiently well.

K. A. Peterson, D. B. Oh, “Diode laser-based tunable ultraviolet sources for combustion diagnostics,” in Laser Applications to Chemical and Environmental Analysis, Trends in Optic and Photonics Series Vol. 36, T. Li, ed. (Optical Society of America, Washington, D.C., 1997), p. 126.

P. Kluczynski, “Second-harmonic generation of 850-nm cw laser diode radiation in KNbO3,” Masters thesis (Department of Experimental Physics, Umeå Univ., Umeå, Sweden, 1997).

The reason for these etalon background signals is that the optical system consists of a multitude of surfaces between which several weak optical etalons can inadvertently be formed. Because a slight change in the alignment of the system will alter the shape as well as the size of these etalon-dominated background signals, two consecutive 4f and 6f spectra will therefore not, in general, look exactly the same. The nf background signals from etalons were characterized previously (see Ref. 11) and are therefore not considered further in this paper.

Cited By

OSA participates in CrossRef's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (9)

Fig. 1
Fig. 1

Schematic diagram of the experimental setup. DL, diode laser; TC, temperature controller; SCS, stabilized current source; FG, function generator; BSO, beam-shaping optics; DP, dispersive prism; PBS, polarizing beam splitter; PMT, photomultiplier tube; PREA, preamplifier; PD, photodetector; FP1 and FP2, Fabry–Perot etalons; LPF, low-pass filter; A/D, analog to digital; TTL, scan trigger pulse transistor–transistor logic.

Fig. 2
Fig. 2

S0even and S2even signals, the two lowest even harmonics of the background signal from a frequency-doubled WM diode-laser system: (a) Measured and (b) calculated signals plotted as functions of the temperature detuning ΔT for a constant laser center frequency and modulation amplitude (2 GHz). Displayed in (a) by the open symbols are experimental data points, whereas (b) shows the corresponding calculated signals. Curves a in both (a) and (b) represent S0even, whereas curves b in both (a) and (b) represent S2even. The solid curve in (a) represents the best fit of expression (1) to the measured data. The origin of the ΔT scale corresponds to the situation in which the crystal center frequency equals the laser center frequency. Because the output power of the frequency-doubled light under unmodulated conditions was experimentally indistinguishable from the S0even signal, curve a in (a) also represents this result.

Fig. 3
Fig. 3

(a), (c) Measured and (b), (d) calculated Sneven background signals plotted as functions of the laser center frequency ν c l expressed in terms of the detuning ν d for a fixed modulation amplitude (ν a = 7.65 GHz). Curves a and b in (a) and (c) show the S0even and the -S2even signals, respectively, whereas curves c and d in (b) and (d) show the S4even and the S6even signals.

Fig. 4
Fig. 4

S2even, S4even, and S6even background-signal strengths plotted as functions of the modulation amplitude ν a for zero detuning as displayed by curves a, b, and c, respectively. The solid curves represent the fits of the form c 0 + c n ν a n .

Fig. 5
Fig. 5

(a) Various nf harmonics of the SBR entity plotted as functions of the modulation amplitude ν a . Curves a, b, and c represent n = 2, 4, 6, respectively. (b) The corresponding nf harmonics of the analytical signal SAS,neven displayed in curves d, e, and f for n = 2, 4, 6, respectively. The HWHM of the analyte was taken to be 2 GHz in the frequency-doubled wavelength region; this value corresponds to the width of the 422.7-nm transition in Ca in an acetylene–air flame.

Fig. 6
Fig. 6

Optical thickness corresponding to a SBR of unity plotted as a function of the modulation amplitude for a variety of detection modes, i.e., (α S/ B=1) n . Curves a, b, and c represent 2f, 4f, and 6f detection, respectively.

Fig. 7
Fig. 7

Various nf harmonics of the WM signal from the detection of Ca in an acetylene–air flame at 422.67 nm plotted as functions of the laser center frequency ν c l expressed in terms of the detuning ν d for a fixed modulation amplitude (ν a = 6 GHz). A solution containing 50 ng/ml of Ca was aspirated into the flame through a conventional nebulizer unit as a function of the laser center frequency. Curves a, b, c, and d represent the signals S0even, S2even, S4even, and S6even, respectively. The S0even signal is given in a different scale from that of the other signals so that it fits into the figure.

Fig. 8
Fig. 8

S2even signal (curve a) and the corresponding drift ΔS2even of the signal strength (curve b) plotted as functions of the crystal-temperature deviation from T 0. The drift ΔS2even was calculated as the maximum drift of the S2even signal for a temperature fluctuation of 10 mK at each crystal temperature.

Fig. 9
Fig. 9

Curve a represents the optical thickness that corresponds to a SAS,2evenS2even ratio of unity detected at 2f, i.e., (α S/ D=1)2, on the basis of the data from curve b of Fig. 8. The analytical signal SAS,2even, whose form is given by the output power S0even of the frequency-doubling system in this plot, is shown for comparison (curve b).

Tables (2)

Tables Icon

Table 1 Diode-Laser and Frequency-Doubling Parameters

Tables Icon

Table 2 Explicit Expressions for the Four Lowest Even Harmonics of the Fourier Components of a Wavelength-Modulated Lorentzian Function on Resonancea : χ̅ n (0, ν̅ a )

Equations (15)

Equations on this page are rendered with MathJax. Learn more.

ISHξd=ζξdIL2  sin2ξdξd2 IL2.
ξd=κξνcc-νcl=κξνd.
ξd=κTT-T0=κTΔT,
SASν=exp-αν-1SPD-ανSPD=-χνα0SPD,
SAS,neven0, ν¯a-χn0, ν¯aα0SPD,
χ¯n0, ν¯a=Anν¯anBn0, ν¯a+Cn0, ν¯a1+ν¯a21/2,
Snevenξd0, ξaan1-bnξa2+1+δn2an-21-bn-2ξa2+an21-bnξa2ξa22ξanSPD.
S/Bn=χnνα0an1-bnξa2+1+δn2an-2×1-bn-2ξa2+an21-bnξa2ξa22-1ξa-n.
ξdT+ΔT=ξdT+κTΔT.
ξcνd=κξνcl-νcc=κξνd,
ξaνa=κξνa,
κξ=2πνcccnFννν=νcc-nSHννν=2νcc.
n2λ=1+Aλ2λ2-B,
ξdT+ΔT=ξdT+ξdTΔT.
ξdT=ξccT=ξccννT,

Metrics