J. D. Bradshaw, M. O. Rodgers, and Douglas D. Davis, "Sequential two-photon laser-induced fluorescence: a new technique for detecting hydroxyl radicals," Appl. Opt. 23, 2134-2145 (1984)
A new approach to the detection of the chemically important transient species, the hydroxyl radical (OH), is reported. This new approach, labeled two-photon laser-induced fluorescence (TP-LIF), has now been tested in the laboratory under atmospheric conditions. The method involves combining IR laser pumping (e.g., 1.4 or 2.8 μm) with UV laser excitation (e.g., 345 or 351 nm). Theoretical predicted signal levels were found to agree very favorably with laboratory measured signal levels. Using laboratory data reported in this study, in conjunction with projected IR energy improvements, it appears that the TP-LIF OH method could be of great value both as a laboratory instrument for studying fundamental chemical processes and as an OH field detection system.
You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Article tables are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Equations are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
Eλ1 (2.5 × 10−4) × Eλ2 (2.1 × 10−2) × Ed (1.7 × 10−4) × Ef (1.3 × 10−3) × Ee (0.8) × V(0.18) × OH(3.8 × 1011)
= 0.08 photons/laser shot
Units: P, photons/laser shot; σ,cm2; a,cm2; kf, sec−1; kd,sec−1; kq,cm3/molecules/sec; [ ], molecules/cm3; l, cm; fi, R, S, γ, Y, Z, Φ, and Lr dimensionless.
Value cited is based on independent experimental measurement of variable; energy, 1.4 μm = 0.04 mJ, 351 nm = 2.0 mJ.
See discussion in text.
Values quoted are those agreed on at the 1982 NASA workshop13 on NxOy and HxOy Instrumentation, Palo Alto, Calif. Kq (H2O2) taken to be the same as kq (H2O).
Taken from JPL publication 81-3, “Chemical and Photochemical Data for Use in Stratospheric Modeling.”
This value of R assumes complete spin, parity, and rotational relaxation, and the loss due to vibrational relaxation is calculated to be 1.35. The magnitude of R has then been adjusted upward by a factor of 1.35 to take into account the fact that the 0.24-cm−1 IR laser partially pumps the second Λ doublet in the Q11 transition. The latter has the effect of reducing the loss of population due to parity relaxation.
The relaxation rate coefficients taken for the calculation of Ef are based on the observation that v′ = 1 → v′ = 0 transfer in OH, via collision with N2, is the dominant relaxation process for v′ = l.47 Note: The UV and IR laser pulse widths are 9–11 nsec.
Table II
Evaluation of TP-LIF OH Sensitivity for Detection in the Middle Free Troposphere (2.8-μm IR Pumping)(7)
Usable energy 10.0 mJ.
Beam diameter 6 mm.
Usable energy 5 mJ.
Beam diameter 4.5 mm.
The effective absorption cross section has been calculated using an operational linewidth of 0.25 cm−1, also see discussion in text.
The reported effective absorption cross section is based on an operational linewidth of 0.25 cm−1. Its value is 1.3 times larger Then given in text due to the contribution from the Q-branch satellite line, also see discussion in text.
Units in Table II are the same as in Table I.
Tables (2)
Table I
Evaluation of Dλ3 for the TP-LIF OH System Based on 1.4-μm IR Pumping
Eλ1 (2.5 × 10−4) × Eλ2 (2.1 × 10−2) × Ed (1.7 × 10−4) × Ef (1.3 × 10−3) × Ee (0.8) × V(0.18) × OH(3.8 × 1011)
= 0.08 photons/laser shot
Units: P, photons/laser shot; σ,cm2; a,cm2; kf, sec−1; kd,sec−1; kq,cm3/molecules/sec; [ ], molecules/cm3; l, cm; fi, R, S, γ, Y, Z, Φ, and Lr dimensionless.
Value cited is based on independent experimental measurement of variable; energy, 1.4 μm = 0.04 mJ, 351 nm = 2.0 mJ.
See discussion in text.
Values quoted are those agreed on at the 1982 NASA workshop13 on NxOy and HxOy Instrumentation, Palo Alto, Calif. Kq (H2O2) taken to be the same as kq (H2O).
Taken from JPL publication 81-3, “Chemical and Photochemical Data for Use in Stratospheric Modeling.”
This value of R assumes complete spin, parity, and rotational relaxation, and the loss due to vibrational relaxation is calculated to be 1.35. The magnitude of R has then been adjusted upward by a factor of 1.35 to take into account the fact that the 0.24-cm−1 IR laser partially pumps the second Λ doublet in the Q11 transition. The latter has the effect of reducing the loss of population due to parity relaxation.
The relaxation rate coefficients taken for the calculation of Ef are based on the observation that v′ = 1 → v′ = 0 transfer in OH, via collision with N2, is the dominant relaxation process for v′ = l.47 Note: The UV and IR laser pulse widths are 9–11 nsec.
Table II
Evaluation of TP-LIF OH Sensitivity for Detection in the Middle Free Troposphere (2.8-μm IR Pumping)(7)
Usable energy 10.0 mJ.
Beam diameter 6 mm.
Usable energy 5 mJ.
Beam diameter 4.5 mm.
The effective absorption cross section has been calculated using an operational linewidth of 0.25 cm−1, also see discussion in text.
The reported effective absorption cross section is based on an operational linewidth of 0.25 cm−1. Its value is 1.3 times larger Then given in text due to the contribution from the Q-branch satellite line, also see discussion in text.
Units in Table II are the same as in Table I.