Development of a Narrow-Band Tunable Picosecond Dye Laser and Its Application to Excited-State Lifetime Measurement of a Chlorinated Aromatic Hydrocarbon

Abstract

Supersonic jet/multiphoton ionization-mass spectrometry (SSJ/MPI-MS) is used in spectrometric analysis primarily because of its high selectivity. This approach provides wellresolved spectral features in the multiphoton ionization spectrum, and interference from other molecules, such as related analogues, can be minimized.In addition, information concerning molecular weight and chemical structure can be readily obtained from the mass spectrum. 1-3 Due to its high spectrometric selectivity, it can be used for trace analysis, on line. Several applications of this method to the on-line real-time monitoring of chlorobenzene derivatives, which are known surrogates of dioxins with strong toxicities, have been reported. [4][5][6][7][8] No on-line monitoring of dioxins, however, has been achieved since numerous toxic and non-toxic isomers and congeners are present at low concentrations in flue gas. Therefore, high sensitivity as well as high selectivity is desirable for the analysis of these compounds. In order to solve this problem, the use of a laser with a pulse duration nearly identical to the lifetime of the singlet-excited-state of the analyte in multiphoton ionization has been proposed. 9,10 In particular, a tunable nearly-transform-limited picosecond laser would be desirable for the efficient multiphoton ionization of dioxins, the excited-state lifetimes of which are considered to be much shorter than 1 ns. A distributed-feedback (DFB) dye laser, 11-13 which is tunable over a wide spectral region and capable of generating a picosecond pulse with a narrow spectral bandwidth, has the potential for application to SSJ/MPI-MS. 14, 15 We recently developed a DFB dye laser with a pulse width and line width of 160 ps and 9.64 pm, respectively, and used it to measure the excited-state lifetimes of monochlorobenzene and dichlorobenzene. 16 More recently, a DFB dye laser with a shorter pulse width (68 ps), which was achieved by a new type of quenching scheme, was developed.17 Therefore, a tunable picosecond laser with a shorter pulse width is useful not only for efficient ionization of molecules with shorter excited-state lifetimes but also for the excited-state lifetime measurement of these compounds.In this study, a transform-limited DFB dye laser with a shorter pulse width (< 25 ps) was developed, using a picosecond Nd:YAG laser as a pump source and employing a thinner cuvette for oscillation. The excited-state lifetime of a highly chlorinated benzene derivative, i.e., 1,2,4-trichlorobenzene, was then measured by means of a pump-probe method in SSJ/MPI-MS. Moreover, potential advantages in efficient ionization of highly chlorinated dioxins and their surrogates are discussed. ExperimentalA block diagram of the DFB dye laser is shown in Fig. 1(a) (cf. Ref. 16). A picosecond Nd:YAG laser (Continuum, Leopard, 120 ps, 10 Hz) was employed as a pump source of the dye laser, in order to suppress additional peaks after a single isolated pulse generated using a nanosecond Nd:YAG laser. [14][15][16][17] In the oscillator stage, t...

Fluorescence lifetime measurement of dibenzofuran and monochlorodibenzofuran

“…It has been reported that the maximal ionization efficiency is obtained when the pulsewidth of the laser is identical to or similar to the excited-state lifetime of the analyte molecule [3,4]. The lifetimes of a few chlorophenols have been reported elsewhere [5,6]. It is, however, well known that the toxicity equivalent (TEQ) is proportional to the concentration of chlorinated dibenzofuran, especially to that of pentachlorodibenzofuran; the correlation factor is reported to be much higher than 0.9, sometimes approaching 0.99 for a sample in the flue gas [7,8].…”

Fluorescence Lifetime Imaging Microscope Consisting of a Compact Picosecond Dye Laser and a Gated Charge-Coupled Device Camera for Applications to Living Cells

“…In this laser, only the initial spike of the laser emission induced by feed back of the beam (reflection at the surface of the dye cell) can be extracted by removing the pump energy remaining in the dye solution by generating a strong quenching beam that oscillates later than the impulse laser oscillation. 12,13 The picosecond pulse from the oscillator stage was then passed through an amplifier cell containing a coumarin 102 solution (7 × 10 -4 M). The pulse energy and the pulse width of the laser were measured by means of a joule meter (Molectron, J3-09) and a photodiode (Hamamatsu, C4258, rise time 50 ps) equipped with a 6-GHz digital oscilloscope (Tektronix, TDS6604B).…”

“…This laser was applied to measuring the singlet-excited state lifetime of a gas-phase aromatic hydrocarbon. 12 The tunable range can be extended from 320 nm to the entire visible region, when a Nd:YAG laser (266 nm) is used as a pump source.…”

Sensitive and Selective Analysis of Polychlorinated Dibenzo-p-dioxins/Dibenzofurans and Their Precursors by Supersonic Jet/Resonance-Enhanced Multiphoton Ionization/Time-of-Flight Mass Spectrometry

“…[66][67][68] We recently reported on a tunable picosecond laser with a pulse width and a line width of 25 ps and 8.78 pm, respectivery. 69 This nearly Fourier-transform-limited pulse has the potential, not only for the efficient ionization of PCDD/Fs and their precursors, but also for the selective ionization of them, since the line width of this laser (∼0.01 nm) is about the same as the bandwidth of PCDD/Fs with the singlet-excitedstate lifetime of several picoseconds.…”