Long Path Length Samples in Thermal Lens Calorimetry

Carter, C. A.; Harris, Joel M.

doi:10.1366/0003702834634055

Cited by 28 publications

(11 citation statements)

References 17 publications

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“…If the focus of the pump laser is positioned in the center of the cell, then little signal enhancement would occur at cell lengths greater than 4 Rayleigh ranges. This behavior is quite different than that obtained for CW laser excited TLS(18).…”

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confidence: 92%

“…The smaller beam waist will result in a reduced interaction length through the sample cell volume. Carter and Harris have calculated the effects of cell length on the CW laser TLS signal (18). In one of the methods utilized in the latter study, the interaction length was found to depend on the Rayleigh range or confocal distance of the focused laser.…”

Section: = R C S ' ( T ) X ( T )mentioning

confidence: 99%

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Pulsed laser thermal lens spectrophotometry of liquid samples using an optical fiber beam guide with interference orthogonal signal processing

Bialkowski¹

1986

Anal. Chem.

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An apparatus for thermal lens spectrophotometry of liquid samplesIsconshucted udngapuleednhgen laserexdtstkn source a m l a w laser probe. Both laser beams are passed through a fused a k a optlcal fiber prlor to bdng Hghtly focused Into the sample cell. The optical flber k used to reduce mode and pointtng varlatlons in the laser outputs. A dlgltal correlation filter is developed and used for estlmatlon of the thermal lens signal. T h k dlgltal estbnatlon procedure exhlblts a consMerably enhanced slgnal-to-nolse ratio over that of other estknatlon methods. Moreover, It is relatively Immune to background Interference and rapM In estlmatlon time. Finally, the effectlve sample path kngth for focused beams In pulsed laser exclted thermal l e n sis examlned from a theoretical b a a . It is found that the slgnal will be very near maximum for cell path lengths on the order of 4 times the Raylelgh range.Pulsed laser excited photothermal spectrophotometry is an ultrasensitive technique for concentration estimation of analytes that do not fluoresce subsequent to absorption of light at the excitation wavelength ( I ) . There are several potential advantages to pulsed laser excitation, over that of continuous wave (CW) excited photothermal lens spectrophotometry (TLS), that have been discussed in a number of recent publications (2-8). The pulsed laser excitation techniques have large theoretical enhancement factors at a small excitation beam radius (2-4), the signal magnitudes are not dependent on solution flow at moderate rates (7,8), in contrast to the related CW laser excited techniques which are very sensitive to flow (!+I1 1, and there is a potentially higher signal-to-noise ratio (SNR) due to the high-frequency components that make up the rapid rise time of the TLS signal (6).However, pulsed laser are in general noisy sources. The pulse energy can vary substantially, and mode or pointing noise can result in a large errors. Mode noise is due to transverse mode fluctuations that will result in different focused beam spatial profiles in the sample, and pointing noise will result in minor shifts in the focus position. The errors associated with the latter two noise sources are due to the sensitivity of the photothermal spectrophotometric signal to the spatial overlap of the pulsed excitation laser beam and that of the CW probe. Pulse energy variations can be corrected for in a simple fashion by monitoring this energy, but the mode and pointing variations are very difficult to detect and the corrections would not be simple. Pointing noise in the pump and probe beams has been found to be a major limiting factor in the accuracy of the pulsed laser excited photothermal deflection technique (6) and appears to be one of the limiting factors in the CW TLS technique as well (12).

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contrasting

confidence: 92%

Section: = R C S ' ( T ) X ( T )mentioning

confidence: 99%

Pulsed laser thermal lens spectrophotometry of liquid samples using an optical fiber beam guide with interference orthogonal signal processing

Bialkowski¹

1986

Anal. Chem.

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“…This is because in this technique, the signal depends on the power density in the excitation laser beam. As a consequence, the signal intensity would not be doubled with the use of a cell with twice the path length (34,35) because in a long path length cell, the spot size of the laser beam will be enlarged as it propagates through the cell (34,35). The consequence of this spot size enlargement is the decrease in the laser power density and in the thermal lens signal because these two terms are known to be inversely proportional to the beam spot size.…”

Section: Resultsmentioning

confidence: 99%

“…In addition, the time constant tc also becomes longer. A longer measurement time is necessary, which as a consequence worsens the detection limit because the fluctuation in the laser intensity increases with time (34). Conversely, the beam spot size within each cell and the time constant remain the same with the use of the two-cell method developed in this work.…”

Section: Resultsmentioning

confidence: 99%

Water as a unique medium for thermal lens measurements

Franko¹,

Tran²

1989

Anal. Chem.

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enues being explored consist of decreasing reagent and dilution volumes and improving the instrumental sensitivity and selectivity by incorporating improved optics and a nanosecond transient recorder. Analysis is also under way that will unveil the experimental trades present between the cell concentration, the substrate concentration, and the incubation time period. Optimization of the procedure will undoubtedly allow for a decrease in cell concentrations with a minimal increase in incubation time. The end goal of these improvements is total elimination of the cell growth period.Registry No. Ala-d-naphthylamide, 720-82-1; Arg-/3naphthylamide, 7182-70-9; di-Cys-d-naphthylamide, 1259-69-4; Gly-d-naphthylamide, 716-94-9; His-(3-naphthylamide, 7424-15-9; Hpro-d-naphthylamide, 3326-64-5; Leu-d-naphthylamide, 732-85-4; Lys-i'j-naphthylamide, 4420-88-6; aminopeptidase, 9031-94-1.

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“…Not only would the linear flow velocity be lower, but the path length would be larger, both of which would increase the thermal lens sensitivity. Thermal lens calorimetry produces a signal which, to first order, is linearly related to path length (35). Very small path length cuvettes, roughly 100 jam wide or smaller, will produce low sensitivity.…”

Section: Resultsmentioning

confidence: 99%