Abstract

Time-resolved measurements of elastic scattering and stimulated Raman scattering (SRS) in micrometer-sized water and carbon tetrachloride droplets irradiated with a pulsed, frequency-doubled Nd:YAG laser (pulse width 8 nsec, λ = 532 nm, peak intensity ~1 GW cm−2) are reported. Elastic scattering of light is instantaneous within our measurement error, estimated to be <±3 nsec. On the other hand, the first Stokes shift in water and multiple-order (through ninth-order) Stokes shifts in carbon tetrachloride are delayed from the elastically scattered light by 5–7 nsec. The delay in SRS is apparently a consequence of structure resonances within the droplet, which acts as an optical cavity with relatively high Q. Quasi-periodic peaks in SRS spectra of water droplets are shown to be associated with elastic-scattering structure resonances having the same mode order.

© 1988 Optical Society of America

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References

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  1. J. B. Snow, S. Qian, R. K. Chang, Opt. Lett. 10, 37 (1985).
    [CrossRef] [PubMed]
  2. S. Qian, R. K. Chang, Phys. Rev. Lett. 56, 926 (1986).
    [CrossRef] [PubMed]
  3. R. G. Pinnick, P. Chylek, M. Jarzembski, E. Creegan, V. Srivastava, G. Fernandez, J. D. Pendleton, A. Biswas, Appl. Opt. 27, 987 (1988).
    [CrossRef] [PubMed]
  4. J. Owen, R. K. Chang, P. W. Barber, Aerosol Sci. Technol. 1, 293 (1982).
    [CrossRef]
  5. R. Thurn, W. Kiefer, Appl. Opt. 24, 1515 (1985).
    [CrossRef] [PubMed]
  6. R. Thurn, W. Kiefer, J. Raman Spectrosc. 15, 411 (1984).
    [CrossRef]
  7. P. Chylek, J. Kiehl, M. Ko, Phys. Rev. A. 18, 2229 (1978).
    [CrossRef]
  8. P. W. Barber, Department of Electrical and Computer Engineering, Clarkson University, Potsdam, New York 13676 (personal communication).

1988

1986

S. Qian, R. K. Chang, Phys. Rev. Lett. 56, 926 (1986).
[CrossRef] [PubMed]

1985

1984

R. Thurn, W. Kiefer, J. Raman Spectrosc. 15, 411 (1984).
[CrossRef]

1982

J. Owen, R. K. Chang, P. W. Barber, Aerosol Sci. Technol. 1, 293 (1982).
[CrossRef]

1978

P. Chylek, J. Kiehl, M. Ko, Phys. Rev. A. 18, 2229 (1978).
[CrossRef]

Barber, P. W.

J. Owen, R. K. Chang, P. W. Barber, Aerosol Sci. Technol. 1, 293 (1982).
[CrossRef]

P. W. Barber, Department of Electrical and Computer Engineering, Clarkson University, Potsdam, New York 13676 (personal communication).

Biswas, A.

Chang, R. K.

S. Qian, R. K. Chang, Phys. Rev. Lett. 56, 926 (1986).
[CrossRef] [PubMed]

J. B. Snow, S. Qian, R. K. Chang, Opt. Lett. 10, 37 (1985).
[CrossRef] [PubMed]

J. Owen, R. K. Chang, P. W. Barber, Aerosol Sci. Technol. 1, 293 (1982).
[CrossRef]

Chylek, P.

Creegan, E.

Fernandez, G.

Jarzembski, M.

Kiefer, W.

R. Thurn, W. Kiefer, Appl. Opt. 24, 1515 (1985).
[CrossRef] [PubMed]

R. Thurn, W. Kiefer, J. Raman Spectrosc. 15, 411 (1984).
[CrossRef]

Kiehl, J.

P. Chylek, J. Kiehl, M. Ko, Phys. Rev. A. 18, 2229 (1978).
[CrossRef]

Ko, M.

P. Chylek, J. Kiehl, M. Ko, Phys. Rev. A. 18, 2229 (1978).
[CrossRef]

Owen, J.

J. Owen, R. K. Chang, P. W. Barber, Aerosol Sci. Technol. 1, 293 (1982).
[CrossRef]

Pendleton, J. D.

Pinnick, R. G.

Qian, S.

Snow, J. B.

Srivastava, V.

Thurn, R.

R. Thurn, W. Kiefer, Appl. Opt. 24, 1515 (1985).
[CrossRef] [PubMed]

R. Thurn, W. Kiefer, J. Raman Spectrosc. 15, 411 (1984).
[CrossRef]

Aerosol Sci. Technol.

J. Owen, R. K. Chang, P. W. Barber, Aerosol Sci. Technol. 1, 293 (1982).
[CrossRef]

Appl. Opt.

J. Raman Spectrosc.

R. Thurn, W. Kiefer, J. Raman Spectrosc. 15, 411 (1984).
[CrossRef]

Opt. Lett.

Phys. Rev. A.

P. Chylek, J. Kiehl, M. Ko, Phys. Rev. A. 18, 2229 (1978).
[CrossRef]

Phys. Rev. Lett.

S. Qian, R. K. Chang, Phys. Rev. Lett. 56, 926 (1986).
[CrossRef] [PubMed]

Other

P. W. Barber, Department of Electrical and Computer Engineering, Clarkson University, Potsdam, New York 13676 (personal communication).

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Figures (4)

Fig. 1
Fig. 1

(a) Schematic of the experimental setup used for measuring time dependence and spectral content of elastic and inelastic (SRS) scattering in small droplets, (b) Typical transient digitizer traces of the PMT signal. The time delay of elastic scattering and SRS is determined by measuring peak-to-peak time differences between the scattered and reference beam pulses.

Fig. 2
Fig. 2

Time-resolved measurements of elastic scattering and SRS from water and CCl4 droplets. Time delays for the first Stokes shift for water drops and for multiple (through ninth-order) shifts for CCl4 drops are shown. The laser pulse width is about 8 nsec; the peak intensity is about 1 GW cm−2. Data points depict averages of 25–50 single laser shot measurements of the delay together with typical one standard deviation. Absolute errors arising from differences in the laser and SRS signal pulse widths and from finite detector time response are estimated to be not more than an additional ±2 nsec.

Fig. 3
Fig. 3

Single-shot SRS spectra of water drops irradiated with green light from a pulsed laser with peak intensity ~1 GW cm−2. Spherical drops range in size from 29- to 130-μm diameter [(a), (b), (d)]. The peaks are quasi-periodic. Spectra for spheroids (c), obtained by detuning the droplet generator from the resonant frequency used in (b) to generate spheres, show a plethora of resonance peaks. The spheroids have nearly the same volume as spheres in (b); their axial ratio was estimated by viewing them through a microscope with 200× magnification.

Fig. 4
Fig. 4

Measured period of peaks appearing in the SRS spectra of spherical water drops (see Fig. 3) as a function of measured drop size. Measurement errors are ±5% in wavelength, ±15% in size for the open data point, and ±2% in size for the filled data points. The measurements are in good agreement with the theoretical prediction [Eq. (1)], which is compelling evidence that there is a unique correspondence between SRS peaks and elastic scattering structure resonances within the drops.

Equations (1)

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Δ λ = λ 2 2 π r arctan ( n 2 1 ) 1 / 2 ( n 2 1 ) 1 / 2 ,

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