Measurement of material properties with optically induced phonons
AssigneeMassachusettes Institute of Technology
InventorsKeith A. Nelson, Anil R. Duggal, John A. Rogers
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Abstract
Samples such as thin polymeric films are analyzed using optically induced phonons by excitation of the sample using radiation preferably absorbed by the sample and probe radiation, preferably not absorbed by the sample, that is diffracted from the surface of the sample. The pulse width of the probe is preferably on the order of the detectable diffraction signal so that the phonon decay from each excitation pulse can be detected and analyzed. The technique is applicable to various samples by inducing a ripple morphology on the sample surface and detection of light diffracted substantially from surface ripple.
Claims58
An apparatus for measuring the properties of a sample of material, comprising:
- a first, excitation source for producing excitation radiation adapted to impinge upon said sample of material, said excitation radiation comprising radiation composed of at least two component beams which interfere within said sample, each incidence of interference of said excitation radiation being sufficient to induce transient phonons in said material which give rise to a transient, time dependent periodic ripple morphology of alternating peaks and valleys on a surface of said sample,
- a detection system for detecting said ripple morphology by diffraction of radiation including:
- a second, probe source for producing probe radiation arranged to be diffracted by the periodic ripple morphology on the surface of said sample to form a diffraction signal which emerges on the same side of said sample as said probe radiation,
- a detector for detecting the diffraction signal from said probe source radiation diffracted by said surface ripple morphology, and
- an analyzer for selectively analyzing said diffraction signal formed by said transient ripple morphology.
A method for measuring the properties of a sample comprising:
- impinging a pulse of excitation radiation upon said sample, said excitation radiation being composed of at least two component beams which interfere within said sample, and being selected such that each incidence of said interference is sufficient to induce transient phonons in said sample which give rise to a transient, time dependent ripple morphology of alternating peaks and valleys on a surface of said sample,
- detecting said ripple morphology by diffraction of probe radiation from said surface having the periodic ripple morphology to form a diffraction signal which emerges on the same side of said sample as said probe radiation, and
- selectively detecting the diffraction signal diffracted by said ripple morphology.
An apparatus for measuring the properties of a thin sample of polymeric material comprising:
- a first, excitation laser source for producing a pulse of radiation adapted to impinge upon said sample, said excitation source comprising radiation composed of at least two component pulses which interfere within said thin film, said excitation radiation adapted to induce transient phonons in said material which give rise to a transient, time-dependent periodic ripple morphology of alternating peaks and valleys on a surface of said sample,
- a detection system for detecting said ripple morphology by diffraction of radiation including:
- a second, probe laser source for producing radiation, said probe radiation being of selected wavelength not substantially absorbed by said sample and arranged to be diffracted by the periodic ripple morphology on the surface of said sample to form a diffraction signal which emerges on the same side of said sample as said probe radiation, and
- a detector for detecting the diffraction signal.
Dependencies are inferred from the claim text.