Search PubMed⌕ Search

Biomedical subjects

Andrew M Weiner

Publications and source records attributed to Andrew M Weiner.

6 recordsLinked to original sources
PubMed2006

Polarized temporal impulse response for scattering media from third-order frequency correlations of speckle intensity patterns.

Second- and third-order frequency correlations of speckle intensity patterns are used to characterize scattering media for multiple polarization states. The polarized temporal responses thus obtained are sensitive to the degree of scatter, with results being predictable by a diffusion model with sufficiently strong scatter. Experimental data are used to reconstruct various transfer functions.

Journal Article↗
PubMed2005

Ultrasensitive second-harmonic generation frequency-resolved optical gating by aperiodically poled LiNbO3 waveguides at 1.5 microm.

We retrieve intensity and phase profiles of 280 fs, 50 MHz optical pulses with 124 aJ coupled pulse energy (960 photons) by second-harmonic generation (SHG) frequency-resolved optical gating, using aperiodically poled LiNbO3 waveguides. The strong nonlinear interaction that is due to confinement within the micrometer-sized waveguide structure and the linearly chirped poling period contribute, respectively, to high SHG efficiency and broad phase-matching bandwidth. The achieved sensitivity is 2.7 x 10(-6) mW2, improving on the previous record for self-referenced complete pulse characterization by 5 orders of magnitude.

Journal Article↗
PubMed2005

Frequency-resolved interferometer measurements of polarized wave propagation in scattering media.

An interferometric technique is utilized to measure both the time- and frequency-domain optical fields scattered by a random medium. The method uses a tunable continuous-wave laser source to make frequency-resolved measurements within a fixed-path-length interferometer. Measured frequency-domain field statistics, with a linearly polarized input, are shown to be zero-mean, circular complex Gaussian for both co- and cross-polarization states. With decreasing scatter, the extracted average impulse responses for co- and cross-polarized states show distinct differences, thereby providing insight into the scattering domain.

Journal Article↗
PubMed2004

400-photon-per-pulse ultrashort pulse autocorrelation measurement with aperiodically poled lithium niobate waveguides at 1.55 microm.

We demonstrate ultrasensitive intensity autocorrelation measurements of subpicosecond optical pulses in the telecommunication band by using aperiodically poled lithium niobate (A-PPLN) waveguides. The tightly confined optical beam in the waveguides and the chirped poling period facilitate simultaneous high second-harmonic generation (SHG) efficiency and broad phase-matching (PM) bandwidth. The resulting measurement sensitivity is 3.2 x 10(-7) mW2, approximately 500 times better than the previous record for intensity autocorrelations. We also show that chirped A-PPLN waveguides retain nearly the same SHG efficiency as the unchirped guide as long as the PM bandwidth is not significantly broader than the input spectrum.

Journal Article↗
PubMed2003

Temporal response of a random medium from speckle intensity frequency correlations.

We reconstruct the temporal response of a random medium by using speckle intensity frequency correlations. When the scattered field from a random medium is described by circular complex Gaussian statistics, we show that third-order correlations permit retrieval of the Fourier phase of the temporal response with bispectral techniques. Our experimental results for random media samples in the diffusion regime are in excellent agreement with the intensity temporal response measured directly with an ultrafast pulse laser and a streak camera. Our speckle correlation measurements also demonstrate sensitivity to inhomogeneous samples, highlighting the potential application for imaging within a scattering medium.

Journal Article↗