We present an analytical perturbation analysis for studying the sensitivity of diffusive photon flux to the addition of a small spherical defect object in multiple-scattering media such as human tissues. As a first simple application of our perturbation method, we derive analytically the photon migration path distributions and the shapes of the so-called banana regions in which the photon migration paths are concentrated. We then derive analytically the sensitivity of detected photon flux densities to the inclusion of small spherical defects in the multiple-scattering medium for both single-source and two-source configurations, at both steady-state (dc) and frequency-modulation conditions, and compare the results with Monte Carlo simulations.

We consider wandering of a nonrelativistic particle in a time-dependent random potential in d spatial dimensions.Its root-mean-square displacement from the initial position increases superdiffusively with time t as t " for d & l, and as t in d = 1. Its kinetic energy increases as t ' for d & l, and as t in d=l. These scaling behaviors hold for both the classical and the corresponding quantum-mechanical problem in continuous space-time and differ from those of lattice models. PACS numbers: 05.40.+j, 42.20. -y, 71.55.Jvwith G(tx[, t) rapidly falling off to zero for~x~& g or t ( & g" for example, G -exp( -x /2("-t /2(, ). The corresponding quantum-mechanical problem described by the time-dependent Schrodinger equation,(3) recently attracted attention in relation to the propagation of directed waves in (d+1)-dimensional highly anisotropic scattering media [1]. Similar in form, though in detail very diAerent, is the random directed polymer problem [8), which is the imaginary-time version of (3).The original, real-time model is interesting in its own right [5][6][7], for example, to model the motion of a light Quantum mechanics of a particle in a time-independent random potential has attracted enormous attention in the past years. On the other hand, interest in the dynamics in a time dependent -random potential started to grow only recently [1-4], though the problem was addressed long ago by Ovchinikov and Erikhman [5] and by others [6,7]. At the classical level this problem is described by Newton's equations dp BU dx p dt Bx' dt m ' for the momentum p and the position x of a particle of the mass m. U(x, t ) is a time-dependent random potential, with zero mean and with short-range correlations both in time and in space, of the form test particle placed in a gas of much heavier particles. If the test particle is at rest at t =0, its velocity will start to grow due to collisions with heavy particles. In a long range of time scales in which its velocity is still relatively small, one can neglect its inAuence on heavy particles and model their effect on the test particle by a time-dependent random potential. This model breaks down at sufficiently large t: The light particle eventually comes into equilibrium with heavy ones -its average velocity is constant while its wandering is ordinary diAusion at large t.Nonetheless, for time scales in which the stricto sensu random potential model is still appropriate, the testparticle velocity typically increases with time. Thus, its wandering, measured by the mean-square displacement from the initial position (x ), cannot be a simple diffusion. Since the particle, on average, gains the energy from the random time-dependent medium, one might expect a superdigusive behavior [1,7] even for t This Letter presents the first deep theoretical insight into superdiAusion of a stricto sensu time-dependent random potential model in d spatial dimensions. We find, for both the classical and quantum cases, that the scaling laws of this superdiffusion are superuniversa/ for any d & 1: (x )'t increa...

The low-frequency torsional modes, index of refraction, and absorption of a tryptophan film and pressed powders from 0.2 to 2.0 THz (6.6-66 cm(-1)) were measured by terahertz time-domain spectroscopy at room temperature. It was found that there were two dominated torsional vibrational modes at around 1.435 and 1.842 THz. The associated relaxation lifetimes ( approximately 1 ps) for these modes of the tryptophan molecule were measured. Using a density-functional calculation, the origins of the observed torsional vibrations were assigned to the chain and ring of the tryptophan molecule.

The Cypate-Bombesin Peptide Analogue Conjugate (Cybesin) was used as a prostate tumor receptor-targeted contrast agent. The absorption and fluorescence spectra of Cybesin were measured and shown to exist in the NIR tissue "optical window". The spectral polarization imaging of Cybesin-stained prostate cancerous and normal tissues shows that prostate cancerous tissue takes-up more Cybesin than that of prostate normal tissue, making Cybesin a potential marker of prostate cancer.Keywords: Prostate cancer; Receptor-targeted; Peptide analogue conjugate; Contrast agent; Spectral polarization imaging; Near-infrared; Absorption; and Fluorescence. IntroductionThe increasing incidence and mortality rate of prostate cancers in men makes early tumor detection research a challenge for oncological specialists. The region of the highest incidence is in the western world, where there are 10-11% chances for a man to develop prostate cancer, and 3-4% chances of dying from the disease (1). Conventional oncology imaging methods for prostate cancer diagnosis, still depend on bulk physical properties of cancer tissue and are not effective for earlystage primary tumors (2). It is well known that diagnosis of a small premalignant lesion is critical for the success of cancer therapy and a key to increase survival rates. Scientists have been looking for methods that emphasize gene-specific or receptor-specific, minimally invasive diagnosis for early-stage tumors (2).Near-infrared (NIR) optical imaging is a powerful tool in cancer research that relies on activating endogenous chromophores or applying contrast agents that can target cancer cells. The use of intrinsic chromophores to differentiate the optical properties of diseased and healthy human tissues has been reported in some studies using fluorescence and absorption (3, 4). The most attractive advantage of optical imaging is the high sensitivity, which can be superior to other in vivo imaging techniques (2). Over the past decade, cyanine dyes have been investigated by several groups (5, 6) as contrast agents for optical detection of tumors. In order to observe fluorescence from a substantial distance within the body, the emission wavelength must be in the NIR wavelength window in which light passing through tissue is less likely to be absorbed or scattered (7). Researchers are interested in cyanine dyes because their emission range of 700 nm to 900 nm is in the tissue "optical window" (8 absorption bands at 950nm and 1195nm due to water which is the main chromophore component in human tissue (4, 9).The investigations of receptor expression in normal and cancer tissue suggest that small peptide-dye conjugates can be used to target over-expressed receptors on tumors contrary to the traditional approach of dyes conjugated to large proteins and antibodies (5, 10, 11). As a small ICG-derivative dyepeptide, Cypate-Bombesin Peptide Analogue Conjugate (Cybesin) was synthesized and used as a contrast agent to detect pancreas tumors in an animal model a few years ago (5). The prior experimenta...

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The dielectric function and momentum relaxation time of carriers for a single-crystal GaSe were investigated using terahertz time-domain spectroscopy over the frequency range from 0.4to2.4THz. The key parameters determined from THz data using the Drude model are: the plasma frequency ωp=2.6±0.2THz, the average momentum relaxation time ⟨τ⟩=56±2fs, and the mobility μ=89cm2∕Vs for electrons. The THz absorption spectrum showed resonance structures attributed to the difference frequency combinations associated with acoustical and optical phonons.

Optical spectroscopic imaging offers a new noninvasive detecting method for microscopic evaluation of laser tissue welding.

Terahertz time-domain spectroscopy is used to investigate the dielectric relaxation properties of liquid CS2. The frequency-dependent absorption coefficient and index of refraction were measured in the frequency range 0.2–2.0 THz. The ultrafast dielectric relaxation time of liquid CS2 was determined to be 630±30 fs by fitting the dielectric function to the Debye model which is attributed to average time for rocking and rotational response of the CS2 molecules possessing an anisotropic polarizability.