Ahn Y, Park J. Efficient Visible Light Detection Using Individual Germanium Nanowire Field Effect Transistors. Appl. Phys. Letts. 2007;91:162102.Abstract

We report photoconductivity (PC) in individual germanium nanowire field effect transistors (GeFETs). PC measurements with a global illumination reveal that GeFETs can be used as a polarization-sensitive nanoscale light detector in the visible range. It is also found that the PC shows sensitive optical response especially in the low intensity regime. We observe a high internal gain in PC in conjunction with strong saturation behavior, which is attributed to the filling of surface trapping states. This mechanism for high internal gain is consistent with spatially resolved scanning photocurrent measurements, whose results confirm that optical absorption is in the linear regime.

Vollmer F, Fischer P. Frequency-domain displacement sensing with a fiber ring-resonator containing a variable gap. Sensors and Actuators A-Physical 2007;134(2):410-413. 2007_vollmer_sensors_actuators.pdf
Ghosh A, Hill W,  Fischer P. Observation of the Faraday effect via beam deflection in a longitudinal magnetic field. Physical Review A 2007;76(5) 2007_ghosh_prl_.pdf
Topolancik J, Vollmer F. All-optical switching in the near infrared with bacteriorhodopsin-coated microcavities. Applied Physics Letters 2006;89:184103. 2006_vollmer_apl.pdf
Cebers A, Dogic Z, Janmey PA. Counterion-mediated attraction and kinks on loops of semiflexible polyelectrolyte bundles. Phys. Rev. Lett. 2006;96:247801. 2006_dogic_prl_96_june.pdf
Barry E, Hensel Z, Dogic Z, Shribak M, Oldenbourg R. Entropy-driven formation of a chiral liquid-crystalline phase of helical filaments. Phys Rev Lett 2006;96(1):018305.Abstract

We study the liquid-crystalline phase behavior of a concentrated suspension of helical flagella isolated from Salmonella typhimurium. Flagella are prepared with different polymorphic states, some of which have a pronounced helical character while others assume a rodlike shape. We show that the static phase behavior and dynamics of chiral helices are very different when compared to simpler achiral hard rods. With increasing concentration, helical flagella undergo an entropy-driven first order phase transition to a liquid-crystalline state having a novel chiral symmetry.

Lewis KC, Bazzaz FA, Liao Q, Orians CM. Geographic patterns of herbivory and resource allocation to defense, growth, and reproduction in an invasive biennial, Alliaria petiolata. Oecologia 2006;148(3):384-95.Abstract

We investigated geographic patterns of herbivory and resource allocation to defense, growth, and reproduction in an invasive biennial, Alliaria petiolata, to test the hypothesis that escape from herbivory in invasive species permits enhanced growth and lower production of defensive chemicals. We quantified herbivore damage, concentrations of sinigrin, and growth and reproduction inside and outside herbivore exclusion treatments, in field populations in the native and invasive ranges. As predicted, unmanipulated plants in the native range (Hungary, Europe) experienced greater herbivore damage than plants in the introduced range (Massachusetts and Connecticut, USA), providing evidence for enemy release, particularly in the first year of growth. Nevertheless, European populations had consistently larger individuals than US populations (rosettes were, for example, eightfold larger) and also had greater reproductive output, but US plants produced larger seeds at a given plant height. Moreover, flowering plants showed significant differences in concentrations of sinigrin in the invasive versus native range, although the direction of the difference was variable, suggesting the influence of environmental effects. Overall, we observed less herbivory, but not increased growth or decreased defense in the invasive range. Geographical differences in performance and leaf chemistry appear to be due to variation in the environment, which could have masked evolved differences in allocation.

Dogic Z, Fraden S. Ordered phases of filamentous viruses. Curr. Opinion in Coll. & Inter. Sci. 2006;11:47-55. 2006_dogic_current_opinion.pdf
Kang KG, Lettinga MP, Dogic Z, Dhont JKG. Vorticity banding in rodlike virus suspensions. Phys. Rev. E  2006;74:026307. 2006_dogic_phys_rev_e.pdf
Fischer P, Champagne B. Nonlinear Optical Properties of Chiral Liquids: Electric-dipolar pseudoscalars in nonlinear optics. In: Challenges and Advances in Computational Chemistry and Physics. 2006 p. 359-381.
Ghosh A, Fischer P. Chiral molecules split light: Reflection and refraction in a chiral liquid. Phys Rev Lett 2006;97(17):173002.Abstract

A light beam changes direction as it enters a liquid at an angle from another medium, such as air. Should the liquid contain molecules that lack mirror symmetry, then it has been predicted by Fresnel that the light beam will not only change direction, but will actually split into two separate beams with a small difference in the respective angles of refraction. Here we report the observation of this phenomenon. We also demonstrate that the angle of reflection does not equal the angle of incidence in a chiral medium. Unlike conventional optical rotation, which depends on the path-length through the sample, the reported reflection and refraction phenomena arise within a few wavelengths at the interface and thereby suggest a new approach to polarimetry that can be used in microfluidic volumes.

Buckingham AD, Fischer P. Direct chiral discrimination in NMR spectroscopy. Chemical Physics 2006;324(1):111-116. 2006_fischer_chemphys.pdf
Wong WP, Halvorsen K. The effect of integration time on fluctuation measurements: calibrating an optical trap in the presence of motion blur. Opt Express 2006;14(25):12517-31.Abstract

Dynamical instrument limitations, such as finite detection bandwidth, do not simply add statistical errors to fluctuation measurements, but can create significant systematic biases that affect the measurement of steady-state properties. Such effects must be considered when calibrating ultra-sensitive force probes by analyzing the observed Brownian fluctuations. In this article, we present a novel method for extracting the true spring constant and diffusion coefficient of a harmonically confined Brownian particle that extends the standard equipartition and power spectrum techniques to account for video-image motion blur. These results are confirmed both numerically with a Brownian dynamics simulation, and experimentally with laser optical tweezers.

Vollmer F, Fischer P. Ring-resonator-based frequency-domain optical activity measurements of a chiral liquid. Opt Lett 2006;31(4):453-5.Abstract

Chiral liquids rotate the plane of polarization of linearly polarized light and are therefore optically active. Here we show that optical rotation can be observed in the frequency domain. A chiral liquid introduced in a fiber-loop ring resonator that supports left and right circularly polarized modes gives rise to relative frequency shifts that are a direct measure of the liquid's circular birefringence and hence of its optical activity. The effect is in principle not diminished if the circumference of the ring is reduced. The technique is similarly applicable to refractive index and linear birefringence measurements.

Ahn Y, Dunning J, J. P. Scanning Photocurrent Imaging and Electronic Band Studies in Silicon Nanowire Field Effect Transistors. Nano Letters 2005;5(7):1367-1370.Abstract

We report optical scanning measurements on photocurrent in individual Si nanowire field effect transistors (SiNW FETs). We observe increases in the conductance of more than 2 orders of magnitude and a large conductance polarization anisotropy of 0.8, making our SiNW FETs a polarization-sensitive, high-resolution light detector. In addition, scanning images of photocurrent at various biases reveal the local energy- band profile especially near the electrode contacts. The magnitude and polarity of the photocurrent vary depending on the gate bias, a behavior that can be explained using band flattening and a Schottky-barrier-type change. This technique is a powerful tool for studying photosensitive nanoscale devices

Vollmer F. Taking detection to the limit. BIF Futura 2005;20:239. 2005_vollmer_biffutura.pdf
Fischer P, Hache F. Nonlinear optical spectroscopy of chiral molecules. Chirality 2005;17(8):421-37.Abstract

We review nonlinear optical processes that are specific to chiral molecules in solution and on surfaces. In contrast to conventional natural optical activity phenomena, which depend linearly on the electric field strength of the optical field, we discuss how optical processes that are nonlinear (quadratic, cubic, and quartic) functions of the electromagnetic field strength may probe optically active centers and chiral vibrations. We show that nonlinear techniques open entirely new ways of exploring chirality in chemical and biological systems: The cubic processes give rise to nonlinear circular dichroism and nonlinear optical rotation and make it possible to observe dynamic chiral processes at ultrafast time scales. The quadratic second-harmonic and sum-frequency-generation phenomena and the quartic processes may arise entirely in the electric-dipole approximation and do not require the use of circularly polarized light to detect chirality. They provide surface selectivity and their observables can be relatively much larger than in linear optical activity. These processes also give rise to the generation of light at a new color, and in liquids this frequency conversion only occurs if the solution is optically active. We survey recent chiral nonlinear optical experiments and give examples of their application to problems of biophysical interest.