Demonstration of a passive subpicostrain fiber strain sensor

We demonstrate a fiber Fabry-Perot (FFP) sensor that is capable of detecting subpicostrain signals, from 100 Hz and extending beyond 100 kHz, using the Pound-Drever-Hall (PDH) frequency locking technique. A low-power diode laser at 1550 nm is locked to a free-space reference cavity to suppress its free-running frequency noise, thereby stabilizing the laser. The stabilized laser is then used to interrogate a FFP sensor whose PDH error signal yields the instantaneous fiber strain.     

Experimental demonstration of variable-reflectivity signal recycling for interferometric gravitational-wave detectors

The results of an experimental demonstration of a benchtop Michelson interferometer with a variable-reflectivity signal mirror are presented. This variable reflectivity is achieved by employment of a second Michelson interferometer. The results are presented in the form of the frequency responses obtained from this configuration with a signal laser injection method. It is shown that the frequency response can be dynamically tuned with independent peak frequency and bandwidth control. Such a configuration gives a tunable frequency response and has an application as a flexible gravitational-wave detector.     

Direct bound-free photodesorption of physisorbed molecules

Because light, weakly adsorbed atoms and molecules have very few bound states, the harmonic oscillator Δv = 1 optical selection rule is invalid for vibrational transitions of the physisorption bond. For such systems, we show that very low power (50 mW) infrared radiation should be sufficient to cause a direct one-photon optical transition from the ground state to continuum translational levels, resulting in photodesorption. Using a simple one-dimensional model, we present computations of the photodesorption rate as a function of photon energy for the Morse potential and several dipole moment functions. The threshold behavior at long wavelengths is analyzed.     

Elastic π± + 3He scattering

Differential cross sections have been measured at θ≈20–120° at 50, 100 and 200 MeV. Salient features of the angular distributions are Coulomb interference effects at 50 MeV and clear spin-flip contributions to π^? compared to π⁺ scattering in the angular region of θ≈80° dominated by the πN p-wave minimum. Comparison with optical model calculations account for the data up to 200 MeV while this first-order scattering theory misses conspicuous features of data at 295 MeV.     

Novel,Monomeric Cyanine Dyes as Reporters for DNA Helicase Activity

The dimeric cyanine dyes, YOYO-1 and TOTO-1, are widely used as DNA probes because of their excellent fluorescent properties. They have a higher fluorescence quantum yield than ethidium homodimer, DAPI and Hoechst dyes and bind to double-stranded DNA with high affinity. However, these dyes are limited by heterogeneous staining at high dye loading, photocleavage of DNA under extended illumination, nicking of DNA, and inhibition of the activity of DNA binding enzymes. To overcome these limitations, seven novel cyanine dyes (Cyan-2, DC-21, DM, DM-1, DMB-2OH, SH-0367, SH1015-OH) were synthesized and tested for fluorescence emission, resistance to displacement by Mg²⁺, and the ability to function as reporters for DNA unwinding. Results show that Cyan-2, DM-1, SH-0367 and SH1015-OH formed highly fluorescent complexes with dsDNA. Of these, only Cyan-2 and DM-1 exhibited a large fluorescence enhancement in buffers, and were resistant to displacement by Mg²⁺. The potential of these two dyes to function as reporter molecules was evaluated using continuous fluorescence, DNA helicase assays. The rate of DNA unwinding was not significantly affected by either of these two dyes. Therefore, Cyan-2 and DM-1 form the basis for the synthesis of novel cyanine dyes with the potential to overcome the limitations of YOYO-1 and TOTO-1.     

Angular momentum polarization in molecular collisions : Classical and quantum theory for measurements using resonance fluorescence

Inelastic or reactive collisions typically produce an anisotropic distribution of rotational angular momentum. An explicit and general treatment is given for the intensity and polarization of resonance fluorescence from molecules produced in such processes. Both classical and quantum results are expressed in terms of bipolar harmonics and state multipoles formed from linear combinations of density matrix elements. The treatment provides an inversion procedure for determining moments of the rotational angular momentum distribution ; twelve independent moments can be obtained. The combinations of angular momentum operators involved are even in eight of these moments and odd in four, with respect to reflection in a plane containing the initial and final relative velocity vectors. Measurements of the even moments require linearly polarized excitation and fluorescence, whereas measurements of the odd moments require circularly polarized excitation. The requisite experimental geometry and other practical aspects are discussed. In the three appendices are discussed the classical limits of transition intensities, a density matrix treatment of atom-rigid-rotor collisions, including analysis of state multipole symmetries ; and the coupling coefficients for parallel angular momenta.