Displacement-noise-free gravitational-wave detection with two Fabry-Perot cavities

We propose two detuned Fabry-Perot cavities, each pumped through both the mirrors, positioned in line as a toy model of the gravitational-wave (GW) detector free from displacement noise of the test masses. It is demonstrated that the noise of cavity mirrors can be completely excluded in a proper linear combination of the cavities output signals. This model is illustrated by a simplified round trip model (without Fabry-Perot cavities). We show that in low-frequency region the obtained displacement-noise-free response signal is stronger than the one of the interferometer recently proposed by S. Kawamura and Y. Chen.     

The output of amplified spontaneous emission lasers

The output of amplified spontaneous emission (ASE) lasers such as X-ray lasers operated without mirrors is calculated exactly for Gaussian and Lorentzian small signal gain profiles by a simple Taylor series expansion. The accuracy of the ‘Linford’ formula commonly used as an approximation for the output of ASE lasers is evaluated by comparison to our exact solutions. The Linford formula is accurate to better than 10% for intensities produced by a Gaussian gain profile, but requires multiplication by a correction factor of at gain length product greater than 5 for Lorentzian gain profiles.     

1.55-μm InGaAs/InGaAlAs MQW vertical-cavity surface-emitting lasers with InGaAlAs/InP distributed Bragg reflectors

High-performance InGaAs/InGaAlAs multiple-quantum-well vertical-cavity surface-emitting lasers (VCSELs) with InGaAlAs/InP distributed Bragg reflectors are proposed for operation at the wavelength of . The lasers have good heat diffusion characteristic, large index contrast in DBRs, and weak temperature sensitivity. They could be fabricated either by metal-organic chemical vapor deposition (MOCVD) or by molecular beam epitaxy (MBE) growth. The laser light-current characteristics indicate that a suitable reflectivity of the DBR on the light output side in a laser makes its output power increase greatly and its lasing threshold current reduce significantly, and that a small VCSEL could output the power around its maximum for the output mirror at the reflectivity varying in a broader range than a large VCSEL does.     

The gated integration technique for the accurate measurement of the autocorrelation function of speckle intensities scattered from random phase screens

A new approach based on the gated integration technique is proposed for the accurate measurement of the autocorrelation function of speckle intensities scattered from a random phase screen. The Boxcar used for this technique in the acquisition of the speckle intensity data integrates the photoelectric signal during its sampling gate open, and it repeats the sampling by a preset number, m. The average analog of the m samplings output by the Boxcar enhances the signal-to-noise ratio by , because the repeated sampling and the average make the useful speckle signals stable, while the randomly varied photoelectric noise is suppressed by . In the experiment, we use an analog-to-digital converter module to synchronize all the actions such as the stepped movement of the phase screen, the repeated sampling, the readout of the averaged output of the Boxcar, etc. The experimental results show that speckle signals are better recovered from contaminated signals, and the autocorrelation function with the secondary maximum is obtained, indicating that the accuracy of the measurement of the autocorrelation function is greatly improved by the gated integration technique.     

Power transients in time-division multiplexed discrete Raman fibre amplifier

In this paper, the effect of addition and/or dropping of wavelength-division multiplexed channels in an all-optical gain-clamped time-division multiplexed (TDM) pumped discrete Raman fibre amplifier (DRFA) has been investigated experimentally and analyzed by numerical simulation. Nineteen signals were amplified in a counter-directionally pumped DRFA consisting of long dispersion compensating fibre. Light of eight DFB lasers was square-wave modulated at to imitate channel addition/dropping and combined with signals from five 10 Gigabit Ethernet transmitters and with six continuous wave signals. Power transients of the surviving channels caused by cross-gain modulation of the DRFA were monitored at the output of the amplifier. All-optical feedback loop was implemented in the form of a ring laser. Theoretical analysis of the TDM-pumped DRFA was based on numerical solution of coupled propagation equations for backward propagating pumps, signals, and both forward and backward propagating spectral components of amplified spontaneous emission powers.     

Heterodyne interferometer for displacement measurement with amplitude quadrature and noise suppression

The high precision displacement measurement in nanoscale is crucial to many applications. We present a heterodyne interferometry with differential phase to amplitude conversion scheme for displacement measurement in nanoscale. In this approach, the differential phase introduced by the displacement is converted into the amplitudes of heterodyne signals in quadrature. Meanwhile, the heterodyne signals in phase quadrature are also achieved so that the displacement can be determined from the amplitude ratio of the quadrature signals, and the direction of displacement can be determined from the phase quadrature. Since the differential phase to quadrature amplitude conversion is achieved through the optical addition and subtraction by polarization tuning, which are based on differential detection concept. Thus the proposed method benefits from the features of differential detection with common phase noise and correlated amplitude noise rejection and that of quadrature detection with real time and wide dynamic range of phase measurement. To demonstrate the capability of proposed method in differential phase measurement, we measure the displacement drove by a commercially available PZT pusher and found close agreement between the experiment and the theory. The experimental evidence of noise suppression is also found with spectral measurements, which demonstrates the resolution of displacement measurement at 60 pm and minimum detectable differential phase of 5.6 × 10⁻⁶ rad/ over 50 kHz.     

Comparison of |Q|=1 and |Q|=2 gauge-field configurations on the lattice four-torus

It is known that exactly self-dual gauge-field configurations with topological charge |Q|=1 cannot exist on the untwisted continuum four-torus. We explore the manifestation of this remarkable fact on the lattice four-torus for SU(3) using advanced techniques for controlling lattice discretization errors, extending earlier work of De Forcrand et al. for SU(2). We identify three distinct signals for the instability of |Q|=1 configurations, and show that these signals manifest themselves early in the cooling process, long before the would-be instanton has shrunk to a size comparable to the lattice discretization threshold. These signals do not appear for the individual instantons which make up our |Q|=2 configurations. This indicates that these signals reflect the truly global nature of the instability, rather than the local discretization effects which cause the eventual disappearance of the would-be single instanton. Monte-Carlo generated SU(3) gauge-field configurations are cooled to the self-dual limit using an -improved gauge action chosen to have small but positive errors. This choice prevents lattice discretization errors from destroying instantons provided their size exceeds the dislocation threshold of the cooling algorithm. Lattice discretization errors are evaluated by comparing the -improved gauge-field action with an -improved action constructed from the square of an -improved lattice field-strength tensor, thus having different discretization errors. The number of action-density peaks, the instanton size, and the topological charge of configurations is monitored. We observe a fluctuation in the total topological charge of |Q|=1 configurations, and demonstrate that the onset of this unusual behavior corresponds with the disappearance of multiple-peaks in the action density. At the same time discretization errors are minimal.     

Polariton kinetics for bosonic condensation in CdTe-microcavities for various Rabi splittings and detunings

The applied Boltzmann relaxation kinetics for stationary and ps-pulsed nonresonant pumping takes the polariton-acoustic phonon and the polariton-polariton scattering into account. For cavities with a vacuum Rabi splitting around , we find for ps-pulse excitation a transient bosonic condensation in the ground state. For microcavities with a large vacuum Rabi splitting of we find for zero detuning, due to the steep increase of radiative losses, a condensation with a macroscopically occupied state in the wavenumber region at which the Bragg mirrors become transparent. With positive detunings which increase the scattering rates, the finite-size Bose-Einstein condensation in the ground state is restored.     

Photo-induced birefringence in semiconductors compared with optical fibers

We analyze the photon-induced birefringence in semiconductors based on pump-probe setups, within the semiconductor Bloch equations formalism and the Luttinger-Kohn model for the band structure. When the pump and probe pulses are well separated in time, the anisotropic momentum space filling of the photo-excited electrons is the only mechanism causing the induced birefringence. The birefringence ratio is then for pump and probe having perpendicular vs. parallel linear polarizations. This ratio is for opposite vs. identical circular polarization. When the pump and probe pulses overlap in time, these birefringence ratios become for linear polarizations and in case of circular polarizations. These predictions differ markedly from those for optical fibers.     

Diode laser spectroscopy of ammonia at 760 nm

A tunable diode laser spectrometer has been employed to examine the unknown overtone absorption lines of NH₃ around (760 nm). The spectrometer sources are commercially available heterostructure AlGaAs tunable diode lasers operating in the “free-running” mode. The detection of the lines has been possible by the use of the wavelength modulation spectroscopy and the second harmonic detection technique. A special algorithm has been used in order to fit the highly modulated absorption lines. The weakest observed resonances have absorption cross sections on the order of ?/molecule or ?/amagat. For some of the more intense lines self-, air-, N₂-, He- and H₂-broadening coefficients have been obtained at room temperature and also some shifting coefficients have been measured.     

Giant intersubband polariton splitting in InAs/AlSb microcavities

The optical response of the intersubband excitation of multiple InAs/AlSb quantum wells embedded in a planar semiconductor microcavity has been studied through angle-dependent reflectance measurements. Using a resonator based on total internal reflection, a strong coupling is demonstrated between the intersubband optical transition and the cavity photon, with the attendant formation of intersubband polaritons. A giant vacuum-Rabi splitting 2Ω_R was observed both at liquid helium temperatures () as well as at 300 K (), for a transition energy . The observed ratio is a record high value (14%) for any strongly-coupled systems, and demonstrates the huge potential of this material for the achievement of the ultra-strong coupling regime predicted theoretically.     

Spectroscopic properties of Ba 6pns (J=0,2) autoionizing series

The investigations on Ba and autoionizing states are carried out through a combination of the isolated core excitation method and proper polarization configuration of lasers. With comparison between the 6pns autoionizing states with different J, the spectroscopic properties of both the and series, such as the configuration interactions with the other series, are discussed in detail.     

Time-dependent all-optical logic-gates with bacteriorhodopsin film

In this paper, we proposed time-dependent AND, NOT and operation based on the relation between input and output intensities of the first-order diffraction beams in degenerate multi-wave coupling. When two coherent green beams are coupled in bacteriorhodopsin (bR) film with a small angle, the intensities of the diffraction beams decrease along with writing time. Based on the phenomenon that the diffraction beams decay along with writing time and the relation between the intensities of input and output beams, we demonstrated the time-dependent optical AND, NOT and operations.     

Laser diode beam shaping with GRIN lenses using the twisted beam approach and its application in pumping of a solid-state laser

We report a novel beam shaping method for laser diodes based on the concept of twisted Gaussian Schell-model beams using GRIN lenses. This method enables a more symmetric pump as well as a compact setup for pumping of solid-state lasers. In the experiment with a standard 2 W diode, the beam quality factors in the two orthogonal directions were equalized to and , respectively, which pumped an intra-cavity frequency-doubled Nd:YAG laser at 946 nm with an output of 28 mW at 473 nm.     

Real-time monitoring of InAs QD growth procedure on InP substrate by spectral reflectance

Using an in situ spectral reflectance (SR) method, we monitored the growth procedure of InAs QD layer on InP substrate grown by low-pressure metalorganic chemical vapor deposition. The surface reconstruction of the InP buffer layer at 530 °C under P-rich condition was determined by the subtraction SR and explained to be (2 × 4)-like structures composed of the P-dimers and [1 1 0] In-dimers. The [1 1 0] and SR signals at different wavelengths showed different behaviors, which was interpreted to be caused by As/P exchange reaction and the other diverse surface processes. This analysis was confirmed by the comparison between SR signal and multibeam optical stress sensor data.     

Model calculations of the energy band structures of double stranded DNA in the presence of water and Na ions

Using the ab initio Hartree-Fock crystal orbital method in its linear combination of atomic orbitals form we have calculated the band structures of poly(-) and poly(-). Here, besides the nucleotide bases, the sugar and phosphate parts of the nucleotide were also taken into account together with their first water shell and Na⁺ ions. We use the notation with a tilde above the abbreviation of a base for the whole nucleotide; for instance poly() means a guanine base with the deoxyribose and PO₄⁻ groups to which it is bound. The obtained band structures were compared with previous single chain calculations as well as with the earlier poly(-) and poly(-) calculation without water but in the presence of counterions. One finds that all the bands of poly(-) and poly(-) are shifted considerably upwards as compared to the previous single chain results (poly(), poly(), poly() and poly()). This effect is explained by the ∼0.2e charge transfer from the sugars of both chains to the nucleotide bases. The fundamental gaps between the nucleotide base-type highest filled and lowest unfilled bands are decreased in both cases by 1-3 eV, because the valence bands are purine-type and the conduction bands pyrimidine-type, respectively, while in the case of single homopolynucleotides they belong to the same base. We also pointed out that the LUMO is mainly Na⁺-like in both investigated cases and several unoccupied bands (belonging to the Na⁺ ions, the phosphate group and the water molecules) can be found between this and the first unoccupied pyrimidine-like empty band.