Rovibrational spectrum and potential energy surface of the N2-N2O van der Waals complex

The rovibrational spectrum of the N₂-N₂O van der Waals complex has been recorded in the N₂O ν₁ region (∼1285 cm⁻¹) using a tunable diode laser spectrometer to probe a pulsed supersonic slit jet. The observed transitions together with the data observed previously in the N₂O ν₃ region are analyzed using a Watson S-reduced asymmetric rotor Hamiltonian. The rotational and centrifugal distortion constants for the ground and excited vibrational states are accurately determined. The band-origin of the spectrum is determined to be 1285.73964(14) cm⁻¹. A restricted two-dimensional intermolecular potential energy surface for a planar structure of N₂-N₂O has been calculated at the CCSD(T) level of theory with the aug-cc-pVDZ basis sets and a set of mid-bond functions. With the intermolecular distance fixed at the ground state value R = 3.6926 Å, the potential has a global minimum with a well depth of 326.64 cm⁻¹ at θ_N2 = 11.0° and θ_N2O = 84.3° and has a saddle point with a barrier height of 204.61 cm⁻¹ at θ_N2 = 97.4° and θ_N2O = 92.2°, where θ_N2(θ_N2O) is the enclosed angle between the N-N axis (N-N-O axis) and the intermolecular axis.     

Sub-wavelength and non-periodic holes array based fully lensless imager

We present a novel concept for microscopic imaging. The proposed microscope-like device does not include an objective lens neither a condenser. Instead, a metallic plate of sub-wavelength hole-array with a varying pitch is used to illuminate the inspected object that is mounted very close to it. As a result, the transmitted spectrum through each hole differs from the others and therefore, each spot of the detected object is illuminated with a unique spectrum. By measuring a single spectrum that is the sum of all the spectra that are transmitted through the sample and by using spectral decomposition algorithms, the spatial transmission pattern of the object can be extracted.     

Emission properties of femtosecond (fs) laser fabricated microstructures in Polystyrene (PS)

We fabricated microstructures and micro craters in thin films and bulk of PS. To the best of our knowledge, this is the first report of the emission from fs laser modified regions of PS when excited at 337, 400, 458, 488 and 514 nm wavelengths with different emission peaks. We systematically studied the emission in context of formation of optical centers and analyzed the spectra of irradiated PS. Change in the excitation wavelength leads to a shift in the emission peak, whereby, we infer that the emission should be due to a myriad of optical centers. Interestingly these optical centers have a similar excitation spectrum. Diphenylbutadiene (DPBD) is probably the main optical center among other optical centers thus formed in the process of fs laser irradiation of PS.     

Growth and characterization of Nd:Lu3ScxGa5 − xO12 series laser crystals

A new series Nd:Lu₃Sc_xGa_5 − xO₁₂ (x = 0.5, 0.8, 1, 1.2 and 1.5) laser crystals have been successfully grown by the optical floating zone method. Their absorption and luminescence spectra were measured at room temperature and spectral parameters were systemically calculated using Judd-Ofelt (JO) theory. The fluorescence τ_f lifetimes were experimentally measured and compared with the theoretical results. Diode-pumped continuous-wave (CW) laser performance at 1.06 μm with mixed crystals was demonstrated. The influence of different x values on laser performance and spectral parameters was also discussed. All the results show that Nd:Lu₃Sc_xGa_5 − xO₁₂ series crystals should be suitable for laser application.     

Tunable optical transmission through square-core metallic nanotube arrays

We propose a square-core metallic nanotube array and investigate its optical transmission property theoretically. We find that the transmission spectra can be tuned by the width of square-core edge, the intertube spacing and the dielectric constants of the core and the embedding medium between the nanotubes. We show that there is a band gap over a wide optical wavelength, and its width, number and position are sensitive to the tunable parameters. We also discuss the situation of the rectangular-core nanotube arrays and present that modification of the size of internal holes leads to redshift of the transmission spectra. Based on the localized nature of the field distributions, we show that there are local plasmonic resonant modes that originate from multipolar plasmon polaritons and a large number of opposing surface charges build up in the gap between adjacent nanotubes.     

The analysis of the error statistics in a 5 × 40 Gbit/s fibre link with hybrid amplification

We quantify the error statistics and patterning effects in a 5 × 40 Gbit/s WDM RZ-OOK SMF/DCF fibre link using hybrid Raman/EDFA amplification. By extensive use of a numerical model, we determine how the error statistics change with the transmission distance. This knowledge is used as a basis for a constrained coding technique in order to improve the transmission error rate. We propose an adaptive constrained code for mitigation of the patterning effects and demonstrate that this approach can substantially reduce the bit error rate (BER) even for very large values of the channel BER (BER > 10^− 1). The proposed technique can be used in combination with forward error correction schemes (FEC) to extend the range of channel BERs that an FEC scheme is effective over.     

Multiwavelength lasers with homogeneous gain and intensity-dependent loss

Using a simple discrete laser model that incorporates only gain and loss, we showed that lasers with homogeneous gain can have multiwavelength continuous wave output if the loss element is a saturable transmitter. The intensity-dependent loss provides an adaptive balance to the different gain values at different wavelengths. The output power spectrum of the multiwavelength laser will be flat if the laser operates near a peak of the transmission of the intensity-dependent loss.     

Polarization-dependence of optical spatial solitons in photoisomerization material

Experimental observation of spatial solitons in azobenzene-doped organic polymer is demonstrated in dye-doped polymer bulk material. Solitons cannot only be formed in this material with linearly polarized light, but also with circularly polarized light. An interesting phenomenon is revealed that the soliton is polarization-dependent. The solitons with the same intensity but with different polarizations have different widths. The experimental results are further theoretically explained with the dynamics model based on a photochemical process, namely photoisomerization.     

Birefringence dispersion in a quartz crystal retrieved from a channeled spectrum resolved by a fiber-optic spectrometer

We present a simple method for measuring the wavelength dependence of both the phase and group birefringences in a quartz crystal of known thickness. The method utilizes interference of polarized waves resolved by a fiber-optic spectrometer as a channeled spectrum (spectral fringes). The fringe order versus the precise position of the interference maximum in the spectrum is fitted to the approximate function, from which the phase birefringence as a function of wavelength is retrieved. We also determine the group birefringence dispersion. The functions measured in a range from 500 to 900 nm are compared with those resulting from the available dispersion relation, and very good agreement is confirmed.     

Partially coherent optical processor for enhancement of partial second order derivatives of an image: Analysis and implementation

We present an optical processor capable to perform partial second derivatives of an image working with partially coherent illumination. The proposed system utilizes a liquid crystal display, onto which images to be derived are displayed. The method is based on the capacity of these devices to generate simultaneously a contrast reverted replica of the image displayed on it. A positive replica of original image is obtained when the LCD is between crossed polarizers, while the negative one is obtained with the LCD is between parallel polarizers. Since the LCD is a diffraction element, both polarizer arrangements may be simultaneously implemented, for example, in a 4f optical processor using polarization filtering of the different diffraction orders. When three images (two replicas of original image displaced in opposite direction and the other one with contrast reverted and centered at the origin.) are imagined across a slightly defocused plane, one obtains an image with enhanced second derivatives in a given direction. No other incoherent (or partially coherent) optical system is presently known which can perform partial second-order derivatives of an image. Experimental results obtained are presented.