1,720,965 research outputs found
Beam deflection and T.I.R. switching in domain-engineered LiNbO<sub>3</sub>
No full textWe have developed a novel electro-optically addressable deflector and switch in a sample of LiNbO3. Patterning and electric-field poling produce areas of oppositely oriented domain regions separated by a sharp boundary. An external electric field applied to this boundary produces equal magnitude refractive index changes, Δn, of opposite sign between adjacent domain regions. For increasing Δn, the incident beam experiences deflection, until a critical value is reached when TIR will occur, thereby leading to complete switching of beam direction. Such a device provides numerous advantages including ease of fabrication, high contrast ratios (TIR is 100% efficient), relatively low drive voltages, large deflections (~8° for an applied field of 1000V), and a wavelength dependence that is superior to other electro-optic devices such as Pockels cells. We will discuss results achieved for light of s and p polarisations, for wavelengths In the visible and the near I.R., with initial contrast ratios >20dB
Electro-optically controlled beam switching via total internal reflection at a domain-engineered interface in LiNbO<sub>3</sub>
No full textWe report a novel switching method that occurs due to the electro-optic effect under applied field when a beam incident on an interface between anti-parallel domains in a sample of LiNbO3 subtends an angle greater than that required for total internal reflection (TIR). We present data obtained for wavelengths of 0.543 and 1.52µm and compare this with a theoretical model. This switch has many attractive properties, as TIR is a 100% efficient process leading to the possibility of high contrast ratios; current data shows contrast ratios greater than 100:1 (20 dB). Other properties include relatively simple fabrication procedure, low drive voltages and a wavelength dependence that is less than other electro-optic devices such as Pockels cells
Power-scaling continuous-wave adaptive laser resonators
No full textWe demonstrate a power-scaling strategy in a continuous-wave adaptive laser resonator that actively corrects, via phase-conjugation, for thermally induced phase distortions introduced by a power-amplifier placed in the output arm of the resonator
Phase conjugate non-reciprocal transmission in multimode optical fibres
No full textCorrection of modal dispersion of light transmitted through multimode optical fibres has been the subject of extensive research to date. At low optical powers photoconductive crystals are typically used to produce phase conjugate correction at the output end of the fibre in doublepass schemes [1]. Double-pass correction schemes vary in their approach to overcome the apparent problem that only one (the e-polarised) polarisation state of the scrambled output from the fibre, can undergo phase conjugate correction. We report the results of our study on the implementation of phase conjugate correction of modal distortion in highly multimode, (300 micron diameter), short (~1m) passive optical fibres using a non-polarisation preserving phase conjugation scheme [2] and its application to a non-reciprocal transmission element. Figure 1 shows a schematic of the set-up used to demonstrate phaseconjugate non-reciprocal transmission characteristics in multimode fibres. An initial vertically polarised Gaussian input beam from an Ar-ion laser is launched into fibre A where it becomes polarization and modally scrambled as it travels along fibre A's length. nie optical power coupled into fibre B, and hence the forward transmission factor is dependent on the distance, z, between fibres A and B. The field from fibre B is then sent to a NPPPC consisting of a self-pumped BaTiO3 crystal. Previous work has shown that the field reflected from such a NPPPC consists of a phase conjugate part which will all couple back from fibre B to A in the reverse direction and a non-phase conjugate part which will have the same transmission characteristics as the forward travelling wave leading to different transmissions for the forward and backward direction
Electro-optically controlled beam deflection and switching via total internal reflection at a domain-engineered interface in LiNbO<sub>3</sub>
No full textWe report a novel beam deflection and switching method that occurs due to the electro-optic effect under applied field when a beam at grazing incidence is incident on an interface between anti-parallel domains in a sample of LiNbO3. We present data obtained for wavelengths of 0.543µm and 1.52µm and compare this with theoretical models. For deflection, improvements can be obtained for both range of angular deflection and transmission uniformity, by faceting the exit face of the device at an optimum angle. A theoretical analysis is presented for this configuration and compared with data obtained for a wavelength of 1.52µm. A practical geometry would permit a deflection of ~140mrad for an applied voltage of 1kV. For switching there are many attractive properties, as TIR is a 100% efficient process this leads to the possibility of high contrast ratios; current data shows contrast ratios greater than 100:1 (20dB). Other properties include relatively simple fabrication procedure, low drive voltages and a wavelength dependence that is less than other electro-optic devices such as Pockels cells
Efficient adaptive self-starting Nd:YVO<sub>4</sub> gain grating laser oscillator
No full textWe present the results of a self-starting continuous-wave diode-pumped Nd:WO4 laser oscillator based on an adaptive intracavity gain-grating technique. The laser produces 12W narrowband output in a TEMoo mode with 36W of diode-pumping
Electro-optically controlled beam deflection and switching in domain-engineered LiNbO<sub>3</sub>
No full textWe report a novel switching method that occurs due to the electro-optic effect under an applied field when a beam incident on an interface between anti-parallel domains in a sample of LiNbO3 subtends an angle greater than that required for total internal reflection (TIR). As the field increases, the induced index change present across the interface region acts to first deflect the beam towards the interface, then when the conditions are reached for TR, to switch the beam with a contrast ratio that should be extremely high, due to the intrinsic nature of the TIR process.We show results for wavelengths in the visible and at 1.5µm, where we obtain contrast ratios >20dB, deflection angles of 8° per kV applied, and an effective insensitivity to wavelength when compared to other devices such as Pockels cells. Experimental data is compared to a 2-d theoretical model for an incident Gaussian beam focussed-at the interface, and good agreement is shown
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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