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10.3390/app12157431 6 Shi J., Ding Y., Tang L., Li X., Bai H., Li X., Fan W., Niu P., Fu W., Yang X. Low-Frequency Terahertz Photonic Crystal Waveguide with a Lilac-Shaped Defect Based on Stereolithography 3D Printing. In addition, Shi et al. proposed an all-dielectric terahertz photonic crystal waveguide with a lilac-shaped defect operating in a 6G terahertz communication window [[6]]. This Special Issue entitled "Optoelectronic Materials, Devices, and Applications" is devoted to gathering a broad array of research papers on the latest advances in the development of optoelectronic materials and devices of semiconductors, fiber optics, power electronics, microwaves, and terahertz. [Extracted from the article]

In this work, we define the efficiency signal conversion numerical parameter, Veff, useful to evaluate the operation efficiency of femtosecond-Optical Parametric Oscillator (fs-OPO) cavities considering the astigmatism effect. For the validation of the Veff, we have performed experimental measurements. We present different high efficiency home-made singly resonant fs-OPO cavities, with signal tuneability from 1.1 µm to 1.6 µm based on a 0.5 mm Periodically Poled Lithium Niobate doped with MgO (MgO:PPLN) crystal. We have also defined the pump energy threshold per crystal unit length, ζ p , t h . Pump threshold, achieved by following the Veff, was 142 mW at 810 nm, and ζ p , t h = 2.10 nJ/mm, the lowest value, in comparison with other studies. The Veff is based on an ABCD matrix Gaussian beam propagation method, which calculates the mode coupling between the pump and signal beams along the crystal under different cavity configurations taking into account the astigmatism. The model was compared and tested with 3 different experimental singly resonant fs-OPO ring cavity configurations that we have defined as single-folded, two-folded, and direct-pump cavity. [ABSTRACT FROM AUTHOR]

This study introduces the concept of dynamic controlled bandpass filter (BPF) to achieve improved synchronisation capability of a single-loop optoelectronic oscillator (OEO) under the effect of externally applied angle modulated signal. The governing equation for synchronisation ability of an OEO using dynamic control BPF has been derived. Theoretical study and comparison of locking capability enhancement using this dynamic BPF over a conventional static BPF are provided which is properly validated by simulation. Finally, the ability of frequency modulation to amplitude modulation conversion has been compared by measuring the total harmonic distortion values of the reconstructed signals. [ABSTRACT FROM AUTHOR]

We report the coexistence of synchronized and unsynchronized states in a mutually coupled star network of nearly conservative non-identical oscillators. Generalized synchronization is observed between the central oscillator with the peripherals, and phase synchronization is found among the peripherals in weakly dissipative systems. However, the basin size of the synchronization region decreases as dissipation strength is increased. We have demonstrated these phenomena with the help of Duffing and Lorenz84 oscillators with conservative, nearly conservative, and dissipative properties. The observed results are robust against the network size. [ABSTRACT FROM AUTHOR]

The trial function approach is a useful technique to modelling soliton solutions for equations that cannot be solved exactly. The authors use the variational approach to find approximate solutions for the dissipative solitons described by the cubic-quintic complex Ginzburg-Landau equation. They find that the evolution equations for the soliton parameters are similar to those derived using the method of moments. The existence of both stationary and pulsating soliton solutions is indicated by both approaches. [ABSTRACT FROM AUTHOR]

An optically tunable frequency-decuple optoelectronic oscillator based on optical frequency comb (OFC) and stimulated Brillouin scattering has been proposed and theoretically analyzed. In the proposed structure, the OFC is generated using a cascaded Mach-Zehnder modulator and a dual-parallel Mach-Zehnder modulator (DPMZM), and multi-pump lights could be obtained instead of one pump. A quintuple Brillouin frequency shift oscillation signal generated by using Brillouin gain-loss compensation principle and carrier phase-shifted double sideband modulation is realized by using the DPMZM to double the oscillation frequency. As a consequence, a decuple frequency shift microwave signal is achieved. Profit from the wavelength-dependent nature of Brillouin frequency shift, a frequency-decuple signal at 10 $$f_{b}$$ which could be tunable from 87.9750 to 94.4750 GHz by simply tuning the wavelength of the tunable laser source is obtained in theory. [ABSTRACT FROM AUTHOR]

Optical Millimeter Wave (MM-Wave) generation with the highest frequency multiplication factor is one of the most promising techniques which can eliminate the need of high frequency local oscillator at the central station. In this paper, a filterless frequency16-tupled optical MM-Wave is generated using dual stage cascaded Lithium Niobate Mach-Zehnder modulators (LN-MZM). By properly adjusting the MZM biasing parameters and phase of the RF signal, eighth order optical sidebands only are generated which can result in 16-tupled millimeter wave at the photo detector. Optical sideband suppression ratio (OSSR) of 61 dB and radio frequency spurious sideband suppression ratio (RFSSR) of 48 dB are achieved in this method. As no filtering is involved in the generation, tunability over entire MM-Wave frequency band can easily be achieved. Impact of various non-ideal parameters such as RF phase, Extinction Ratio(ER), optical input power imbalance between the arms on the optical and RF sidebands is analyzed. The transmission performance of this scheme is evaluated by modulating 2.5 Gbps data and transmitting the same over10 km, 20 km and 25 km Radio over Fiber (RoF) links. Further, the impact of the laser linewidth on the transmission performances is also analysed and presented. [ABSTRACT FROM AUTHOR]

The distribution of Lyapunov exponents is calculated in the two-parameter region, and parameter is set carefully to reproduce bursting state from the optical parametric oscillator thus can be consistent with the previous experiments. The input field amplitude is changed to trigger different modes of outputs and then external noise is imposed to detect the transition of subharmonic mode and fundamental mode, it could be helpful to understand the potential mechanism for electromagnetic radiation-induced transition of electrical activities in neurons. [ABSTRACT FROM AUTHOR]

We report a high-power, long-wavelength infrared ZnGeP (ZGP) optical parametric oscillator (OPO) pumped by a Q-switched Tm,Ho:GdVO laser. The wavelength tuning range of 7.8-9.9 μm is realized by rotating the external angle of the ZGP crystal. We obtain an output power over 30 mW across the whole wavelength range and achieve a 1.71 W output power at 8.08 μm by transmitting the OPO parameters, corresponding to an idler laser slope efficiency of 12.1%. [ABSTRACT FROM AUTHOR]

A "chimera state" is a dynamical pattern that occurs in a network of coupled identical oscillators when the symmetry of the oscillator population is broken into synchronous and asynchronous parts. We report the experimental observation of chimera and cluster states in a network of four globally coupled chaotic opto-electronic oscillators. This is the minimal network that can support chimera states, and our study provides new insight into the fundamental mechanisms underlying their formation. We use a unified approach to determine the stability of all the observed partially synchronous patterns, highlighting the close relationship between chimera and cluster states as belonging to the broader phenomenon of partial synchronization. Our approach is general in terms of network size and connectivity. We also find that chimera states often appear in regions of multistability between global, cluster, and desynchronized states. [ABSTRACT FROM AUTHOR]

We present the operational principle of a coherent Ising machine (CIM) based on a degenerate optical parametric oscillator (DOPO) network. A quantum theory of CIM is formulated, and the computational ability of CIM is evaluated by numerical simulation based on c-number stochastic differential equations. We also discuss the advanced CIM with quantum measurement-feedback control and various problems which can be solved by CIM. [ABSTRACT FROM AUTHOR]

We present a numerical study for the design of efficient :PPLN based pulsed nanosecond optical parametric oscillator (OPO), with input pump pulses of top-hat transverse intensity profile, and a double-pass pump cavity configuration. In particular, we investigate the effect of domain shape on the conversion efficiency. We considered two types of domain structures: "perfect vertical-wall" and "wedge-shaped" domains and our numerical results show that at higher pump pulse energies, the conversion efficiency saturates, and the saturated efficiency is almost independent of the domain shapes. Based on our study, we also propose a new scheme for development of compact high-power OPO sources using :PPLN chips of relatively short lengths and large cross-sectional area. [ABSTRACT FROM AUTHOR]

High efficient and high power 2 $$\upmu $$ m room temperature Ho:YAG laser resonantly dual-end-pumped by two orthogonally polarized diode-pumped Tm:YLF lasers at 1.91 $$\upmu $$ m was demonstrated. A maximum continuous wave output power of 61.9 W was generated, corresponding to the slope efficiency of 63.9 % with respect to the incident pump power and optical-to-optical conversion efficiency of 59.9 %. At 20 kHz of the pulsed repetition frequency, we achieved a less than 25 ns FWHM pulse, with the maximum output energy per pulse of 2.84 mJ as well as a peak power of approximately 113.6 kW. A beam quality of $$M^{2}<$$ 1.6 was achieved. [ABSTRACT FROM AUTHOR]

Introduction: Fractional photothermolysis induces microscopic, localized thermal injury in the skin surrounded by undamaged viable tissue in order to promote wound healing. Objective: This study evaluated acute histologic changes following each single pass of various fractional lasers and radiofrequency (RF). Methods: Three male domestic swine were used. We used fractional Erbium:glass (Er:glass), Erbium:yttrium-aluminum-garnet (Er:YAG), CO2 lasers, and fractional ablative microplasma RF. We analyzed features and average values of the diameter, depth, and vertical sectional areas treated with each kind of laser and RF. Results: The microscopic treatment zone (MTZ) of fractional Er:glass resulted in separation of dermoepidermal junction with no ablative zone. Fractional Er:YAG provided the most superficial and broad MTZ with little thermal collateral damage. Fractional CO2 resulted in a narrow and deep 'cone'-like MTZ. Fractional RF resulted in a superficial and broad 'crater'-like MTZ. Conclusions: This study provides the first comparison of MTZs induced by various fractional lasers and RF. These data provide basic information on proper laser and RF options. We think that these findings could be a good reference for information about fractional laser-assisted drug delivery. [ABSTRACT FROM AUTHOR]

Finding the ground states of the Ising Hamiltonian maps to various combinatorial optimization problems in biology, medicine, wireless communications, artificial intelligence and social network. So far, no efficient classical and quantum algorithm is known for these problems and intensive research is focused on creating physical systems-Ising machines-capable of finding the absolute or approximate ground states of the Ising Hamiltonian. Here, we report an Ising machine using a network of degenerate optical parametric oscillators (OPOs). Spins are represented with above-threshold binary phases of the OPOs and the Ising couplings are realized by mutual injections. The network is implemented in a single OPO ring cavity with multiple trains of femtosecond pulses and configurable mutual couplings, and operates at room temperature. We programmed a small non-deterministic polynomial time-hard problem on a 4-OPO Ising machine and in 1,000 runs no computational error was detected. [ABSTRACT FROM AUTHOR]

Optical parametric oscillator is an attractive way of generating tunable mid-infrared light in the spectral range where lasers simply do not exist--for the needs of spectroscopy, medical applications, remote sensing, etc. We will go through the fundamentals of the optical parametric oscillator first and then introduce the related new phase-matching, cavity design, and spectroscopic techniques. [ABSTRACT FROM AUTHOR]

A mid-infrared optical parametric oscillator (OPO) with an idler wavelength of 3.85 μm at a repetition rate of 200 kHz is presented, and a high-repetition-rate electro-optic (EO) Q-switched Nd:GdVO4 laser with a double-crystal RbTiOPO4 EO modulator is used as the pump source. The OPO is designed as an extracavity singly resonant optical parametric oscillator. The threshold value of the OPO system is only 1.3 W at 1.06 μm. When the MgO: periodically poled lithium niobate (MgO: PPLN) crystal is operated at 90°C and the pump power is 10.5 W with a repetition of 200 kHz, a maximum average output power of 1.82 W at idler wave-length of 3.85 μm and pulse width of 14.3 ns are obtained. The slope efficiency of the 3.85-μm laser with respect to the pump laser is 21.3%. The M2 factors of the 3.85-μm laser are 1.84 and 1.76 in the parallel and perpendicular directions, respectively. The mid-infrared tunability of 3.7 to 3.9 μm can be achieved by adjusting the temperature of MgO:PPLN crystal from 210 to 35°C. [ABSTRACT FROM AUTHOR]

The defect chalcopyrite crystal HgGa2S4 has been employed in a 1064-nm pumped optical parametric oscillator to generate <7 ns long idler pulses near 6.3 μm with energies as high as 3 mJ, tunable in a broad spectral range from 4.5 to 9 μm. [ABSTRACT FROM AUTHOR]

In this paper we report the design and development of an electro-optically Q-switched diode pumped Nd:YAG laser with intracavity optical parametric oscillator, generating ~ 5 ns laser pulses of ~8 mJ energy at eye safe wavelength of 1534 nm. A Z-shaped laser resonator has been designed with porro prism end reflector in Q-switch arm containing RTP Q-Switch and a suitably oriented waveplate. The gain arm consists of a Ø3 x 72 mm Nd: YAG laser rod, pumped from one side by 3 x 5 bar laser diode array stack emitting total optical peak power of 740 W at 804 nm at 38 °C. Thermoelectric coolers (TECs) have been employed to maintain the optimum temperature of laser diode arrays and the combined heat load from the pump chamber and TECs is distributed over the system base plate with embedded heat pipes. Such cooling mechanism has eliminated the requirement of fins and fans in the laser system. Eye safe radiation is out-coupled through intra cavity KTA OPO (5 x 5 x 20 mm³) placed in the gain arm. Laser was operated at 20 Hz for several duty cycles of 10 min on and 10 min off and output energy remained stable within ±0.5 mJ without any forced air/liquid cooling. [ABSTRACT FROM AUTHOR]

Realization of a wideband tunable optoelectronic oscillator based on a chirped Mach-Zehnder modulator (MZM) and a chirped fiber Bragg grating is proposed and demonstrated. By simply adjusting the direct-current bias of the chirped MZM, the frequency of the oscillating signal is tuned. A theoretical model is established, then verified by an experiment. A high-purity microwave signal with a tunable frequency from 5.8 to 11.8 GHz is generated. The single-sideband phase noise of the generated signal is -112.6 dBc/Hz at a frequency offset of 10 kHz. [ABSTRACT FROM AUTHOR]

Intracavity amplification of the idler radiation of a nanosecond optical parametric oscillator (OPO) is achieved within a single dual-grating PPLN crystal composed of a uniform-grating section followed by a fan-out grating section. While all the OPO wavelength-tuning capabilities are preserved, this configuration leads to a 60 % increase of the 4-μm idler power and a significant beam quality improvement when compared to a conventional singly resonant OPO. [ABSTRACT FROM AUTHOR]

Within the last 50 years the light and specially the laser has fomented great advances in several areas of science and technology. During the past decade the use of optical stimuli in the biomedical research field have been of great interest for both academy and industry. Two research branches that can be highlighted due to its growth are: direct optical stimulation and optogenetic. The first one uses different parameters of light to optimize the desired effect on the tissue interaction. The other branch works with genetic engineering technics to make cells sensitive to light. The neural stimulation by infrared (direct optical stimulation) does not require direct contact with the tissue and has higher spatial selectivity when compared to electrical stimulation, but it has restricted ability to activate (depolarize) neurons. The optogenetic, however, can be used to manipulate the neural tissue depolarizing or hyperpolarizing encoded neurons, as well as monitor activations by encoding fluorescent proteins sensitive to voltage. The stimulation by infrared optical or optogenetic, has been applied only to animal models although there is a great possibility for human applications. In the future, it may even replace existing techniques such as electrical brain stimulation to treat specific neurological diseases. [ABSTRACT FROM AUTHOR]

This article present a development of low phase noise 14-bit digitally controlled oscillator (DCO) based on ring oscillator with quadrature output in 0.18-μm CMOS technology. Proposed design use digital control and feed-forward technique to obtain wider output swing and stable quadrature output on even number of stages respectively. Designed DCO has tuning frequency range from 212 MHz to 1 GHz. Phase noise at 1-MHz frequency offset is −123.93 dBc/Hz, which is the lowest among the recently published result. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1479-1483, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26824 [ABSTRACT FROM AUTHOR]

Abstract: A scheme is proposed to produce two-color continuous-variable (CV) entanglement in nondegenerate optical parametric oscillator with an injected signal (INOPO). The quantum correlations between signal and idler beams are calculated by applying sufficient inseparability criteria for bipartite CV entanglement. The results indicate that two-color CV entangled beams can be produced when the INOPO is operating both below and above the threshold. The injected signal does not markedly diminish the quantum correlations between the signal and idler beams. The degree of entanglement dependence on damping rates is also investigated. [Copyright &y& Elsevier]

We demonstrate a high efficiency mid-infrared laser source based on optical parametric oscillator (OPO) assisted by an intracavity optical parametric amplification (OPA). The OPA-assisted-OPO scheme was realized in one piece of commensurable dual-periodic superlattice in which the signal light generated from the OPO process serves as the pump light for the OPA process. A maximum output power of 508 mW at 3.92 μm was achieved under a pump power of 2.85 W at 1.064 μm. The pump-to-idler conversion efficiency is 17.8% and the slope efficiency is 23.8%, and the enhancements of them are 58.9% and 67.6%, respectively, comparing with the standard OPO scheme. [ABSTRACT FROM AUTHOR]

Optical parametric oscillator (OPO) tunable in the range 970-1460 nm has been developed using bet barium borate (BBO) crystal as the gain medium and second harmonic of Nd:YAG laser as pump source. Two sets of resonators were used to cover the range; first was nearly-degenerate (970-1180 nm) and the second was non- degenerate (1240-1460 nm). The measured threshold pump pulse energy was nearly 8 mJ. Maximum signal pulse energy of about 14 mJ was obtained for pump pulse energy of nearly 31 mJ. Power scaling efficiency was about 70 per cent. The signal pulse width was ~5 ns corresponding to the pump pulse width of ~ 9 ns. OPO signal beam quality was Gaussian, although the pump beam was top-hat multimode. [ABSTRACT FROM AUTHOR]

Abstract: The carrier-envelope phase (CEP) characteristics of the tunable infrared laser pulses from a noncollinear optical parametric amplifier (OPA) with passively stabilized CEP are investigated experimentally. We compare the CEP fluctuation of different wavelength outputs from the OPA which is seeded by the idler pulse of a difference frequency generation (DFG) process. It is found that when the OPA output is tuned to a longer wavelength, the CEP fluctuation becomes less sensitive to the jitter of laser intensity and the phase mismatch, and therefore more stable CEP for the longer wavelength output pulses is realized. [Copyright &y& Elsevier]

Abstract: An eye-safe KTA OPO pumped by a Nd:YLF laser is demonstrated and a comparison with that pumped by a Nd:YVO4 laser is performed. Although the slope efficiency of the continuous-wave free-running Nd:YLF laser is lower than that of the Nd:YVO4 laser, the performance of KTA OPOs pumped by the Q-switched Nd:YLF laser is better, especially at lower repetition rates. The slope efficiency of KTA OPO pumped by a Nd:YLF laser is 14.6% at 30kHz and 11.04% at 10kHz. The better energy storage ability of Nd:YLF makes it an excellent laser medium in IOPOs. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the semiconductor lasers used as transmitters and receivers in transverse magnetic (TM) and transverse electric (TE) mode for optic oscillators. It explains the experimental setup, which includes the transmitter laser and the receiver laser and presents the numerical results for chaos synchronization properties of polarization-rotated optical feedback and injection in semiconductor lasers.

In this paper we present the dependency of a quantitative measurement of the first-order longitudinal mode beating of an injection-seeded optical parametric oscillator (OPO) on its injection-seeding state. We show the correlation of the intensity of the first-order longitudinal mode beating and the side-mode suppression of an injection-seeded OPO. We further demonstrate that the mode-beating intensity can be used as an indicator for the spectral purity of an injection-seeded OPO. [ABSTRACT FROM AUTHOR]

The optical transmission T(λ) as well as the reflection R(λ) spectra has been recorded, in the spectral range of 500-2500 nm, for thermally deposited Sm doped a-Se films. The X-ray diffraction technique was used to critically identify the structural nature of the studied films. The current optical theories and models were applied to analyze the recorded spectra and to calculate various interesting optical parameters. These include: dispersion of the two components of both complex refractive index (ñ=n-ik) and complex dielectric constant (ϵ1 and ϵ2), energy gap (Eg), Urbach energy (Eu), single oscillator energy (Eo), lattice oscillating strength (E1), material dispersion M(λ) and the wavelength at zero material dispersion (λc). At this point, a similar non-monotonic trend is observed for the compositional dependence of various parameters. This has been ascribed to the disorder and/or structural defects introduced due to the incorporation of Sm, up to 0.008 % Sm, in the a-Se matrix. Besides, a trial has been made thus estimating the inter-band transitions for the Se-Sm samples investigated. [ABSTRACT FROM AUTHOR]

Abstract: A high repetition rate mid-infrared singly resonant optical parametric oscillator (OPO) using MgO-doped multi-grating periodically poled LiNbO3 (MgO:PPLN) is demonstrated. A 1064nm Q-switched Nd:YVO4 laser at 10kHz repetition rate and pulse width of 17.8ns was used to pump the OPO. The period of the quasi-phase matched (QPM) grating in the multi-grating MgO:PPLN chip varied from 25.5 to 31.5μm in steps of 0.5μm. This corresponds to the generation of a signal beam from 1.37 to 1.64μm and an idler beam from 3.0 to 4.8μm, respectively. A maximum signal power of 250mW and idler power of 140mW has been obtained with an input pump beam of power 1.92W, for a grating period of 30.5μm. A maximum optic–optic conversion efficiency of 20% and 7.4% in the idler has been observed. It has been observed that the output power increases as the period of the grating increases. [Copyright &y& Elsevier]

The dynamics of glycerol ablation at atmospheric pressure was studied using fast photography. A mid-infrared optical parametric oscillator was used to irradiate a droplet of glycerol at normal incidence. The wavelength of the infrared source was tunable and was varied between 2.7 and 3.5 μm for the studies. After an adjustable delay, an excimer pumped dye laser was used to illuminate the expanding plume, and the 90° scattered light was imaged with a high-speed CMOS camera. The time delay between the IR and UV lasers was varied up to 1 ms with a particular emphasis in the early stages of plume evolution below 1 μs. The threshold fluence for plume formation varied between 1000 and 6000 J/m2, and the minimum fluence corresponded to the OH stretch absorption of glycerol near 3.0 μm, which also corresponded to the greatest scattered light signal and duration of material emission. The velocity of the expanding plume was measured and ranged from >300 m/s near the OH stretch absorption to <100 m/s near the 3.4 μm CH stretch. Plume modeling calculations suggest that material removal is driven by phase explosion in the stress confinement regime that is at a maximum near the wavelength of the OH stretch absorption. [ABSTRACT FROM AUTHOR]

In this paper, we present a compact source of narrow-band energy-time-entangled photon pairs in the telecom regime based on a Ti-indiffused periodically poled lithium niobate (PPLN) waveguide resonator, i.e. a waveguide with end-face dielectric multi-layer mirrors. This is a monolithic doubly resonant optical parametric oscillator (OPO) far below threshold, which generates photon pairs by spontaneous parametric down-conversion (SPDC) at around 1560 nm with a 117MHz (0.91 pm)-bandwidth. A coherence time of 2.7 ns is estimated by a time correlation measurement and a high quality of the entangled states is confirmed by a Bell-type experiment. Since highly coherent energy-time-entangled photon pairs in the telecom regime are suitable for long distance transmission and manipulation, this source is well suited to the requirements of quantum communication. [ABSTRACT FROM AUTHOR]

We demonstrate that for a given pump source, there is an optimum pump threshold to achieve the maximum single-frequency output power in singly resonant optical parametric oscillators. Therefore, cavity losses and parametric amplification have to be adjusted. In particular, continuous-wave output powers of 1.5 W were achieved with a 2.5 cm lithium niobate crystal in comparison with 0.5 W by a 5 cm long crystal within the same cavity design. This counter-intuitive result of weaker amplification leading to larger powers can be explained using a model from L.B. Kreuzer (Proc. Joint Conf. Lasers and Opt.-Elect., p. 52, ). Kreuzer also states that single-mode operation is possible only up to pump powers which are 4.6 times the threshold value. Additionally, implementing an outcoupling mirror to increase losses, single-frequency waves with powers of 3 W at 3.2 µm and 7 W at 1.5 µm could be generated simultaneously. [ABSTRACT FROM AUTHOR]

Stability and tuning characteristics of continuous-wave optical parametric oscillators (CW OPOs) are affected by various thermal effects arising from optical absorption in nonlinear crystals. In this paper, we present an experimental study of such effects in a singly resonant CW OPO. The OPO operates in the 3-μm mid-infrared region and it is based on a MgO-doped periodically poled lithium niobate crystal. We focus our study on two thermally induced phenomena that have been recently reported to exist in singly resonant CW OPOs: optical bi-stability and thermal self-locking. Thermal self-locking effect, which is known to alter the stability and tuning properties of doubly and triply resonant CW OPOs, is shown to be also of importance in singly resonant OPOs. We report the stability and tuning characteristics of a thermally loaded OPO and discuss a simple temperature-tuning method that can be used to scan the OPO idler frequency continuously over several THz. [ABSTRACT FROM AUTHOR]

The authors report on cascaded synchronisation in coupled chaotic multiple time-delay electro-optical semiconductor lasers. The authors derive the existence and sufficient stability conditions for the synchronisation regimes. Analytical results are fully supported by numerical simulations. The results are important for chaos-based long-haul communication systems. [ABSTRACT FROM AUTHOR]

Abstract: A kinetic model which takes into account gas jet photoionization by an ultrashort linearly polarized EUV/X-ray free electron laser (FEL) pulse, a self-generated low frequency electric field, and elastic electron scattering on atoms is introduced to study the photoionization two-stream (PITS) instability. The evolution of PITS instability is described in terms of an integral equation for electron density perturbations. This paper presents a generalization of previous theories of the PITS instability in collisionless plasmas. The instability is produced by the anisotropy of photoionized electrons and is strongly affected by electron–atom collisions. Relaxation of the PITS instability is studied for different relations between the FEL pulse duration, the instability growth time, and the electron collision time. [Copyright &y& Elsevier]

Abstract: Objective: Aim of the present investigation was to prove whether a combination therapy using 308nm excimer laser phototherapy and topical Calcipotriol application is more effective than a monotherapy to treat stable plaque psoriasis. Material and methods: In a one center open trial, 36 patients (21 men, 15 women) with stable, moderate to severe, plaque-type psoriasis vulgaris received 308nm UVB dose of 200–1200mJ/cm2 to affected areas, delivered by an 308nm XTRAC™ XeCl excimer laser (PhotoMedex, Radnor, PA, USA). One side of either, back, leg or arm was additionally treated with Calcipotriol ointment twice daily, starting 0–7 days before the treatment with the 308nm laser. The other side was treated with the 308nm laser and Vaseline only. To evaluate the efficiency of both therapy concepts, a modified Psoriasis Area and Severity Index (PASI) score was calculated, which was initially found to be 31 per side on average. Results: Clearing of infiltration, erythema and scales was achieved at 25% after 2 sessions for the excimer laser treated side without Calcipotriol, and 40% in the Calcipotriol plus excimer laser treated side. Discussion: With the 308nm excimer laser (FDA approved), higher doses of UVB can be administered to the psoriatic plaques while sparing the non-affected skin. Plaques clear faster in fewer sessions at a lower cumulative dose. The combination of 308nm excimer laser phototherapy with Calcipotriol improves the reduction of infiltration and scales of psoriatic plaques considerably. Compared to narrow-band UVB monotherapy, the narrow-band UVB plus Calcipotriol treatment needed fewer sessions of excimer laser treatment, fewer days to achieve a reduction of the PASI parameter and a lower cumulative dosage. [Copyright &y& Elsevier]

The intrinsic synchronization, multi-color outputs and related carrier-envelope phases (CEP) among pulses bring advantages to synchronously pumped femtosecond optical parametric oscillators and the pumping sources for broadband frequency comb generation and ultrashort waveform coherent synthesis. In this paper, we discuss our latest research results in this field, which cover the following aspects: the phase relationship and energy conservation law in an OPO and related experimental verification; control of the pumping Ti:sapphire femtosecond laser's CEP by self-referencing technology, and its repetition-rate locking by piezoelectric transducer (PZT); CEP locking of the pulses from the OPO by beating the non-phase-matched visible outputs against pump supercontinuum to obtain a driving signal for a fast PZT on the OPO end mirror; the generation of a broadband frequency comb spanning from 400 nm to 2.4 µm with 1.2 kHz bandwidth; and the realization of coherent interference between phase controlled pump pulses and signal second harmonic pulses. [ABSTRACT FROM AUTHOR]

Abstract  The influence of the parameters of a laser on the divergence and the light radii of a beam formed by a plane optical resonator and transformed by an optical system is considered. The studies are conducted for a broad range of Fresnel numbers characteristic of lasers. [ABSTRACT FROM AUTHOR]

Contactlless and nondestructive material testing is of increasing interest in modern material sciences, where the measurement of the material properties of fibers and foils has become important in the development of new materials like composites, fiber bundles, or fiber-reinforced ceramics. However, strain measurement methods making use of laser speckle shifts induced by translation and deformation of the specimen turned out to be very useful when measuring stress-strain-relations or thermal expansions of specimens to which strain gauges are not applicable, either due to the geometric dimensions of the specimen or for environmental conditions, e.g., high temperatures. Using laser-optical methods, one is confronted with the problem of calculating the speckle-pattern-shift values from a time series of images in the presence of the speckle decorrelation effects. In this paper, we give an overview of the most common methods and present a novel algorithm based on the maximum-likelihood principle, which yields sufficient accuracy for the common measurement tasks. Moreover, we show the application of two different optical strain-measurement setups used to measure mechanical and thermal strain. [ABSTRACT FROM AUTHOR]

Selective laser trabeculoplasty (SLT) is an innovative technology used newly in glaucoma treatment. It can be used as a primary treatment in open angle glaucoma as well as as an adjunct to present ocular hypotensive therapy. In this treatment modality using a Q-switched, frequency doubled Nd:YAG laser with very short pulses, the target of the laser is the melanin content of trabecular cells. Consequently, there is no collateral thermal injury in nonpigmented nearby structures and tissues. Short-term as well as long-term studies have shown SLT to be at least as efficient and as safe as argon laser trabeculoplasty. Primary treatment seems similar in efficiency as drug treatment (monotherapy). SLT has two theoretical advantages of being safer and repeatable due to its property of not damaging the trabecular meshwork. However, its repeatability still awaits to be supplemented with long term clinical studies. In addition SLT's efficacy in pseudoexfoliative glaucoma and pigmentary glaucoma and the issue of how much of the angle should be treated for optimal therapy appear to be areas still needing to be assessed. [ABSTRACT FROM AUTHOR]

Abstract: Optical parametric oscillators are coherent light sources showing properties that are not encountered with usual laser sources. This article deals with optical architectures that take advantage of the specific properties of the three-wave mixing parametric interaction. We show that optical cavities can be specifically designed to increase either the optical conversion of the parametric process or to reduce dramatically the emitted line width. To cite this article: A. Berrou et al., C. R. Physique 8 (2007). [Copyright &y& Elsevier]

We developed a noncollinear optical parametric/Ti:sapphire hybrid chirped pulse amplification system, which consists of a two-pass optical parametric amplifier and multipass Ti:sapphire amplifiers with adaptive phase control. The use of the parametric amplifier instead of a regenerative amplifier broadened the final spectrum significantly, resulting in 11-fs pulses with a peak power of 18 GW at 5 kHz. [ABSTRACT FROM AUTHOR]

Theoretical investigations of dynamical behavior in optical parametric oscillators (OPO) have generally assumed that the cavity detunings of the interacting fields are controllable parameters. However, OPOs are known to experience mode hops, where the system jumps to the mode of lowest cavity detuning. We note that this phenomenon significantly limits the range of accessible detunings and thus may prevent instabilities predicted to occur above a minimum detuning from being evidenced experimentally. As a simple example among a number of instability mechanisms possibly affected by this limitation, we discuss the Hopf bifurcation leading to periodic behavior in the monomode mean-field model of a triply resonant OPO and show that it probably can be observed only in very specific setups. [ABSTRACT FROM AUTHOR]

High-speed, oxide-confined, inverted polarity (n-up), polyimide-planarised 850 nm vertical-cavity surface-emitting lasers (VCSELs) were fabricated and characterised. The lasers exhibit a -3 dB frequency modulation bandwidth (f3dB) up to 15.2 GHz with a 10 µm oxide aperture diameter, at the lowest current density (Jbias) ever reported of 6.4 kA/cm2. The ratio f3dB2/Jbias=36.1 (GHz2/kA/cm2) represents a 21% increase when compared with the highest previously reported ratio. The threshold voltage and current were as low as 1.45 V and 0.9 mA, respectively, with a series resistance of 65 Ω. A rate-equation-based thermal VCSEL model was used to predict the device performance at different temperatures. Good agreements between measured and simulated DC characteristics were obtained. [ABSTRACT FROM AUTHOR]