bluuebunny/crossref_metadata_2025 huggingface dataset:
High speed optical waveguide modulator based on resonant tunnelling effect
Authors: Figueiredo J. M. L. , Ironside C. N , Stanley C. R. , Leite A. M. P.
Published: February 2023

Electroabsorption modulation requires the application of an external electric field to increase the absorption coefficient either by the Franz-Keldysh effect or the Quantum-Confined Stark effect. Reverse biased p-i(MQW)-n diodes have been used to generate these electric fields. Here we present an entirely new approach employing the Resonant Tunnelling (RT) effect in Double Barrier Quantum Wells (DBQW) embedded in an unipolar optical waveguide to generate and switch at high frequency an electric field across the waveguide core, allowing efficient high speed optical intensity modulation requiring a few hundred millivolt as RF drive signal with a bandwidth - voltage ratio of 33GHz/V, the highest reported for an electroabsorption modulator.
Nanoclusters formation by Laser Ablation
Authors: Marine W. , Patrone L. , Sentis M.
Published: February 2023

In this communication we present a new synthesis method of silicon nanoclusters (Sin, where n > 20) by conventional laser ablation technique. Ablation and deposition were performed by ArF excimer laser (λ = 193 nm, pulse duration t = 15 ns, FWHM) in different background gases: He, Ar, O2, H2 or their mixtures. Typically, the gas pressure was about 0.1-5 Torr.
Unidirectional Ring TI3+:AL2O3 Laser Operation at the Wavelength of an Atomic Absorption Line Using Bi-Directional Passive Self-Injection
Authors: Deneva M.A. , Nenchev M.N. , Barbe R. , Keller J.C
Published: February 2023

Passive self-injection locking (PSIL) laser spectral control yields efficiency close to that in the optimized non-selective cavity and avoids the optical damage of the selectors [1,2]. Its principle lies in the spectrally selective re-injection in the cavity of a part of the output beam. We show (theory, experiment) that such control entails as addition the principle of novel technique for producing in a purely optical and simple manner high power unidirectional ring laser generation which is spectrally fixed at a chosen reference atomic absorption line. Such lasers are of interest as wavelength standards, in laser isotope separation and in DIAL lidars.
Single-frequency traveling-wave laser on GSGG:Cr, Nd crystal with the acoustooptic nonreciprocal element
Authors: Nanii O. E. , Voronin V.G. , Nikol’ski M. Yu. , Shcherbakov I.A.
Published: February 2023

The theory and experimental investigation of single-frequency traveling-wave laser on GSGG:Cr,Nd crystal [1] with the acoustooptic (A-O) nonreciprocal element. Unidirection operation were induced using A-O modulator with self-feeding back the diffracted beams [2,3].
Passively Q-switched single-frequency Nd:YAG ring laser with feedback and phase conjugation
Authors: Pashinin P. P. , Shklovsky E. J. , Tumorin V.V. , Tang C.-Y.
Published: February 2023

Q-switched Nd:YAG lasers producing narrow-linewidth pump beams are imperative for efficient and reliable operation of diverse devices based on nonlinear optical conversion, such as harmonic generators, optical parametric oscillators etc. At present injection seeding1 is considered to be the most advanced method to produce single-frequency oscillation in Q-switched solid-state lasers. However the injection seeded systems are rather complicated as they virtually employ two lasers: low power, frequency-stabilized. narrow-bandwidth oscillator and a regenerative amplifier. Alternative optical schemes based on ring resonator arrangement, being much simpler, sutler from relatively low pulse energy, usually 10...20 mJ. Besides some promising ring arrangements are poorly investigated with respect to pulse-to-pulse energy/shape stability.
Room-temperature pulsed operation of 1.52 μm vertical cavity lasers obtained by localised fusion
Authors: Syrbu A.V. , Iakovlev V.P. , Berseth C.-A. , Rudra A. , Kapon E.
Published: February 2023

We have shown recently that localized fusion of InP to GaAs provides high quality interfaces, low voltage drop p-GaAs/p-InP junctions and additional lateral current confinement in InGaAsP/InP edge emitting laser diodes fused on p-GaAs substrates1,2. In the present study’, the concept of localized fusion is extended to the fabrication of InGaAsP/InP long wavelength vertical cavity-surface emitting lasers (VCSELs) with double fused n- and p-AlGaAs/GaAs distributed Bragg reflectors (DBR).
Extremely Low Relative Intensity Noise Single-Mode Vertical Cavity Surface Emitting Lasers
Authors: Wiedenmarm D. , Schnitzer P. , Schmid W. , Jung C. , Grabherr M. , Jäger R. , Michalzik R. , Ebeling K. J.
Published: February 2023

In optical interconnection and high quality analog transmission systems relative intensity noise (RIN) characteristics of vertical cavity surface emitting lasers (VCSELs) are important since RIN imposes limitations on receiver sensitivity and bit error rates. In the past, only a few investigations have been dedicated to the noise spectra of VCSELs, especially under distant optical feedback, which is inherently present in low cost optical interconnects. The investigated 850 nm single mode VCSELs were fabricated by solid source MBE for multi-Gbit/s data rate optical transmission systems [1].
Diode-pumped continuous-wave optical parametric oscillator
Authors: Klein M. E. , Lee D. -H. , Meyn J.-P. , Beier B. , Boller K.-J. , Wallenstein R.
Published: February 2023

So far, diode-pumped operation of continuous-wave optical parametric oscillators (cw-OPO) has been possible only by resonating two or three of the interacting waves, in order to reduce the threshold to below the available diode pump power. [1,2] We demonstrate a cw-OPO which is directly pumped by a diode-laser and is operated with a cavity which provides low losses only for the signal wave.
Micro-milling with nanosecond pulses of a frequency-tripled Nd:YAG-laser
Authors: Hellrung Dirk , Gillner Arnold , Poprawe Reinhart
Published: February 2023

The development of diode pumped solid state lasers with high beam quality improves the quality of laser beam removed micro-structures and opens the possibility to use this technology as a new manufacturing method for producing micro-tools. Predestined materials for the 3-dimensional micro-structuring by laser beam removal are hard materials such as ceramics and hard metals, which can be processed only by time and cost expensive technologies. These tools can be used for forming processes of metal parts, like stamping, embossing or cutting.
Fibre optic jacket removal by pulsed laser ablation
Authors: Barnier F , Dyer P E , Snelling H V , Byron K C
Published: February 2023

Excimer lasers are currently used for the ablation of polymers in a number of applications [1]. Carbon dioxide lasers can also produce good quality etch features in polymers provided the laser wavelength is matched to a strong absorption band in the material [1]. In the present work the stripping of polymer jackets from fibre optic cables by pulsed ultraviolet and infrared laser ablation has been investigated, a technique which is closely analogous to laser wire stripping [2]. There is interest in generating bare lengths of telecommunication fibres to facilitate access to the cladding and core for a wide range of applications, including fabrication of Bragg Gratings which can act as wavelength selectors or sensors. Laser stripping offers possible advantages over chemical etching both in terms of the degree of control that can be exercised and from an environmental standpoint.
Enhanced Nonlinear Optical Response of Cantor-Like and Fibonacci-Like Quasiperiodic Structures
Authors: Sibilia C. , Tropea F. , Bertolotti M.
Published: February 2023

In the present work we study the enhancement of the nonlinear susceptibility in a quasiperiodic layered structure, comparing the optical properties of a periodic with those of a fractal structure. The considered fractal-structures are realized by following a triadic-Cantor sequence or the Fibonacci sequence. They are realized by alternating layers of two different materials (a,b) possessing linear refractive indices n, and nb and nonlinear susceptibilities (we suppose only third-order nonlinearity) χaNL and χbNL, respectively. The two constituent materials are assumed to be lossless, and the response time of the composite is essentially the same as that of the nonlinear constituent. We assume that the thickness of each layer is much larger than an atomic dimension but much smaller than the incident wavelength. Consequently, the structural properties of each constituent material are essentially the same as those of a bulk sample, but the propagation of light through the structure can be described in terms of effective linear and nonlinear optical susceptibilities. We consider a TM polarization of the electric field , so that the electric field becomes nonuniformly distributed inside the layers of the composite (because the normal component of the displacement vector and not that of the electric vector is continuous at the boundary) A consequence of the fact that the electric field is nonuniformly distributed inside the layers of the structure is that, under certain circumstances, the effective susceptibility of the composite can exceed those of its constituent materials.
Materials Synthesis and Processing with Ultrafast Lasers
Authors: Pronko P. P. , VanRompay P. A , Mourou G.
Published: February 2023

As compact ultrafast laser systems, that are affordable and reliable, continue to be developed, interest in their application to practical problems in materials science also continues to expand. Solid state, diode pumped, and fiber based ultrafast laser systems are sufficiently commonplace to encourage an intensification of such applications research. Controlled output levels for 100 femtosecond lasers, operating at 10 Hz to 1 kHz, in the hundred micro-joule to several millijoule energy range are currently available in reliable commercial systems. This opens the opportunity for direct application of these devices to thin film synthesis, growth processing, and micro-fabrication.
Dynamics of femtosecond laser induced ablation from solid surfaces
Authors: Sokolowski-Tinten K. , Bialkowski J. , Cavalleri A. , Boing M. , Schüler H. , von der Linde D.
Published: February 2023

Advantages of ultrashort laser pulses in material processing applications have been demonstrated in a number of cases, but the fundamental processes leading to structural modifications of laser-irradiated surfaces are not well understood as yet. In this work we have investigated the dynamics of ablation from different absorbing and non-absorbing solid materials after excitation with 100 fs laser pulses. Using ultrafast time-resolved microscopy [1] the reflectivity of the excited surface is measured with both femtosecond time and micrometer spatial resolution.
Epitaxial Pr,Yb:LiYF4 Waveguides for Upconversion Lasers
Authors: Rogin P. , Huber G.
Published: February 2023

Upconversion lasers based on lanthanide doped host materials have been known for several years. The efficiency of their multiphoton excitation schemes depends critically on the absence of competing nonradiative processes, depleting the intermediate energy levels involved as well as the upper laser level. For this reason, fluoride host materials generally outperform oxides due to their lower phonon energies and, consequently, lower multiphonon relaxation rates. In this work, we concentrate on LiYF4 (YLF) codoped with Pr3+ and Yb3+, allowing for a sensitized avalanche upconversion mechanism [1] to produce red (639.5 nm) output upon pumping at ~ 835 nm. The threshold pump intensity of this process is in the order of 105 to 106 W/cm2, requiring a tightly focused pump beam. In bulk media, the high divergency of such a beam results in a very short gain medium, where only a small part of the incident light is absorbed, giving rise to a poor overall efficiency. A longer gain medium, as demonstrated with fluoride glass fibres, allows for a far better performance. In a disordered host material, however, the inhomogeneous broadening of the spectral lines reduces the peak gain cross section. Therefore, it seems promising to combine the advantages of the fibre geometry and a crystalline host by using crystalline waveguides.
80 μm Wide InAlGaAs Laser Diodes with 44 % Wallplug Efficiency at 7 W cw Output Power
Authors: Schmitt A. , Mikulla M. , Chazan P. , Walther M. , Kiefer R. , Braunstein J. , Weimann G.
Published: February 2023

For high power laser diodes, a high wallplug efficiency is a key-requirement for improved reliability at elevated output power levels. We report on MBE-grown high-power InAIGaAs-laser diodes with a wallplug efficiency of 44 % at an output power of more than 7 W cw.
How to Increase Transmission Power Budget by Combatting SPM Induced Distortion with Optimum Pre- and Post-Compensation of Dispersion in 10-40gbit/S NRZ and RZ Unrepeatered Systems
Authors: Røryset Arne , Hjelme Dag Roar
Published: February 2023

Implementing long repeaterless transmission at high bitrates on conventional single mode fibre (SMF) at 1.55µm may be a cost-effective network design. Dispersion compensation is necessary due to high dispersion, while distortion due to self phase modulation (SPM) must be cambatted since high input powers is necessary to achieve high power budget. In this paper we demonstrate numerically that the power budget may be increased considerable if the amount of pre- and post-compensation is optimized. Furthermore, our results shows that optimum modulation format depends on the selected compensation scheme.
Tunable Fabry-Perot Micro-Filters for Telecommunication System Diagnostics
Authors: Kajava T. , Kaivola M. , Ludvigsen H. , Niemi T. , Tammela S.
Published: February 2023

With the increase of speed and bandwidth of modem optical telecommunication systems, the need for various spectral diagnostic measurements of system components increases as well. For such applications, we introduce temperature-tunable Fabry-Perot filters made of silicon. Depending on the design parameters, the filter can serve either as a frequency discriminator, as an accurate wavelength meter, or as a spectrum analyzer. These devices are compact, rugged and inexpensive, and allow a full automation of the measurement procedure.
Search on the Lasing Action on the Titanium r → m Transitions
Authors: Keiman V.A. , Zhmenyak Yu.V. , Rybak A.S. , Shpenik Yu.O.
Published: February 2023

A large progress was achieved during the 30-year period of development of the lasers on selfterminating transitions (RMT) - laser transitions from the upper resonant to the lower metastable levels. The number of obtained laser lines on RMT of atoms and ions is not less than 44. The parameters of lasing are also impressive: average power of 120 W (CuI transitions) can be generated from a single laser tube with record conversion efficiency for all types of high-power visible lasers (3.2%) based on stored energy. The same device gives a maximum average output power of 201 W with an efficiency of 1.9%.
Improvement of CuBr laser beam quality with hydrogen additives
Authors: Stoilov V. , Astadjov D. , Vuchkov N. , Sabotinov N.
Published: February 2023

The development of high-power CuBr lasers for micromachining and other technology applications requires an investigation and control of the beam quality of these lasers. An important laser system property is the laser power density, Ps obtained after focusing the output radiation. It is equal to where Pout is the average laser output power, θ is the divergence of die laser output power and F is the focus length of the output focusing optical system. It is clear that Ps is proportional to the quantity Pout/θ2 which is an inherent property of the light emitted from a laser. This quantity represents the laser power spatial intensity because θ2 is actually the solid angle in which laser output is concentrated. This laser power spatial intensity can be quantified in W.mrad−2, for example. The inverse - square dependence of laser power spatial intensity on the divergence of laser output power means that higher laser power density can be more easily obtained by improving the beam divergence. Thus, a serious decrease in laser beam divergence should sharply' reduce the demand for too high laser output.
Analysis of Mictrostructured Edge-Emitting Semiconductor Lasers for Short-Pulse Generation
Authors: Avrutin E.A. , Allan B.D. , De La Rue R.M. , Marsh J.H. , Arnold J.M. , Izutsu M. , Aitchison J.S. , Krauss T.F.
Published: February 2023

Recent successes in fabrication of compact DBR lasers using photonic microstructure (1-D photonic bandgap) mirrors[1] open the doors for a number of applications for these microctructures, including high-speed, short-pulse optoelectronic devices. Experimentally, modulation bandwidths above 30 GHz have been demonstrated in a laser with a (non­optimum) short DBR mirror [2]. Here, we shall discuss the possibility of applying the extreme compactness, strong stop-band effects and very dispersive stop-band edges of photonic microstructure devices for achieving solitonic-type pulse shaping at moderate power levels or self-oscillatory behaviour. In particular, we shall assess the possibility of using microsutructure reflectors to achieve an ultracompact, very high frequency version of Q-switched semiconductor lasers, including dispersive self-Q-switching, and the requirements to microcavity reflectors used for such an application.
Nearly Degenerate Four-Wave Mixing in Semiconductor Optical Amplifiers
Authors: Girardin François , Guekos Georg , Mecozzi Antonio
Published: February 2023

Semiconductor optical amplifiers (SOAs) are now good candidates for applications in all-optical signal processing. The travelling waves effects observed in long SOAs can be used to increase the performance in applications based on cross-gain modulation and four-wave mixing (FWM). We show and explain here the nearly degenerate FWM behavior of 1 and 1.5 mm long 1.55 μm bulk SOAs which is dominated by a strong effective index modulation.
Tunable Dual-Wavelength Optical Pulses Generated from a Semiconductor Laser Using an External Cavity with a Two-Chromatic Fibre Grating
Authors: Zhao Y. , Shu C.
Published: February 2023

Dual-wavelength picosecond pulses have received considerable interest for multichannel signal transmission and dispersion related measurements [1]. A simple fibre-optic external cavity is reported here for the generation of tunable dual-wavelength pulses from a semiconductor laser.
Stability and Transients of Continuous-Wave Intracavity Singly-Resonant Optical Parametric Oscillators
Authors: Turnbull G.A. , Dunn M.H. , Ebrahimzadeh M.
Published: February 2023

Intracavity frequency-conversion is well established as an efficient method of generating continuous-wave (cw) visible light. Recent demonstrations, e.g. [1], of intracavity singly-resonant optical parametric oscillators (ICSRO's) have extended this work to produce Watt-level, cw outputs tunable through the infrared. It is well known, however, that at high powers intracavity up-conveision can suffer from dynamic instabilities (the Green Problem), which present design constraints to the power­scaling of such systems. We show here that ICSRO’s do not suffer from the same problems of instability, though do exhibit novel transient behaviour, and as such represent practical cw sources capable of high output powers and conversion efficiencies.
Energy combining by a three-beam pumped optical parametric amplifier
Authors: Piskarskas A. , Dubietis A. , Danielius R. , Tamošauskas G.
Published: February 2023

The optical parametric amplifiers (OPA) exhibit such attractive features as broad gain bandwidth and tunability, so they could be easily matched to virtually any of existing sources of ultrashort pulses. The OPA, in contrary to other nonlinear devices such as second-harmonic or sum-frequency generators allow the use of multitude of pump beams with the condition that each of those satisfies the non-collinear phase-matching constraints with a single signal beam. This feature of OPA has. been demonstrated by simultaneous phase­matching of two [1] or three [2] pump beams in order to narrow both spectral and spatial bandwidth of the emitted parametric superfluorescence.
Temporal phase behavior from cascaded three wave mixing
Authors: Albert O. , Etchepare J.
Published: February 2023

β–BBO crystal is an efficient material for three wave mixing processes like SHG, OPO or OPA. Different wave mixing processes that have the same wavevector matching condition can occur simultaneously. As an example, ω1 + ω2 → ω3 and ω3 − ω2 → ω1 or ω3 − ω1 → ω2 correspond to cascaded χ(2) effects where the initial pulse wavelengths are recovered. Choosing type I phase matching, we have studied the transient cascaded phase induced on the initial pulses. Compared with a direct Kerr n2 nonlinearity this cascaded phase shift is much more efficient (It is 50 times greater in β–BBO), and by detuning the phase matching one can also choose the phase shift sign[1]. Using a time resolved experiment [2], we have measured in the femtosecond regime the time dependence of the phase shift during sum and difference frequency generation and OPA processes. Due to group velocity mismatch between the pulses, the temporal dependence of the cascaded χ(2) phase is asymmetric with regard to the pulse temporal amplitude center. It results in an associate nonlinear chirp. This chirp, previously calculated[3,4] but never measured before to our knowledge, is difficult to compensate and limits the use of this efficient cascaded χ(2) n2.
Nonlinear Optical Anisotropy of Metallic Surfaces
Authors: Lohner F. P. , Villaeys A. A.
Published: February 2023

These last years, many experimental results have been published to emphasize the nonlinear optical properties of metallic surfaces. Two recent experiments done by Murphy et al. (Phys. Rev. Lett. 63, 318 (1989)) and Janz et al. (Phys. Rev. B 44, 8, 3943 (1991)) have stressed the polarization anisotropy as well as the azimuthal anisotropy of the (111) surface of Aluminum.
A Novel Ballastless Spark Preionization Scheme for High Repetition Rate Transversely Excited Atmospheric Pressure Carbon Dioxide Lasers
Authors: Choudhary P. , Kumar Manoj , Reghu T. , Nath A. K.
Published: February 2023

Use of spark arrays situated along the length of the main discharge electrodes is an attractive method for preionizing the main discharge volume of transversely excited atmospheric pressure CO2 (TEA-CO2) lasers (1). In this preionization scheme, some series ballasting elements i.e., capacitors, resistors or inductors are required to distribute the preionization energy uniformly among all the spark pins. Ideally, capacitors are best suited for this purpose as they do not limit the peak current through the spark channels, but they suffer from the disadvantage of limited life span. Though, inductors and resistors also can be used for this purpose but they limit the peak current through the sparks and hence reduce the effectiveness of preionization.
Mode Quality Control in Large Area, RF Excited CO2 Laser Employing Split-Wave Hybrid Resonator
Authors: Adams Michael , Byron Sian , Chace Adam , Schemmer James , Vitruk Peter
Published: February 2023

Gas discharge excitation at 40.68 MHz (ISM frequency in the VHF-band) is proven to be efficient for non-wave-guide, diffusion-cooled, large area CO2 laser employing a novel type of resonator cavity referred to as split-wave hybrid (SWH) resonator [1]. SWH resonator approach represents a custom resonator concept in the design of sealed-off, high power, single mode CO2 lasers for industrial applications. Electrode walls in the SWH resonator act as wave-front-splitting mirrors similar to a Fresnel double mirror or Lloyd mirror interferometer [2].
Transient Dynamics of Self-Starting Holographic Laser Oscillators
Authors: Syed K. S. , Crofts G. J. , Damzen M. J.
Published: February 2023

Self-starting laser systems which use gain gratings written within a laser amplifier to form a loop resonator (see figure 1) have been demonstrated using flashlamp-pumped Nd:YAG [1] and laser-pumped Ti:Sapphire [2]. Such systems, termed Self-Starting Holographic Laser Oscillators (SSHLO), rely on the gain grating to control the lasing mode. SSHLO’s and have been shown to correct for intra-cavity phase distortions and produce high quality TEM00, SLM [1] and tunable [2] self Q-switched outputs.
Phase conjugation in BaTiO3 using orthogonally polarized light waves
Authors: Jullien P. , Mathey P. , Lompré P. , Odoulov S. , Sturman B.
Published: February 2023

It is well known that degenerated backward four wave mixing is an attractive technique for the generation of the phase conjugate light waves using photorefractive crystals. Generally, large reflection coefficients are reached when gratings are recorded via diffusion charge transport process. In this paper, we consider the phase conjugation in BaTiO3 using an unusual geometry where the refractive index gratings cannot be classically recorded and when they appear through the high order mixing processes with the scattered light.
Laser Induced Surface Optical Damage Associated with UV Laser Cleaning of Sub-micron Contaminant Particles from Glass Surfaces
Authors: Kane D M , Halfpenny D R
Published: February 2023

During the past several years there have been many investigations of UV laser cleaning of surfaces, including dielectrics and semiconductors. There has been little discussion of surface or bulk optical damage that might accompany UV laser cleaning. It is generally assumed and/or demonstrated that the threshold fluence for optical damage is significantly larger than the cleaning fluence for the particular material. However, it is a well known fact that any surface contamination reduces the fluence threshold for surface optical damage.
Laser Cleaning of Oxidized Mettalic Surfaces
Authors: Alloncle Patricia , Isselin Jean-Christophe , Provost Marjorie , Autric Michel
Published: February 2023

The surface cleaning effect is investigated here using Nd YAG and Excimer User irradiation The different kind of mechanisms encountered are studied as function of laser interaction parameters: energy density: 0.1J/cm2 - 10J/cm2, pulse duration : 10ns - 20ns, wave length radiation: 248nm - 532nm - 1064nm, laser repetition rate: 1Hz - 200Hz.
Micro lens arrays generated by ultraviolet laser irradiation of doped polymethylmethacrylate
Authors: Beinhom F. , Ihlemann J.
Published: February 2023

Polymethylmethacrylate (PMMA) doped with 0.25 wt% of 1,3-diphenyltriazen (DPT) was illuminated with single subablative excimer laser pulses of about 30 ns duration at 308 nm wavelength. Illumination of the polymer surface was earned out by 7:1 demagnifying mask projection using circular apertures. The resulting spotsize on the sample was varied between diameters of 10 and 300 µm. The fluence was varied between the onset of visible surface changes at about 400 mJ/cm2 and the beginning of single pulse mass removal at about 5 J/cm2.
Ultraviolet Laser Lithography of Conjugated Polythiophene Thin Films
Authors: Wone T.K.S. , Lam Y.L. , Chan Y.C. , Hu X. , Liu H.
Published: February 2023

The lithographic patterning of conjugated polymer thin films is important for both device applications such as light emitting diodes and for microlithography. Previous patterning methods which include selective photoelectrochemical deposition and scanning electrochemical microscopy were limited by either the small size of the pattern or the need for photoconductive substrates. In this presentation, we demonstrate that conjugated polymers from the polythiophene series can be patterned directly (without resist) by using the 325nm ultraviolet (UV) radiation from a helium cadmium (He-Cd) laser. These results are an extension of the previous work by Abdou et al [1] and Hu et al [2] on laser irradiation effects on the polythiophenes. Four polymers: polythiophene (PTh), poly (3-methylthiophene) (P3MT), poly (3-butylthiophene) (P3BT) and poly (3-hexylthiophene) (P3HT) were prepared. Both PTh and P3MT were deposited electrochemicallv onto indium tin oxide (ITO) coated glass substrates. The substituted polythiophenes, P3BT and P3HT were synthesized chemically by Grignard coupling and oxidative polymerisation and were dissolved in chloroform to form dilute solutions. Thin films of P3BT and P3HT about 100nm thick were obtained by the dip coating technique. Lithographic patterning was performed using a custom-built UV laser writing system. The He-Cd laser has an output power of 15mW and the power intensity at focus is 286kWcm−2. After line patterns were written, the samples were observed by optical microscopy and atomic force microscopy (AFM). It was found that at sufficiently high incident fluences, all four polymers can be ablated directly into grooves several microns wide and up to 500µm long. The groove widths generally changed slightly with fluence but decreased rapidly near the respective cutoff fluences where no grooves could be formed (Fig. 1). At fluences below about 105 Wem−2, cross-linking was observed in both P3BT and P3HT Films. This renders the irradiated areas insoluble in chloroform and after development in this solvent, line structures 1-6µm wide were found on the glass substrate. Some of these line structures had rippled sidewalls and were attributed to solvent infusion effects. The significance of the present results is that both positive and negative tone lithographic patterning have been demonstrated. The ablation of PTh and P3MT in particular overcomes the difficulty of patterning these insoluble and infusible polymers. The mechanisms of the observed patterning processes will be explained and the linewidth trends shown in Fig.1 and other experiments will be discussed. This direct-write process should have potential applications in polythiophene based devices and conductive resists.
Laser-induced damage thresholds of SiO2 films grown with different assistance parameters: a comparative study performed by the photoacoustic mirage technique
Authors: Alvisi M. , De Nunzio G. , Perrone M. R. , Rizzo A. , Scaglione S. , Vasanelli L.
Published: February 2023

The quality of laser beams strongly depends on the optical characteristics of the cavity mirrors; thus the development of good quality UV/VUV coated optical components is much requested by researchers and industry. The choice of the deposition technique has a considerable influence on the film features: the use of ion assisted techniques is a means of improving the compactness and adhesion of films, while limiting the temperature of the substrate during the deposition.
Crystalline Carbon Nitride Thin Films Deposition by DC Arc Source Evaporation with Pulsed Laser Ablation
Authors: Kim J.I. , Kudryashov S.I. , Zorov N.B. , Ya. Yu. Kuzyakov
Published: February 2023

Production of crystalline carbon nitride(CN) thin films with nitrogen content up to 57 % has remained an intriguing problem in the field of material science. Up to date numerous investigations in CN thin films deposition resulted in nanocrystalline specimen with nitrogen content less than 45 %. We reported about crystalline CN thin films deposition by nitrogen DC arc source evaporation combined with pulsed laser ablation(PLA) as a source of gas phase carbon.
Assessment of the wavelength conversion capabilities of active Vertical Cavity Components for free space reconfigurable routing systems
Authors: Plouzennec L. , Annetts P.J. , de Bougrenet de la Tocnaye J.L. , White I.H.
Published: February 2023

The goal of this presentation is twofold : firstly, to discuss the advantages of combining Active Vertical Cavity Components (AVCC) and free-space optics in the implementation of reconfigurable wavelength multiplexing systems, and secondly, to discuss and investigate experimentally the capability of such a devices to provide wavelength conversion. Finally, we present possible extensions to Wavelength Division Multiplexing (WDM) involving both system and technological aspects.
Strained photonic lattices realized by coupled vertical cavity surface emitting lasers
Authors: Pier H. , Kapon E. , Moser M.
Published: February 2023

Periodic two- and three-dimensional photonic structures have attracted considerable attention recently due to the prospects of forming photonic bandgap structures useful for controlling photon modes and light-matter interaction. Such periodic structures are also of interest because of the possibility of producing “photonic lattice” structures displaying interesting and useful coherent optical coupling phenomena. Here, we report the investigation of the effect of strain on photonic lattices made using coherently coupled two-dimensional arrays of microcavities.
RF Excited Diffusively Cooled Kilowatts Carbon monoxide slab waveguide Laser
Authors: Xin Jianguo , Jiao Wentao , Sheng Yanlin
Published: February 2023

In the past few years, an area scaling technique with the advantages of simplicity and easy achieving compact high power lasers have been well developed and applied in the field of RF excited waveguide carbon dioxide and Xe and Ar lasers, which employs an RF gas discharge excited slab hollow waveguide and an unstable optical resonator combined with a diffusive cooling technique to obtain a compact high power laser. In this paper, we shall present an RF gas discharge excited carbon monoxide area scaling laser. In this laser, the top electrode was cooled with the tap water and the bottom electrode was cooled with the liquid nitrogen to maintain the slab waveguide gas discharge region at a very low temperature The discharge region has a size of 500mm length × 178mm width × 2mm height. In the experiments, a slab waveguide region was excited by a RF transverse gas discharge at a frequency of 93MHz, a new type of optical resonator consisting of a concave mirror with a curvature radius of 5390mm, a convex mirror with a curvature radius of 4330mm and a flat feedback mirror was employed, the output aperture size is 2mm × 45mm, a gas composition of CO : He : Xe : O2 at a ratio of 8.7 : 87 : 3.9 : 0.4 with operation pressures between 50 torr and 70 torr was used, by which a maximum of laser power output of over 1 Kilowatts was obtained.
Effect of Molecular Sieve on Transient Output-Reduction and Laser Parameters in DC Discharged /Room Temperature Operated FAF CO Laser
Authors: Kodama Yutaka , Sato Heihachi
Published: February 2023

The output power tends to transiently decrease with discharge time in a dc electrically pumped fast axial-flow (FAF) CO laser. This output reduction is mainly caused by both the temperature rise of gas mixture and deactivation of the excited CO molecule due to its dissociation into CO2 and O2 molecules.1 Especially, the latter seems to be predominant in the room temperature operated FAF CO laser system. The gas temperature rise due to the discharge can be compensated by fast gas-circulation through a heat exchanger along with either ethanol/dry ice coolants (or liquid nitrogen at subroom temperature operation) , whereas the CO2 molecules generated through the discharge process cannot be avoided at room temperature operation, though, it is well trapped with a cold trap of liquid nitrogen. Thus, we shall try to recover the output reduction transiently induced above by adsorbing the generated CO2 molecules by molecular sieve for the room temperature operation together with theoretical explanation. In addition, we shall also examine how the laser parameters such as the small-signal gain γ0.v saturation intensity Is and a measure of partial homogeneity m are influenced with insertion of molecular sieve.
Computer modelling of the plasma kinetics and spatio-temporal evolution of the intracavity laser field intensity in a kinetically enhanced copper vapour laser
Authors: Carman R.J. , Withford M. J. , Brown D.J.W. , Piper J.A.
Published: February 2023

Following investigations into the influence of halogens and halogen donor buffer gas additives in high temperature or “elemental” copper vapour lasers [1], a new sub-class of laser has recently been developed in our laboratory based on H2-HCl-Ne buffer gas mixtures. This device, known as a kinetically enhanced copper vapour laser (KE-CVL), typically produces laser output powers 2-3 times higher than from a similar sized elemental copper laser employing a standard H2-Ne buffer gas mix, and at significantly higher wallplug efficiencies [2]. Furthermore, the spatio-temporal evolution of the optical gain and intracavity laser field intensities on both transitions (510.6nm and 578.2nm) is substantially different in the KE-CVL resulting in more uniform radial beam profiles, reduced beam divergence and improved overall beam quality.
Phase conjugation in CO2 laser medium: theory and experiment
Authors: Ionin A. A. , Kotkov A. A. , Napartovich A. P. , Seleznev L. V. , Svotin P. A.
Published: February 2023

Phase conjugation (PC) processes at degenerate four-wave mixing (DFWM) in the active medium of a pulsed e-beam controlled discharge CO2-laser were studied both experimentally and theoretically. The experiment was carried out with the following parameters: laser gas mixture CO2:N2:He=1:2:4, gas pressure 0.3 bar, active medium length 1.2 m, resonator length 12 m (17.7 m for single line laser), interaction angle ~10 mrad at DFWM without optical delay between probe wave and co-propagating pump one. Integral PC reflectivity (PCR) strongly depends on such parameters as: specific input energy (Fig. 1); intensity ratio for probe J3 and co-propagating pump J1 wave (Fig.2); coherency of the laser radiation, that varied by rotation of mutual polarization or with optical delay between probe wave and co-propagating pump one; geometry of DFWM; output mirror reflectance Rout (8-80%) (PCR was maximum with Rout of 8% but best quality of PC signal was observed with Rout =80%); gas mixture composition and pressure, being maximum for a mixture with a low fraction of helium and at higher pressure (up to 0.6 bar). A periodical dependence of PCR on optical delay between probe and co-propagating pump wave with periods 10−3 and 10−5 m was observed. The PCR did not depend on spectral content and a degree of linear polarization of the laser radiation.
Volume holographic data storage and processing using phase-coded multiplexing
Authors: Müller K.-O. , Denz C. , Heimann T. , Tschudi T.
Published: February 2023

Optical volume holographic memories provide the potential for high storage capacity, parallel readout of data pages with short access times and high data transfer rates. Multiple image storage in a single region of a photorefractive crystal can be achieved using different addressing techniques as angular, wavelength, or phase-coded multiplexing. In combination with spatial multiplexing, volume holographic memories may achieve the storage of more than 1 Terabyte of information. Among these techniques, orthogonal phase-coded multiplexing [1] offers several advantages over angular and wavelength multiplexing, having the same storage capacity. A holographic data storage system based on phase-coded multiplexing operates with a fixed wavelength and a fixed geometry, avoiding mechanically moving parts. At the same time it provides short readout times and high energy efficiency. The signal-to-noise ratio of phase-coded multiplexing for a given number of holograms is more than two orders of magnitude higher than for angular and wavelength multiplexing [2]. Moreover, it allows to perform arithmetic operations as addition and subtraction of two or more data pages directly during readout of the memory [3]. Image processing operations like comparison of two stored images or image inversion and the logical operations OR, XOR and NOT with digital data pages can be realized in that way. Therefore, using phase-coded optical memories, high capacity data storage and high speed data processing becomes possible simultaneously.
Crystal Growth and Optical Properties of Potassium Lithium Niobate for Frequency Doubling of Diode Lasers
Authors: Jiang Q. , Han T. P. J. , Gallagher H. G.
Published: February 2023

Potassium Lithium Niobate (KLN) has excellent potential as a non-linear medium for direct second harmonic generation (SHG) of semiconductor diode lasers. KLN crystallises in a tungsten bronze structure and space group P4bm within the compositional range K3−yLi2−x+yNb5+xO15+2x, 0.15 <X <2, -0.5 <Y <0.6. It exhibits only one ferroelectric transition from a paraelectric to ferroelectric phase well above room temperature at a Curie point of around 420 °C. Previous results indicate that KLN possesses appropriate birefringence for non-critical phase matching (NCPM) in the wavelength range of interest and large non-linear optical coefficients for efficient SHG output at sub-milliwatt pump power levels [1].
Optical Control of Domain Structures in Lithium Tantalate
Authors: Brown Paul T , Ross Graeme W , Smith Peter G R , Eason Robert
Published: February 2023

The patterning of domain structures in ferroelectric crystals continues to attract great interest for numerous non linear optical and photonic applications, including blue light generation from semi-conductor diode lasers, via quasi phase matching.
Spectroscopy of Single Trapped Ions and Application to Frequency Standards
Authors: Walther H.
Published: February 2023

Single ions trapped and laser cooled provide ideal objects for high resolution spectroscopy and frequency standards. For the latter purpose we are investigating the 5s2 1S0 → 5s5p 3P0 transition of In+. With a natural linewidth of only 1.1 Hz this resonance offers very high resolution and is highly immune to frequency shifts due to external electromagnetic fields, because it connects two levels with vanishing electronic magnetic momenta [1]. The wavelength of this clock transition is 236.5 nm and is technically very convenient, since it coincides with the fourth harmonic of the 946 nm Nd:YAG laser line. So this intrinsically frequency stable solid-state laser can be used to excite the transition [2]. For laser cooling and fluorescence detection of the indium ion the 5s2 1So -> 5s5p 3P1 transition at 230.6 nm can be employed. The use of the relatively narrow intercombination line for laser cooling allows us to study optical sideband cooling in the strong binding regime, where the oscillation frequencies of the ion in the trap (around 1 MHz) are larger than the optical linewidth of 360 kHz. In this parameter range laser cooling is possible to the quantum ground state of the vibrational motion in the trap corresponding to a temperature of roughly 100 μK. The same low temperature was obtained with sideband cooling of a small Coulomb crystal consisting of two ions, creating an interesting new quantum few-particle system.
Interface sensitivity of magneto-optical second harmonic generation from ultrathin cobalt films
Authors: Tessier G. , Malouin C. , Georges P. , Brun A. , Pavlov V. , Meyer P. , Ferré J. , Beauvillain P. , Mathet V.
Published: February 2023

The nonlinear Magneto-optical Second Harmonie Generation (MSHG, also called NOMOKE for NOnlinear MOKE) derives its specific interface magnetisation sensitivity from the magnetisation (M) dependent second order ±χ(2)(± M) tensor [1]. Indeed, the comparison of measurements taken on Au/Co/Au and Pt/Co/Pt structures using both MSHG and the bulk magnetisation sensitive Magneto-Optical Kerr Effect (MOKE) in longitudinal configuration exhibit interesting differences, showing the interface sensitivity of MSHG.
Whole-field fluorescence lifetime imaging with picosecond resolution for biomedicine
Authors: Cole M. J. , Dowling K. , Dayel M. J. , French P. M. W. , Lever M. J. , Dymoke-Bradshaw A. K. L. , Hares J. D.
Published: February 2023

Fluorescence lifetime measurements permit both detection of specific fluorophores and monitoring of their local environment for biomedical imaging and other applications. Fluorescence Lifetime Imaging (FLIM) is particularly exciting since it can provide non invasive functional/diagnostic imaging by exploiting the sensitivity of fluorescence lifetime to the local environment (e.g. [Ca2+], pH etc.) e.g. [1]. The recent development of user-friendly and relatively portable ultrafast laser technology and the availability of ultrafast gated optical image intensifiers (GOI’s) mean that this technology can be readily applied to almost any optical imaging modality including microscopy and endoscopy. We report a FLIM system, based on a GOI and an all-solid-state diode pumped Cri:LiSAF oscillator-amplifier system [2]. This potentially provides a portable and relatively inexpensive instrument.
Synthesised Longitudinal Images of the Retina of the Living Eye Generated Using Transversal OCT Images Acquired at Different Depths
Authors: Podoleanu Adrian Gh. , Seeger Mauritius , Webb David J. , Jackson David A. , Fitzke Fred W. , Wade Alex R.
Published: February 2023

Usually, when collecting longitudinal OCT slices (slices roughly perpendicular to the surface of the retina), an OCT has to be assisted by a scanning laser ophthalmoscope (SLO), a fundus camera or a simple CCD visualisation unit to guide the selection of the image to be taken. Quite often, the procedure has to be repeated several times to locate some features in the retina. With a system as described in this paper, once a collection of transversal (roughly parallel to the retina) OCT images is stored, a longitudinal image at any position can be synthesised.
Manipulation of a Microscopic Object Using Plural Optical Fibers
Authors: Taguchi Kozo , Ueno Hideki , Ikeda Masahiro
Published: February 2023

The laser beam trapping method is considered to be useful for manipulation of microscopic objects and biological cells because of noninvasive technology. Its operation principle is based upon the electromagnetic momentum preservation. In this paper, novel optical trapping technologies using plural optical fibers[1][2] are reported. This optical fiber trapping method has following merits: (i) optical trapping systems using optical fibers are simple and inexpensive, (ii) trapped objects can be moved easily and freely synchronized to the trapping fiber, (iii) optical sources can be changed easily using optical connectors.
Competitive Vertical Cavity and Edge Emitting Quantum Dot Lasers
Authors: Bimberg D. , Ledentsov N.N. , Grundmann M. , Heinrichsdorff F. , Ustinov V.M. , Kop’ev P.S. , Maximov M.V. , Alferov Zh.I. , Lott J.A.
Published: February 2023

Significant improvements in characteristics of injection lasers were proposed for quantum dots (QDs) as gain medium [1]. However, there was a lack of fruitful ideas to fabricate QDs which can be used for realistic devices.
Vertically Coupled Quantum Dot Injection Laser Grown on InP (100) Substrate
Authors: Zaitsev S.V. , Gordeev N. Yu. , Kopchatov V.I. , Ustinov V.M. , Zhukov A.E. , Egorov A. Yu , Kovsh A.R. , Kop’ev P.S.
Published: February 2023

Continuing our studies of ultra-low threshold injection lasers based on self-organized vertically coupled quantum dots (VECODs) [1-3] we have studied the possibility of achievement of lasing via states of InAs VECODs placed into InGaAs matrix as an active layer of a separate confinement laser heterostructure grown on InP (100) substrate The experimental wafer includes 3 sheets of such dots formed at 500 °C and separated by 5 nm thick InGaAs spacers. It was shown using TEM that lateral size of quantum dots (QDs) significantly exceeds that of InGaAs/GaAs dots and makes about 50 nm. At the same time vertical size of them is even slightly less than in InGaAs/GaAs system and is equal to only 4-5 nm. The density of dots is 8·109cm−2 [4].
Strong self-phase modulation in periodically poled Lithium Niobate under subpicosecond pump pulses
Authors: Traynor N.J. , Lefort L. , Alam S. , Biffi G. , Grudinin A.B. , Ross G.W. , Hanna D.C.
Published: February 2023

Recent progress in fabrication of PPLN offers new effects, the observation of which is very difficult in traditional materials. So far the main activity has been focussed on efficient second harmonic generation and parametric oscillation. Here we present results on strong nonlinear interactions in PPLN, which have to date received little attention, but offer very interesting applications requiring relatively low powers.