Showing papers by "IPG Photonics published in 2021"

Two-octave-wide (3-12 µm) subharmonic produced in a minimally dispersive optical parametric oscillator cavity.

Abstract: We report a subharmonic (frequency-divide-by-2) optical parametric oscillator (OPO) with a continuous wavelength span of 3 to 12 µm (-37dB level) that covers most of the molecular rovibrational "signature" region. The key to obtaining such a wide spectral span is the use of an OPO with a minimal dispersion-through the choice of intracavity elements, the use of all gold-coated mirrors, and a special "injector" mirror. The system delivers up to 245 mW of the average power with the conversion efficiency exceeding 20% from a 2.35 µm Kerr-lens mode-locked pump laser.

Kerr-lens mode-locked Cr:ZnS oscillator reaches the spectral span of an optical octave

Abstract: We report, to the best of our knowledge, the first super-octave femtosecond polycrystalline Cr:ZnS laser at the central wavelength 2.4 µm. The laser is based on a non-polarizing astigmatic X-folded resonator with normal incidence mounting of the gain element. The chromatic dispersion of the resonator is controlled with a set of dispersive mirrors within one third of an optical octave over 2.05–2.6 µm range. The resonator’s optics is highly reflective in the range 1.8–2.9 µm. The components of the oscillator’s output spectrum at the wavelengths 1.6 µm and 3.2 µm are detected at –60 dB with respect to the main peak. Average power of few-cycle Kerr-lens mode-locked laser is 1.4 W at the pulse repetition frequency 79 MHz. That corresponds to 22% conversion of cw radiation of Er-doped fiber laser, which we used for optical pumping of the Cr:ZnS oscillator.

Weldability improvement by wobbling technique in high power density laser welding of two aluminum alloys: Al-5052 and Al-6061

Abstract: This paper presents a new approach in laser welding of Al-5052 and heat Al-6061 aluminum alloys, which are challenging materials for a good laser welding quality. The process consists of applying very small size of 0.1 mm to provide a high density of power that aims at imposing a high amount of heat that is required for aluminum alloys; simultaneously the wobbling technique is implemented to reduce the risk of overheating in the welding area. Having relied on the capability of the wobbling technique to distribute the generated heat, welding results contained negligible thermal defects compared to the usual defects such as underfill, undercut, and root reinforcement. The resulted welding zones show a fully penetrated welding quality for both alloys with a smooth weld seam at the top and root surface. Analysis indicates a higher tensile strength of 190 MPa for Al-5052 corresponding to an 18% decrease from the base metal, while this reduction of mechanical strength in the welded zone for Al-6061 was about 27%. Also, the hardness profile of Al-5052 reveals a small reduction in the fusion zone in contrast to Al-6061, for which a high hardness decrease happens in the welded zone. This approach is more profitable for the cost-effectiveness of the process since the laser power is set at a low range as the high-power density is mainly related to the small size of the spot diameter.

Low-threshold supercontinuum generation in polycrystalline media

Abstract: Until recently, the generation of super-octave continua in bulk materials at full repetition rates of femtosecond (fs) oscillators has been limited to a few special cases of Kerr lens mode-locked Ti:sapphire lasers. In 2019, we described a 3.4-octave fs source with 50 nJ pulse energy at the repetition rate of 78 MHz based on polycrystalline Cr:ZnS [Vasilyev et al., Optica6, 126 (2019)OPTIC82334-253610.1364/OPTICA.6.000126]. Here we explain the mechanism of fs supercontinuum generation in transition-metal doped polycrystalline II-VI semiconductors at relatively low (nJ-level) pulse energy. We demonstrate that this new supercontinuum regime is enabled by a complex, yet well-reproducible, interplay between the effects arising from the third-order nonlinearity, the quadratic nonlinearities, and thermal optical effects in the medium. We also demonstrate the control of fs pulse propagation in disordered $\chi ^{ (2)}$ media via the control of the material microstructure.

Single-mode 3kW Ytterbium fiber amplifier with diffraction-limited divergence in all-fiber format and compact modular package

Abstract: We report 3kW test data of Single-Mode (SM) Ytterbium-doped fiber amplifier with diffraction-limited divergence for narrow linewidth seed sources in compact modular package with all-fiber format. Measured M2 values of output beam in full power range are < 1.1. The fiber amplifier has been pumped by direct laser diodes and has 3m output delivery cable terminated with IPG connector. The fiber amplifier in modular package has ≥ 40% wall-plug efficiency and 15nm spectral bandwidth in 1055-1070nm wavelength range. The amplifier operates up to 3kW at linewidths of 60GHz and 30GHz with polarized and depolarized seed sources respectively. The amplifier data and non-linear SBS, SRS and MI effects are discussed for different input linewidth and test conditions.

Degree of polarization of photoluminescence from facets of InP as a function of strain: some experimental evidence.

Abstract: Previous work demonstrated a good fit to the degree of polarization (DOP) of luminescence measurements on {110} facets of InP using a simple dependence of DOP of luminescence on strain: ${-}{K_e} ({e_1} - {e_3})$, where ${K_e}$ is a positive calibration constant, and ${e_1}$ and ${e_3}$ are normal components of strain in the plane of the facet and along $\langle 1\bar 10\rangle$ and $\langle 001\rangle$ directions [Appl. Opt.43, 1811 (2004)APOPAI0003-693510.1364/AO.43.001811]. Recent analytic modeling, which by necessity to be analytic must make simplifying assumptions, has suggested that unless the measurements are along crystallographic axes, the dependence of the DOP of luminescence on strain is more complicated: ${-}{K_e} (1.315 {e_1} - 0.7987 {e_3})$ for measurements from an InP facet, with a similar “excess” ${e_1}$ for GaAs [Appl. Opt.59, 5506 (2020)APOPAI0003-693510.1364/AO.394624]. In this work, we fit finite element simulations (FEM) to DOP measurements of the photoluminescence from facets of InP bars with ${\{111\} _B}$ v-grooves that have been placed in a cylindrical bending moment. We find that the more complicated dependence of DOP on strain, as derived by the analytic model, fits the data better than the previously assumed simple dependence. This finding thus corroborates the analytical model and should have an impact on understanding the strain-dependent operation of optoelectronic devices.

Circuit Simulators: Linear Case

Abstract: This chapter discusses the basic of simulators where the focus is on linear systems. We start with a simple circuit network and use it as a demonstration of how an arbitrary circuit network can be built as a matrix equation. This is a natural environment for AC analysis, and we start with such a simulation and compare to a professional simulator. We then extend the analysis to include linear transient simulation where we include elements like capacitors and inductors so that one can demonstrate various integration methods.

New-Frontiers (NF) Class In-Situ Exploration of Venus: The Venus Climate and Geophysics Mission Concept

Abstract: More than 85% of the 23 investigations developed by VEXAG are largely accomplished via a NF mission centered on a variable-altitude balloon (aerobot) supported by a science/comm orbiter. Circling Venus >15 times over ~90 days, the aerobot repeatedly visits 52–62 km alts as it semi-continuously samples a host of environmental & surface parameters.

Overview of Numerical Methods

Abstract: This chapter describes a number of topics that are full-fledged research subjects in and of themselves and to do them justice in a just a few pages is not possible. The hope of the author is to present the material in such a way as to wet the readers’ appetite. The importance of numerical methods in solving various kinds of problems is paramount in modern product engineering and scientific research. Both the engineering and scientific communities are heavily involved in the development and use of these methodologies. In an effort to contain these vast subject matters, the focus will be on methods the reader is likely to encounter in an electrical engineering context and as such certain types of approximations to differential equations will be highlighted. The same thing goes for matrix equations where we here only use simple examples to highlight the fundamental ideas. The more advanced iterative methods that have been so successful in recent decades are mentioned briefly with an accompanying Python code example. Nonlinear equations and how to solve them efficiently is likewise another intense field of study, and over the years many methods have been developed that are in wide use in the scientific/engineering community today. Here we describe a method that is perhaps the most important to know due to its relative ease of implementation attributed to Isaac Newton, although other researchers such as Joseph Raphson were also involved over the years. Even though the presentation is held at a fundamental level, some basic familiarity with numerical methods, corresponding to an introductory class on the subject, will be helpful since we will be rather brief. We will start the chapter discussing differential equations and how one might implement them numerically. We will discuss implementations of what is called initial value problems where the state is known at a certain moment in time, and from then on, the system develops according to the governing equations. We will present implementations commonly used in circuit simulators. The chapter continues with nonlinear solution methods, and we wrap up the presentation with a description of matrix solvers. Rather than going through the mathematical theories behind these methods, we choose to present the basic ideas using examples, and for the interested reader a much more in-depth discussion of these issues can be found in Chap. 7 and the references at the end of the chapter. The importance of the subject matter presented in this chapter cannot be overstated, and it is the hope of the author the reader will explore the topic more deeply on his or her own.

Octave-spanning polycrystalline Cr:ZnS laser

Abstract: We report the first femtosecond polycrystalline Cr:ZnS oscillator with an octave-spanning spectrum. Average power of the laser is 1.4 W at the mid-IR central wavelength 2.4 µm and the pulse repetition frequency 79 MHz.

45 dB Single-Stage Single-Frequency Cr:ZnSe Amplifier for 2.2-2.6 μm Spectral Range

Abstract: We report 45 dB single stage Cr:ZnSe amplifier operating over 2.2-2.6 μm spectral range seeded by CW Cr:ZnSe single frequency laser. The maximum output energy of 1.6 mJ was demonstrated in 25 ns pulses at 1000 Hz repetition rate.

Epilogue: Simulators in Practice

Abstract: This book has so far looked at the basic principles behind circuit simulators. With the help of the provided codes, the reader has hopefully gained a better understanding of what simulators do well and what they perhaps do less well. Armed with this knowledge, this chapter will discuss best practices when using simulators and working on design projects. It is by necessity a subjective viewpoint, but the hope is the reader will learn something helpful along the way. Different developers will have different experiences and as such slightly different approaches to design work. All in all, we will stay away from controversial and very subjective approaches and stay true to what a designer is most likely to encounter in the industry.

Circuit Simulation: Nonlinear Case

Abstract: After the chapter on linear simulators, we will venture into the nonlinear aspects of circuit simulators by first looking at nonlinear DC operating point simulations. This was historically perhaps the most difficult problem to solve since one usually does not have an actual starting point unlike a transient solution where one often starts from the DC point and look at small changes with the new timestep. After the DC discussion, we will do full nonlinear transient simulations with active devices. The chapter ends with exploring other developments in circuit simulation such as periodic steady-state simulators. They have been extraordinarily helpful with circuit development, and we will examine several implementations using working code examples.

Parameter optimization for laser welding of dissimilar aluminum alloy: 5052-H32 and 6061-T6 considering wobbling technique

Abstract: The wobbling technique which consists of oscillating the laser beam at high frequency and in a specific pattern is an innovative way to enhance the quality of weld. The wobbling widens the area covered by the laser beam resulting in a wider seam that provides improved mechanical properties. The study investigated the effect of parameters such as the laser power, the gap between the two butt-welded plates, and the amplitude of oscillation using Taguchi’s method by setting a L9 design of experiments. The laser power level has a low range as the spot diameter is kept at a very small size to increase the power density and improve the energy efficiency of the laser welding process. The results revealed the optimal welding set-up and conditions to enhance the mechanical properties of welds. The value of laser power and the amplitude is optimized relatively to the ultimate tensile strength and the weld shape expressed by the depth to width ratio (D/W) that is correlated to the ductility. A fitness function combined with the steepest descent method applied to regression analysis allows figuring out the optimal parameters defined by the value of laser power at 1118 W and an amplitude of 0.8 mm resulting in a predicted welded part with 206.8 MPa of tensile strength and 4.5% of ductility.

Mathematics Behind Simulators

Abstract: This appendix describes some of the mathematical details behind the circuit analysis in a more formal way than elsewhere in the book We will first discuss an electrical network in terms of directed graphs where we define basic entities relevant for circuit theory and their properties This will lead into nodal analysis and finally modified nodal analysis The following section will discuss the solution of differential equations in terms of difference equations This is a huge subject, and we will only have space to highlight some of the important aspects of this subject For the interested reader, the references will contain many pointers for future study

Modeling Harmonic and Supercontinuum Generation in Polycrystalline Materials

Abstract: We develop a comprehensive model to simulate random quasi-phase-matched frequency conversion in polycrystalline media, and present simulations which shed light on the mechanisms of supercontinuum generation and the properties of generated radiation in zinc-blende materials.

Clusters of Cesium-Lead-Iodide Perovskites in the Zeolite Matrix.

Abstract: Small clusters of cesium-lead-iodide perovskites (CLIPs) have been prepared in the Na-X zeolite matrix and studied by means of spectroscopy and quantum chemical modeling. Regularity of pores in single crystals of zeolite assures the formation of clusters of a certain size. By the first-principles quantum chemical calculations, we have determined that clusters Cs4PbI6, Cs5Pb2I9, and probably Cs7Pb5I16 with a size of 0.74, 1.29, and 1.36 nm, respectively, have elevated stability compared to other species, and they fit into the pores of Na-X zeolite. Electronic energy spectra of these clusters have been calculated and compared with experimentally measured ones.