Laser Configuration Research Articles

Ultra-Flat Supercontinuum Generation in an All-Fiber Self-Q-Switched Er/Yb Laser

A supercontinuum source based on a self-Q-switched Er/Yb-codoped fiber laser has been experimentally demonstrated. At different pump powers, starting at a moderate value of 1.1 W, self-Q-switched pulses with a broad flat spectrum of ~ 560 nm width spanning over the range ~1600 – 2160 nm at −5 dB level (considering the Raman peak) are obtained. Such wide spectrum can be achieved directly at the output of the fiber laser resonator, making the structure compact and robust. With a maximum pump power of 4.9 W, the repetition rate, average output power, peak power and pulse energy are approximately 14.7 kHz, 465 mW, 66 kW and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$31~\mu \text{J}$ </tex-math></inline-formula> , respectively. This compact SC laser configuration has the merits of simple cavity design, low cost and good robustness, which provide a SC source that can be easily applied to numerous areas, such as spectroscopy, optical communications, metrology and biomedical applications.

Effects of electron heating and surface rippling on Rayleigh–Taylor instability in radiation pressure acceleration

The acceleration of ultrathin targets driven by intense laser pulses induces Rayleigh–Taylor-like instability. Apart from laser and target configurations, we find that electron heating and surface rippling, effects inherent to the interaction process, have an important role in instability evolution and growth. By employing a simple analytical model and two-dimensional particle-in-cell simulations, we show that the onset of electron heating in the early stage of the acceleration suppresses the growth of small-scale modes, but it has little influence on the growth of large-scale modes, which thus become dominant. With the growth of surface ripples, a mechanism that can significantly influence the growth of these large-scale modes is found. The laser field modulation caused by surface rippling generates an oscillatory ponderomotive force, directly modulating transverse electron density at a faster growth rate than that of ions and eventually enhancing instability growth. Our results show that when surface deformation becomes obvious, electron surface oscillation at 2ω0 (where ω0 is the laser frequency) is excited simultaneously, which can be seen as a signature of this mechanism.

An aluminum coated all-fiber mirror and a Mach–Zehnder interferometer for developing a switchable and tunable multi-wavelength laser

In this paper, a tunable and switchable multi-wavelength erbium doped linear fiber laser, based on an optical fiber loop mirror containing a Mach–Zehnder interferometer (MZI) and an aluminum coated optical fiber cleaved end is presented. The MZI, obtained by core-offset splicing a piece of photonic crystal fiber (PCF) between two segments of a single mode fiber (SMF), acts as a wavelength selective filter (WSF). The full reflecting mirror implemented is obtained by thermal evaporation of aluminum on a cleaved fiber end, technique which has not been deeply explored for compact fiber laser configurations. In this way, both optical loop mirror and the aluminum coated fiber work together to make a resonant cavity. By rotating the wave plates of a polarization controller, the polarization state of the cavity modes diversifies, and the laser setup can emit one, two, three or four laser wavelengths, which can be switched from 1526 to 1562 nm. In addition, this laser arrangement can be tuned within a 5 nm interval and has a side-mode suppression ratio of 42 dB for single-wavelength operation. Finally, the proposed laser configuration achieved a high stability for more than an hour at room temperature.

Chromosome Analysis and Sorting Using Conventional Flow Cytometers.

The fluorescent dyes Hoechst (HO) and Chromomycin A3 (CA3) are commonly used for bivariate flow karyotyping to distinguish individual chromosomes from one another based on differences in base composition and DNA content. However, analysis of chromosomes using this fluorescent dye combination requires a flow cytometer equipped with lasers of specific wavelengths and higher power than is typical of conventional flow cytometers. This unit presents a chromosome staining technique with a dye combination of DAPI and propidium iodide (PI). Chromosomes stained using this dye combination can be analyzed on conventional flow cytometers equipped with a typical configuration of lasers and optics. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Cell culture and metaphase harvest of suspension cell line Alternate Protocol 1: Cell culture and metaphase harvest of adherent cell line Basic Protocol 2: Preparation of chromosome suspension using polyamine isolation buffer Basic Protocol 3: Staining chromosomes with DAPI and propidium iodide Alternate Protocol 2: Staining chromosomes with Hoechst and Chromomycin A3 Basic Protocol 4: Bivariate flow karyotyping on a cell analyzer Basic Protocol 5: Bivariate flow karyotyping on a cell sorter Basic Protocol 6: Purification of flow-sorted chromosomes.

A Laser Shock-Based Disassembly Process for Adhesively Bonded Ti/CFRP Parts

The application of adhesively bonded joints in aerospace structural parts has increased significantly in recent years and the general advantages of their use are well-documented. One of the disadvantages of adhesive bonding is the relevant permanence, when compared to traditional mechanical fastening. End-of-life processes generally require the separation of the adherents for repair or recycling, and usually to achieve this, they combine large mechanical forces with a high temperature, thus damaging the adherents, while consuming large amounts of energy. In this work, a novel disassembly technique based on laser-induced shock waves is proposed for the disassembly of multi-material adhesively bonded structures. The laser shock technique can generate high tensile stresses that are able to break a joint, while being localized enough to avoid damaging the involved adherents. The process is applied to specimens made from a 3D-woven CFRP core bonded to a thin Ti layer, which is a common assembly used in state-of-the-art aircraft fan blades. The experimental process has been progressively developed. First, a single-sided shot is applied, while the particle velocity is measured at the back face of the material. This method proves ineffective for damage creation and led to a symmetric laser configuration, so that the tensile stress can be controlled and focused on the bond line. The symmetric approach is proved capable of generating a debonding between the Ti and the CFRP and propagating it by moving the laser spot. Qualitative assessment of the damage that is created during the symmetric experimental process indicates that the laser shock technique can be used as a material separation method.

Experimental Investigation on the Mode Characteristics of an Excited-State Quantum Dot Laser under Concave Mirror Optical Feedback

In this paper, we experimentally investigated the mode configuration of an excited-state quantum dot laser (ESQDL) under concave mirror optical feedback, and the influences of the feedback strength on the mode characteristics were analyzed. The results showed that after introducing concave mirror optical feedback, some longitudinal modes of the excited-state (ES) existing in a free-running ESQDL could be suppressed. When the feedback strength increased to a certain extent, the ground-state (GS) emission occurred and co-existed with the ES emission. By further increasing the feedback strength, all the longitudinal modes of the ES emission were suppressed, and only the longitudinal modes of the GS emission could be observed. As a result, the emission-state switching from the ES to GS emission was realized. When the ESQDL was biased at a larger current, the feedback strength required to achieve emission-state switching was stronger.

Spectral Pulsations of Dissipative Solitons in Ultrafast Fiber Lasers: Period Doubling and Beyond

AbstractPeriod doubling is a universal bifurcation of central importance in all disciplines of nonlinear science, which generally signals the existence of chaotic dynamics in the vicinity of the system parameters. Although observed in diverse ultrafast laser configurations, there is still no consensus on its physical origin. Real‐time spectral characterization techniques have recently allowed revisiting pulsating dynamics, from period‐2 to long‐period pulsations. Following a contextual review, this article presents a variety of bifurcation sequences entailing the spectral pulsations of dissipative solitons. These experiments, using ultrafast fiber lasers operated in both chromatic dispersion regimes, are confronted with numerical simulations to demonstrate that self‐phase modulation represents a general mechanism triggering period‐2 bifurcations. In addition, by ramping up the pump power, original sequences of period‐doubling bifurcations intertwined with more complex bifurcations are presented, where entrainment phenomena are unveiled. These findings provide a more general understanding of the period‐doubling bifurcation in ultrafast laser systems while highlighting their potentially intricate combinations with complex bifurcations, which may be exclusively observable from the spectral domain.

Compact nanosecond Yb:YAG/V:YAG solid-state laser generating switchable radially and azimuthally beams.

We demonstrated a compact self-starting nanosecond Yb:YAG/V:YAG solid-state laser with cylindrical vector beams output modulated by the intracavity mode converter S-waveplate experimentally. We can deliver the stable Q-switched pulse with the highest repetition rate 3.61 kHz and minimum pulse width 26 ns at the wavelength of 1030.07 nm with the help of the V:YAG crystal. In addition, the switchable radially and azimuthally polarized beams can be realized with polarization extinction ratios of 92.3% and 89.6%, respectively. The compact laser configuration can provide solutions for generating stable nanosecond structured light, and may benefit the applications like micro/nano material processing.

Nanometer-Thin Stacks of MXenes (Ti3C2Tx and Ta4C3Tx) for Applications as Nonlinear Photonic Devices

Two-dimensional (2D) carbides of transition metals, so called “MXenes”, maintain excellent optical properties and unique layer stacking form via hydrogen bonds in contrast to other low-dimensional materials. These promising features have attracted increasingly research interest in the field of ultrafast photonics. In this work, titanium carbide (Ti3C2Tx) and tantalum carbide (Ta4C3Tx), as two promising MXene materials for photonic applications, are experimentally synthesized by the ultrasound-assisted liquid phase exfoliation technique. The morphology of prepared few-layer Ti3C2Tx and Ta4C3Tx has been systematically characterized by transmission electron microscopy and X-ray diffraction analysis. Density functional theory is performed to obtain their electronic band structures, demonstrating metallic properties and verifying their optical absorption at 1 μm. Their tempting optical modulation properties for multi-gigahertz pulsed laser emission are demonstrated by using them as saturable absorbers in a waveguide laser cavity. Particularly, high-performance Q-switched mode-locked lasers with/without laser mirrors are realized based on the hybrid waveguide laser configuration, delivering 1 μm laser pulses with durations as short as 30 ps. The results presented in this work show the great potential of metallic MXenes and waveguide structures for applications in functional photonic devices.

Helium as a Surrogate for Deuterium in LPI Studies

Helium or neopentane can be used as surrogate gas fill for deuterium (D2) or deuterium-tritium (DT) in laser-plasma interaction studies. Surrogates are convenient to avoid flammability hazards or the integration of cryogenics in an experiment. To test the degree of equivalency between deuterium and helium, experiments were conducted in the Pecos target chamber at Sandia National Laboratories. Observables such as laser propagation and signatures of laser-plasma instabilities (LPI) were recorded for multiple laser and target configurations. It was found that some observables can differ significantly despite the apparent similarity of the gases with respect to molecular charge and weight. While a qualitative behaviour of the interaction may very well be studied by finding a suitable compromise of laser absorption, electron density, and LPI cross sections, a quantitative investigation of expected values for deuterium fills at high laser intensities is not likely to succeed with surrogate gases.

Histopathological effects of laser fiber diameter in different laser modulations: an experimental exvivo study

We aimed to compare the histopathological effects of different laser fiber diameters on kidney tissue using different modulations of holmium laser. An ex vivo trial was performed employing veal kidneys. A 100 W HoYAG laser device (Cyber Ho, Quanta System, Samarate, Italy) was employed, accompanied by 550 μm and 272 μm laser fibers for all experimental procedures. Incision depth (ID), vaporization area (VA), coagulation area (CA), surface section (SS), lateral effect (LE) and total laser area (TLA, calculated as VA+CA) were assessed. Histopathological measurement results of different laser fiber diameters were compared in Standard mode (SM) and Virtual BasketTM (VB) mode. In SM and VB, a statistically significant difference was found in the mean CA values between 272 (μm) and 550 (μm) laser diameters (p: 0.02 and p&lt;0.001, respectively). In SM, the lowest and highest mean CAs were observed with the 272 (μm) lasers at 0.5 J-40 Hz and 1.5 J-40 Hz laser configurations (0.263±0.003 mm2 and 1.353±0.015 mm2, respectively). In VB, the lowest and highest mean CAs were observed with the 550 (μm) at 0.5 J-20 Hz and 1 J-20 Hz laser settings (0.987±0.014 mm2 and 1.969±0.029 mm2, respectively). We found that both SM and VB modulations have higher CA values, a measure of hemostasis, in 550 μm fibers compared to 272 μm fibers.

Ultra-high spectral purity laser derived from weak external distributed perturbation

Ultra-high spectral purity lasers are of considerable research interests in numerous fields such as coherent optical communication, microwave photonics, distributed optical fiber sensing, gravitational wave detection, optical clock, and so on. Herein, to deeply purify laser spectrum with compact size under normal condition, we propose a novel and practical idea to effectively suppress the spontaneous radiation of the laser cavity through weak external distributed perturbation. Subsequently, a laser configuration consisting of a main lasing cavity and an external distributed feedback cavity is proposed. The feedback signal with continuous spatio-temporal phase transition controlled by a distributed feedback structure is injected into the main cavity, which can deeply suppress the coupling rate from the spontaneous radiation to the stimulated emission and extremely purify the laser spectrum. Eventually, an ultra-narrow linewidth on-chip laser system with a side mode suppression ratio greater than 80 dB, an output linewidth of 10 Hz, and a relative intensity noise less than -150 dB/Hz is successfully obtained under normal conditions. The proposed concept in this work provides a new perspective for extreme regulation of laser parameters by using weak external distributed perturbation, which can be valid for various gain-type lasers with wide wavelength bands.

Implementation of Traveling Wave Models of Grating-Based Integrated Optical Devices for Circuit Simulation

This paper presents the development and use of a traveling wave model of waveguide-based grating devices for use as a compact model in a circuit-level simulator. Both passive and active devices are modeled, with the grating being characterized by coupling coefficients for the two counter-propagating waves. It is shown how the implicit carrier frequency can be offset from the Bragg frequency using two possible methods: either by the static detuning of the model or introducing a phase modulation into the coupling coefficients. Other physical aspects of the model are addressed such as dispersion and energy conservation. A comparison to a 1D Yee-cell model is used to verify the applicability of the traveling wave model. As an example of the circuit simulation of a passive device, an optical code generating application is used and it is noted that for a passive device the interface between the compact model and the circuit simulator is not a concern. Using traveling-wave-based laser simulations of grating-based laser structures it is demonstrated that the model captures the complex behaviour of the devices. In particular the lasing frequency is naturally produced from the model and the introduction of delay elements into the structure can be used to restrict the laser to single mode operation. A number of examples are used to illustrate important aspects of its use as a compact model. Firstly, it is shown that an operating point for either of the laser configurations can be constructed and detuning used to produce an un-modulated output, allowing for much more efficient simulations. A final example uses a directly modulated laser to illustrate the effect of back reflection on the stability of the laser simulation.

Molybdenum Aluminum Boride as the Q-Switcher and Mode-Locker in the Erbium-Doped Fiber Laser Configuration

Molybdenum Aluminum Boride as the Q-Switcher and Mode-Locker in the Erbium-Doped Fiber Laser Configuration

Properties and Applications of Random Lasers as Emerging Light Sources and Optical Sensors: A Review.

In a random laser (RL), optical feedback arises from multiple scattering instead of conventional mirrors. RLs generate a laser-like emission, and meanwhile take advantage of a simpler and more flexible laser configuration. The applicability of RLs as light sources and optical sensors has been proved. These applications have been extended to the biological field, with tissues as natural scattering materials. Herein, the current state of the RL properties and applications was reviewed.

Polarization-multiplexed dual-comb fiber laser based on an all-polarization-maintaining cavity configuration

In this study, we present a polarization-multiplexed, erbium-doped dual-comb fiber laser based on an all-polarization-maintaining cavity configuration. We observed that the dual-comb fiber laser easily realized the self-starting mode-locking operation due to the non-linear amplifying loop mirror (NALM) with a non-reciprocal phase shifter. Furthermore, owing to the sharing of the NALM part, the two outputs from this laser configuration had similar center wavelengths, with small different repetition rates (∆frep). In the free-running operation, the standard deviation of relative stability for Δfrep of 2.09 kHz was measured to be 1.59 Hz, and the full width at half-maximum of the relative beat note between the two frequency combs in the optical frequency domain was approximately 1 kHz. These results show that the two frequency combs from this laser configuration have high relative stability and mutual coherence.

An actively Q-switched multi-wavelength ytterbium fiber laser with cascaded polarization-maintaining Bragg gratings

In this paper, we investigate the multi-wavelength lasing characteristics of an actively Q-switched ytterbium-doped fiber laser with two cascaded polarization maintaining fiber Bragg gratings (PM-FBGs). By properly adjusting the polarization states in the cavity, a total of 15 wavelength combinations, including single-, dual-, tri-, and quad-wavelength emission states, have been achieved. Stable Q-switched pulses with repetition rates ranging from 10 to 28 kHz are obtained. The influence of repetition rate and pump power upon the pulse width are also investigated. The high spectral stability in lasing operation indicates effectiveness of the proposed cascaded PM-FBGs in actively Q-switched multi-wavelength fiber laser configurations.

On‐Demand Polarization Controllable Liquid Crystal Laser

AbstractA polarization controllable band‐edge liquid crystal (LC) laser configuration is presented that provides on‐demand control of the polarization state of the laser using a four electrode in‐plane configuration to drive a nematic LC layer. By controlling the orientation of the electric field, and thus the orientation of the optic axis of the nematic LC, as well as the retardance, any laser polarization state (e.g., circular, elliptical) can, in principle, be created that is aligned along any desired direction in a plane perpendicular to the propagation direction. After calibrating the tuneable nematic device with a He‐Ne laser that has a well‐defined polarization state, control of the LC laser polarization is then demonstrated, where it is shown that different polarization states and orientations thereof can be obtained by changing the relative combination and amplitudes of the voltages applied to each of the four electrodes. It is found, however, that achieving a pure linear polarization state is challenging, which may indicate that the polarization from the LC laser is not a well‐defined circularly polarized state. These thin‐film LC lasers with full polarization control are potentially important for a variety of different applications ranging from the biomedical to the display industries.

Terahertz quantum cascade laser frequency combs with optical feedback.

Optical feedback exists in most laser configurations and strongly affects laser performances depending on the feedback strength, length, and phase. In this paper, we investigate the frequency comb behaviour of a semiconductor quantum cascade laser emitting around 4.2 THz with external optical feedback. A periodic evolution of the laser inter-mode beatnote from single-line to multiple-line structures is experimentally observed with a minor change of optical feedback length (phase) on the wavelength scale. The comb stability of the laser with feedback is also measured and compared with the same laser without feedback. Furthermore, our simulations reveal that the dynamical oscillations invoked by optical feedback are responsible for the measured multiple-line beatnotes. It is found that the characteristic feedback period is determined by the half wavelength of the laser, while the comb operation is maintained at most feedback length positions. Therefore, terahertz quantum cascade laser combs are robust against the minor position vibration of the feedback mirror in practice, owing to the much smaller feedback phase change than that of common near-infrared laser diodes.

High-power wavelength-tunable and power-ratio-controllable dual-wavelength operation at 1319 nm and 1338 nm in a Q-switched Nd:YAG laser

We report the first demonstration on three types of 1.3 μm spectral region in a Q -switched Nd:YAG laser. In order to dissipate the heat deposition effectively to obtain good beam quality, the Nd:YAG rod crystal with 1° cut-angle on end faces is side-pumped by the quasi-continuous-wave pulsed laser diode. A Suprasil etalon is well designed as the intracavity mode-selector to obtain wavelength-tunable single line or power-ratio-controllable dual line operation at 1319 nm and 1338 nm. With the pump pulse width of 200 μs and pump power of 410 W, the acousto-optic Q -switched laser delivered a pulse width of 117 ns at 400 Hz repetition rate, and the M 2 factor was measured to be about 1.87. 1319 nm together with 1338 nm single-wavelength laser achieved an average output power of 47.6 W and 39.9 W with a linewidth of 0.48 nm and 0.32 nm, and a tunable range of 111.2 pm and 108.6 pm, respectively. Among dual-wavelength oscillation, both lines can be tuned at almost equal intensity level with 45.7 W total output power, which is input into an LBO crystal to generate red light of 11.4 W for 659 nm, 6.7 W for 664 nm, and 7.5 W for 669 nm. The 1.3 μm wavelength-selectable operation realized by using the same laser configuration may enhance the application in the fields of tunable lasers and THz frequency generation.