Tunable Pulses Research Articles

Polarized spectroscopic properties and 1046 nm laser operation of Yb3+:Ca3TaGa3Si2O14 crystal

A Yb3+:Ca3TaGa3Si2O14 single crystal was grown by the Czochralski method. Polarized absorption and fluorescence spectra of the crystal were measured at room temperature. The peak absorption cross sections at 977 nm are 3.69 × 10−20 and 2.03 × 10−20 cm2 for σ and π polarizations, respectively. The crystal has a broad gain band with a full width at half-maximum of 58 nm around 1 μm for σ polarization when the inversion parameter is 0.2. The intrinsic fluorescence lifetime of the 2F5/2 multiplet of the crystal was fitted to be 634 μs. Pumped by a 976 nm diode laser, a 1046 nm continuous-wave laser with a maximum output power of 2.8 W and a slope efficiency of 52.6% was achieved in the crystal. The results show the Yb3+:Ca3TaGa3Si2O14 crystal may be a potential gain medium for tunable and ultrashort pulse lasers at 1 μm.

Tunable optical nonlinearity of indium tin oxide for optical switching in epsilon-near-zero region

Abstract The propagation of light in the epsilon-near-zero (ENZ) region of materials exhibits intriguing linear and nonlinear optical phenomenon that have been extensively exploited for a plethora of applications. Here, we show that the optical properties as well as the ENZ wavelength of magnetron-sputtered indium tin oxide (ITO) thin films could be judiciously engineered. The measurement of nonlinear optical properties reveals that the control of deposition conditions allows for the tuning of absorptive optical nonlinearity between saturable absorption and reverse saturable absorption. The ENZ wavelength for the ITO film is deduced as around 1553 nm. We obtain the highest third-order nonlinear absorption coefficient and imaginary part of third-order nonlinear susceptibility for the ITO thin film through Z-scan method as −50.56 cm/GW and ∼38 × 10−14 e.s.u. at 1050 nm, and −64.50 cm/GW and ∼45 × 10−14 e.s.u. at 1550 nm, respectively. We demonstrate further that the strong saturable absorption of the ITO thin film enables Q-switched pulse laser generation in ∼1050 and ∼1550 nm regions with tunable repetition rates and pulse energies. The present results suggest the great application potential of the ITO thin film in the field of nonlinear optical devices.

Standardized excitable elements for scalable engineering of far-from-equilibrium chemical networks.

Engineered far-from-equilibrium synthetic chemical networks that pulse or switch states in response to environmental signals could precisely regulate the kinetics of chemical synthesis or self-assembly. Currently, such networks must be extensively tuned to compensate for the different activities of and unintended reactions between a network's various chemical components. Modular elements with standardized performance could be used to rapidly construct networks with designed functions. Here we develop standardized excitable chemical regulatory elements, termed genelets, and use them to construct complex in vitro transcriptional networks. We develop a protocol for identifying >15 interchangeable genelet elements with uniform performance and minimal crosstalk. These elements can be combined to engineer feedforward and feedback modules whose dynamics match those predicted by a simple kinetic model. Modules can then be rationally integrated and organized into networks that produce tunable temporal pulses and act as multistate switchable memories. Standardized genelet elements, and the workflow to identify more, should make engineering complex far-from-equilibrium chemical dynamics routine.

Influence of phonon harmonicity on spectrally pure resonant Stokes fields

Due to their highly coherent emission, tunability, and compactness, integrated single-frequency diamond Raman lasers are interesting tools for applications in integrated quantum technology, high-resolution spectroscopy, or coherent optical communications. While the fundamental emission linewidth of these lasers can be Fourier limited, their thermo-optic characteristics lead to drifts in their carrier frequency, posing important challenges for applications requiring ultrastable emission. We propose here a method for measuring accurately the temperature-dependent index of refraction of diamond by employing standing Stokes waves produced in a monolithic Fabry-P\'erot diamond Raman resonator. Our approach takes into account the influence of temperature on the first-order phonon line and the average lattice phonon frequency under intense stimulated Raman scattering conditions. We further utilize this model to calculate the value of the average phonon frequency and then the temperature-dependent thermo-optic coefficient. The theory is accompanied by the demonstration of tunable Fourier-limited Stokes nanosecond pulses with a stabilized center frequency deviation of less than $4$ MHz.

Spectral purification of single-frequency Stokes pulses in doubly resonant integrated diamond resonators

Pulsed spectrally pure light is required for applications in high-resolution spectroscopy, optical coherent communications, and quantum technologies. In this work, we report on the efficient generation of high peak power, single-frequency, and tunable nanosecond pulses utilizing stimulated scattering, with an increased spectral brightness by exploiting double resonances in an integrated diamond Raman resonator. The device is based on a miniature monolithic Fabry–Perot design pumped by a milliwatt-class average power Q-switched single-frequency pulsed laser at 532 nm. Our device was capable of enhancing the peak spectral brightness by greater than three times compared with conventional singly resonant diamond Raman lasers by tuning the effective resonator length at pump and Stokes wavelengths simultaneously. Our results facilitate the integration of pulsed and power scalable single frequency sources into hybrid photonic integrated platforms with a broad range of applications.

Tunable Microwave Pulse Generation Based on a Time-Domain Mode Locked Optoelectronic Oscillator

A tunable microwave pulse generator is proposed and demonstrated. In this study, a time-domain mode locked optoelectronic oscillator (OEO) is realized by utilizing a dual-parallel Mach-Zehnder modulator (DPMZM). One branch of the DPMZM is modulated by the feedback signal and another branch is modulated by an inject signal. When the frequency of the injected signal is equal to an integer multiple of the oscillation mode space, the time-domain mode locking is achieved in the OEO loop and the microwave pulse trains are generated. In the experiment, the phase noise of the generated signal is −93 dBc/Hz, the frequency range of the generated signal is 6–12 GHz, the time duration of the generated microwave pulse can be adjusted from 620 ns to 2970 ns, and the repetition rate of the generated microwave pulse can be set to 185.1 kHz, 370.2 kHz and 555.3 kHz.

2.1 μm Band Dissipative Soliton Resonance Mode-Locked Ho-Doped Tunable Fiber Laser

We report a 2.1 μm band mode-locked holmium-doped fiber (HDF) laser with tunable wavelength and pulse width in dissipative soliton resonance (DSR) region for the first time to our knowledge. A piece of HDF is pumped by a home-made 1.9 μm band fiber source, and a nonlinear-amplifying-loop-mirror structure is used to realize mode-locking operation with net anomalous dispersion. The repetition rate of pulse is 8.97 MHz. The pulse duration can be adjusted from 1.16 to 3.93 ns with the increase of pump power, while maintains a constant peak power. At the maximum pump power of 2.1 W, the pulse energy is up to 2 nJ. Moreover, the central wavelength is in the tunable range from 2054.4 to 2076 nm by appropriately adjusting the polarization controllers. We also explore the nonlinear correlation characteristic of DSR pulse by changing the length of high nonlinear fiber.

Extra-cavity manipulation from traditional scalar to flexible vector solitons

Soliton manipulation is considered as an effective way to generate complicated and controllable vector solitons. Here, we experimentally acquire flexible vector solitons deriving from standard scalar solitons by route-assisted and birefringence-enhanced structures along the laser output port. These vector solitons with weak interaction between two polarized components possess tunable pulse numbers, intensities, and intervals. These results would be a significant complement for soliton polarization dynamics as well as a valuable soliton light source for various practical applications.

Polarization multiplexed active mode-locking optoelectronic oscillator for frequency tunable dual-band microwave pulse signals generation.

We propose and experimentally demonstrate a polarization multiplexed active mode-locking optoelectronic oscillator (AML-OEO) based on a single dual-polarization binary phase-shift keying (DP-BPSK) modulator for frequency tunable dual-band microwave pulse signal generation. In order to realize mode-locking, two single-tone signals whose frequency are integer multiple of the free spectrum range (FSR) of AML-OEO are applied as active modulation signals (AMSs) at the bias ports of the DP-BPSK modulator. By dividing the AML-OEO into two loops with polarization demultiplexing, both the carrier frequency and pulse repetition frequency (PRF) of the dual-band microwave pulses are independently adjustable. In the experiment, microwave pulses with different PRFs of 162.4 kHz, 324.8 kHz and 812 kHz are generated based on fundamental, second-order harmonic and fifth-order harmonic mode-locking, respectively. In addition, the carrier frequency tunability within 4∼10 GHz is verified by inserting a frequency tunable electrical filter. The phase noise of the generated pulse signal at 10 kHz offset is better than -125 dBc/Hz.

New Architecture of Solid-State High-Voltage Pulse Generators

The application of the nanosecond pulsed electric field (nsPEF) for biomedical treatments has gained more interest in recent decades due to the development of pulsed power technologies which provides the ability to control the electric field dose applied during tests. In this context, the proposed paper describes a new architecture of solid-state high-voltage pulse generators (SS-HVPG) designed to generate fully customised sequences of quasi-rectangular pulses. The idea is based on the combination of semiconductor switches (IGBT/MOSFET) known for their flexibility and controllability with special magnetic switches to build compact and modular generators. The proposed structure is inspired by the most known pulse generator of Marx, but mixes its two variants for negative and positive polarities. Thus, the polarity of the generated pulses can be freely selected. In addition to that, the use of IGBTs/MOSFET ensures a tunable repetition rate and pulse width. The capacitors are charged via a series of magnetic switches and a flyback DC–DC converter which provides fast and efficient charging and also an adjustable amplitude of the output pulses. The design can be easily simplified giving two other modified structures, based on the same idea, for mono-polar operating (only positive or only negative pulses) with a reduced number of switches. A SPICE simulation of the generator and results of experimental tests carried out on a three stages generator are presented. The obtained results confirm the operating principle and the claimed performances of the new structure.

Agile femtosecond synchronizable laser source from a gated CW laser

In this letter we demonstrate agile femtosecond pulse generation with a widely tunable repetition rate (10–100 MHz) from a continuous wave laser diode optically gated by a Mach–Zehnder electro-optic intensity modulator. Initial sub-50 ps pulses are strongly spectral broadened (>5 nm) by self-phase modulation in a polarization maintaining single-mode fiber. A tunable optical pulse train with pulse durations of a few hundred femtoseconds is obtained using a simple fixed grating compressor, thanks to spectral broadening saturation phenomena. The source is easily synchronized with low timing jitter using an external clock signal.

Spatially selective excitation of spin dynamics in magneto-photonic crystals by spectrally tunable ultrashort laser pulses

Abstract In this work, we tackle the problem of the spatially selective optical excitation of spin dynamics in structures with multiple magnetic layers. The 120 fs circularly polarized laser pulses were used to launch magnetization precession in an all-dielectric magneto-photonic crystals (MPC) formed by magnetic layers sandwiched between and inside two magnetic Bragg mirrors. Optical pump-probe experiments reveal magnetization precession triggered via ultrafast inverse Faraday effect with an amplitude strongly dependent on the pump central wavelength: maxima of the amplitude are achieved for the wavelength tuned at the cavity resonance and at the edge of the photonic bandgap. The optical impact on the spins caused by the inverse Faraday effect and spectrum of this effect are found to correlate mostly to the direct Faraday effect. We show that even though the pump laser pulses propagate along the whole structure tuning their wavelength allows localization of a larger spin precession either in the cavity layer or in the Bragg mirror layers selectively. The results pave the way to the ultrafast optical control of magnetization dynamics at a sub-wavelength scale that is vital for modern magneto-photonics and magnonics.

Unveiling the Native Morphology of Extracellular Vesicles from Human Cerebrospinal Fluid by Atomic Force and Cryogenic Electron Microscopy.

Extracellular vesicles (EVs) are membranous structures in biofluids with enormous diagnostic/prognostic potential for application in liquid biopsies. Any such downstream application requires a detailed characterization of EV concentration, size and morphology. This study aimed to observe the native morphology of EVs in human cerebrospinal fluid after traumatic brain injury. Therefore, they were separated by gravity-driven size-exclusion chromatography (SEC) and investigated by atomic force microscopy (AFM) in liquid and cryogenic transmission electron microscopy (cryo-TEM). The enrichment of EVs in early SEC fractions was confirmed by immunoblot for transmembrane proteins CD9 and CD81. These fractions were then pooled, and the concentration and particle size distribution were determined by Tunable Resistive Pulse Sensing (around 1010 particles/mL, mode 100 nm) and Nanoparticle Tracking Analysis (around 109 particles/mL, mode 150 nm). Liquid AFM and cryo-TEM investigations showed mode sizes of about 60 and 90 nm, respectively, and various morphology features. AFM revealed round, concave, multilobed EV structures; and cryo-TEM identified single, double and multi-membrane EVs. By combining AFM for the surface morphology investigation and cryo-TEM for internal structure differentiation, EV morphological subpopulations in cerebrospinal fluid could be identified. These subpopulations should be further investigated because they could have different biological functions.

Single Gene Mutations in Pkd1 or Tsc2 Alter Extracellular Vesicle Production and Trafficking.

Simple SummaryExtracellular vesicles shed from primary cilia may be involved in renal cystogenesis. The disruption of the Pkd1 gene in our cell culture system increased the production of EVs in a similar way that occurs when the Tsc2 gene is disrupted. Disruption of the primary cilia depresses EV production, and this may be the reason that the combined Kif3A/Pkd1 mutant mouse has a less severe phenotype than the Pkd1 mutant alone. We initiated studies aimed at understanding the renal trafficking of renally-derived EVs and found that single gene disruptions can alter the EV kinetics based on dye tracking studies. These results raise the possibility that EV features, such as cargo, dose, tissue half-life, and targeting, may be involved in the disease process, and these features may also be fertile targets for diagnostic, prognostic, and therapeutic investigation.Patients with autosomal dominant polycystic kidney disease (ADPKD) and tuberous sclerosis complex (TSC) are born with normal or near-normal kidneys that later develop cysts and prematurely lose function. Both renal cystic diseases appear to be mediated, at least in part, by disease-promoting extracellular vesicles (EVs) that induce genetically intact cells to participate in the renal disease process. We used centrifugation and size exclusion chromatography to isolate the EVs for study. We characterized the EVs using tunable resistive pulse sensing, dynamic light scattering, transmission electron microscopy, and Western blot analysis. We performed EV trafficking studies using a dye approach in both tissue culture and in vivo studies. We have previously reported that loss of the Tsc2 gene significantly increased EV production and here demonstrate that the loss of the Pkd1 gene also significantly increases EV production. Using a cell culture system, we also show that loss of either the Tsc2 or Pkd1 gene results in EVs that exhibit an enhanced uptake by renal epithelial cells and a prolonged half-life. Loss of the primary cilia significantly reduces EV production in renal collecting duct cells. Cells that have a disrupted Pkd1 gene produce EVs that have altered kinetics and a prolonged half-life, possibly impacting the duration of the EV cargo effect on the recipient cell. These results demonstrate the interplay between primary cilia and EVs and support a role for EVs in polycystic kidney disease pathogenesis.

Widely tunable two-color x-ray free-electron laser pulses

Widely tunable two-color x-ray free-electron laser pulses

Tunable anisotropic pulse photo response of ZrS3 crystal at cryogenic temperatures

Two-dimensional (2D) transition metal trichalcogenides (TMTCs) have been considered promising candidates for next-generation electronic devices. TMTCs containing quasi-one-dimensional chain structure, in contrast to two-dimensional (2D) Transition Metal Dichalcogenides (TMDCs), provide significant advantages in electronics and optoelectronics device modeling and engineering to enhance device performance. In this study, we present a pulse photoresponse application of a device based on the DVT-grown ZrS3 crystal at different cryogenic temperatures. It also includes anisotropy produced due to the layered growth of the TMC materials. Two types of contact arrangements were made to verify the anisotropic behaviour. The device was illuminated under light sources having different wavelengths (Blue-470 nm, Green-540 nm and Red-670 nm). It shows good stability under ambient conditions towards the variable wavelength source in both types of contact arrangements. The results indicate that ZrS3 is a potential candidate for optoelectronic devices even in uncommon conditions.

Ultra-high harmonic mode-locking with a micro-fiber knot resonator and Lyot filter.

We report on ultra-high harmonic mode-locking with a repetition rate of up to ∼1 THz by combining a microfiber knot resonator (MKR) and a Lyot filter. The harmonic mode-locked pulses are tunable by changing the diameter of MKR, which agrees well with the theoretical calculation. Our results indicate that the ultrafast pulse generation mechanism is due to the dissipative four-wave mixing mode-locking technique. This work provides a simple and efficient scheme to generate tunable ultrafast pulses with a high repetition rate for various applications, such as THz generation and ultrafast data communication.

Thulium-doped fiber laser mode-locked by nonlinear polarization rotation in a chalcogenide tapered fiber.

We demonstrate a thulium-doped fiber laser that is mode-locked thanks to nonlinear polarization rotation (NPR) in a chalcogenide tapered fiber. The high nonlinearity of the tapered fiber leads to a combined reduction in mode-locking threshold power and cavity length compared to any all-silica NPR based mode-locked lasers. In the continuous wave mode-locking regime, the laser generates stable, tunable solitons pulses. In the Q-switched mode-locked regime, it allows single and multiwavelength pulses, tunable central wavelength and tunable multiwavelength separation.

Long seed, short pump: converting Yb-doped laser radiation to multi-µJ few-cycle pulses tunable through 2.5-15 µm.

We present a setup for generating broadband (up to 1050 cm-1) and broadly tunable (2.5-15 µm) mid-infrared pulses using an Yb-doped femtosecond laser as the pump source. Our scheme, comprising two parametric amplifiers and a mixing stage, exploits favorable group velocity matching conditions in GaSe pumped at 2 µm to directly produce sub-70 fs pulses throughout the tuning range without any additional dispersion compensation, while 30-50 fs pulse durations are achieved with simple dispersion compensation by propagation through thin bulk media. The generated pulses have sub-1% short- and long-term energy noise, as well as stable spectral parameters, while delivering 0.5-2 W average mid-IR power. We expect the source to be useful for various spectroscopic applications in the mid-IR.

Extracellular vesicles derived from human Sertoli cells: characterizations, proteomic analysis, and miRNA profiling.

Extracellular vesicles (EVs) contain thousands of proteins and nucleic acids, playing an important role in cell-cell communications. Sertoli cells have been essential in the testis as a "nurse cell". However,EVs derived from human Sertoli cells (HSerCs) have not been well investigated. EVs were isolated from HSerCs via ultracentrifugation and characterized by transmission electron microscopy, tunable resistive pulse sensing, and Western blotting. The cargo carried by HSerCs-EVs was measured via liquid chromatography-mass spectrometry and GeneChip miRNA Arrays. Bioinformatic analysis was performed to reveal potential functions of HSerCs-EVs. A total of 860 proteins with no less than 2 unique peptidesand 88 microRNAswith high signal values wereidentified in HSerCs-EVs. Biological processes related to molecular binding, enzyme activity, and regulation of cell cycle were significantly enriched. Specifically, many proteins in HSerCs-EVs were associated with spermatogenesis and regulation of immune system, including Septins, Large proline-rich protein BAG6,Clusterin, and Galectin-1. Moreover, abundant microRNAs within HSerCs-EVs (miR-638, miR-149-3p, miR-1246, etc.) had a possible impact on male reproductive disorders such as asthenozoospermia and oligozoospermia. Our study has shown that HSerCs-EVs contain diverse components such as proteins and microRNAs. Further research is required to evaluate HSerCs-EVs in spermatogenesis, which are underutilized but highly potent resources with particular promise for male infertility.