Optical Cycles Research Articles

Sub-6 optical-cycle Kerr-lens mode-locked Tm:Lu2O3 and Tm:Sc2O3 combined gain media laser at 2.1 μm.

We present a combined gain media Kerr-lens mode-locked laser based on a Tm:Lu2O3 ceramic and a Tm:Sc2O3 single crystal. Pulses as short as 41 fs, corresponding to less than 6 optical cycles, were obtained with an average output power of 42 mW at a wavelength of 2.1 μm and a repetition rate of 93.3 MHz. Furthermore, a maximum average power of 316 mW with a pulse duration of 73 fs was achieved.

Electron Dynamics and Thomson Scattering for Ultra-Intense Lasers: Elliptically Polarized and OAM Beams

We investigated the classical nonlinear Thomson scattering (TS), from a single relativistic electron, generated by either: (a) an incoming plane wave monochromatic laser radiation and general elliptical polarization or (b) incoming radiations with intrinsic orbital angular momentum (OAM). Both (a) and (b) propagate along the z direction, with wave vector k0, frequency ω0, and initial phase φ0≠0 and have any intensity. Item (a) enables obtaining general electron TS Doppler frequencies and other quantities, for fusion plasmas. We explored the possibility of approximating nonlinear TS with OAM beams (Item (b)) by means of nonlinear TS with plane wave beams (Item (a)). For Item (a), a general explicit solution of the Lorentz relativistic equation and the subsequent TS are given in terms of ζ=ω0t−k0z (t denoting time). In particular, it includes the cases for linear and circular polarizations and φ0≠0 for fusion plasmas, thereby extending previous studies for φ0=0. The explicit solutions give rise to very efficient computations of electron TS Doppler frequencies, periods of trajectories, and drift velocities, and the comparisons with ab initio numerical solutions (for Item (a)) yield an excellent match. The approximate approach, using explicit solutions for Item (a), towards TS OAM (employing ab initio numerical computations for Item (b)), extending previously reported ones) yields a quite satisfactory agreement over time spans including several optical cycles, for a wide range of laser intensities, polarizations, and electron energies. The role of φ0≠0 was analyzed. A simple quantitative criterion to predict whether the agreement between the two approaches (a) and (b) would be observed over a given time span is discussed.

Experimental Optical Properties of Single-Photon Emitters in Aluminum Nitride Films

Single-photon emitters (SPEs) are one of the building blocks in quantum information processing. Here, we report detailed experimental optical properties of the SPEs in aluminum nitride (AlN) films at 10 K. The high-quality AlN films are grown by metal–organic chemical vapor deposition on graphene/sapphire substrates, which can conquer the large lattice and thermal mismatches between the sapphire and AlN. We report the defects in AlN with a relatively high Debye–Waller factor up to ∼29% and near-perfect linear polarization SPEs with a saturation count rate of 1.43 × 10⁶ counts/s. The power-dependent second-order autocorrelation measurements are used to study the transition kinetics, which can be described using a three-level model. The polarization measurements of absorption and emission reveal the optical cycle mechanism, where a particular zero-phonon line may be excited via multiple mechanisms. This work provides some insight into the nature of the optical properties and energy-level structures of AlN defects, which pave the way to integrated on-chip quantum photonics.

Dispersive mirror characterization and application for mid-infrared post-compression

This paper presents a second harmonic assisted spectrally resolved interferometric technique that can overcome the limited spectral resolution of commercially available spectrometers in the mid-infrared. The discussed scheme was validated by measuring the group delay of several well-known and frequently used materials. Our main motivation was to characterize the spectral phase shift of newly designed and manufactured dispersive mirrors to be used for mid-infrared (MIR) post-compression. These mirrors were successfully implemented in the post-compression stage of our MIR laser system, where pulse duration was shortened below two optical cycles and the pulse peak power increased by 30.3% compared to the original output.

Multifunctional modified polylactic acid nanofibrous scaffold incorporating sodium alginate microspheres decorated with strontium and black phosphorus for bone tissue engineering

Polylactic acid (PLA) nanofibrous scaffolds have received extensive attention in the field of tissue engineering due to their excellent degradability, biocompatibility and the biomimetic extracellular matrix (ECM) topographies. However, the cell affinity and osteogenic activity of PLA scaffolds is not satisfactory because of their intrinsic hydrophobicity, the absence of cell recognition sites and the nucleation sites of the in vivo biomineralization. Furthermore, effective anti-inflammatory activity for the in vivo scaffold could not be ignored, so a strategy to develop a multifunctional PLLA (poly-L-lactic acid) nanofibrous scaffold with improved hydrophilicity, osteoinductivity, excellent near-infrared photothermal-responsive drug release capacity and anti-inflammatory activity via incorporating sodium alginate microspheres decorated with strontium and ibuprofen-loaded black phosphorus (BP + IBU@SA microspheres) into aminated modified PLLA nanofiber network is proposed in this study. Scanning electron microscopy (SEM) observation showed that the BP + IBU@SA microspheres were homogeneously dispersed into the modified PLLA matrix with uniform nanofiber structure and the chemical composition of the as-prepared scaffolds was confirmed by X-ray diffraction analysis (XRD) and elemental mapping. The photothermal property of the scaffolds was assessed under near-infrared (NIR) light irradiation, the results manifested that the entrapment of BP nanosheets endowed PLLA nanofibrous scaffold with significantly high photothermal conversion efficiency and optical cycle stability. Meanwhile, the scaffold also displayed an excellent photothermal-responsive intelligent drug release performance toward Sr2+ and ibuprofen. Moreover, the in vitro studies revealed that the as-developed scaffolds possessed a good biocompatibility for cell adhesion and proliferation and an improved bioactivity to induce apatite formation. All these results indicated the potential of the fabricated scaffolds in tissue engineering applications.

Sub-five-optical-cycle pulse generation from a Kerr-lens mode-locked Yb:CaYAlO4 laser.

Direct generation of ultrashort few-optical-cycle pulses in various wavelength regions has attracted great attention in recent decades. In this paper, generation of less than five-optical-cycle pulses from a Kerr-lens mode-locked ${\rm Yb}{:}{\rm CaYAlO}_4$ laser is demonstrated. Pumped by a 976 nm fiber laser, stable near-Fourier-transform-limited ultrashort soliton pulses centered around 1080 nm with a repetition rate of ${\sim}{113.7}\;{\rm MHz}$ were obtained. The obtained pulses have a pulse duration as short as 17 fs if a ${{\rm Sech}^2}$-shaped pulse profile is assumed, corresponding to about 4.68 optical cycles. To the best of our knowledge, this is the shortest pulse directly generated from mode-locked rare-earth-doped solid-state oscillators.

Research on Smart Mattress Based on Fiber Unbalanced Sagnac Loop

Because the contact vital sign detection system is monitored through skin contact, it affects the user’s comfort and causes inconvenience. And most of the non-contact equipment is not high precision, or the cost is too high. To solve the above problems, this article is based on the physiological activity of slight vibration in multimode optical fiber micro bending deformation which result in the change of light intensity principle, considering the structure of the optical fiber Sagnac loop sensor has simple structure, low cost, but the signal to noise ratio is poor and is not sensitive to low frequency signal, this paper designed a based on intelligent mattress of non-equilibrium sagnac loop structure. The mattress can obtain the heart impact map signal in real time by changing the small light intensity, and obtain the heart rate, respiration rate and other information through the algorithm processing the signal. Mattress in the design of the sensing optical fiber module will be connected to two different types of optical fiber of Unbalanced Sagnac loop structure, solve the balance Sagnac loop structure of optical fiber access signal noise is bigger, poor sensitivity were weakness, go through the serpentine line way of embedded mattress, and using the mattress cover material for optical fiber micro bending cycle critical mechanical adjustment cycle, the mattress is of high sensibility. Cardiac and respiratory signals obtained in the laboratory were compared with those obtained from the balanced Sagnac loop, and through the fast Fourier transform (FFT) in frequency domain signal is analyzed, the vital signs of signal more clearly this mattress stable and less noise, change the tester for many times after tests, get the signal of high accuracy, the error is very small. The experiment shows that the mattress can realize the non-sensory vital signs signal detection, convenient for users to monitor their physical conditions in real time in daily work and life, and can timely notify the family members and medical staff in emergency, to avoid the occurrence of accidents.

1.9 μm Few-Cycle Pulses Based on Multi-Thin-Plate Spectral Broadening and Nonlinear Self-Compression

In attosecond and strong-field physics, the acquisition of few-cycle laser sources open up a new area. We report a nonlinear pulse compression technology combining multi-thin-plate spectral broadening and nonlinear self-compression that generates a 0.52 mJ, good spatial quality characteristics and a spectral bandwidth supporting a 14 fs Fourier transform limited duration at 1 kHz repetition rate and at a center wavelength of 1.9 μm. The total energy transfer efficiency is up to 83%. Pulse to pulse stability of the energy output is 0.7% (RMS). The pulse duration is near 3 optical cycles. This pulse compression approach can be a key-enabling technology for the next generation of extreme photonics, attosecond research and coherent x ray-science, and it also can be further extended to mid-infrared lasers with longer wavelengths and higher peak power.

17.8 fs broadband Kerr-lens mode-locked Yb:CALGO oscillator.

Pulses as short as 17.8 fs with a spectral bandwidth of 145 nm and central wavelength of 1118 nm have been generated from a Kerr-lens mode-locked Yb:CALGO oscillator. The oscillator operating at an average power of 26 mW and a repetition rate of 95.9 MHz is pumped by a cost-effective single-mode fiber coupled laser diode emitting 800 mW at 976 nm. The dispersion is compensated using a prism pair combined with broadband chirp mirrors. To the best of our knowledge, the pulse durations corresponding to approximately 4.8 optical cycle pulses are the shortest achieved durations through a Yb-doped bulk oscillator.

Franck-Condon Tuning of Optical Cycling Centers by Organic Functionalization.

Laser induced electronic excitations that spontaneously emit photons and decay directly to the initial ground state ("optical cycling transitions") are used in quantum information and precision measurement for state initialization and readout. To extend this primarily atomic technique to large, organic compounds, we theoretically investigate optical cycling of alkaline earth phenoxides and their functionalized derivatives. We find that optical cycle leakage due to wave function mismatch is low in these species, and can be further suppressed by using chemical substitution to boost the electron-withdrawing strength of the aromatic molecular ligand through resonance and induction effects. This provides a straightforward way to use chemical functional groups to construct optical cycling moieties for laser cooling, state preparation, and quantum measurement.

Carbon dopants carriers facilitators as agents for improving hole extraction efficiency of cobalt tetraoxide nanoparticles employed in fabrication of photodetectors

(CH3NH3)3Bi2I9 perovskites have attracted enormous attention due to their lower toxic and more stable nature than CH3NH3PbI3 counterparts. However, higher bandgap and lower carrier mobility hinder the application of (CH3NH3)3Bi2I9 in optoelectronics. Hence, we employed carbon doping of Co3O4 hole extractors to reduce the bandgap of (CH3NH3)3Bi2I9, minimize non – radiative recombination rate and improve surface morphology of the (CH3NH3)3Bi2I9 particles. Consequently, photodetectors based on carbon-doped Co3O4 display reduced internal resistance, high photocurrent and low dark current values. The fabricated photodetectors display high responsivity (1.56 × 106 μA/W), high detectivity (5.74 × 1012 Jones), high sensitivity (8.23 × 103) and fast optical switching times (< 10 ms) values under device testing conditions of 2.0 V bias voltage, 10 mW/cm2 power intensity of solar illumination and ambient room conditions. The linearity and stability of the photodetectors over wide range of light intensities and 100 optical switching cycles were also demonstrated respectively.

Numerical and laboratory attoclock simulations on noble-gas atoms

We conduct a systematic theoretical study of strong field tunneling ionization of noble-gas atoms, from He to Kr, by elliptically polarized laser pulses in the so-called attoclock setup. Our theoretical model is based on a numerical solution of the time-dependent Schr\"odinger equation in the single active electron approximation. We simulate laboratory measurements utilizing few optical cycle pulses to benchmark our calculations against experiment. We further conduct ``numerical attoclock'' simulations with short, nearly single-cycle pulses to test various tunneling ionization models. We examine the attoclock offset angles as affected by the target orbital structure and the laser pulse intensity. Finally, we exclude a finite tunneling time scenario and attribute the attoclock offset angle entirely to the Coulomb field of the ion remainder as was recently demonstrated for the hydrogen atom [U. S. Sainadh et al., Nature (London) 568, 75 (2019)].

Ultrashort high energy electron bunches from tunable surface plasma waves driven with laser wavefront rotation.

We propose to use ultrahigh intensity laser pulses with wave-front rotation (WFR) to produce short, ultraintense surface plasma waves (SPW) on grating targets for electron acceleration. Combining a smart grating design with optimal WFR conditions identified through simple analytical modeling and particle-in-cell simulation allows us to decrease the SPW duration (down to a few optical cycles) and increase its peak amplitude. In the relativistic regime, for Iλ_{0}^{2}=3.4×10^{19}W/cm^{2}μm^{2}, such SPW are found to accelerate high charge (few 10s of pC), high energy (up to 70 MeV), and ultrashort (few fs) electron bunches.

Enhanced Pulse Compression within Sign-Alternating Dispersion Waveguides

We show theoretically and numerically how to optimize sign-alternating dispersion waveguides for maximum nonlinear pulse compression, while leveraging the substantial increase in bandwidth-to-input peak power advantage of these structures. We find that the spectral phase can converge to a parabolic profile independent of uncompensated higher-order dispersion. The combination of an easy to compress phase spectrum, with low input power requirements, then makes sign-alternating dispersion a scheme for high-quality nonlinear pulse compression that does not require high powered lasers, which is beneficial for instance in integrated photonic circuits. We also show a new nonlinear compression regime and soliton shaping dynamic only seen in sign-alternating dispersion waveguides. Through an example SiN-based integrated waveguide, we show that the dynamic enables the attainment of compression to two optical cycles at a pulse energy of 100 pJ which surpasses the compression achieved using similar parameters for a current state-of-the-art SiN system.

High signal to noise absorption imaging of alkali atoms at moderate magnetic fields.

We present an improved scheme for absorption imaging of alkali atoms at moderate magnetic fields, where the excited state is well in the Paschen-Back regime, but the ground state hyperfine manifold is not. It utilizes four atomic levels to obtain an approximately closed optical cycle. With the resulting absorption of the corresponding two laser frequencies, we extract the atomic column density of a 39K Bose-Einstein condensate. The scheme can be readily applied to all other alkali-like species.

Compact high-flux hard X-ray source driven by femtosecond mid-infrared pulses at a 1 kHz repetition rate.

A novel, to the best of our knowledge, table-top hard X-ray source driven by femtosecond mid-infrared pulses provides 8 keV pulses at a 1 kHz repetition rate with an unprecedented flux of up to 1.5×1012 X-ray photons/s. Sub-100 fs pulses at a center wavelength of 5 µm and multi-millijoule energy are generated in a four-stage optical parametric chirped-pulse amplifier and focused onto a thin Cu tape target. Electrons are extracted from the target and accelerated in a vacuum up to 100 keV kinetic energy during the optical cycle; the electrons generate a highly stable K α photon flux from the target in a transmission geometry.

Replication-Related Control Over Cell Division in &lt;i&gt;Escherichia Coli&lt;/i&gt; is Growth-Rate Dependent

How replication and division processes are coordinated in the cell cycle is a fundamental yet poorly understood question in cell biology. In Escherichia coli different data sets and models have supported a range of conclusions from one extreme where these two processes are tightly linked to another extreme where these processes are completely independent of each other. Using high throughput optical microscopy and cell cycle modeling, we show that in slow growth conditions replication and division processes are strongly correlated, indicating a significant coupling between replication and division. This coupling weakens as the growth rate of cells increases. Our data suggest that the underlying control mechanism in slow growth conditions is related to unreplicated chromosome blocking the onset of constriction at the midcell. We show that the nucleoid occlusion protein SlmA does not play a role in this process and neither do other known factors involved in positioning bacterial Z-ring relative to the chromosome. Altogether this work reconciles different ideas from the past and brings out a more nuanced role of replication in controlling the division process in a growth-rate dependent manner.

SESAM mode-locked Tm:LuYO3 ceramic laser generating 54-fs pulses at 2048 nm.

Mode-locked laser operation near 2.05 µm based on a mixed sesquioxide Tm:LuYO3 ceramic is demonstrated. Continuous-wave and wavelength-tunable operation is also investigated. Employing a GaSb-based semiconductor saturable absorber mirror as a saturable absorber, a maximum average output power of 133 mW is obtained for a pulse duration of 59 fs. Pulses as short as 54 fs, i.e., eight optical cycles are generated at a repetition rate of ∼78MHz with an average output power of 51 mW. To the best of our knowledge, this result represents the shortest pulse duration ever achieved from Tm-based solid-state mode-locked lasers.

Single-Cycle Optical Control of Beam Electrons.

We report the single-cycle optical control of a freely propagating electron beam with an isolated cycle of midinfrared light. In particular, we produce and characterize a modulated electron current with peak-cycle-specific subfemtosecond structure in time. The direct effects of the carrier-envelope phase, amplitude, and dispersion of the optical waveform on the temporal composition, pulse durations, and chirp of the free-space electron wave function demonstrate the subcycle nature of our control. These results and concept may create novel opportunities in free-electron lasers, laser-driven particle accelerators, ultrafast electron microscopy, and wherever else high-energy electrons are needed with the temporal structure of single-cycle light.

Multi-millijoule, few-cycle 5 µm OPCPA at 1 kHz repetition rate.

A table-top midwave-infrared optical parametric chirped pulse amplification (OPCPA) system generates few-cycle pulses with multi-10 GW peak power at a 1 kHz repetition rate. The all-optically synchronized system utilizes ZnGeP2 nonlinear crystals and a highly stable 2 µm picosecond pump laser based on Ho:YLiF4. An excellent energy extraction is achieved by reusing the pump pulse after the third parametric power amplification stage, resulting in 3.4 mJ idler pulses at a center wavelength of 4.9 µm. Pulses as short as 89.4 fs are achieved, close to only five optical cycles. Taking into account the pulse energy, a record high peak power of 33 GW for high-energy mid-IR OPCPAs beyond 4 µm wavelength is demonstrated.