Excellent Energy Stability Research Articles

Tunable electronic and optical properties of a type-II GaP/SiH van der Waals heterostructure as photocatalyst: A first-principles study

In this study, a novel GaP/SiH heterostructure was successfully predicted and constructed. Subsequently, an in-depth and systematic investigation was conducted to explore its structural, electronic, transport and optical properties. The calculated structural performance results revealed that the GaP/SiH heterostructure was a typical type-II van der Waals heterostructure, exhibiting excellent energy stability, mechanical stability and thermodynamic stability. In particular, the formation of the GaP/SiH heterostructure significantly reduced the bandgap of the materials to 2.24eV, and the type-II energy band arrangement effectively suppressed the recombination of photogenerated carriers. Furthermore, the biaxial and vertical strains could finely modulate the electronic structure of the GaP/SiH heterojunction. The electron mobility of the GaP/SiH heterostructure was measured to be 1573.91 cm2 V⁻1 s⁻1, indicating its superior charge carrier transport capabilities. Meanwhile, the GaP/SiH heterostructure also exhibited excellent optical absorption performance in the visible and UV region up to 2.34 × 106 cm−1. Thus, the GaP/SiH heterostructure will be a strong candidate for photocatalytic applications due to its excellent light absorption properties, electrical properties, and stability.

MX6C2H monolayers: The novel two-dimensional tunable Dirac cone materials family and quantum spin Hall insulators

Two-dimensional (2D) Dirac cone materials have many interesting physical properties. Therefore, people have been trying to find 2D materials with Dirac cones. Here, based on first principle calculations, we studied a new 2D Dirac cone material family MX6C2H monolayers (M = N,P,As and Sb, X = C,Si,Ge and Sn). The calculation of the cohesive energy indicated that the MX6C2H sheets have excellent energy stability. And the phonon spectrum showed their excellent dynamical stability. The electronic calculation revealed that the 2D MX6C2H monolayers have graphene-like band structures and ultra-high Fermi velocities comparable to graphene. The spin–orbit–coupling effect can open a sizable topological band gap in SbSn6C2H monolayer so that it can be effectively classified as quantum spin Hall insulators. In addition, the Dirac cone of PC6C2H monolayer can be adjusted by applying in-plane uniaxial strain, which is much easier than that of graphene. These interesting properties indicate that the novel 2D MX6C2H system has potential application value in nanoelectronics.

Spatio-spectral couplings in saturated collinear OPCPA.

Ultrafast laser pulses featuring both high spatio-temporal beam quality and excellent energy stability are crucial for many applications. Here, we present a seed laser with high beam quality and energy stability, based on a collinear optical parametric chirped pulse amplification (OPCPA) stage, delivering 46 µJ pulses with a 25 fs Fourier limit at 1 kHz repetition rate. While saturation of the OPCPA stage is necessary for achieving the highest possible energy stability, it also leads to a degradation of the beam quality. Using simulations, we show that spectrally dependent, rotationally symmetric aberrations dominate the collinear OPCPA in saturation. We experimentally characterize these aberrations and then remove distinct spatial frequencies to greatly improve the spectral homogeneity of the beam quality, while keeping an excellent energy stability of 0.2 % rms measured over 70 hours.

A Yb:YAG dual-crystal regenerative amplifier

An Yb:YAG dual-crystal regenerative amplifier was developed. The thermal effects were largely decreased by the dual-crystal configuration and optimized cavity design. The chirped pulse was amplified to 3.5 mJ with excellent energy stability (root mean square ∼0.95%) and beam quality (M2 < 1.1) at a repetition rate of 1 kHz using chirped pulse amplification (CPA) systems. A single space-saving simple-to-align chirped volume Bragg grating (CVBG) was used as a stretcher/compressor, which yielded 2-mJ pulses with a pulse duration of 1.9 ps after compression with an efficiency of 94.3%. A low-cost highly compact kilohertz high-energy ultrafast laser system solution was obtained.

High-stability, high-energy Nd:glass rod regenerative amplifier with compensation for cavity misalignment.

We report on an Nd:glass large-mode rod regenerative amplifier with a pulse energy of 125 mJ at 1053 nm. The amplifier contains a linear-type resonator, which is designed in Stability Zone II with a misalignment sensitivity factor of 12.9 m. A method is proposed for analyzing the sensitivity of the mode displacement on the gain media to cavity misalignment, and the optimum solution to compensation for cavity misalignment is obtained and applied to the amplifier. The amplifier exhibits excellent energy stability with a fluctuation of 0.47% (RMS) within 7 h and high spatial beam quality with M2=1.17. The beam pointing stability in the horizontal and vertical axes within 7 h is 2.7 and 3.6 µrad (RMS), respectively.

High-power few-cycle Cr:ZnSe mid-infrared source for attosecond soft x-ray physics

The development of mid-infrared, high-energy pulses of extremely short pulse duration is of great importance to the strong-field physics community, as it enables extension of the high-harmonic cutoff towards the keV range of photon energies. Here we demonstrate a C r 2 + : Z n S e laser amplifier delivering 7 mJ, 100 fs pulses at 1 kHz repetition rate and 2.4 µm central wavelength with excellent energy stability and beam quality. These pulses are post-compressed to 39 fs, 6.2 mJ, and 115 GW peak power in a novel nonlinear compression scheme. The laser system was used to generate coherent soft x-ray radiation up to 0.6 keV covering the entire water window, which is of high importance for bio-relevant applications. The obtained results open a wide range of applications in nonlinear optics, attosecond and strong-field physics, and remote sensing.

Off-axis eight-pass neodymium glass laser amplifier with high efficiency and excellent energy stability.

A new relay-imaged off-axial eight-pass laser amplifier with several joules energy and 1Hz repetition rate was demonstrated. The extraction efficiency and pulse-to-pulse energy stability were greatly improved. Under the single-pass small-signal gain of 3.6, a net gain of 900 and an effective extraction efficiency of 42.4% in the beam aperture were realized. Pulse-to-pulse energy stability of 0.83% (peak-valley) and 0.17% (root-mean-square) was achieved by the significant saturation of eight-pass amplification, which, to the best of our knowledge, is the best energy stability in several-joules-class amplifiers. The far-field quality was 2.52 times the diffraction limit, and the near-field modulation of the 90% beam aperture was 1.28. No parasitic oscillations or pencil beams were observed. Moreover, another key feature of the proposed amplifier was the ability to remarkably improve the pulse contrast with a unique design.

CO2-Tea pulse clipping using pulsed high voltage preionization for high spatial resolution I.R. Lidar systems

An extra-cavity CO2-TEA laser pulse clipper for high spatial resolution atmospheric monitoring is presented. The clipper uses pulsed high voltageto facilitate the breakdown of the gas within the clipper cell. Complete extinction of the nitrogen tail, that degrades the range resolution of LIDARS, is obtained at pressures from 375 up to 1500 Torr for nitrogen and argon gases whereas an attenuation coefficient of almost 102 is achieved for helium. Excellent energy stability and pulse width repeatability were achieved using high voltage pre-ionized gas technique.

A highly stable laser diode pumped cryogenic Yb:YAG nanosecond regenerative amplifier

A diode-pumped cryogenic-cooled nanosecond Yb:YAG regenerative amplifier based on the disk concept has been developed and used in a joule-class MOPA laser system. The output pulse energy is more than 11 mJ at a 10 Hz repetition rate at 163 K. An excellent energy stability of 1.8% fluctuations is achieved.

Ultrabroadband TW-class Ti:sapphire laser system with adjustable central wavelength, bandwidth and multi-color operation

We demonstrate a versatile tunable and highly stable ultrabroadband Ti:sapphire chirped pulse amplification system with a compressed pulse energy of 20 mJ at 100 Hz repetition rate. High power Ti:Sa systems in principle do not offer wavelength tunability due to gain narrowing. Here we demonstrate transform limited pulse generation from 15 fs to 94 fs with tunable central wavelength (λc from 755 nm to 845 nm) and bandwidth (130 nm<Δλ<16 nm) as well as multi-color, time synchronized, sub-100 fs pulses with user defined central wavelength separation. The unique wavelength tunability capabilities have been expanded into the UV and deep-UV by second and third harmonic generation with excellent energy stability. Enhanced energy stability is achieved by multiplexing six ultrastable diode-based solid state pump lasers.

High-energy, kHz-repetition-rate, ps cryogenic Yb:YAG chirped-pulse amplifier

We demonstrate amplification of picosecond laser pulses to 40?mJ at a 2?kHz pulse repetition frequency (PRF) from a two-stage cryogenic chirped-pulse Yb:YAG amplifier, composed of a regenerative amplifier (RGA) and a two-pass booster amplifier. The RGA produces 8.2mJ of energy at 2kHz PRF and 13.2mJ at 1kHz PRF with excellent energy stability (approximately 0.3% rms) and beam quality (M(2)<1.1). Pulse stretching and compression are achieved by using a chirped fiber Bragg grating and a multilayer dielectric grating pair, respectively. Compressed 15?ps pulses from the RGA are obtained with a throughput efficiency of approximately 80% (approximately 6.5 mJ for 2kHz). The booster amplifier further amplifies the pulses to 40mJ at 2kHz PRF, and approximately 32 mJ, approximately 15 ps pulses are expected after compression. The amplifier chain seeded from a femtosecond Yb-fiber laser enables the optical self-synchronization between signal and pump in optical parametric chirped-pulse amplifier applications.

Electrical activation and lattice location of B and Ga impurities implanted in Si

The aim of this work is to investigate the correlation between the electrical and structural properties of Si samples doped with B, Ga and B + Ga. The samples have been prepared by implanting the selected dopants into a Si layer previously amorphized by Si ion implantation. A thermal treatment at 550 °C has been used to recover the crystalline quality and to activate the implanted dopants. The lattice location of the implanted impurities has been determined by means of accurate channelling measurements, using standard RBS techniques and selected nuclear reactions for Ga and B, respectively. In particular the 11B(p,α) 8Be * nuclear reaction has been used to determine the B lattice location at 0.7 MeV proton energy. Analyses have been performed using an HVEE coaxial Cockroft–Walton singletron accelerator with a maximum terminal voltage of 3.5 MV and excellent energy stability over the entire accelerating voltage range, recently installed at the department of Physics (University of Catania). Hall mobility and carrier fluence have been measured and the latter has been compared to the B and Ga substitutional fluence.

Analysis of free electron laser performance utilizing the National Bureau of Standards’ cw mictrotron

The National Bureau of Standards’ (NBS) cw racetrack microtron (RTM) will be utilized as a driver for a free electron laser (FEL) oscillator. The NBS RTM possesses many exceptional properties of value for the FEL: (i) cw operation; (ii) energy from 20–185 MeV; (iii) small energy spread and emittance; (iv) excellent energy stability; and (v) high average power. The 1D FEL gain formula predicts that the FEL would oscillate at the fundamental approximately from 0.25–10 μm when upgrading the peak current to ≥2 A. In this paper, we present 3D self-consistent numerical results including several realistic effects, such as emittance, betatron oscillations, diffraction, and refraction. The results indicate that the design value of the transverse emittance is small enough that it does not degrade the FEL performance for intermediate to long wavelengths, and only slightly degrades the performance at the shortest wavelength under consideration. Due to the good emittance, the current density is high enough that focusing, or guiding, begins to manifest itself for wavelengths &amp;gt;2.0 μm.

A high stability vibrating wire profile monitor

The excellent energy stability of the electrostatic accelerator is in general not matched by the spatial stability of its emergent beam. This is usually of minor importance in a stand-alone environment but becomes a serious performance limitation in a coupled accelerator system. This work describes a particle beam profile monitor intended for use at beam levels of 10−9 A or greater as a sensing element in an active spatial stabilization system.

The three-stage tandem accelerator

The position of this new accelerator among the tools of nuclear physics is yet to be determined. Beam currents of 10 mA and energies as high as 30 MeV are probably achievable within the next ten years. The accelerator has all the advantages of constant voltage acceleration. Two forms of the accelerator are described, one with negative ion injection and the other with neutral beam injection. Of the two, neutral beam injection has not only the virtue of having been tried successfully but has the greatest potential for the future. The technical problems associated with the vacuum and ion optics are described and it is pointed out that from an initial 10 mA of positive ions a target current of 191 μA of energetic protons is theoretically possible. Tests with a three stage tandem accelerator are described which show the various loss mechanisms involved in the accelerator. A small beam of 0.3 mμA was obtained, however, at an energy of 15 MeV and with the excellent energy stability of ±1 in 100 000. Results of experiments in which a neutral helium beam was injected into a tandem accelerator are also mentioned. In conclusion it is shown that neither the vacuum nor the optical problem pose any insoluble problems. Current high vacuum techniques should insure pressures of 10−7 torr in the accelerator. Injection of a converging neutral beam should solve the optical problem and high currents will eventually be obtained.