Three-fold efficiency improvement via temporal and spatial pulse shaping in 3 μ m OPCPA

年 第 47 卷 第 3 期 目前影响高次谐波广泛应用的一个主要瓶颈 是它的光通量很低, 对于常用的 Ti:sapphire 激光 (800 nm) 而言谐波的转换效率通常小于 10 -5 [25][26][27] .若使用波长更长的红外激光可以有效提高光子的最 大能量 -截止位置, 但是转换效率急剧下降 (单原 子 ∼ λ -5 ).从实际应用的角度来看, 高次谐波的产生 需要解决以下几个问题 [28] : 提高转换效率、扩展截 止位置、选择性增强和抑制某阶或某一范围的谐波 (见图 1).实验中观察到的高次谐波通常都是在稠密的气 体中产生, 它不仅与单个原子在激光场中的响应 (诱 导偶极矩) 有关 [29]

Only recently researchers started to investigate the frequency conversion of high power picosecond pulses produced by regenerative amplification1. The high power densities easily achieved with short, pulses allow efficient generation of parametric fluorescence. However, experiments show that the efficiencies achieved in these systems are not as high as one would expect from a simple calculation, due to the temporal and spatial pulse shape, which has to be considered in a reasonably accurate model2,3. We performed calculations on the efficiency of the parametric conversion for various temporal and spatial pulse profiles and for different arrangements of a picosecond optical parametric generator (OPG) and optical parametric amplifier (OPA) combination. In the numerical simulation and the experiments we used a KTP crystal pumped with the fundamental of an all-solid-state Nd:YAG regenerative amplifier.

The use of laser beams made up of ultrafast pulses for the processing of materials can be bothered by the consequences of optical Kerr effect (OKE) cumulated by the propagation through optical devices (windows, laser crystal, prisms, lenses, …). The latter are mainly a reduction of the intensity in the focal plane accompanied by a distortion of the temporal and spatial pulse shape. We present a comparative study on such distortions for Gaussian, super-Gaussian and LG10 (one central peak surrounded by a ring) beams. It is demonstrated that the LG10 beam shows sensitivity to OKE which is smaller than that of the Gaussian LG00, and super-Gaussian beams. As a result, the focusing performances of the LG10 beam are quite superior to that observed with Gaussian or super-Gaussian beam: a higher on-axis intensity, a narrower intensity pattern, and a temporal shape and an energy fluence almost undistorted.

Ultrafast or ultrashort pulsed lasers have become integral in numerous industrial applications due to their high precision, non-thermal interaction with materials, and ability to induce nonlinear absorption. These characteristics have expanded their use in microfabrication, semiconductor processing, automotive engineering, and biomedical fields. Temporal pulse shaping reduces laser pulse durations, often to shorter timescales than many physical and chemical processes, enabling greater control. Meanwhile, spatial shaping improves efficiency and precision in micro- and nanofabrication and biomedical applications. Advances in optical parametric amplifiers (OPAs) and chirped-pulse amplifiers (CPAs) have allowed for more refined temporal and spatial shaping, ensuring the preservation of high peak power while achieving ultrashort pulse durations. Additionally, spatial light modulators (SLMs) have facilitated sophisticated beam shaping, which, when combined with ultrafast lasers, supports applications like computer-generated holography and nanoscale fabrication. These developments underscore the growing utility and versatility of ultrafast lasers in both research and industrial contexts.

The method for generating temporal flat-top waveform and spatial flat-top profile femtosecond pulse beam by phase and polarization controlling is proposed and demonstrated. Based on direct wave front phase modulating, flat-top spatial intensity distribution can be obtained. Combining a folded 4f zero-dispersion system with a polarization controlling setup, the temporal flat-top waveform is generated. Experimental results indicate that for the input both temporal and spatial Gaussian pulse beam with 363 fs temporal width and 1.5 mm beam waist, the temporal width of the output shaped pulse beam is 1.2 ps and 1.9mm beam waist, and the rms variation is about 9.2%, which prove that the temporal flat-top and spatial flat-top femtosecond pulse beam can be generated effectively.

A temporal femtosecond pulse shaping device, based on all-diffractive method, is designed for arbitrary waveform generation. The key components of the device are micro-gratings arranged in line. By changing the period and phase pattern of each grating, the diffraction angle, phase and amplitude of the first order diffraction light can be modulated. Experimental results are consistent well with simulation results, which indicate that arbitrary temporal waveforms can be gained by using micro-gratings array. Additionally, the configuration of the device allows for multiple outputs and can operate over a large wavelength range from ultraviolet to infrared pulse.

The conditions for the formation of a fully atomized laser-ablated plume using subpicosecond laser pulses have been studied theoretically and implemented experimentally. It is shown that the low-intensity wings, which generally exist in the spatial distribution of laser intensity in the focal plane and can contain a substantial part of the incident laser energy, are responsible for low-threshold phase transformations of the target and this is the major source of particulates in the ablated plume. By truncating these wings with a simple aperture and positioning the target in the image plane of that aperture, particulates can be eliminated from the plume. This is demonstrated in experiments on deposition of Si films using the truncated beam in combination with the proper choice of laser fluence. This results in an almost totally atomized plume and consequently in droplet-free deposition of thin films.

In this paper, we investigate the interaction between the three-level Λ-type quantum dot (QD)-based gain medium and the dipolar localized surface plasmon (LSP) mode of a silver nanoparticle. Previously, we demonstrated that a linearly chirped Gaussian pump pulse can enhance the peak value of the number of LSPs, provided there exists a detuning between the Gaussian pulse central frequency and the energy levels of QDs [ Phys. Rev. A 109 , 063505 ( 2024 ) PLRAAN 1050-2947 10.1103/PhysRevA.109.063505 ]. We explored both time-independent and time-harmonic detuning scenarios, elucidating their effects on the spaser emission. Expanding upon this work, here we present a study showcasing the impact of specially designed V- and Λ-shape chirped Gaussian pump pulses on stimulating the intense LSP. We conduct a comparative analysis of the spaser dynamics with differently shaped pump pulses: unchirped, linear chirped (both positive and negative), and specially designed Λ- and V-shape chirps. The study reveals that with time-independent detuning, a Gaussian pulse with a V-shape chirp performs better. Conversely, with harmonic time-dependent detuning, Λ-shape chirp is more effective for a certain noise frequency range.

Modeling and simulation of laser cleaning of tapered micro-slots with different temporal pulses

This paper presents recent proposals that have been made in the field of optical pulse shaping techniques based on the space-time duality, with an especial attention to their application for the design of encoder/decoder pairs in all-fibre Optical Code Division Multiple Access (OCDMA) systems. Two different proposals are presented, one based on an Optical Fourier Transformer using a dispersive media and the other based on the temporal self-imaging effect. Fiber Bragg Gratings are used as dispersive elements and electro-optic modulators for the amplitude or phase coding, allowing the electrical reconfiguration of the codes. Experimental results, both for coherent and incoherent schemes, are shown for the two systems transmitting at data rates of 1.25 Gbps and 10 Gbps respectively with a fixed codification rate of 10 Gcps and using a subset of the Hadamard codes with a length of 8 chips.

Electron sources play a crucial role in electron microscopes, particle accelerators and novel light sources. In most cases, the electron source parameters determine the downstream parameters because it is non-trivial to compress or cool electron pulses. For many applications requiring transversely coherent electrons, needle tips have been the preferred electron source for decades, well-known in high-resolution electron microscopy. Recently, these sources have found significant interest in ultrafast applications, where electron pulses are emitted through the illumination of a needle tip with femtosecond laser pulses. We will give an overview of recent developments in ultrafast needle tip-based electron sources. In addition, we will show how the interaction of laser pulses with electron pulses downstream of the source element can help to shape electron beams with highly intriguing properties, such as attosecond pulses, high-energy beams or electron pulses with small energy widths. The most promising approach to accelerate and shape the electron pulses is based on near-field techniques, which, depending on the parameter range, can either be classified as dielectric laser acceleration or photon-induced near-field electron microscopy physics. Finally, we will provide details of the state-of-the-art in two-photon or ponderomotive schemes for temporal electron pulse shaping, before concluding this chapter with a brief review of applications and future outlook.

Mode locking with an antiresonant ring is a powerful technique for producing stable trains of ultrashort pulses. This structure1 was first applied to visible dye lasers by placing a saturable absorber within an antiresonant ring that forms the high-reflectivity end mirror of a linear laser cavity. Nearly transform-limited 65 fs pulses have been generated with enhanced pulse stability.2 By using the additive pulse mode-locking (APM) representation, we describe the antiresonant ring (ARR) as a pulse-shaping reflector, which returns a temporally narrowed pulse to the main laser cavity. When a nonlinear element is incorporated within the ARR, an intensity-dependent reflectivity is predicted. A nonlinear element introduces temporal or spectral pulse shaping of the two counterpropagating fields within the ring. If the pulse shaping is unbalanced for the two fields, then preferential reflection of the high-intensity portions of the incident pulse can occur, resulting in a temporally narrowed pulse being returned to the laser gain medium. Results will be presented for a saturable absorber, a saturable amplifier, and a Kerr-type nonlinearity, such as an optical fiber.

A proposed system of extremely narrow multisoliton pulse generation is presented. A PANDA system can be used to create signals in the form of chaotic noise inserted into an add/drop system. The capacity of the output signals can be improved by generation of multisoliton pulses with pulse width (FWHM) and free spectrum range (FSR) of picometres and picoseconds size. Multisoliton of dark and bright can be generated and propagated within the system. This system can be used to improve the scribing of the micro channels or the solar cell thin films. Using the ultra-short laser pulses, the micro channels with exact depths and well-defined outlines can be generated and fabricated without causing any damage to the ultra-thin-film solar cells. Results obtained show that controlling of the signals can be performed when the additional Gaussian laser pulse is used in the add port of the nonlinear system. In this work high capacity of narrow spatial and temporal multisoliton pulse with FWHM of 5 pm and 2.6 ps and FSR of 190 pm and 101 ps were simulated respectively where the central wavelength of the input power was selected to 1.55m.

Ultrashort near-infrared femtosecond laser pulses have become the tool of choice for high-precision processing of transparent ultrawide bandgap materials, ranging from material ablation, amorphization, waveguide writing to optical data storage. The processing precision with ultrashort laser pulses is fundamentally limited in the lateral direction by diffraction, while self-absorption and self-reflection are limiting the achievable depth. In this chapter, we present one of the possible pathways to overcome these limits by utilizing temporal pulse-shaping technology. In the following, we review and discuss the main light-matter interaction mechanisms, multiphoton and avalanche excitation, and how ultrashort and temporally shaped femtosecond laser pulses address them differently, allowing the control over the spatial carrier distribution and the subsequent material processing. We demonstrate the potential of temporal pulse shaping as a tool for controlled nanostructuring below the typical limits by discussing our in situ and postmortem experimental and numerical studies on the spatial distribution of laser excitation in water, high-aspect-ratio structuring of fused silica, and the optoporation of cells.

We report on the design, fabrication, and testing of ferroelectric patterned materials in the guided-wave and polaritonic regime. We demonstrate their functionality and exploit polariton confinement for amplification and coherent control using temporal pulse shaping.