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Imaging multiple Rydberg wave packets from shaper-generated two-color femtosecond pump-probe sequences
摘要： We combine a bichromatic white light polarization pulse shaping scheme with angle- and energy-resolved photoelectron spectroscopy to image the dynamics of atomic Rydberg wave packets. Background-free detection of the Rydberg dynamics is performed using shaper-generated bichromatic linearly and circularly polarized femtosecond pump-probe pulse sequences. Photoelectron momentum distributions from linearly polarized bichromatic fields feature pronounced time-, energy-, and angle-dependent dynamics, which result from the interference of s-, d-, and g-type photoelectron wave packets from the ionization of the Rydberg np and nf series. Detailed analysis of the highly differential data allows us to extract the dynamics of both Rydberg wave packets separately. The results are experimentally verified by additional pump-probe studies with bichromatic circularly polarized pulse sequences, which exclusively map the dynamics of the Rydberg nf series via g-type photoelectron wave packets.
关键词： Rydberg wave packets,pump-probe spectroscopy,photoelectron imaging,femtosecond lasers,polarization pulse shaping
更新于2025-09-23 15:23:52
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Enhancing Perovskite Solar Cell Performance through Femtosecond Laser Polishing
摘要： Nonradiative recombination loss is a key process that determines the performance of perovskite solar cells, and how to control it is significant for the research and development of perovskites. Generally, traditional chemical modification/passivation methods are complicated and prone to secondary contamination. Here, we demonstrate femtosecond (fs) laser polishing as a promising technique to ameliorate the surface of perovskite films, to reduce nonradiative recombination loss and improve solar cell performance. The high-intensity fs laser pulses can remove around 20-nm thick perovskite top-layer through ionization process, help to decrease the grain boundary density and enlarge the grain size of perovskite films after recrystallization. We believe that fs laser polishing is a time-effective and highly precise technique which is suitable for large-scaled device production, thus will trigger more applications in optoelectronics.
关键词： femtosecond lasers,perovskites,recombination,passivation,solar cells
更新于2025-09-23 15:21:01
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Non-Fourier Estimate of Electron Temperature in Case of Femtosecond Laser Pulses Interaction with Metals
摘要： This work is devoted to the electron temperature variation in metals through interaction with femtosecond laser pulses. Our study was inspired by the last mathematical breakthroughs regarding the exact analytical solutions of the heat equation in the case of flash laser-matter interaction. To this purpose, the classical Anisimov’s two temperature model was extended via the 3D telegraph Zhukovsky equation. Based upon this new approach, the computational plots of electron thermal fields during the first laser pulse interaction with a gold surface were inferred. It is shown that relaxation times and coupling factors over electron thermal conductivities (g/K) govern the interaction between the laser pulse and metal sample during the first picoseconds. The lower the factor g/K, the higher the electron temperature becomes. In contrast, the lower the relaxation time, the lower the electron temperature.
关键词： two temperature model,3D telegraph equation,femtosecond lasers-metal interaction,metals
更新于2025-09-23 15:21:01
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Fabrication of Tapered Circular Depressed-Cladding Waveguides in Nd:YAG Crystal by Femtosecond-Laser Direct Inscription
摘要： Crystalline materials are excellent substrates for the integration of compact photonic devices bene?ting from the unique optical properties of these materials. The technique of direct inscription with femtosecond lasers, as an advantage over other techniques, has opened the door to the fabrication of true three-dimensional (3D) photonic devices in almost any transparent substrate. Depressed-cladding waveguides have been demonstrated to be an excellent and versatile platform for the integration of 3D photonic circuits in crystals. Here, we present the technique that we have developed to inscribe tapered depressed-cladding waveguides with a circular section for the control of the modal behavior. As a proof of concept, we have applied the technique to fabricate structures in Nd:YAG crystal that e?ciently change the modal behavior from highly multimodal to monomodal, in the visible and near infrared, with reduction factors in the waveguide radius of up to 4:1. Our results are interesting for di?erent devices such as waveguide lasers, frequency converters or connectors between external devices with di?erent core sizes.
关键词： femtosecond lasers,crystalline dielectrics,photonic device,micro-processing,waveguide
更新于2025-09-23 15:19:57
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Nonlinear compression of high-power laser pulses: compression after compressor approach
摘要： The peak power of present-day lasers is limited by the pulse energy that the diffraction gratings of an optical compressor can withstand. A promising method to overcome this limitation is reviewed: the pulse power is increased by shortening its duration rather than increasing the pulse energy, the pulse being shortened after passing a compressor (Compression after Compressor Approach (CafCA)). For this purpose, the pulse spectrum is broadened as a result of self-phase modulation, and the pulse is then compressed by dispersion mirrors. Application of this idea, known since the 1960s, to lasers whose power is over 1 TW has been restrained until recently by a number of physical problems. These problems and possible methods to solve them are discussed in detail. The experimental results obtained over the past few years demonstrate the efficiency of the technique (compression by a factor of 5) in the range up to 250 TW. CafCA features three undisputed merits: simplicity and low cost, negligible loss of pulse energy, and applicability to any high-power laser.
关键词： nonlinear laser pulse compression,ultrahigh power femtosecond lasers,phase self-modulation,small-scale self-focusing
更新于2025-09-19 17:13:59
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Advances in Ultrafast Optics || 1. Ultrafast ultrahigh-intensity laser pulses
摘要： Generation of high intensity laser pulses has been regarded as one of the most important research topics since the invention of lasers. High intensity lasers are normally constructed using the master oscillator power amplifier (MOPA) configuration to boost the energy of short laser pulses. This configuration has been used in various locations such as the Shenguang facilities in China and the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL) in the USA; the latter is currently the largest laser facility in the world. This type of giant laser facility is usually employed for high-cost and large-scale scientific projects involving complex technology and only a few countries can perform this type of laser research. Because of the low repetition rate and long pulse duration of the achieved laser pulses, these laser facilities are not suitable for large-scale applied research. Furthermore, the output laser intensity is limited. For example NIF, constructed in 2009, includes 192 ultraviolet (UV) beams with the total energy up to 1.8 megajoules (MJ, 106 J). However, the peak power is only approximately 500 terawatts (TW; 1012 W) [1] because the pulse duration is at the nanosecond (ns; 10?9 s) level; the separation time between two pulses is as long as a few hours. At the other end of the scale, several research institutes have developed tabletop laser systems within regular-scale labs through the amplification of ultrashort-pulse lasers at the femtosecond (fs; 10?15 s) level. These lasers have peak powers at the petawatt (PW; 1015 W) level [2–4], a repetition rate of 1 hertz (Hz) [5], and a focus intensity reaching 1022 W/cm2 [6]. As a result of the 1991 discovery of the Kerr-lens mode-locking (KLM) phenomenon by the Sibbett group in the UK [7], along with the development of chirped pulse amplification (CPA) technology by the US-based Mourou group in 1985 [8], and research on ultrashort pulses, ultrahigh-intensity lasers have been advancing at an unprecedented pace since the late 1980s. New scientific records associated with significant breakthroughs have been made on a continuous basis. Ultrashort-pulse laser research has developed in two explorative directions. One path of development targets extremely short pulse duration promoted by mode-locking technology. Currently, laser pulse duration can reach the few-cycle level; in addition, attosecond (as; 10?18 s) laser pulses can be achieved using new physical mechanisms [9–11]. The second research trend is the ongoing extension of the laser peak power limit. An increasing number of femtosecond ultrahigh-intensity laser facilities with peak powers at the terawatt or even petawatt level have been developed [2–5], serving as powerful tools for in-depth research on ultrafast, ultrahigh-intensity laser pulses. Ultrashort pulses and ultrahigh-intensity laser technology are not only extensively employed in the fields of micromanufacturing [12–14] and medicine [15, 16] but have also been successfully and prominently implemented in various research areas, such as the exploration of atomic and molecular motion patterns [17, 18], laboratory simulations in astrophysics [19], and precision spectroscopy [20]. These applications have facilitated the emergence of many new subfields and groundbreaking scientific achievements. One of the two most representative events was the award of the 1999 Nobel Prize in Chemistry to the American researcher, Prof. A. H. Zewail. This prize was awarded for work on chemical kinetics using femtosecond laser pulses. The second representative achievement was the joint sharing of one half of the 2005 Nobel Prize in Physics by Profs. J. L. Hall and T. W. H?nsch; this prize was awarded for their achievements regarding the femtosecond laser frequency comb technique. With state-of-the-art features and innovative applications, ultrashort pulses, ultrahigh-intensity lasers have become crucial tools in the field of optical physics. Therefore, this chapter will first briefly review the essential technology and associated progress in research.
关键词： ultrahigh-intensity lasers,femtosecond lasers,laser technology,Kerr-lens mode-locking,petawatt lasers,optical physics,chirped pulse amplification,ultrafast lasers
更新于2025-09-16 10:30:52
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Use of heavily doped germanosilicate fibres with a small core diameter in stretchers of ultrashort laser pulses at a wavelength of 1.03 μm
摘要： The use of a heavily doped germanosilicate fibre with a W-profile refractive index and small core diameter in stretchers of ultrashort laser pulses with their subsequent amplification and compression in all-fibre laser systems is considered. The application of fibres of this type makes it possible to stretch, amplify, and then compress a laser pulse with minimum distortions of its initial shape and width. Due to the dispersion properties of these fibres, which allow the pulse duration to be increased significantly at a small fibre length and the third-order positive dispersion of the diffraction-grating-based output compressor to be compensated for, amplified pulses with an energy of 2 mJ and width of 250 fs, free of a picosecond pedestal, are obtained. Several types of fibres intended for the use in stretchers of ultrashort laser pulses are comparatively analysed from the point of view of their dispersion compatibility with a diffraction-grating-based output compressor.
关键词： nonlinear self-phase modulation,fibre lasers,heavily doped germanosilicate fibre,group-velocity dispersion,femtosecond lasers,amplification of ultrashort laser pulses
更新于2025-09-16 10:30:52
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Asymmetric magnetic reconnection driven by ultraintense femtosecond lasers
摘要： Three-dimensional asymmetric magnetic reconnection (AMR) driven by ultraintense femtosecond (fs) lasers is investigated by relativistic particle-in-cell (PIC) simulation. The reconnection rate is found to be only one-third of that in the previous symmetric reconnection PIC simulations. Similar to the case of dayside reconnection at geomagnetopause, magnetic X- and velocity stagnation points are not colocated, with the X-point at the lower ?eld side and the stagnation point at the higher ?eld side. Moreover, the moving direction of the X-point as reconnection evolving with the laser irradiation is determined by dBH=dBL, and the moving of stagnation point is dominated by neHBL=neLBH, where dB and ne are the magnetic ?eld disturbance and the electron density with the subscripts “H” for the higher ?eld side and “L” for the lower ?eld side, respectively. Then, the hosing instability triggered by AMR and the merging of two parallel currents resulting in the tilt of the electron beam generated by the weak laser are also investigated.
关键词： hosing instability,particle-in-cell simulation,reconnection rate,ultraintense femtosecond lasers,asymmetric magnetic reconnection
更新于2025-09-16 10:30:52
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Double-Track Waveguides inside Calcium Fluoride Crystals
摘要： Calcium Fluoride (CaF2) was selected owing to its cubic symmetry and excellent luminescence properties as a crystal of interest, and ultrafast laser inscription of in-bulk double-track waveguides was realized. The guiding properties of these waveguides in relation to the writing energy of the femtosecond pulse are presented. The modified double-track waveguides have been studied by systematic developments of beam propagation experiments and numerical simulations. Furthermore, an adapted model and concepts were engaged for the quantitative and qualitative characterization of the waveguides, particularly for the transmission loss measurements and the three-dimensional refractive index mappings of the modified zones. Additionally, polarization-dependent guiding was investigated.
关键词： Calcium Fluoride,quantitative phase imaging,waveguides,femtosecond lasers,cubic crystal,micro-processing,double-track,photonic device,direct laser writing (DLW),refractive index change
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Extension of Mid-IR Lasing Spectral Region using Cr:ZnSe and Cr:CdSe Combined Active Medium
摘要： High intensity femtosecond solid-state lasers in mid-infrared (mid-IR) region are of significant interest for many applications such as laser processing, ultrafast spectroscopy, high-order harmonic generation, and laser plasma acceleration. Transition metal (TM) doped chalcogenides (Cr:ZnSe, Cr:CdSe, Fe:ZnSe etc.) are attractive laser media for high intensity mid-IR femtosecond lasers, since they have broad fluorescence spectrum and large stimulated-emission cross section in the mid-IR region [1]. Extension of lasing region by combining of fluorescence region of TM doped chalcogenides can contribute to generate mid-IR ultrashort pulses. Combined active medium method [2-4], by which multiple laser media are used inside a laser cavity simultaneously, is suitable for equipping lasing characteristics of multiple laser media on one laser oscillator. This method has high potential to oscillate ultrashort pulses directly from a solid-state laser, however the method has not been realized in the mid-IR region. In this study, we report on extension of mid-IR lasing region using Cr:ZnSe and Cr:CdSe combined active medium (CAM). We obserbed that wavelength tunability was extended when using Cr:ZnSe and Cr:CdSe CAM than when using Cr:ZnSe and Cr:CdSe indipendently. This is the first report that CAM technique based on Cr2+ doped chalcogenides was demonstrated in the mid-IR region.
关键词： Cr:CdSe,femtosecond lasers,combined active medium,mid-IR lasing,Cr:ZnSe
更新于2025-09-12 10:27:22