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- 摘要
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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) - High-Harmonic Probe for Relativistic Laser-Matter Interactions Driven by Ultrashort Pulses in the Mid-Infrared
摘要： High-order harmonic generation (HHG) is one of the central effects in strong-field nonlinear-optical physics. Within the past two decades, HHG has been at the heart of a paradigm-shifting breakthrough to attosecond physics. Much less limelight has been given to the ability of HHG to serve as a highly sensitive and in many ways unique analytical tool. When used in this modality, HHG can help detect and understand ultrafast electron dynamics in complex gas-phase, solid-state, and laser-plasma systems. Here, we extend this concept by using HHG as a probe for relativistic laser–matter interactions driven by ultrashort pulses in the mid-infrared.
关键词： mid-infrared,relativistic laser–matter interactions,ultrashort pulses,High-order harmonic generation
更新于2025-09-12 10:27:22
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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) - Third Harmonic Generation with Ultrashort Pulses in a C <sub/>2</sub> Cl <sub/>4</sub> Filled Liquid Core Fiber
摘要： Currently third harmonic generation (THG) in fibers is in focus of research, due to the prospects of enabling efficient generation of entangled photon triplets via the inverse, but spontaneous process. To date, microstructured and tapered fibers are the most prominent platforms to provide the high index contrast between the core and cladding material necessary to enable phase-matching (PM) to higher order modes (HOMs). Here, we employ a liquid core fiber (LCF) combining a silica cladding and a highly nonlinear core material, which can be temperature-tuned during operation [1]. We report the first experimental demonstration of THG in a liquid-core step-index-fiber formed by a silica capillary and a C2Cl4 filled core (Fig. 1b). The core liquid provides an enhanced electronic nonlinear coefficient compared to silica [2] and the LCF was designed to be single mode at the pump wavelength (1.55 μm). The modal dispersion of the fiber is engineered such that two HOMs at the TH wavelength are phase-matched within the spectrum of the ultrashort pump pulses, see Fig. 1a. An optofluidic mount is used for retaining, filling and launching pulses into the LCF. The LCF is pumped with 30 fs (Fig.1c) and 100 fs (Fig.1d) pulses (Toptica FemtoFiber pro IR and IRS-II, both at 80 MHz repetition rate). After filtering residual pump light the TH spectra are recorded for increasing power using a spectrum analyzer (Ando AQ6315A). The experimental results are shown in Fig.1c and d. In either case two distinct spectral peaks are visible in the TH corresponding to the two phase-matched HOMs. The images above Fig. 1d show the imaged output employing narrow bandpass filters, confirming the existence of individual modes. Comparing the efficiency for both pump pulses, the THG onset occurs at higher powers and the overall conversion is reduced for the shorter pulses. The high normal dispersion at the pump limits the effective conversion length due to dispersive pulse broadening. In conclusion, the capability of LCF for THG was demonstrated and future research towards quantum light generation in LCF can be envisioned.
关键词： liquid core fiber,higher order modes,phase-matching,ultrashort pulses,third harmonic generation
更新于2025-09-12 10:27:22
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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) - Monolithic and In-Line Method for the Measurement of Time-Dependent Polarization of Ultrashort Pulses
摘要： Many recent applications of vector pulses require the characterization of time-dependent polarization of ultrashort laser pulses. For a precise measurement, the relative phase between the vector components is crucial. We propose a monolithic, in-line, single-channel interferometer setup, which allows the full determination of the time-evolving polarization state of the pulse, retrieving with precision the relative phase thanks to its great stability (~10-3). This is possible due to the use of a birefringent material (3-mm calcite) to delay the x- and y-components of the pulse. A linear polarizer (LP) is used to measure three projections with a spectrometer: 0o and 90o for the spectral amplitude of the x- and y-components, respectively, and 45o for the spectral interferences of the delayed components. By analysing the latter using Fourier-transform filtering, it is possible to retrieve the full relative phase (including constant term). The spectral phase of one component is measured with a standard temporal measurement device. Also, the system needs to be calibrated in amplitude and phase by measuring the same three spectral projections for a pulse linearly polarized at 45o. The polarization state of the vector pulses is characterized both in the spectral and the temporal domains: intensity, ellipticity, azimuth and phase difference.
关键词： Fourier-transform filtering,birefringent material,interferometer,ultrashort pulses,time-dependent polarization
更新于2025-09-12 10:27:22
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Nonlinear Fiber Optics || Cross-phase modulation
摘要： So far we have focused on optical pulses whose spectrum is centered at a single wavelength. When two or more pulses, launched at different wavelengths, propagate simultaneously inside a fiber, they interact with each other through the fiber’s nonlinearity. In general, such an interaction can generate new waves under appropriate conditions through a variety of nonlinear phenomena such as stimulated Raman or Brillouin scattering and four-wave mixing; these are discussed in Chapters 8 to 10. The nonlinearity can also couple two optical fields through cross-phase modulation (XPM), without inducing any energy transfer between them [1]. The XPM phenomenon is discussed in this chapter. A set of two coupled nonlinear Schr?dinger (NLS) equations is derived in Section 7.1, assuming that each wave maintains its state of polarization. These equations are used in Section 7.2 to discuss how the XPM affects the phenomenon of modulation instability. Section 7.3 focuses on the soliton pairs whose members support each other through their XPM-mediated nonlinear interaction. The effects of XPM on the shape and the spectrum of ultrashort pulses are described in Section 7.4 by solving the coupled NLS equations. Several applications of XPM are discussed in Section 7.5. A vector theory of XPM is developed in Section 7.6 to account for the polarization effects. In Section 7.7 we extend this theory to the case of birefringent fibers. The case of two counterpropagating waves is discussed in Section 7.8.
关键词： modulation instability,soliton pairs,counterpropagating waves,birefringent fibers,polarization effects,ultrashort pulses,nonlinear Schr?dinger equations,cross-phase modulation
更新于2025-09-12 10:27:22
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Robust Ultrashort Light Bullets in Strongly Twisted Waveguide Arrays
摘要： We introduce a new class of stable light bullets that form in twisted waveguide arrays pumped with ultrashort pulses, where twisting offers a powerful knob to tune the properties of localized states. We find that, above a critical twist, three-dimensional wave packets are unambiguously stabilized, with no minimum energy threshold. As a consequence, when the higher-order perturbations that accompany ultrashort pulse propagation are at play, the bullets dynamically adjust and sweep along stable branches. Therefore, they are predicted to feature an unprecedented experimental robustness.
关键词： ultrashort pulses,stability,twisted waveguide arrays,three-dimensional wave packets,light bullets
更新于2025-09-12 10:27:22
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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) - High Repetition Rate, Wavelength-Tunable Mid-IR Source Driven by ps-Pulses from a Ho:YLF Amplifier at 2 μm
摘要： The generation of ultrashort pulses in the mid-infrared (mid-IR) spectral region is highly demanded for a multitude of applications such as spectroscopy, materials processing, or biomolecular and chemical sensing. For many of the aforementioned applications a high pulse repetition frequency (PRF) is desirable, since it reduces measurement time and improves spectroscopic signal-to-noise ratio. However, most of the ultrafast mid-IR sources are limited to a PRF below 10 kHz as they rely on regenerative amplifier-based pump sources for optical parametric chirped pulse amplification (OPCPA) [1-3]. The herein applied Pockels cell represents a bottleneck for PRF tuning usually below 10 kHz. Just recently, we presented a 2-μm, sub-10 ps pulse laser system with millijoule-level pulse energy, which is in principle not limited by the PRF [4]. This laser system benefits from its simplified, compact CPA-free architecture and high efficiency. In this contribution we use a similar laser system as front-end to pump nonlinear ZnGeP2 (ZGP) crystals in order to approach the wavelength range between 2.5 and 9 μm. This compact mid-IR source benefits from the broad spectral and PRF tunability as well as a remarkably simple experimental scheme.
关键词： ultrashort pulses,ZnGeP2 crystals,wavelength-tunable,mid-IR,high repetition rate,Ho:YLF amplifier
更新于2025-09-11 14:15:04
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High Energy Ultrafast Laser at 2 μm Using Dispersion engineered Thulium-Doped Fiber
摘要： We report on demonstration of high energy pulse laser at 2 μm by employing a normal dispersion fiber attained by a waveguide dispersion engineering. The normal dispersion fiber has a W-type refractive index profile, with a Thulium(Tm)-doped core. In contrast to a strong anomalous dispersion at 2 μm in a step-index fiber, the design allows strong waveguide dispersion that can generate normal dispersion at the Tm emission band. Mode area scalability of this fiber is discussed under the normal dispersion requirement. The Tm-doped fiber (TDF) is deployed in a ring cavity to produce mode-locked pulses near 2 μm. Subsequently, the pulse is amplified with more than 27 dB gain through the normal dispersion TDF. The output pulse energy reaches up to ~525 nJ at 1852 nm without pulse breaking due to the engineered dispersion. The achieved pulse energy is record high for all-fiber configuration near 2 μm, to our knowledge.
关键词： dispersion shift,Fiber Lasers,Thulium,Specialty Fiber,Ultrashort Pulses
更新于2025-09-11 14:15:04
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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) - Video-Rate Phase Retrievals from Dispersion Scan Traces using Artificial Neural Networks
摘要： The full characterization of ultrashort pulses is crucial for all their applications. Lately, the dispersion scan (d-scan) technique has been developed, which stands out by its simplicity [1, 2]. Therefore, it is a promising candidate for a low-maintenance pulse characterization technique. The reconstruction of the spectral phase from a d-scan measurement relies on optimization algorithms [3, 4]. Considering the fact that the spectral phase of the pulses is directly imprinted on the d-scan trace, the phase reconstruction can also be regarded as an image recognition task. During the last few years, artificial neural networks have shown excellent performance in different fields, e.g. image recognition [5]. Here we present the retrieval of spectral phases from d-scan traces using deep neural networks (DNN) that is more than 3000 times faster than conventional optimization algorithms (16 ms) [6]. Our DNN is an optimized variant of the DenseNet-BC architecture that has already shown great performance in image recognition tasks [7]. Training our shallow variant of the DenseNet takes only 12 h using a low cost GPU (NVIDIA GeForce GTX 1080 Ti). After training with up to 1.5 × 106 different, randomly generated traces, we can employ the network for reconstruction of the spectral phases from a d-scan traces. Fig. 1(a) and (b) show a randomly generated d-scan trace and its corresponding reconstruction, respectively. The spectral intensity (black curve), the original spectral phase (blue curve) and the retrieved phase (red dashed curve) are depicted in Fig. 1(c). Additionally, Fig. 1(d) compares the original and the reconstructed temporal pulse shapes (same color code). The consistency between the original and the retrieved phases and their corresponding temporal shapes shows the excellent performance of the DNN. Furthermore, to prove the fidelity of phase reconstruction from experimentally measured traces, we retrieved the spectral phase from a Ti:sapphire based amplifier system [8]. Compared to a differential evolution optimization algorithm, we observe identical full width at half maximum pulse durations, as well as nearly identical temporal pulse shapes. We believe that DNNs combined with single-shot d-scan setups [9] enable video-rate measurements with an inherent error estimation due to the redundancy in the data.
关键词： deep neural networks,spectral phase retrieval,dispersion scan,ultrashort pulses
更新于2025-09-11 14:15:04
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Control of THz field waveform emitted from air plasma by chirping two-color laser pulses
摘要： Few-cycle terahertz pulses can be effectively generated in air plasma by mixing an ultrashort laser pulse with its second harmonic. The temporal overlap between these two pulses is critical, which can degrade with the mismatch of group velocities. However, the overlap between the fundamental and second harmonic can be controlled by pre-stretching the temporally separated pulses. In this paper, we study the role of chirp and the relative phase between the fundamental and its second harmonic in the formation of the terahertz waveform. We demonstrate experimentally and explain within the context of transient photocurrent model, that the combination of chirping and relative phase shifting can provide a powerful tool to control the waveform of the terahertz pulse.
关键词： Dispersion,Plasma physics,Nonlinear optics,THz generation,Ultrashort pulses
更新于2025-09-11 14:15:04
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Evidence of depolarization and ellipticity of high harmonics driven by ultrashort bichromatic circularly?polarized fields
摘要： High harmonics generated by counter-rotating laser fields at the fundamental and second harmonic frequencies have raised important interest as a table-top source of circularly polarized ultrashort extreme-ultraviolet light. However, this emission has not yet been fully characterized: in particular it was assumed to be fully polarized, leading to an uncertainty on the effective harmonic ellipticity. Here we show, through simulations, that ultrashort driving fields and ultrafast medium ionization lead to a breaking of the dynamical symmetry of the interaction, and consequently to deviations from perfectly circular and fully polarized harmonics, already at the single-atom level. We perform the complete experimental characterization of the polarization state of high harmonics generated along that scheme, giving direct access to the ellipticity absolute value and sign, as well as the degree of polarization of individual harmonic orders. This study allows defining optimal generation conditions of fully circularly polarized harmonics for advanced studies of ultrafast dichroisms.
关键词： circularly polarized fields,high harmonics,ultrafast dichroisms,ultrashort pulses,polarization state
更新于2025-09-10 09:29:36