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Nonlinear Optics
摘要： The mid-infrared atmospheric window of 3–5.5 μm holds valuable information regarding molecular composition and function for fundamental and applied spectroscopy. Using a robust, mode-locked fiber-laser source of < 11 fs pulses in the near infrared, we explore quadratic (χe2T) nonlinear optical processes leading to frequency comb generation across this entire mid-infrared atmospheric window. With experiments and modeling, we demonstrate intrapulse difference frequency generation that yields few-cycle mid-infrared pulses in a single pass through periodically poled lithium niobate. Harmonic and cascaded χe2T nonlinearities further provide direct access to the carrier-envelope offset frequency of the near infrared driving pulse train. The high frequency stability of the mid-infrared frequency comb is exploited for spectroscopy of acetone and carbonyl sulfide with simultaneous bandwidths exceeding 11 THz and with spectral resolution as high as 0.003 cm?1. The combination of low noise and broad spectral coverage enables detection of trace gases with concentrations in the part-per-billion range.
关键词： few-cycle pulses,mid-infrared,frequency comb,spectroscopy,nonlinear optics
更新于2025-09-23 15:21:01
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Asymmetry flip in angle-resolved photoelectron spectra of rare gas atoms by intense circularly polarized few-cycle pulses
摘要： We examine the phenomenon of the flip in the asymmetry in the emission direction of photoelectrons from rare gas atoms upon the ionization by a circularly polarized few-cycle laser field, and derive an analytical formula representing the photoelectron kinetic energy at which the asymmetry flip occurs based on the semiclassical tunnel ionization theory. We show that the energy at which the asymmetry flip occurs varies sensitively to the duration of few-cycle laser pulses and propose that the pulse duration can be determined experimentally using this analytical formula for the asymmetry flip energy.
关键词： asymmetry flip,photoelectron spectra,rare gas atoms,circularly polarized few-cycle pulses
更新于2025-09-23 15:21:01
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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) - CPA-Free High Repetition Rate Few-Cycle OPCPA
摘要： Optical Parametric Chirped-Pulse Amplification (OPCPA) systems have become a key-enabling light source providing high energies at high repetition rates and covering a wide range of wavelengths from the visible to the mid-infrared with few cycle pulse durations. However, most systems are complex and rather bulky due to large fiber or regenerative amplifiers used as a pump source. The additional need for a stretcher and compressor in the pump laser adds complexity, timing jitter and reduces the overall optical-to-optical efficiency. In this work, we present a novel approach that allows a high repetition rate, few-cycle OPCPA system based on a compact and CPA-free solid-state amplifier system. We recently demonstrated the feasibility of the concept using two subsequent direct diode pumped solid-state amplifier modules (neoVAN-2P, neoLASE GmbH) based on Nd:YVO4 as a pump laser. We were able to amplify the ultrabroadband pulses from a home-built, octave-spanning Ti:sapphire laser to generate few-cycle pulses with a duration of 8.7 fs with an energy of 18 μJ at 10 kHz repetition rate. The compact, CPA-free system has a reduced system footprint and high efficiency as no losses in a compressor are occurring. For the amplification of few-cycle signal pulses, stretching to more than a few ps and subsequent recompression is problematic and limited the achievable pulse duration in our previous system. Insufficient temporal overlap between pump and signal pulses in the OPA stages will however cause lower parametric conversion efficiency and a significantly higher super-fluorescence background. In this work, we show for the first time a compact few-cycle OPCPA system using a newly developed Yb:YAG solid-state amplifier as pump source. The Yb:YAG amplifier modules are capable of generating pump pulses with a duration of < 600 fs. These output parameters are ideally suited for few-cycle OPCPA pumping and eliminate the above mentioned drawbacks of the previous approach. The high pump power and short pulse duration delivered by the amplifier modules enable a similar performance of the OPCPA as typical high repetition rate, rod-fiber based systems at the benefit of CPA-free operation and compactness. As the amplifier modules are equipped with an efficient CPA-free, directly diode pumped solid-state pump source with all-optical synchronization to an ultra-broadband Ti:sapphire seed oscillator. The availability of such portable, breadboard-user-friendly OPCPA will be a great benefit for many applications as spectroscopy, nonlinear imaging or even attosecond physics.
关键词： Yb:YAG,solid-state amplifier,few-cycle pulses,high repetition rate,OPCPA
更新于2025-09-19 17:13:59
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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) - Numerical Investigation of Broadband OPCPA Configurations for Direct Amplification of TW-Level, Two-Cycle Pulses
摘要： Generation of intense, isolated attosecond pulses is the main motivation for the development of laser systems which are producing few-cycle, TW-level pulses. The ELI-ALPS Single Cycle Laser (SYLOS) aims to provide 20 TW single cycle pulses at 1 kHz repetition rate. Due to the requirements for stability and high average power the most promising approach for generating mJ-level, few-cycle pulses is noncollinear optical parametric chirped pulse amplification (NOPCPA). BBO and LBO are the two most favoured nonlinear materials in the visible and near-infrared spectral range, due to their broad gain bandwidth and high damage threshold. It was demonstrated that BBO and LBO can support 5.5 fs and 7 fs pulse durations respectively when 450 nm and 515 nm pumping was used. Even shorter, sub-5 fs pulse durations can be achieved by utilizing two-color pumping, that is, the second- and third-harmonic of a Nd:YAG pump laser in subsequent amplifier stages. The latter solution is the most promising, however at 1 kHz repetition rate there is a risk of optics degradation due to high average power UV light. In this work, two alternative solutions were examined numerically for few-cycle pulse amplification. In the first one, single LBO crystal is used in a phase-matching configuration when the gain bandwidth supports 5 fs pulse duration. In the other solution, spectral multiplexing was utilized in a so-called BBO-sandwich configuration. The principle of the BBO-sandwich is that two thin BBO crystals packed close to each other with slightly different phase-matching angles, but the non-collinear angle between the signal and pump beams is the same in both crystals. As a result, a broader gain bandwidth can be achieved which can support 5 fs pulse duration. These broadband phase-matching configurations were numerically examined using an advanced 3D, OPCPA modelling software. The results of these simulations were well applicable either to rule out or to confirm certain configurations during the experimental development of ELI-ALPS SYLOS laser system. In most cases, the predicted total bandwidths were matched well with the experimental results, even when the spectrum shapes showed difference due to the model approximations. Numerical simulations predicts that the amplified spectrum supports 5 fs Fourier-limited duration and the spectral phase does not contain any fast oscillations thus the pulses are compressible to 5.5 fs. The output pulse energy is 50 mJ before pulse compression and the calculated Strehl-ratio is 0.77. The theoretical findings are also proved by the experimental results, which indicates that these phase-matching configuration are viable candidates for the production of TW-level, few-cycle pulses.
关键词： TW-level pulses,few-cycle pulses,broadband OPCPA,noncollinear optical parametric chirped pulse amplification,LBO,BBO
更新于2025-09-12 10:27:22
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Propagation of few-cycle pulses in a nonlinear medium and an integrable generalization of the sine-Gordon equation
摘要： The generalized sine-Gordon equation is obtained under the theoretical investigation of interaction of few-cycle pulses in a nonlinear medium modeled by a set of four-level atoms. This equation is derived without the use of the slowly varying envelope approximation and is shown to be integrable in the frameworks of the inverse scattering transformation method. Its solutions describing the propagation of the solitons and breathers and their interaction are investigated. In the case of different signs of the parameters of the equation considered, it is revealed, in particular, that the collision of solitons with opposite polarities can lead to an appearance of the short-living pulse having extraordinarily large amplitude, whose dynamics is similar to that of rogue waves. Also, the solitons of “rectangular” form and the breathers with rectangular oscillations exist in the case of the same signs of the parameters.
关键词： few-cycle pulses,generalized sine-Gordon equation,rogue waves,breathers,solitons,nonlinear medium
更新于2025-09-09 09:28:46
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Three-dimensional carrier-envelope-phase map of focused few-cycle pulsed Gaussian beams
摘要： We derive an analytical expression that describes the complete three-dimensional carrier-envelope-phase (CEP) distribution in the focal volume of ultrashort pulsed Gaussian beams focused by spherical mirrors or lenses. The focal CEP map depends on the so-called factor g specifying the frequency dependence of the beam width of the source few-cycle pulse, on its chirp, and on the small chromatic aberration introduced by a lens without appreciably distorting or broadening the few-cycle pulse. We show how to tailor the CEP map of mirror-focused and lens-focused few-cycle pulses in order to produce negligible transversal and axial CEP variations in specific regions of the focal volume for phase-sensitive interactions of light with matter taking place in a volume or on a surface. We propose a quasiachromatic doublet lens that can implement in practice these tailored CEP distributions.
关键词： CEP map,carrier-envelope-phase,few-cycle pulses,chromatic aberration,Gaussian beams
更新于2025-09-09 09:28:46