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Compression of femtosecond pulses in a wide wavelength range using a large-mode-area tapered fiber
摘要： We report the design of a tapered fiber that can be used for the compression of pulses at different central wavelengths. The proposed fiber is a three-layer W-type large-mode-area fiber, which has been tapered to transform the mode area from 1700 μm2 to 900 μm2. We determine the exact length of the maximum pulse compression and numerically demonstrate the compression of a 250 fs, 100 kW peak power input pulse to 15 fs, 850 kW at 1.55 μm wavelength and compression of 250 fs, 120 kW peak power input pulses to 28 fs, 700 kW and to 46 fs, 500 kW at 1.8 μm and 2 μm wavelengths, respectively. Such a fiber can find wide ranging applications, including in communication, spectroscopy and medicine.
关键词： ultrafast processes in fiber,large-mode-area fiber,high peak power femtosecond pulses,pulse shaping,tapered fiber,pulse compression
更新于2025-09-23 15:22:29
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Second harmonic generation at 544a??nm of a femtosecond laser
摘要： We study second harmonic generation (SHG) at 544 nm of the 0-type (e + e - e) quasi-phase-matching based on a femtosecond laser at 1088 nm. The green pulse with the spectrum width of 0.6 nm and the peak power of 17.7 kW is obtained at the pump power density of 2.81 GW/cm2 and the conversion e?ciency is 21 %. As the propagation distance along the PPMgLN crystal increases, the spectrum at 544 nm becomes narrower and narrower and the pulse duration broadens very seriously.
关键词： Group velocity match,544 nm laser,Second harmonic generation,PPMgLN,Ultrafast optics,Femtosecond pulses
更新于2025-09-23 15:21:01
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Ytterbium laser system for studying parametric amplification of femtosecond pulses with a centre wavelength of a??2 ??m
摘要： A laser system is developed with an optical synchronisation of a femtosecond signal with a pump channel. The signal of a driving ytterbium fibre laser with a 60 MHz repetition rate of stretched femtosecond pulses is amplified in energy from several nanojoules to 0.4 mJ at a pulse repetition rate of 3 kHz in a wide-band amplifier and then is compressed in time to 250 fs. The obtained radiation is used for generating femtosecond laser pulses with a centre wavelength of ~2 mm, pulse energy of above 20 mJ, duration of several field oscillations, and phase stabilisation between the electromagnetic field and envelope. The other pulse of the driving fibre laser provides optical synchronisation and a minimal time delay and is directed to a regenerative Yb : YAG disk amplifier for amplification to an energy of 4 mJ at a pulse repetition rate of 3 kHz and duration of 20 ps. A multipass disk amplifier is developed for further increasing the energy of pump chirped pulses to an energy of 70 mJ at a pulse repetition rate of 10 Hz and duration of 400 ps for studying parametric amplification under sub-nanosecond pumping.
关键词： parametric amplification,Yb :YAG disk amplifier,ytterbium fibre laser,femtosecond pulses,pulse compression
更新于2025-09-23 15:19:57
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High-Repetition-Rate Femtosecond Laser Processing of Acrylic Intra-Ocular Lenses
摘要： The study of laser processing of acrylic intra-ocular lenses (IOL) by using femtosecond laser pulses delivered at high-repetition rate is presented in this work. An ultra-compact air-cooled femtosecond diode laser (HighQ2-SHG, Spectra-Physics) delivering 250 fs laser pulses at the fixed wavelength of 520 nm with a repetition rate of 63 MHz was used to process the samples. Laser inscription of linear periodic patterns on the surface and inside the acrylic substrates was studied as a function of the processing parameters as well as the optical absorption characteristics of the sample. Scanning Electron Microscopy (SEM) Energy Dispersive X-ray Spectroscopy (EDX), and micro-Raman Spectroscopy were used to evaluate the compositional and microstructural changes induced by the laser radiation in the processed areas. Diffractive characterization was used to assess 1st-order efficiency and the refractive index change.
关键词： Raman spectroscopy,femtosecond pulses,laser processing,ophthalmic polymers
更新于2025-09-19 17:13:59
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Generation of Terahertz Radiation in Gas Media with Variable Structure when Focusing Two-Color Femtosecond Laser Pulses
摘要： The possibility of modulating the power of terahertz radiation generated in the laser plasma produced when focusing two-color femtosecond laser pulses in air, when using a gas jet directed to the plasma formation region, is demonstrated.
关键词： terahertz radiation,laser plasma,femtosecond pulses
更新于2025-09-16 10:30:52
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Laser-Induced-Electro-Explosion Synthesis of Powder Materials (LIEES)
摘要： In this paper, a method for the synthesis of microspheres containing titanium carbide by laser radiation is described. The formation of microspheres is carried out by the action of femtosecond laser radiation on the surface of titanium in the reaction medium - the saturated hydrocarbon. Hexane was used as a hydrocarbon. The obtained microspheres have an average size of 1-3 μm and can be used in applications of additive engineering, powder metallurgy as the main raw material, or as an alloying additive. To increase the efficiency of particle output, a method of laser action combining with electric current is proposed. The behavior of an electric discharge in the plasma channel area was studied.
关键词： laser radiation,metal powders,femtosecond pulses,ablation in a liquid,plasma channel
更新于2025-09-16 10:30:52
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Femtosecond laser system based on thin rod Yb : YAG active elements with an output power of 110 W
摘要： A three-stage laser amplification system based on thin Yb : YAG rods with diode laser pumping is developed and fabricated. In this system, the average power of a continuous train of femtosecond pulses from a Yb : KGW master oscillator with a pulse repetition rate of 80 MHz and initial pulse duration of 128 fs was raised by a factor of 100 to above 100 W. Preliminarily chirped laser pulses provided compensation of dispersion in optical elements of the system and obtaining 580-fs output pulses. The longer duration of output pulses relates to spectrum narrowing in the amplifiers.
关键词： diode-pumped laser amplifier on Yb :YAG,high average radiation power,femtosecond pulses
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) - Harmonic Concatenation of 1.5-Femtosecond-Pulses in the Deep UV
摘要： Waveforms with durations short enough to probe the electronic timescale can be generated both in the extreme UV and in the IR-VIS region of the electromagnetic spectrum. In the deep UV (DUV), where for example many basic aromatic molecules absorb radiation and undergo photochemical reactions, pulses with such extremely short durations have not yet been demonstrated. A fundamental difficulty is rooted in the large group velocity dispersion of any optical component in the DUV, causing a DUV pulse to be readily broadened and distorted before it reaches the sample. The present record for the shortest DUV pulses is 2.8 fs. Here, a scheme for the coherent synthesis of DUV waveforms is presented. The principle is the concatenation of spatial and temporal harmonics that are created by two noncollinear IR-VIS pulses. Cascaded processes of frequency conversion and self-diffraction in a thin MgF2 plate yield a multifaceted emission pattern of temporal and spatial harmonics. The emission angle Φ of the harmonic orders depends on the frequency. Broadband waveforms arise, of which the lower frequency bands belong to one spatial harmonic, and the higher frequency bands belong to the other spatial harmonic. In order to synthesize ultrashort waveforms from these frequency bands, their phases must be adjusted. This is accomplished by controlling the groove-envelope phase (φGEP) of the fundamental pulses, which is determined by their delay on the subcycle timescale. Using temporal harmonics of third order, the concatenation of two spatial harmonics synthesizes DUV pulses of 1.5 fs. A generic feature is that these waveforms are spatially separated from the fundamental pulses and are therefore available for immediate spectroscopy usage without any subsequent optical elements.
关键词： Harmonic concatenation,femtosecond-pulses,spatial harmonics,deep UV,temporal harmonics,coherent synthesis
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) - Avoidance of Cross-Phase Modulation in Femtosecond Stimulated Raman Scattering
摘要： Raman scattering has become a powerful method in analytic spectroscopy and label-free imaging to study the chemical composition of a sample. Especially coherent Raman scattering (CRS) techniques such as stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS) are developed further and show a great potential, due to their amplified signal in comparison to spontaneous Raman scattering. In CRS the interaction of light pulses with molecular vibrations are investigated, typically resulting in a characteristic molecular spectrum. However, especially CARS spectra are effected by the non-resonant contribution to the Raman scattering signal, resulting in a non-specific background and a distortion of the lineshape. SRS is free of a non-resonant background but is affected by two-photon absorption, cross-phase modulation (XPM) [1], and thermal scattering (temperature-induced refractive index change) [2]. The resulting artefacts in SRS become relevant for high pulses energies and ultra-short pulses. One example, where high pulse energies and ultra-short pulses are needed, is the field of spatial resolution enhancement in CRS. All techniques to overcome the diffraction limit by Abbe are based on depleting one of the scattering resources, as for example the pump or probe photons [3]. High pulse energies in the order of up to 200-300 nJ are needed, leading to also unwanted spectral distortions through XPM [4]. In this paper, we present the avoidance of spectral XPM artefacts in femtosecond stimulated Raman scattering, based on a systematic study varying the pump pulse duration in the high pulse energy regime. To study the effects of different pump pulse durations on the FSRS spectra a setup as shown in Fig. 1 (a) was realized, which consists of a folded Fourier filter, to freely choose the pump pulse duration, and a supercontinuum generation in a gadolinium vanadate crystal (GdVO4) working as broadband probe pulse source. After combining the two beams at the dichroic mirror (DM) measurements with different peak powers of the pump pulse, time delays between pump and probe and varying pump pulse durations were performed. For pump pulses with a duration between 2 ps and 3 ps the Raman spectra are nearly unaffected by XPM, whereas pulses shorter than 1 ps show a significant XPM induced distortion of the stimulated Raman lineshape and a reduction of the Raman resonance maximum, becoming visible as a negative stimulated Raman loss (SRL) signal on the high wavenumber side of the Raman resonances. Thus, it is favourable to choose pump pulses with a longer pulse duration in the regime of high peak power to reduce the impact of cross-phase modulation in stimulated Raman scattering.
关键词： stimulated Raman scattering,Raman scattering,femtosecond pulses,spectral distortions,cross-phase modulation
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) - Femtosecond-Driven Up-Conversion in a Radially Poled LiNbO <sub/>3</sub> Microresonator
摘要： Nowadays, there are plenty of different techniques developed for the generation of Optical Frequency Combs (OFCs), but Mode Locked Laser (MLL) OFC is still the most commonly used and commercially available one [1]. Although MLLs are capable of producing very high-peak power OFCs with femtosecond pulse durations, it is sometimes challenging to apply them directly for a number of reasons. First, MLLs typically produce OFCs with repetition frequencies (fr) below 1 GHz, so additional filtering of the unwanted modes is required for the applications in telecommunications, astrocombs etc. Second, many spectral regions – namely mid-infrared, visible and ultraviolet – are difficult to access by MLLs, which implies the use of external parametric up- and down-conversion. One promising platform for such spectral transfer is high Q-factor optical microresonators based on second order (χ(2)) nonlinear crystals, since not only do they provide the desired spectral transfer, but also open up opportunities for the miniaturization of the system. In addition, such microresonators support whispering gallery modes that possess very low mode volumes, making it possible to enhance nonlinear (χ(2)) processes. This is a significant advantage over the already existing bulk analogs.
关键词： Mode Locked Laser,microresonators,second harmonic generation,femtosecond pulses,Optical Frequency Combs
更新于2025-09-12 10:27:22