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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) - Nd,Gd:SrF <sub/>2</sub> Laser Generating 600 fs Pulses at 0.9 W of Pump Power
摘要： Fluoride crystals (CaF2, SrF2) doped with neodymium Nd3+ and codoped with non-active ions as Y3+, La3+, or Gd3+ for breaking clusters of active ions, have become recently interesting active media for the diode-pumped mode-locked lasers. They possess broader emission spectra as well as longer fluorescence lifetime in comparison with widely used crystals such as Nd:YAG or Nd:YVO4. The femtosecond Nd,Y:SrF2 laser generating 97 fs pulses was reported in the Ti:sapphire pumped system [1]. We have reported continuously mode-locked operation of this laser pumped by a 2 W multimode laser diode and mode-locked using a semiconductor saturable absorber generating pulses with the duration of 258 fs [2]. In laser systems with La3+ codoped crystals, which have wider tunability than Y3+ codoped crystals, passively mode-locked 354 to 1200 fs and continuous-wave 1044 to 1081 nm tunable operation was reported in the system pumped by 4 W laser diode [3]. Recently a new Nd,Gd:SrF2 crystal has been investigated and the dual wavelength mode-locked picosecond operation was reported for pump power higher than 3.8 W [4]. We reported femtosecond operation of laser with this crystal and obtained pulses as short as 228 fs with output power of 2 x 50 mW in system pumped by 2 W laser diode for absorbed pump power of 1320 mW [5]. In the present contribution we report on operation of this novel laser with a Brewster cut crystal in passively mode locked regime for extremely low pump power. Laser system schematic is similar as in ref. [5] and is shown in Fig. 1. A 5 mm long Brewster cut 0.5%Nd, 5%Gd:SrF2 crystal was pumped by a multimode 2 W laser diode at 796 nm and passively mode-locked using a semiconductor saturable absorber mirror (SAM). Using a chirped mirror M3 with GDD equal to -650 fs2 it was possible to achieve continuously mode locked regime at absorbed pump power of only 320 mW, with output power of 2 x 12 mW behind the mirror M4 in linearly polarized beams with nearly Gaussian spatial profile and pulse duration of 740 fs (assuming sech2 pulse shape). For higher absorbed pump power of 632 mW (905 mW incident on the crystal) the total output power of 2 x 20 mW was achieved with a pulse duration of 600 fs. The autocorrelation curve is shown in Fig. 2 together with the measured spectrum 3.3 nm wide, and centered at 1051.5 nm. The absorbed pump power is 2 - 4 times smaller in comparison with our previous results. The calculated time-bandwidth product of 0.536 gives potential to get shorter pulses (down to 352 fs) with optimum GVD compensation.
关键词： diode-pumped,semiconductor saturable absorber mirror,femtosecond pulses,Nd,Gd:SrF2,mode-locked lasers
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) - Soliton Self-Compression and Spectral Broadening of 1 μm Femtosecond Pulses in Single-Domain KTiOPO <sub/>4</sub>
摘要： Efficient, diode-pumped high energy femtosecond laser systems around 1 μm based on Yb-gain media are readily commercially available. However, owing to the gain bandwidth limitations, the pulses generated in such lasers are substantially longer than the ones generated in Ti:Sapphire systems. A simple, energy-scalable pulse self-compression scheme for the pulses around 1 μm thus would be of great interest for many applications, including time-resolved pump-probe spectroscopy, high-harmonics generation, etc. The self-phase modulation during nonlinear propagation in filaments in gasses is often employed for pulse self-compression [1,2]. Such schemes typically require rather bulky setups and careful control of group velocity dispersion. Some years ago it has been shown theoretically that Raman-active molecules in gaseous form could be used for mid-infrared pulse compression [3]. Here we exploit highly-efficient interaction of optical pulses with phonon-polaritons in KTiOPO4 (KTP) [4] for self-compression of fs pulses at 1 μm. The experimental setup consists of a 1030 nm femtosecond pump laser. The pulses were loosely focused by a f=150 mm lens to a beam waist with 1/e2 radius of 160 μm in a 10 mm-long, 5mm-thick single-domain KTP sample. The pulses were polarized along the c-axis of the crystal. The dependence of the pulse output spectrum as a function of the beam focus position in the crystal is shown in Fig.1 (a), where 300 fs full width at half maximum (FWHM) input pulses from a fiber-based system were employed. The broadest spectrum was obtained with the focal plane being located close to the entrance of the crystal. We employed time-resolved digital holography [5] to verify the coupling of the optical pulse with phonon-polariton wave during propagation through the crystal. Characterization experiments with 173 fs FWHM pulses derived from a commercial solid-state laser system were conducted using a custom-built d-scan setup [6]. The setup included chirped mirrors covering the spectral region of Fig.1 (a).
关键词： Femtosecond Pulses,KTiOPO4,Spectral Broadening,Soliton Self-Compression,Phonon-polaritons
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) - A 290 W Radially Polarized Output Power from a Single-Stage Single-Crystal Yb:YAG Amplifier
摘要： Radially polarized beams exhibit interesting properties for material processing, as well as for different scientific applications such as optical trapping, plasmon excitation or data storage. With a thin-disk multipass amplifier radially polarized ultra-short pulses with an average output power of 635 W were demonstrated in [1]. For 100 W class operation, single-crystal fiber (SCF) amplifiers are an alternative approach to the thin-disk architecture. This approach reduces the costs and the complexity of the overall laser system significantly. The highest average output power demonstrated with an SCF amplifier was 160 W for a linearly polarized Gaussian seed beam [2] and 85 W for a ring-shaped radially polarized seed beam [3]. In this contribution, we present the amplification of a ring-shaped radially polarized seed beam in a single-stage SCF amplifier to an average output power of 290 W in continuous-wave (CW) operation and 270 W in femtosecond pulsed operation. This is, to the best of our knowledge, the highest average output power of a radially polarized beam demonstrated so far with an SCF amplifier.
关键词： femtosecond pulses,Radially polarized beams,high power lasers,single-crystal fiber amplifiers
更新于2025-09-11 14:15:04
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[IEEE 2017 IEEE Workshop on Recent Advances in Photonics (WRAP) - Hyderabad (2017.12.18-2017.12.19)] 2017 IEEE Workshop on Recent Advances in Photonics (WRAP) - Utilization of Segmented Cladding Fiber for the Generation of High Energy Femtosecond Pulse Trains
摘要： Generation of high-peak-power, femtosecond pulse train and pulse doublet has been numerically demonstrated by exponentially decreasing the dispersion along the length of the large-mode-area segmented-cladding fiber. Such pulse trains find applications in various nonlinear optical processes.
关键词： pulse doublet,femtosecond pulses,large mode area fiber,pulse train,Segmented cladding fiber
更新于2025-09-10 09:29:36
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Optimum chirp for efficient terahertz generation from two-color femtosecond pulses in air
摘要： We compare detailed spatio-temporal propagation simulations with experiments on generation of terahertz (THz) pulses in single ?laments with two-color optical excitation, which elucidates the mechanism whereby positively chirped optical pulses lead to the maximum THz yield. The long-wavelength components in the leading edge of the positively chirped 2x-pulse preserve the overlap with the x-pulse. The THz yield is extremely sensitive to the temporal overlap: for a 35-fs x-pulse, the yield decreases by an order of magnitude upon a x–2x pulse shift of only 5 fs.
关键词： terahertz,chirp,two-color excitation,femtosecond pulses,THz generation
更新于2025-09-04 15:30:14
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Soft X-ray Absorption Spectroscopy of Aqueous Solutions Using a Table-Top Femtosecond Soft X-ray Source
摘要： We demonstrate the feasibility of soft X-ray absorption spectroscopy in the water window using a table-top laser-based approach with organic molecules and inorganic salts in aqueous solution. A high-order harmonic source delivers femtosecond pulses of short wavelength radiation in the photon energy range from 220 eV to 450 eV. We report static soft X-ray absorption measurements in transmission on the solvated compounds CO(NH2)2, CaCl2, and NaNO3, using flatjet technology. We monitor the absorption of the molecular samples between the carbon (≈280 eV) and nitrogen (≈400 eV) K-edges and compare our results with previous measurements performed at the BESSYII facility. We discuss the roles of pulse stability and photon flux in the outcome of our experiments. Our work paves the way towards table-top femtosecond, solution phase soft X-ray absorption spectroscopy in the water window.
关键词： aqueous solution,high-order harmonic source,flatjet technology,soft X-ray absorption spectroscopy,table-top laser-based approach,femtosecond pulses,water window
更新于2025-09-04 15:30:14