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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 Power, Ultrafast Yellow Laser using Fourth-Harmonic Generation of Ultrafast Mid-IR Cr <sup>2+</sup> :ZnS Laser in MgO:PPLN Crystal
摘要： The ultrafast optical radiation in the yellow spectral region is of great interest for variety of scientific and technological applications including astronomy, spectroscopy and medicine, with potential to revolutionize eye surgeries through exquisite accuracy [1, 2]. However, it is relatively difficult to access the yellow region, especially when good beam quality, high power and high efficiency are required. Till date, various types of yellow lasers have been reported [3, 4] mostly in CW regime and nanosecond timescales. Here, we report on a compact, high- power, high repetition-rate, ultrafast source of yellow radiation. Using an ultrafast Cr2+:ZnS laser of average power of 4.5 W with spectral width of Δλ=138 nm centered at 2.36 μm, producing output pulses of width ~40 fs at a repetition rate of 80 MHz, and two stage single-pass second harmonic generation (SHG), we have generated ultrafast radiation of power 1 W tunable across 577-589 nm. The schematic of the experimental setup is shown in Fig. 1(a). The single-pass SHG of Cr2+:ZnS laser in a 2 mm long 5% mol doped MgO:PPLN multi-grating crystal (Λ=33.15 - 35.25 μm), giving second harmonic (SH) pulses of 90 fs at 1.18 μm, with a maximum average power of 2.3 W at a single-pass efficiency as high as 65%. Further the 1.18 μm radiation is frequency-doubled in a 1 mm long and 0.5×1 mm2 in aperture, MgO:PPLN crystal (Λ=8.9 -9.45 μm) producing yellow radiation. The acceptance bandwidth (FWHM) and temporal walk-off length (LT) of the second crystal are calculated to be 3 nm and 288 μm, respectively. In order to optimize the focusing condition for maximum fourth harmonic generation (FHG) efficiency, we pumped the crystal at constant power of 1.3 W at 1.18 μm and recorded the fourth harmonic (FH) power as a function of focusing parameter, ξ =L/b, where, L is the length of the crystal and b=2πnw0 2/λ, w0 is the beam waist radius, n is the refractive index of the crystal and λ is the input wavelength.
关键词： Cr2+:ZnS laser,MgO:PPLN crystal,fourth-harmonic generation,ultrafast yellow laser
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) - Tunable Near 3-μm Difference Frequency Generation using Ytterbium and Broadband Seed Erbium Fiber Lasers
摘要： The absorption peaks corresponding to vibrational energy levels of various molecules are located in the mid-infrared (mid-IR) spectral range. For instance, the interatomic bonding of hydrogen and another heavier element (e.g. C-H, O-H, N-H) that is a part of some organic and inorganic molecules is characterized by the absorption peak located near 3μm wavelength. Laser sources operating at this wavelength can be useful tools for medical applications, non-metallic materials processing, and spectroscopy [1]. The study of the interaction of various organic substances with mid-IR radiation is rather challenging because of their great diversity and chemical composition complexity. An application of the laser source with high output power and tunable wavelength can significantly facilitate possible investigation problems [2,3]. This research is devoted to the elaboration of the tunable laser source of mid-IR radiation using single pass difference frequency generation of the pump (1.03 μm) and seed (1.55 μm) radiation in periodically poled lithium niobate (PPLN) crystal (see Fig.1 (a)). Pulsed ytterbium and erbium fiber lasers were used as the pump and seed radiation sources respectively. Both of them were assembled basing on a MOPA optical scheme, pulse duration was about 2 ns and repetition rate was 3 MHz. The average output power of Yb-laser was up to 50 W, which is five times higher than the maximum power of Er laser source. The wavelength corresponding to the difference frequency generation for these fiber lasers lies in the 3 μm region. The spectrum of the seed radiation was considerably broadened in the delivery fiber due to the four-wave mixing and Raman scattering. So that, it was possible to obtain the seed radiation in the spectral range from 1.55 m to 1.60 μm. The selective parametric amplification region of seed radiation can be shifted by changing PPLN temperature, as a result, the idler radiation wavelength tuning was achieved. We obtained the idler tuning in 2.9–3.1 μm wavelength range by changing the PPLN temperature from 45 °C to 110 °C. This tuning range was restricted by the spectral width of the Er-laser radiation. The idler radiation power varied from 5.5 W to 8.0 W in the whole tuning range (see Fig.1 (b)). The conversion efficiency reached 15% in respect to the Yb-laser power. As we were not able to measure directly the mid-IR radiation spectrum but it was derived using the experimentally measured spectrum of the amplified seed radiation. Normalized calculation results are shown in Fig.1 (c). The spectral width of the output mid-IR radiation reached 20-30 nm (at a 3 dB FWHM level).
关键词： tunable laser source,mid-infrared,difference frequency generation,PPLN crystal,erbium fiber laser,ytterbium fiber laser
更新于2025-09-11 14:15:04