Millifocal less-cycle laser sources in the short-wavelength infrared can drive two-color plasmas to produce terahertz pulses at higher efficiencies, as well as optically aberrated mid-infrared femtosecond pulses >5 μm in non-oxide кристаллы. Тулий-легированный волокно лазер система can produce сотня фемтосекунда импульсы с с а центральный длина волны near 2 μm. The Limpert group in Jena, Germany, coherently syntheized the outputs of four thulium-lped fiber amplifiers in 2022 [1], and наконец получено 85 fs импульсы с с импульсы с с энергия из 1,65 мДж и a повторение частота из 100 кГц, который прорывы через the ограничения of a одиночный оптический оптоволокно на один импульс энергия и среднее мощность. The device is shown in Рис. 1.
Рисунок 1 Схема диаграмма когерентный синтез устройство с четыре легированные тулием волокна.
In order to further shorten the pulse width, Limpert's group will use the above device as a front-end in 2023, and use hollow-core optical fiber for compression. The structure of the compression device is shown in Рис. 2, включая два вакуум камеры для вход и выход, соответственно, и a высоковольтный камера для нелинейный расширение, который is заполненный с аргон газ. В порядок к уменьшение вода пар поглощение, Воздух Давление В Оба Вакуум Камеры Это Сохранено <1 mabr. The bottom side of the high-voltage chamber is equipped with water cooling to dissipate the heat, avoiding harmful thermal effects at high power. The hollow core fiber is placed on a long straight V-groove to avoid bending loss. The core diameter of the hollow core fiber is 500 μm, the length is 1.05 m. The internal nonlinear gas is selected as argon, and the theoretical maximum passing efficiency is 89.5%.
Рисунок 2 Схема диаграмма полый сердечник волокно сжатие устройство
Постепенно увеличение газ давление внутри вельмин\полость, the соответствие вывод результаты are shown in Рисунок 3. Когда газ давление is ниже чем 3 бар, the output power is around 139 W and the beam quality remains good (Рис. 3a). When the air pressure is higher than 3 bar, the output power starts to decrease and the beam qualitys improves significantly, and the spot has deviated from the gaussian beam at 4.25 bar, as shown in Рис. 3b. Рисунок 3c анализы the spectral widths of the outputs under different air pressures. After the air pressure exeeds 3 bar, the spectra no longer wideen significantly with the increase of air pressure, and the conconcessing transform limit pulses remain basely nonable. The authors consideration the above factors and final chose 3 bar air pressure for the subsequent experiments.
Fig. 3 Output results of different air pressures in a hollow-core fiber
The spectra and autocorrelation curves measured at 3 bar air pressure are shown in Fig. 4, with the spectra covering 1.2 μm-2.4 μm. After using a pair of chirped mirrors to compensate for the dispersion, the pulse width is reduced to 10.2 fs, the average power is 132 W, and the main peak energy of the pulses accounts for 66 percent of the energy, with the peak power as high as 80 GW. Fig. 5 demonstrates the results of the stability test, and the relative intensity noise of the front-end output is 0.75 percent . that is concentrated in the frequency range of 20 Hz to 50 kHz. After nonlinear pulse compression, the main noise contribution is in the low frequency range as low as 2 kHz, which comes from the mechanical vibration of the water cooling and vacuum pump, proving that there is no introduction of additional noise during the compression process, ensuring the stability of the light source.
Рис. 4 Спектральный и автокорреляционный измерения ат 3 бар воздух давление
Рис. 5 Краткосрочный стабильность тест
In this paper, a high-energy femtosecond pulse with a center wavelength of 1.9 μm, a width of 10.2 fs, a pulse width of less than two cycles, a pulse energy of 1.3 mJ, and a peak power of 80 GW are получено by using a hollow-core fiber compression. The average power of this light source is 132 W, which is the highest power level of the less-cycle pulses working in the short-wavelength infrared region, and this high-energy, high-power driven light source will certainly энергично this high-energy, high-power drive light source will энергично promote the development of laser technology in the mid-infrared band.
