[21a-211A-1~11] 3.6 Ultrashort-pulse and high-intensity lasers

▲ [21a-211A-8] Generating sub-100 nJ soft x-ray super continuum at 120-eV region by a fully stabilized three-channel optical waveform synthesizer

〇(P)Bing Xue¹, Yuxi Fu¹, Koutaro Nishimura², Akira Suda², Katsumi Midorikawa¹, Eiji E. Takahashi¹ (1.RAP, RIKEN, 2.Tokyo University of Science)

Keywords:optical waveform synthesizer, High-order harmonics, Soft X-ray super continuum

Previously, we reported a 50 mJ three-channel optical waveform synthesizer operating at 10 Hz and applied high order harmonic generation in argon gas. In this work, the synthesizer’s performance is updated and applied to generate broadband (>30 eV) soft X-ray supercontinuum at 100 eV in neon gas. Briefly, The typical single shot CEP noise of the 10-Hz pump pulses has been stabilized to be 524 mrad.. By introducing Mach-Zehnder (MZ) interferometer and balanced optical cross-correlator (BOC), the delay jitters are successfully suppressed (MZ for both < 20 as, BOC for signal & pump < 245 as). The synthesized pulses are focused by using two separated long focal length lenses (4.5 m for pump pulse, 3.5 m for signal and idler pulses) into a 10 cm long neon gas filled cell. The focused intensity in the three-color case is measured to be 4.4 × 10¹⁴ W/cm² with 20 mJ, 4.3 mJ and 1.6 mJ input pulse energy for pump, signal and idler, respectively. A broadband (>30 eV) continuum harmonic spectrum is generated around the cut-off region (90 ~ 120 eV) when using synthesized pulse input (gas pressure: 8.8 torr). By increasing the pump pulse energy up to 25 mJ and using a 5 cm length cell, we further extend the supercontinuum to 100 ~ 130 eV and obtain higher intensity. Taking our previous experimental results [1] into account, the continuum soft-x-ray spectrum (100 ∼ 130 eV) is evaluated to be approximately 42 nJ, which supports 100 as transform-limited pulses. Our supper continuum HH intensity is almost 1,000-fold higher than the energies previously reported [2].
[1] E. J. Takahashi, et al., Appl. Phys. Lett. 84, 4 (2004)
[2] E. Goulielmakis, et al., Single-cycle nonlinear optics. Science 320, 1614-1617 (2008)