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).