We report, for the first time, to the best of our knowledge, a femtosecond mode-locked Fe:ZnSe laser. Passive mode locking is implemented using graphene as a saturable absorber. The laser operates at 4.4 µm with a repetition frequency of 100 MHz and 415 mW output power pumped by a fiber 7 W Er:ZBLAN laser. The pulse duration of about 732 fs is retrieved from the first-order autocorrelation function. Additionally, we observe pulsed nanosecond oscillation under continuous-wave pumping and strong amplitude modulation caused by Kerr self-focusing. This Letter fills the gap in operating regimes of Fe:ZnSe lasers and paves the way for the development of powerful ultrafast high-repetition-rate mid-IR sources for the most advanced fields of science.

We have investigated nonlinear laser ̶ matter interaction inside silicon under tight focusing conditions by continuously tuning driving pulse duration from femtosecond to picosecond timescales. Such tailoring of laser pulse width provides a new route for energy delivery into a microvolume avoiding two-photon absorption and plasma defocusing in the pre-focal region. As a result, we have achieved values of saturated deposited energy density and plasma electron concentration of as high as 1 kJ cm −3 and 10 19 cm −3 respectively, which is lower than the threshold of irreversible structural transformation. For further increase of energy delivery inside silicon, a two-color technique supported by extremely tight focusing can be realized, forming a roadmap to the 3D industrial micromachining of planar bulk silicon.

We have developed a robust optical parametric amplifier (OPA) based on three-AgGaS-crystal pumping by a Cr:Forsterite GW femtosecond laser system, generating 150 fs pulses in dual bands of 1.6-2.0 μm (signal wave) and 3.5-5.5 μm (idler wave). By introducing a negative prechirp to the pump, a combined efficiency in two waves of greater than 10% was achieved, with signal energy up to 110 μJ and idler energy up to 43 μJ. Operation parameters of the system (intensity up to 90  TW/cm) make OPA a promising tool for driving nonlinear optical phenomena, including generation of optical harmonics and laser-induced extreme states of matter in solids and liquids. As a proof of principle, we generated harmonics up to the sixth order and sum frequencies in 5 mm thick polycrystalline ZnSe.

We present a method of ultrafast laser-induced microplasma mapping based on the third harmonic generation at tightly focused laser beams in solids. The technique gives a submicron resolution and can be applied for two-dimensional imaging of laser-induced microplasma with the electron density as low as 10−5 ncr produced by a femtosecond laser driver at the plasma formation threshold. High sensitivity and contrast are dictated by nonlinear behavior of the third harmonic yield with the laser field. The demonstrated method gives an opportunity to increase the precision of plasma volume determination in the field of material microstructuring.

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