E. A. Migal

Mid-IR (4–5 µm) femtosecond multipass amplification of optical parametric seed pulse up to gigawatt level in Fe2+:ZnSe with optical pumping by a solid-state 3 µm laser

We demonstrate a first-of-its-kind efficient amplification of a broadband tunable (from 3.8 to 4.8 µm) mid-IR femtosecond seed pulse generated from a AgGaS2-based optical parametric amplifier pumped by a Cr:forsterite laser in a multi-pass Fe2+:ZnSe amplifier optically pumped by a solid-state nanosecond Cr:Yb:Ho:YSGG laser. A total gain of 2000 for an input seed energy of 40 nJ has been obtained. The magnitude of the output energy reaches 80 µJ at a pulse duration of 200 fs.

Toward sub-terrawatt mid-IR (4-5 micrometer) femtosecond hybrid laser system based on parametric seed pulse generation and amplification in Fe2+: ZnSe

For the first time, an experimentally measured seed pulse gain of about 2 cm−1 allows possibilities in the scaling power of such a femtosecond laser system in terawatts. The concept of a subterawatt power level hybrid femtosecond mid-IR (4–5 μm) laser system, based on a weak pulse from an optical parametric mid-IR seeder that is amplified in chalcogenide monocrystalline Fe2+:ZnSe, to gain medium has been proposed and designed. The method and approach for optimizing the choice of nonlinear medium, its length, and the required light intensity for the efficient non-linear self-compression of an ultrashort pulse has also been proposed and considered.

Broadband femtosecond parametric amplification in KTA close to mid-IR transparency cutoff

We report an increase in conversion efficiency and significant broadening of signal and idler bandwidth in the collinear KTA optical parametric amplifier operating close to mid-IR transparency cutoff (5.2 μm) for a visible and near IR pump. Using a 1.24 μm pump we have produced 2 μJ idler pulses at 3.8 μm central wavelength with a bandwidth supporting 65 fs transform limited duration. Further tuning to mid-IR up to 5 μm could be achieved with a 620 nm pump.

Generation of Broadband Near-Infrared (2–2.5 μm) Radiation from an Optical Parametric Amplifier Driven by a Cr:Forsterite Laser Near Dispersion Anomalies of Tuning Curves

Pulses with a spectral width of 450 nm at a wavelength of 2.2 μm are generated in a parametric amplifier based on a type-I BBO crystal pumped by the second harmonic (620 nm) of a Cr:forsterite laser. Such a broadband radiation is obtained in a specific regime of the group velocity matching near the vertical region of the tuning curve. The generated pulses can be compressed to a duration of about 2.5 optical cycles (34 fs) in a medium with positive group-velocity dispersion.

Real-Time Monitoring of the Energy Deposition under the Tight Focusing of Femtosecond Laser Radiation into a Bulk Transparent Dielectric Based on Third Harmonic Signal

It has been found that the third harmonic generated under the tight focusing of a near-infrared (1.24-μm) femtosecond laser pulse indicates the energy deposition into the bulk transparent dielectric and can be used as a feedback system in the process of microstructuring. A third harmonic signal is sensitive to a change in both the size of a laser-induced microplasma and the free-electron density, which allows the detection of the microplasma with submicron longitudinal sizes. It has been shown that the method based on the third harmonic is universal and can be applied in both single-pulse and two-color microstructuring.

Mid-IR (4–5 μm) hybrid sub-GW Fe 2+ :ZnSe femtosecond laser system

We demonstrate an efficient amplification of the broadband tunable (from 3.8 μm up to 4.8 μm) mid-IR femtosecond (∼200 fs) seed pulse in optically pumped Fe2+:ZnSe amplifier [1]. The experimental setup is sketched in Fig. 1a. Seed radiation was generated in two-stage AGS-based optical parametric amplifier pumped by Cr:forsterite laser [2]. Mid-IR output radiation with energy up to 1 μJ was then directed into a multipass amplifier. Iron-doped ZnSe crystal was pumped by Q-switched Cr:Yb:Ho:YSGG laser with 40 ns pulse duration, total energy of 20 mJ, operating at 2.85 μm wavelength [3]. In order to prevent carbon dioxide absorption, the last OPA stage and multi-pass amplifier was placed in the chamber, where atmospheric air was substituted by noble gas. Prior to the main experiments, gain evolution measurements were carried out. They have shown that the lifetime of population inversion of Fe2+:ZnSe strongly depends on the temperature. It increases from 350 ns (at room temperature) up to 1 μs (at 7 degrees Celsius) paving the way for multi-pass amplification. As a result, femtosecond seed radiation with energy 0.7 μJ centered at 4.3 μm was amplified in six-pass Fe2+:ZnSe amplifier up to the energy 70 μJ (Fig. 1b), which corresponds to 0.5 GW peak power. Decreasing of the input energy down to 40 nJ did not prevent to decrease in output energy. Therefore the total gain was about 2000. Inset in fig. 1 (b) presents far-field beam profile of amplified pulses. Substitution of air by argon removes spectral distortions in the laser pulse caused by the absorption by atmospheric CO2 molecules. It does not radically improve the amplification process in Fe2+:ZnSe but stabilizes the operating regime (Fig. 1c).

Efficient femtosecond mid-IR (4–5 μm) AGS OPA pumped by Cr:Forsterite laser

Femtosecond mid-IR laser sources are of great demand due to its usefulness in a number of applications ranging from strong field phenomena to medical and environmental sensing. Nowadays devices based on OPA and OPCPA techniques had become a typical approach to produce mid-IR radiation. However, with Ti:Sapphire pump laser efficiency of OPAs in 4–5 μm range is rather low mainly due to the lack of suitable nonlinear crystals, whereas OPCPA schemes are incredibly complex [1, 2].

Gigawatt mid-IR (4-5 μm) femtosecond hybrid Fe2+:ZnSe laser system

We demonstrate a first-of-its-kind efficient chirped pulse amplification of broadband mid-IR (4-5 μm) femtosecond seed pulse (230 ps, 4μJ) generated in AgGaS2 based OPA driven by Cr:forsterite laser in multi-pass Fe2+:ZnSe amplifier optically pumped by solid-state Q-switched Cr:Yb:Ho:YSGG laser (2.85 μm, 30mJ, 5Hz, 0.6 J/cm2). The system delivers 1.2 mJ at pulse duration of 230 ps. Straightforward compression to 150 fs pulse is achievable with 70% efficiency using diffraction grating pair with peak power of about 6 GW. Further non-linear compression in a bulk CaF2 due to the SPM and anomalous GVD should provide the enhancement of peak power up to 20 GW. Possible routes to reach sub-TW and even TW power level in mid-IR are discussed.