R. Lopez-Martens

Generation of 4.3 fs, 1 mJ laser pulses via compression of circularly polarized pulses in a gas-filled hollow-core fiber

We report the generation of 4.3 fs, 1 mJ pulses at 1 kHz using a hollow-core fiber compressor seeded with circularly polarized laser pulses. We observe up to 30% more energy throughput compared to the case of linearly polarized laser input, together with significantly improved output spectral stability. Seeding with circularly polarized pulses proves to be an effective approach for high-energy operation of the hollow-fiber compression technique.

Frequency chirp of harmonic and attosecond pulses

We study the phase of the atomic polarization in the process of high-order harmonic generation. Its dependence on the laser intensity and the harmonic order induce a frequency variation in time (chirp) respectively of the harmonic pulses and attosecond pulses. We review the recent experimental results on the temporal characterization of the harmonic emission and show that measurements performed using very different techniques (like XFROG and RABITT), probing the phase in different parameter spaces, can be connected through the mixed phase derivatives, demonstrating the common underlying physics.

Carrier-envelope phase stabilization and control using a transmission grating compressor and an AOPDF

Carrier-envelope phase (CEP) stabilization of a femtosecond chirped-pulse amplification system featuring a compact transmission grating compressor is demonstrated. The system includes two amplification stages and routinely generates phase-stable (approximately 250 mrad rms) 2 mJ, 25 fs pulses at 1 kHz. Minimizing the optical pathway in the compressor enables phase stabilization without feedback control of the grating separation or beam pointing. We also demonstrate for the first time to the best of our knowledge, out-of-loop control of the CEP using an acousto-optic programmable dispersive filter inside the laser chain.

Efficient generation of cross-polarized femtosecond pulses in cubic crystals with holographic cut orientation

We report here an alternative and more efficient orientation of cubic crystals for generation of cross-polarized femtosecond laser pulses. We show both theoretically and experimentally that the cross polarized wave generation (XPWG) is more efficient when the fundamental beam propagates along the [011] direction (holographic cut) in the crystal than along the [001] direction previously reported. With the [011]-cut BaF2 crystal we measured the highest XPWG conversion efficiencies. We prove other very important advantages of the [011]-cut approach: weak induced phase mismatch and no need for its compensation.

Broadband attosecond pulse shaping

We present experiments on the control over spectral amplitude and phase of attosecond pulses, using metallic and semiconductor thin-film dispersive filters. A pulse duration as short as 130 as is obtained.

Generation of high-fidelity, down-chirped sub-10fsmJ pulses through filamentation for driving relativistic laser-matter interactions at 1kHz

The authors present a simple add on for multicycle, multimJ Ti:sapphire-based amplifier systems to efficiently generate 9.5fs pulses with 1.8mJ. Filamentary propagation yields spectrally broadened pulses carrying an unexpected large group-delay dispersion of −500fs2 which allows linear propagation of the few-cycle pulses towards target areas without need of any sophisticated dispersion control. Pulse compression could easily be achieved by transmission through a combination of different glass substrates. The pulse wave front, the low energy fluctuations, and the good temporal contrast make this source well suited for relativistic laser-solid experiments with intense few-cycle pulses at kilohertz repetition rate.

Single attosecond pulse production with an ellipticity-modulated driving IR pulse

We theoretically study attosecond pulse production via high-harmonic generation using a driving laser pulse with a time-dependent ellipticity. The theoretical approach produces results that agree with our experimental data obtained using 35 fs driving laser pulses and is further used to study the generation of single attosecond pulses with shorter laser pulses. We find an equation for the duration of the temporal window created by the time-varying driving laser polarization in which high-harmonic emission can occur. We formulate the necessary requirements concerning the driving laser field in order to confine the high-harmonic emission in the form of a single attosecond pulse. Indeed, we show that using incident 12 fs laser pulses single attosecond pulses can be produced for certain carrier-envelope phase (CEP) values of the driving pulse. For 6 fs incident laser pulses, single attosecond pulses are produced for all values of the CEP (the intensity of the attosecond pulse still depends on the actual value of the CEP). If implemented with state-of-the-art 5 fs laser pulses, this technique can even lead to the production of sub-100 as pulses.

Efficient hollow fiber compression scheme for generating multi-mJ, carrier-envelope phase stable, sub-5 fs pulses

We show that a standard hollow-core fiber (HCF) compressor device can be used to efficiently compress multi-mJ energy laser pulses down to few-cycle duration, when seeded with linearly chirped, circularly polarized pulses. With this approach, we routinely generate carrier-envelope phase (CEP)-locked, 1.6 mJ, 4.8 fs pulses using only 3 mJ, 25 fs pulses as the seed.

Spectral reshaping and pulse compression via sequential filamentation in gases.

We provide a theoretical description of the spatio-temporal dynamics of sequential filamentation in noble gases that can lead to pulse compression down to nearly single-cycle pulses. We show that the strong pulse compression occurs as a result of serially-generated on-axis filaments and spectral filtering of an extensive blue-shifted compressible spectra. We show that the dynamics of this sequential filamentation can be readily tuned by varying the gas pressure and can be scaled to various pulse energies.

Cross-polarized wave generation in the UV region

We demonstrate experimentally the generation of cross-polarized femtosecond pulses in BaF2 crystal in the UV region. We show that unsaturated cross-polarized wave generation in the UV is six times more efficient than in the visible region, and we deduce the corresponding wavelength dispersion of the third-order nonlinearity.