Benedikt W. Mayer

Mid-infrared pulse generation via achromatic quasi-phase-matched OPCPA

We demonstrate a new regime for mid-infrared optical parametric chirped- pulse amplification (OPCPA) based on achromatic quasi-phase-matching. Our mid-infrared OPCPA system is based on collinear aperiodically poled lithium niobate (APPLN) pre-amplifiers and a non-collinear PPLN power amplifier which is operated in an achromatic phase-matching configuration. The idler output has a bandwidth of 800 nm centered at 3.4 µm. After compression, we obtain a pulse duration of 44.2 fs and a pulse energy of 21.8 µJ at a repetition rate of 50 kHz. We explain the wide applicability of the non-collinear QPM amplification scheme we used, including how it could enable octave-spanning OPCPA in a single device when combined with an aperiodic QPM grating.

Sub-four-cycle laser pulses directly from a high-repetition-rate optical parametric chirped-pulse amplifier at 3.4 μm.

We generate sub-four-cycle pulses (41.6 fs) with 12 μJ of pulse energy in the mid-infrared spectral range (center wavelength 3.4 μm) from a high-repetition-rate, collinear three-stage optical parametric chirped-pulse amplifier (OPCPA) operating at 50 kHz. Apodized aperiodically poled MgO:LiNbO3 crystals with a negative chirp rate are employed as gain media to achieve ultrabroadband phase-matching while minimizing optical parametric generation. The seed pulses are obtained via a 1.56 μm femtosecond fiber laser, which is spectrally broadened in a dispersion-shifted telecom fiber to support 1000 nm bandwidth idler pulses in the mid-infrared.

Breakdown of the dipole approximation in strong-field ionization.

We report the breakdown of the electric dipole approximation in the long-wavelength limit in strong-field ionization with linearly polarized few-cycle mid-infrared laser pulses at intensities on the order of 10¹³ W/cm². Photoelectron momentum distributions were recorded by velocity map imaging and projected onto the beam propagation axis. We observe an increasing shift of the peak of this projection opposite to the beam propagation direction with increasing laser intensities. From a comparison with semiclassical simulations, we identify the combined action of the magnetic field of the laser pulse and the Coulomb potential as the origin of our observations.

75 MW few-cycle mid-infrared pulses from a collinear apodized APPLN-based OPCPA

We present an ultra-broadband optical parametric chirped-pulse amplification (OPCPA) system operating at 3.4 µm center wavelength with a peak power of 75 MW. The OPCPA system is split into a pre- and a power-amplifier stage. Both stages are based on apodized aperiodically poled MgO:LiNbO3 (APPLN). The collinear mixing configuration allows us to manipulate the spectral phase of the output mid-infrared pulses by sending the near-infrared seed pulses through a pulse shaper. The system delivers clean 75-fs pulses with record-high 700 mW average power, corresponding to 7 µJ of pulse energy at a repetition rate of 100 kHz.

Design constraints of optical parametric chirped pulse amplification based on chirped quasi-phase-matching gratings.

Chirped quasi-phase-matching (QPM) gratings offer efficient, ultra-broadband optical parametric chirped pulse amplification (OPCPA) in the mid-infrared as well as other spectral regions. Only recently, however, has this potential begun to be realized [1]. In this paper, we study the design of chirped QPM-based OPCPA in detail, revealing several important constraints which must be accounted for in order to obtain broad-band, high-quality amplification. We determine these constraints in terms of the underlying saturated nonlinear processes, and explain how they were met when designing our mid-IR OPCPA system. The issues considered include gain and saturation based on the basic three-wave mixing equations; suppression of unwanted non-collinear gain-guided modes; minimizing and characterizing nonlinear losses associated with random duty cycle errors in the QPM grating; avoiding coincidentally-phase-matched nonlinear processes; and controlling the temporal/spectral characteristics of the saturated nonlinear interaction in order to maintain the chirped-pulse structure required for OPCPA. The issues considered place constraints both on the QPM devices as well as the OPCPA system. The resulting experimental guidelines are detailed. Our results represent the first comprehensive discussion of chirped QPM devices operated in strongly nonlinear regimes, and provide a roadmap for advancing and experimentally implementing OPCPA systems based on these devices.

Frequency-domain nonlinear optics in two-dimensionally patterned quasi-phase-matching media.

Advances in the amplification and manipulation of ultrashort laser pulses have led to revolutions in several areas. Examples include chirped pulse amplification for generating high peak-power lasers, power-scalable amplification techniques, pulse shaping via modulation of spatially-dispersed laser pulses, and efficient frequency-mixing in quasi-phase-matched nonlinear crystals to access new spectral regions. In this work, we introduce and demonstrate a new platform for nonlinear optics which has the potential to combine these separate functionalities (pulse amplification, frequency transfer, and pulse shaping) into a single monolithic device that is bandwidth- and power-scalable. The approach is based on two-dimensional (2D) patterning of quasi-phase-matching (QPM) gratings combined with optical parametric interactions involving spatially dispersed laser pulses. Our proof of principle experiment demonstrates this technique via mid-infrared optical parametric chirped pulse amplification of few-cycle pulses. Additionally, we present a detailed theoretical and numerical analysis of such 2D-QPM devices and how they can be designed.

Breakdown of dipole approximation in strong field ionization

Ionization with a few-cycle mid-infrared laser field results in an electron momentum shift directed opposite to the beam pressure. This result represents a breakdown of the dipole approximation, in contrast to previous observations of photon-momentum-transfer.

Non-dipole Effects on Rescattered Photoelectrons from Strong-field Ionization with Elliptical Polarization

We study strong-field ionization with elliptically polarized mid-IR pulses beyond the long-wavelength limit of the dipole approximation. Rescattering creates a sharp structure in 3D photoelectron momentum distributions influenced by non-dipole effects.

Broadband 2D-QPM Frequency Domain OPA

We demonstrate broadband mid-IR frequency-domain OPA (FOPA) in the Fourier-plane of a 4f pulse shaper via two-dimensional (2D) quasi-phasematching (QPM) device adapted to the pump intensity profile and spatial chirp of the mid-infrared beam.

Exploring characteristics of strong-field ionization dynamics in the mid-infrared regime

We present a study of features in photoelectron momentum distributions from strong-field ionization of noble gases for few-cycle pulses in the mid-infrared regime and assign characteristics to their classical and quantum mechanical origin.