Numerical study of spatiotemporal distortions in noncollinear optical parametric chirped-pulse amplifiers

During amplification in a noncollinear optical parametric amplifier the spatial and temporal coordinates of the amplified field are inherently coupled. These couplings or distortions can limit the peak intensity, among other things. In this work, a numerical study of the spatiotemporal distortions in BBO-based noncollinear optical parametric chirped-pulse amplifiers (NOPCPAs) is presented for a wide range of parameters and for different amplification conditions. It is shown that for Gaussian pump beams, gain saturation introduces strong distortions and high conversion efficiency always comes at the price of strong spatiotemporal couplings which drastically reduce the peak intensity even when pulse fronts of the pump and the signal are matched. However, high conversion efficiencies with minimum spatiotemporal distortions can still be achieved with flat-top pump beam profiles

Ultrashort pulse generation in the mid-IR

Recent developments in laser sources operating in the mid-IR (3–8μm) have been motivated by the numerous possibilities for both fundamental and applied research. One example is the ability to unambiguously detect pollutants and carcinogens due to the much larger oscillator strengths of their absorption features in the mid-IR spectral region compared with the visible. Broadband sources are of particular interest for spectroscopic applications since they remove the need for arduous scanning or several lasers and allow simultaneous use of multiple absorption features thus increasing the confidence level of detection. In addition, sources capable of producing ultrashort and intense mid-IR radiation are gaining relevance in attoscience and strong-field physics due to wavelength scaling of re-collision based processes. In this paper we review the state-of-the-art in sources of coherent, pulsed mid-IR radiation. First we discuss semi-conductor based sources which are compact and turnkey, but typically do not yield short pulse duration. Mid-IR laser gain material based approaches will be discussed, either for direct broadband mid-IR lasers or as narrowband pump lasers for parametric amplification in nonlinear crystals. The main part will focus on mid-IR generation and amplification based on parametric frequency conversion, enabling highest mid-IR peak power pulses. Lastly we close with an overview of nonlinear post-compression techniques, for decreasing pulse duration to the sub-2-optical-cycle regime.Peer ReviewedPostprint (author's final draft

Bulk continuum generation: the ultimate tool for laser applications and spectroscopy

This thesis investigates bulk continuum generation. A full study of all relevant parameter is given. In addition, its application in ultrafast and widly tunable amplifiers and spectrometers is shown

Third-generation femtosecond technology

Chirped pulse amplification in solid-state lasers is currently the method of choice for producing high-energy ultrashort pulses, having surpassed the performance of dye lasers over 20 years ago. The third generation of femtosecond technology based on short-pulse-pumped optical parametric chirped pulse amplification (OPCPA) holds promise for providing few-cycle pulses with terawatt-scale peak powers and kilowatt-scale-average powers simultaneously, heralding the next wave of attosecond and femtosecond science. OPCPA laser systems pumped by near-1-ps pulses support broadband and efficient amplification of few-cycle pulses due to their unrivaled gain per unit length. This is rooted in the high threshold for dielectric breakdown of the nonlinear crystals for even shorter pump pulse durations. Concomitantly, short pump pulses simplify dispersion management and improve the temporal contrast of the amplified signal. This thesis covers the main experimental and theoretical steps required to design and operate a high-power, high-energy, few-cycle OPCPA. This includes the generation of a broadband, high-contrast, carrier envelope phase (CEP)-stable seed, the practical use of a high-power thin-disk regenerative amplifier, its efficient use for pumping a multi-stage OPCPA chain and compression of the resulting pulses. A theoretical exploration of the concept and its extension to different modes of operation, including widely-tunable, high-power multi-cycle pulse trains, and ultrabroadband waveform synthesis is presented. Finally, a conceptual design of a field synthesizer with multi-terawatt, multi-octave light transients is discussed, which holds promise for extending the photon energy attainable via high harmonic generation to several kiloelectronvolts, nourishing the hope for attosecond spectroscopy at hard-x-ray wavelengths

Parametric amplification of optical phonons

Amplification of light through stimulated emission or nonlinear optical interactions has had a transformative impact on modern science and technology. The amplification of other bosonic excitations, like phonons in solids, is likely to open up new remarkable physical phenomena. Here, we report on an experimental demonstration of optical phonon amplification. A coherent mid-infrared optical field is used to drive large amplitude oscillations of the Si-C stretching mode in silicon carbide. Upon nonlinear phonon excitation, a second probe pulse experiences parametric optical gain at all wavelengths throughout the reststrahlen band, which reflects the amplification of optical-phonon fluctuations. Starting from first principle calculations, we show that the high-frequency dielectric permittivity and the phonon oscillator strength depend quadratically on the lattice coordinate. In the experimental conditions explored here, these oscillate then at twice the frequency of the optical field and provide a parametric drive for lattice fluctuations. Parametric gain in phononic four wave mixing is a generic mechanism that can be extended to all polar modes of solids, as a new means to control the kinetics of phase transitions, to amplify many body interactions or to control phonon-polariton waves

CEP-stable Tunable THz-Emission Originating from Laser-Waveform-Controlled Sub-Cycle Plasma-Electron Bursts

We study THz-emission from a plasma driven by an incommensurate-frequency two-colour laser field. A semi-classical transient electron current model is derived from a fully quantum-mechanical description of the emission process in terms of sub-cycle field-ionization followed by continuum-continuum electron transitions. For the experiment, a CEP-locked laser and a near-degenerate optical parametric amplifier are used to produce two-colour pulses that consist of the fundamental and its near-half frequency. By choosing two incommensurate frequencies, the frequency of the CEP-stable THz-emission can be continuously tuned into the mid-IR range. This measured frequency dependence of the THz-emission is found to be consistent with the semi-classical transient electron current model, similar to the Brunel mechanism of harmonic generation

Development of a high intensity Mid-Ir OPCPA pumped by a HO:YLF amplifier

The continuous development of laser sources delivering ultra-short light pulses underpins much of the current progress in experimental science, particularly in the domain of physics concerned with strong-field phenomena. Laser systems that allow scaling of strong-field experiments to unexplored regions of the electromagnetic spectrum, specially the mid-IR range (2 µm < lambda < 20 µm), have proved to be a powerful tool enabling the study of new physical processes. It is becoming clear however, that conventional laser sources are unsuited for this purpose, and in order to fully investigate these novel regimes a new generation of laser systems is required. This thesis describes a new laser source of high-intensity, mid-IR light. A long-wavelength pumped optical parametric chirped pulse amplifier (OPCPA) design is chosen as the architecture for this laser, overcoming many of the drawbacks hindering other approaches. This thesis presents two novel sub-systems required for the successful development of a mid-IR OPCPA. The first is a compact, fibre-driven source of broadband mid-IR pulses relying on difference frequency generation (DFG) in the nonlinear crystal CdSiP2. This laser is the seed source in the OPCPA and supports transform-limited pulses corresponding to less than 3 optical cycles at the operating wavelength of 7 µm. The second sub-system is a pump source based on a Ho:YLF chirped pulse amplifier (CPA) pumped by commercial Tm-fibre laser. The pump system delivers over 0.25 J of pulse energy at a wavelength of 2052 nm. The laser system described in this thesis is a developmental milestone towards the realisation of a multi-mJ source of few-cycle duration, carrier-to-envelope phase (CEP) stable mid-IR pulses. The system is designed to operate at a centre wavelength of 7 µm, delivering pulses with an energy of 0.2 mJ and a temporal duration of 180 fs at 100 Hz repetition rate. The output parameters of the laser presented in this work lead to a peak power of 1.1 GW and potentially a peak intensity of 7·1014 W/cm2. These values are already compatible with strong-field experiments and enable a ponderomotive force 77 times larger than a standard Ti:Sapphire laser.El desarrollo de fuentes de luz láser que emiten pulsos ultracortos sustenta una parte importante del progreso actual en ciencia experimental, especialmente en el ramo de la física relacionada con los fenómenos de campo electromagnético intensos. Los sistemas láser que permiten escalar experimentos de campo electromagnético intenso a regiones sin explorar del espectro electromagnético, especialmente en el rango del infra-rojo medio (2 µm < lambda < 20 µm), han demostrado ser una poderosa herramienta facilitando el estudio de nuevos procesos físicos. Sin embargo, las fuentes láser convencionales no son adecuadas para este propósito, y para investigar a fondo estos nuevos regímenes se requiere una nueva generación de sistemas láser. Esta tesis describe una nueva fuente láser de luz de infra-rojo medio de alta intensidad. La arquitectura que elegimos es un amplificador de pulso óptico dispersado paramétrico (OPCPA por sus siglas en inglés) bombeado con una longitud de onda larga y superando así muchos de los inconvenientes de otros diseños. Esta tesis presenta dos sub-sistemas nuevos necesarios para el desarrollo exitoso de un OPCPA de infra-rojo medio. El primero es una fuente compacta de infra-rojo medio basada en un láser de fibra generando pulsos de banda ancha utilizando generación por diferencia de frecuencia (DFG por sus siglas en inglés) en el cristal no lineal CdSiP2. Este láser es la fuente origen del OPCPA y genera pulsos con un ancho de banda compatible con una duración menor a 3 ciclos ópticos a la longitud de onda central de 7 µm. El segundo subsistema es una fuente de bombeo basada en un amplificador de pulso dispersado (CPA por sus siglas en inglés) en el material Ho:YLF bombeado por un láser comercial de fibra dopada con tulio. El sistema de bombeo proporciona más de 0.25 J de energía por pulso a una longitud de onda de 2052 nm. El sistema láser descrito en esta tesis es un paso importante hacia el desarrollo de una fuente de infra-rojo medio capaz de generar pulsos con energía de multi-mJ de pocos ciclos ópticos de duración y fase de portador a envolvente estable (CEP por sus siglas en inglés). El sistema está diseñado para operar a una longitud de onda central de 7 µm, generando pulsos con una energía de 0.2 mJ y una duración temporal de 180 fs a una frecuencia de repetición de 100 Hz. La especificación del láser presentado en este trabajo conduce a una potencia máxima de 1.1 GW y potencialmente a una intensidad máxima de 7 · 1014 W / cm2. Estos valores ya son compatibles con experimentos de campo fuerte y permiten una fuerza pondero-motriz 77 veces mayor que un láser estándar de Titanio-Zafiro