Abstract-On the effect of third-order dispersion on phase-matched terahertz generation via interfering chirped pulses

Spencer W. Jolly, Frederike Ahr, Koustuban Ravi, Nicholas H. Matlis, Franz X. Kärtner, and Andreas R. Maier

Chirp-and-delay experimental setup (a), identical to the previous work in Ahr et al. [18]. This HR-PR combination produces a train of pulses rather than two pulses of equal energy. A waveplate is used to match perfectly the polarization of the IR light to the PPLN crystal axis. The beam is matched to the aperture of the PPLN crystal using a telescope, the parameters of which depend on the PPLN aperture. A Teflon plate separates the drive laser from the generated THz at the output of the crystal, whose energy is detector using a pyroelectric detector (b). The frequency of the generated THz is verified using an interferometer (c).

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-27-24-34769

High-energy narrowband terahertz (THz) pulses, relevant for a plethora of applications, can be created from the interference of two chirped-pulse drive lasers. The presence of third order dispersion, an intrinsic feature of many high-energy drive lasers, however, can significantly reduce the optical-to-THz conversion efficiency and have other undesired effects. Here, we present a detailed description of the effect of third-order dispersion (TOD) in the pump pulse on the generation of THz radiation via phase-matching of broadband highly chirped pulse trains. Although the analysis is general, we focus specifically on parameters typical to a Ti:Sapphire chirped-pulse amplification laser system for quasi-phase-matching in periodically-poled lithium niobate (PPLN) in the range of THz frequencies around 0.5 THz. Our analysis provides the tools to optimize the THz generation process for applications requiring high energy and to control it to produce desired THz waveforms in a variety of scenarios.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Molecular polarizability anisotropy of liquid water revealed by terahertz-induced transient orientation

Peter Zalden, Liwei Song, Xiaojun Wu, Haoyu Huang, Frederike Ahr, Oliver D. Mücke, Joscha Reichert, Michael Thorwart, Pankaj Kr. Mishra, Ralph Welsch, Robin Santra, Franz X. Kärtner, Christian Bressler,

https://www.nature.com/articles/s41467-018-04481-5

Reaction pathways of biochemical processes are influenced by the dissipative electrostatic interaction of the reagents with solvent water molecules. The simulation of these interactions requires a parametrization of the permanent and induced dipole moments. However, the underlying molecular polarizability of water and its dependence on ions are partially unknown. Here, we apply intense terahertz pulses to liquid water, whose oscillations match the timescale of orientational relaxation. Using a combination of terahertz pump / optical probe experiments, molecular dynamics simulations, and a Langevin dynamics model, we demonstrate a transient orientation of their dipole moments, not possible by optical excitation. The resulting birefringence reveals that the polarizability of water is lower along its dipole moment than the average value perpendicular to it. This anisotropy, also observed in heavy water and alcohols, increases with the concentration of sodium iodide dissolved in water. Our results enable a more accurate parametrization and a benchmarking of existing and future water models.

Abstract-Towards Millijoule Narrowband Terahertz Pulses Using the Chirp-and-Delay Technique

Spencer W. Jolly, Frederike Ahr, Nicholas H. Matlis, Vincent Leroux, Timo Eichner, Koustuban Ravi, Hideki Ishizuki, Takunori Taira, Franz X. Kärtner, and Andreas R. Maier

https://www.osapublishing.org/abstract.cfm?uri=CLEO_QELS-2018-FF1E.3

We show generation of THz pulses of combined energy above 0.5 mJ at 0.361 THz using the chirp-and-delay technique.

© 2018 The Author(s)

Abstract-Millijoule-scale narrowband terahertz pulses via phase manipulation of pump laser pulses

Spencer W. Jolly, Nicholas H. Matlis, Frederike Ahr, Vincent Leroux, Timo Eichner, Anne-Laure Calendron, Hideki Ishizuki, Takunori Taira, Franz X. Kärtner, Andreas R. Maier

https://arxiv.org/abs/1802.02508

Electromagnetic radiation at terahertz (THz) frequencies is a useful tool in probing and controlling matter and light in new and interesting ways, especially at high peak-fields and pulse energies. Generating THz radiation often employs nonlinear optical processes, for which the overlapping of stretched, broadband near-infrared (NIR) pulse copies within nonlinear crystals is common. Here we show that for narrowband THz generation, the higher-order phase present on the NIR pulses offers control of the properties of the THz, for example creating temporally complex THz with multiplexed NIR pulses. We manipulate the phase of two NIR pump pulses independently to remove higher order effects and generate record mJ-level THz in two crystals simultaneously, with an average total energy of 604 microjoule at 361 GHz with 1% bandwidth. This high pulse energy combined with such a narrow bandwidth has broad implications for accelerator applications, resonant driven material studies, and nonlinear THz spectroscopy.

Abstract-Narrowband terahertz generation with chirped-and-delayed laser pulses in periodically poled lithium niobate

Frederike Ahr, Spencer W. Jolly, Nicholas H. Matlis, Sergio Carbajo, Tobias Kroh, Koustuban Ravi, Damian N. Schimpf, Jan Schulte, Hideki Ishizuki, Takunori Taira, Andreas R. Maier, and Franz X. Kärtner

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-11-2118&origin=search

We generate narrowband terahertz (THz) radiation in periodically poled lithium niobate (PPLN) crystals using two chirped-and-delayed driver pulses from a high-energy Ti:sapphire laser. The generated frequency is determined by the phase-matching condition in the PPLN and influences the temporal delay of the two pulses for efficient terahertz generation. We achieve internal conversion efficiencies up to 0.13% as well as a record multicycle THz energy of 40 μJ at 0.544 THz in a cryogenically cooled PPLN.

© 2017 Optical Society of America

Abstract-Narrowband terahertz generation with chirped-and-delayed laser pulses in periodically poled lithium niobate

Frederike Ahr, Spencer W. Jolly, Nicholas H. Matlis, Sergio Carbajo, Tobias Kroh, Koustuban Ravi, Damian N. Schimpf, Jan Schulte, Hideki Ishizuki, Takunori Taira, Andreas R. Maier, and Franz X. Kärtner

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-11-2118

We generate narrowband terahertz (THz) radiation in periodically poled lithium niobate (PPLN) crystals using two chirped-and-delayed driver pulses from a high-energy Ti:sapphire laser. The generated frequency is determined by the phase-matching condition in the PPLN and influences the temporal delay of the two pulses for efficient terahertz generation. We achieve internal conversion efficiencies up to 0.13% as well as a record multicycle THz energy of 40 μJ at 0.544 THz in a cryogenically cooled PPLN.

© 2017 Optical Society of America

Abstract-Temperature dependent refractive index and absorption coefficient of congruent lithium niobate crystals in the terahertz range

Xiaojun Wu, Chun Zhou, Wenqian Ronny Huang, Frederike Ahr, and Franz X. Kärtner
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-23-29729

Optical rectification with tilted pulse fronts in lithium niobate crystals is one of the most promising methods to generate terahertz (THz) radiation. In order to achieve higher optical-to-THz energy efficiency, it is necessary to cryogenically cool the crystal not only to decrease the linear phonon absorption for the generated THz wave but also to lengthen the effective interaction length between infrared pump pulses and THz waves. However, the refractive index of lithium niobate crystal at lower temperature is not the same as that at room temperature, resulting in the necessity to re-optimize or even re-build the tilted pulse front setup. Here, we performed a temperature dependent measurement of refractive index and absorption coefficient on a 6.0 mol% MgO-doped congruent lithium niobate wafer by using a THz time-domain spectrometer (THz-TDS). When the crystal temperature was decreased from 300 K to 50 K, the refractive index of the crystal in the extraordinary polarization decreased from 5.05 to 4.88 at 0.4 THz, resulting in ~1° change for the tilt angle inside the lithium niobate crystal. The angle of incidence on the grating for the tilted pulse front setup at 1030 nm with demagnification factor of −0.5 needs to be changed by 3°. The absorption coefficient decreased by 60% at 0.4 THz. These results are crucial for designing an optimum tilted pulse front setup based on lithium niobate crystals.

© 2015 Optical Society of America

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Abstract-Terahertz generation in lithium niobate driven by Ti:sapphire laser pulses and its limitations

Xiaojun Wu, Sergio Carbajo, Koustuban Ravi, Frederike Ahr, Giovanni Cirmi, Yue Zhou, Oliver D. Mücke, and Franz X. Kärtner  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-18-5403

Optics Letters, Vol. 39, Issue 18, pp. 5403-5406 (2014)
http://dx.doi.org/10.1364/OL.39.005403

We experimentally investigate the limits of 800-nm-to-terahertz (THz) energy conversion in lithium niobate at room temperature driven by amplified Ti:sapphire laser pulses with tilted pulse front. The influence of the pump central wavelength, pulse duration, and fluence on THz generation is studied. We achieved a high peak efficiency of 0.12% using transform limited 150 fs pulses and observed saturation of the optical-to-THz conversion efficiency at a fluence of 15  mJ/cm2 for this pulse duration. We experimentally identify two main limitations for the scaling of optical-to-THz conversion efficiencies: (i) the large spectral broadening of the optical pump spectrum in combination with large angular dispersion of the tilted pulse front and (ii) free-carrier absorption of THz radiation due to multi-photon absorption of the 800 nm radiation.

© 2014 Optical Society of America