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We present THz generation in a back-cooled spintronic THz emitter in reflection geometry, excited with a high-average power Yb-laser providing up to 18.5 W at 400 kHz repetition rate. This allows us to increase the THz power.

In this work, we perform Terahertz (THz) Kerr Effect (TKE) experiments on several types of molecular liquids with dissolved iodide anions. We couple high intensity single-cycle THz pulses to the re-orientational motions of the aforementioned liquids and observe a subsequent energy transfer to the translational degrees of freedom of the ionic solutes manifesting as an increase of their translational kinetic energy. Surprisingly, this solvent-to-solute energy transfer is found to scale significantly with the particular intermolecular interactions of the liquids, being more dramatic when a hydrogen-bonding network is present. Our observations set the basis for future coherent control of chemical reactions in the liquid state, by means of THz radiation.

In bilayers consisting of a normal metal (N) with spin-orbit coupling and a ferromagnet (F), the combination of the spin-Hall effect, the spin-transfer torque, and the inverse spin-Hall effect gives a small correction to the in-plane conductivity of N, which is referred to as spin-Hall magnetoresistance (SMR). We here present a theory of the SMR and the associated off-diagonal conductivity corrections for frequencies up to the terahertz regime. We show that the SMR signal has pronounced singularities at the spin-wave frequencies of F, which identifies it as a potential tool for all-electric spectroscopy of magnon modes. A systematic change of the magnitude of the SMR at lower frequencies is associated with the onset of a longitudinal magnonic contribution to spin transport across the F-N interface., Comment: 21 pages, 9 figures

We demonstrate phase-resolved detection of femtosecond voltage transients in a scanning tunneling microscope induced by ultrabroadband THz pulses from a spintronic emitter, and probe hot electron dynamics inside the photoexcited junction on the nano-femtoscale.

The anomalous Hall effect (AHE) is a fundamental spintronic charge-to-charge-current conversion phenomenon and closely related to spin-to-charge-current conversion by the spin Hall effect. Future high-speed spintronic devices will crucially rely on such conversion phenomena at terahertz (THz) frequencies. Here, it is revealed that the AHE remains operative from DC up to 40 THz with a flat frequency response in thin films of three technologically relevant magnetic materials: DyCo

The spin Hall effect in heavy-metal thin films is routinely employed to convert charge currents into transverse spin currents and can be used to exert torque on adjacent ferromagnets. Conversely, the inverse spin Hall effect is frequently used to detect spin currents by charge currents in spintronic devices up to the terahertz frequency range. Numerous techniques to measure the spin Hall effect or its inverse were introduced, most of which require extensive sample preparation by multi-step lithography. To enable rapid screening of materials in terms of charge-to-spin conversion, suitable high-throughput methods for measuring the spin Hall angle are required. Here, we compare two lithography-free techniques, terahertz emission spectroscopy and broadband ferromagnetic resonance, to standard harmonic Hall measurements and theoretical predictions using the binary-alloy series Au$_x$Pt$_{1-x}$ as benchmark system. Despite being highly complementary, we find that all three techniques yield a spin Hall angle with approximately the same $x$~dependence, which is also consistent with first-principles calculations. Quantitative discrepancies are discussed in terms of magnetization orientation and interfacial spin-memory loss., Comment: 9 pages, 3 figures

In THz-gated Scanning Tunneling Microscopy (THz-STM), the electric field of a single-cycle THz pulse acts as a transient bias modulating the STM-junction, enabling control of the tunneling current on femtosecond time scales. Optimal operation of a THz-STM requires exact knowledge and precise control of the THz near field waveform. In this regard, we demonstrate THz near field sampling via THz-induced modulation of ultrafast photocurrents in a metal-metal junction, and characterize in detail the coupling of broadband (1-30 THz) single-cycle THz pulses generated from a spintronic emitter to the STM tip. Specifically, we show that employing NIR laser pulses with a curved wavefront for THz generation allows for precise control of the phase, amplitude and bandwidth of the THz near field. Depending on the excitation conditions, THz near fields with frequencies up to 10 THz and peak voltages of several volts can be achieved at 1 MHz repetition rate.

In laser-excited ferromagnetic heterostructures, both ultrafast local magnetization dynamics and spin-transport processes can lead to a THz emission. Here, we demonstrate that the THz emission spectroscopy is a powerful tool to investigate ultrafast magnetization dynamics in laser-excited magnetic systems. The polarity of emitted THz can be used to distinguish which process, local or non-local, dominates the emission of THz in a ferromagnetic heterostructure. The measured THz radiation can be used for rigorous reconstruction of ultrafast magnetization process in the laser-excited magnetic material.

Coupling phase-stable single-cycle terahertz (THz) pulses to scanning tunneling microscope (STM) junctions enables spatio-temporal imaging with femtosecond temporal and \r{A}ngstrom spatial resolution. The time resolution achieved in such THz-gated STM is ultimately limited by the sub-cycle temporal variation of the tip-enhanced THz field acting as an ultrafast voltage pulse, and hence by the ability to feed high-frequency, broadband THz pulses into the junction. Here, we report on the coupling of ultrabroadband (1-30 THz) single-cycle THz pulses from a spintronic THz emitter(STE) into a metallic STM junction. We demonstrate broadband phase-resolved detection of the THz voltage transient directly in the STM junction via THz-field-induced modulation of ultrafast photocurrents. Comparison to the unperturbed far-field THz waveform reveals the antenna response of the STM tip. Despite tip-induced low-pass filtering, frequencies up to 15 THz can be detected in the tip-enhanced near-field, resulting in THz transients with a half-cycle period of 115 fs. We further demonstrate simple polarity control of the THz bias via the STE magnetization, and show that up to 2 V THz bias at 1 MHz repetition rate can be achieved in the current setup. Finally, we find a nearly constant THz voltage and waveform over a wide range of tip-sample distances, which by comparison to numerical simulations confirms the quasi-static nature of the THz pulses. Our results demonstrate the suitability of spintronic THz emitters for ultrafast THz-STM with unprecedented bandwidth of the THz bias, and provide insight into the femtosecond response of defined nanoscale junctions., Comment: 5 figures, supporting information available

We explore power and bandwidth scaling for the generation of highly-temporally-confined THz transients from spintronic emitters, driven by the 250-fs and 20-fs pulses of a high-power 28-MHz Yb-based laser, spectrally centered at 1030 nm.

We investigate ultrafast magnetization dynamics in encapsulated iron films, benefitting from their laser-induced terahertz emission. Combined with first-principles theoretical modeling, the experimental results provide quantitative insights into the observed magnetization dynamics.

Reliable modulation of terahertz electromagnetic waveforms is important for many applications. Here, we rapidly modulate the direction of the electric field of linearly polarized terahertz electromagnetic pulses with 1–30 THz bandwidth by applying time-dependent magnetic fields to a spintronic terahertz emitter. Polarity modulation of the terahertz field with more than 99% contrast at a rate of 10 kHz is achieved using a harmonic magnetic field. By adding a static magnetic field, we modulate the direction of the terahertz field between angles of, for instance, −53° and 53° at kilohertz rates. We believe our approach makes spintronic terahertz emitters a promising source for low-noise modulation spectroscopy and polarization-sensitive techniques such as ellipsometry at 1–30 THz.

Coherently excited phonons are unique tools to control material properties, drive phase transitions or even access hidden phases on ultrafast time scales. The increasing availability of high-field THz and mid-infrared sources facilitates targeting of specific resonantly driven phonon modes, while leaving the material in its electronic ground state. Nevertheless, this direct excitation is restricted to IR-active modes, whereas purely Ramanactive modes are symmetry protected against even intense resonant THz fields. Thus, for Raman-active modes, nonlinear excitation mechanisms must be employed, which are either mediated through modulation of the electric polarizability or through anharmonicities of the crystal lattice. Respectively, these difference-frequency processes are conventional impulsive stimulated Raman scattering (ISRS) and, more recently, ionic Raman scattering (IRS), which both lack the precise selectivity of resonant excitation. Here, we present the THz sum-frequency counterparts of these two mechanisms, which are more selective, nonimpulsive, and provide direct control over the phonon phase. We demonstrate THz sum-frequency excitation of the archetypal Raman-active phonon in diamond. This two-photon absorption process, the upconversion counter part of ISRS, directly imprints the carrier-envelope phase of the light field onto the coherent phonon’s phase. Additionally, our theoretical formalism based on first-principles calculations in combination with phenomenological modeling predicts an efficient sum-frequency counterpart for IRS, which was subsequently confirmed by other experimental research groups. In summary, we complete the map of photonic and ionic Raman excitation mechanisms with their sumfrequency counterparts, providing a comprehensive guide for selective excitation of coherent phonons and other Raman-active modes by strong THz fields.

THz emission spectroscopy is a powerful tool to access ultrafast magnetization dynamics in laser-excited magnetic systems. Here, we demonstrate femtosecond terahertz magnetometry, a method that can be used to rigorously reconstruct the (sub)picosecond-timescale magnetization dynamics in photoexcited magnetic sample from the detected THz emission. Considering the propagation of the THz field from the surface of the sample to the THz electro-optic sampling unit, we establish the transfer function, which allows us to obtain the ultrafast magnetization dynamics in the laser-excited sample in a calibrated manner.

We study the impact of an external electric DC field on antenna-coupled spintronic THz emitters driven by a 90 fs, 1550 nm laser oscillator. Simultaneous application of external electric and magnetic field shows a quadratic decrease in peak-peak THz pulse with increase in the bias voltage. We ascribe this decrease to Joule heating caused by the DC current flowing through the spintronic material.

The anomalous Hall effect (AHE) is a fundamental spintronic charge-to-charge-current conversion phenomenon and closely related to spin-to-charge-current conversion by the spin Hall effect. Future h ...

A review on the recent development of intense laser-driven terahertz (THz) sources is provided here. The technologies discussed include various types of sources based on optical rectification (OR), spintronic emitters, and laser-filament-induced plasma. The emphasis is on OR using pump pulses with tilted intensity front. Illustrative examples of newly emerging applications are briefly discussed, in particular strong-field THz control of materials and acceleration and manipulation of charged particles.

Understanding the transfer of spin angular momentum is essential in modern magnetism research. A model case is the generation of magnons in magnetic insulators by heating an adjacent metal film. Here, we reveal the initial steps of this spin Seebeck effect with, 14 pages, 5 figures

The dielectric response of liquids in the terahertz (THz) and sub-THz frequency range arises from low-energy collective molecular motions, which are often strongly influenced by intermolecular interactions. To shed light on the microscopic origin of the THz dielectric response of the simplest alcohol, methanol, we resonantly excite this liquid with an intense THz electric-field pulse and monitor the relaxation of the induced optical birefringence. We find a unipolar THz-Kerr-effect signal which, in contrast to aprotic polar liquids, shows a weak coupling between the THz electric field and the permanent molecular dipole moment of the liquid. We assign this weak coupling to the restricted translational rather than rotational nature of the excited mode. Our approach opens a new avenue to the assignment of the dielectric spectrum of liquids to a microscopic origin.

We measure the inverse spin Hall effect of Cu

The speed of writing of state-of-the-art ferromagnetic memories is physically limited by an intrinsic gigahertz threshold. Recently, realization of memory devices based on antiferromagnets, in which spin directions periodically alternate from one atomic lattice site to the next has moved research in an alternative direction. We experimentally demonstrate at room temperature that the speed of reversible electrical writing in a memory device can be scaled up to terahertz using an antiferromagnet. A current-induced spin-torque mechanism is responsible for the switching in our memory devices throughout the 12-order-of-magnitude range of writing speeds from hertz to terahertz. Our work opens the path toward the development of memory-logic technology reaching the elusive terahertz band., Science Advances, 4 (3), ISSN:2375-2548

In stimulated Raman scattering, two incident optical waves induce a force oscillating at the difference of the two light frequencies. This process has enabled important applications such as the excitation and coherent control of phonons and magnons by femtosecond laser pulses. Here, we experimentally and theoretically demonstrate the so far neglected up-conversion counterpart of this process: THz sum-frequency excitation of a Raman-active phonon mode, which is tantamount to two-photon absorption by an optical transition between two adjacent vibrational levels. Coherent control of an optical lattice vibration of diamond is achieved by an intense terahertz pulse whose spectrum is centered at half the phonon frequency of 40 THz. Remarkably, the carrier- envelope phase of the THz pulse is directly transferred into the phase of the lattice vibration. New prospects in general infrared spectroscopy, action spectroscopy, and lattice trajectory control in the electronic ground state emerge.

This article provides an overview and illustrative examples of how the electric and magnetic fields of intense terahertz transients can be used to resonantly, and even nonresonantly, control matter and light. It discusses the fundamental interaction mechanisms of intense terahertz radiation with matter.

As such, terahertz spectroscopy cannot resolve the spin structure of conducting particles. Here we introduce the spin sensitivity to terahertz spectroscopy by using the spin-valve configuration of the sample. As a result, the number density and momentum scattering time of conduction electrons in a ferromagnetic metal can be resolved according to their spin.

Most properties of liquid water are determined by its hydrogen-bond network. Because forming an aqueous interface requires termination of this network, one might expect the molecular level properties of interfacial water to markedly differ from water in bulk. Intriguingly, much prior experimental and theoretical work has found that, from the perspective of their time-averaged structure and picosecond structural dynamics, hydrogen-bonded OH groups at an air/water interface behave the same as hydrogen-bonded OH groups in bulk liquid water. Here we report the first experimental observation of interfacial water's libration (i.e. frustrated rotation) using the laser-based technique vibrational sum frequency spectroscopy. We find this mode has a frequency of 834 cm$^{-1}$, $\approx 165$ cm$^{-1}$ higher than in bulk liquid water at the same temperature and similar to bulk ice. Because libration frequency is proportional to the stiffness of water's rotational potential, this increase suggests that one effect of terminating bulk water's hydrogen bonding network at the air/water interface is retarding rotation of water around intact hydrogen bonds. Because in bulk liquid water the libration plays a key role in stabilizing reaction intermediates and dissipating excess vibrational energy, we expect the ability to probe this mode in interfacial water to open new perspectives on the kinetics of heterogeneous reactions at aqueous interfaces., Comment: Manuscript: 14 pages, 3 figures Supplementary Information: 12 pages, 10 figures

Few cycle THz transients pump electronic transitions coupled to the spin system in thulium orthoferrite to trigger coherent magnons. Exploiting this novel driving mechanism we realize the first nonlinear interaction between THz pulses and spins.

Using terahertz spectroscopy we directly resolved the fundamentals of spin-dependent conductivity in ferromagnetic metals. We quantified the differences in conduction by Fermi-level electrons with opposite spins on the sub-100 fs timescale of electron momentum scattering.

Future information technologies, such as ultrafast data recording, quantum computation or spintronics, call for ever faster spin control by light1-16. Intense terahertz pulses can couple to spins on the intrinsic energy scale of magnetic excitations5,11. Here, we explore a novel electric dipole-mediated mechanism of nonlinear terahertz-spin coupling that is much stronger than linear Zeeman coupling to the terahertz magnetic field5,10. Using the prototypical antiferromagnet thulium orthoferrite (TmFeO3), we demonstrate that resonant terahertz pumping of electronic orbital transitions modifies the magnetic anisotropy for ordered Fe3+ spins and triggers large-amplitude coherent spin oscillations. This mechanism is inherently nonlinear, it can be tailored by spectral shaping of the terahertz waveforms and its efficiency outperforms the Zeeman torque by an order of magnitude. Because orbital states govern the magnetic anisotropy in all transition-metal oxides, the demonstrated control scheme is expected to be applicable to many magnetic materials.

Terahertz magnetic fields with amplitudes of up to 0.4 Tesla drive magnon resonances in nickel oxide while the induced dynamics is recorded by femtosecond magneto-optical probing. We observe distinct spin-mediated optical nonlinearities, including oscillations at the second harmonic of the 1 THz magnon mode. The latter originate from coherent dynamics of the longitudinal component of the antiferromagnetic order parameter, which are probed by magneto-optical effects of second order in the spin deflection. These observations allow us to dynamically disentangle electronic from lattice-related contributions to magnetic linear birefringence and dichroism---information so far only accessible by ultrafast THz spin control. The nonlinearities discussed here foreshadow physics that will become essential in future subcycle spin switching.

We use slow-light photonic crystals to enhance optical switching and modulation in silicon. By using dispersion-engineered designs, a switch as short as 5 ¿m was achieved, in which we have demonstrated rerouting of optical pulses on a 3-ps time scale through the absorption of a femtosecond pulse. We additionally demonstrate a modulator with a Mach-Zehnder interferometer (MZI) configuration with flat-band slow-light photonic crystal phase shifters that is designed to give a large group-index-bandwidth product. An extinction ratio in excess of 15 dB is obtained over the entire 11-nm bandwidth of the modulator.

Fundamental quantum optical processes in photogenerated excitons in Cu2O are demonstrated using few-cycle terahertz pulses and field-sensitive electro-optic sampling: (i) In a dilute ensemble of 3p excitons, stimulated terahertz emission from internal transitions to the energetically lower 2s state is observed at a photon energy of 6.6 meV, with a cross section of 10-14 cm2. (ii) An optically dark, dense, and cold 1s-paraexciton gas is prepared by two-photon generation of electron-hole pairs and subsequent phonon cooling. Intense multi-terahertz fields of order MV/cm coherently promote 70% of the quasiparticles from the 1s to the 2p state via a partial internal Rabi oscillation. Electro-optic detection monitors the Larmor precession of the Bloch vector directly in the time domain, with femtosecond resolution. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The optical properties of single-wall carbon nanotube sheets in the far-infrared have been investigated with THz time-domain spectroscopy. Over a wide frequency range from 1 THz to 40 THz, the complex dielectric function of the nanotube sample has been derived. Our data can be excellently reproduced by a Drude-Lorentz model function. The extracted fit parameters such as Lorentz resonance frequency and plasma frequency are consistent with values obtained by scanning tunneling techniques. We discuss the origin of both the Lorentz and Drude contribution in terms of direct and indirect optical transitions.

We apply intense terahertz (THz) electromagnetic pulses with field strengths exceeding 2 MV cm(-1) at ~1 THz to window and substrate materials commonly used in THz spectroscopy and determine the induced optical birefringence. Materials studied are diamond, sapphire, magnesium oxide (MgO), polymethylpentene (TPX), low-density polyethylene (LDPE), silicon nitride membrane (SiN) and crystalline quartz. We observe a Kerr-effect-type transient birefringence in all samples, except in quartz and Si, where, respectively, a linear electrooptic signal and a response beyond the perturbative regime are found. We extract the nonlinear refractive indices and the electrooptic coefficient (in the case of quartz) of these materials and discuss implications for their use as windows or substrates in THz pump-optical probe spectroscopy.

Topological insulators are candidates to open up a novel route in spin based electronics. Different to traditional ferromagnetic materials, where the carrier spin-polarization and magnetization are based on the exchange interaction, the spin properties in topological insulators are based on the coupling of spin- and orbit interaction connected to its momentum. Specific ways to control the spin-polarization with light have been demonstrated: the energy momentum landscape of the Dirac cone provides spin-momentum locking of the charge current and its spin. We investigate a spin-related signal present only during the laser excitation studying real and imaginary part of the complex Kerr angle by disentangling spin and lattice contributions. This coherent signal is only present at the time of the pump-pulses’ light field and can be described in terms of a Raman coherence time. The Raman transition involves states at the bottom edge of the conduction band. We demonstrate a coherent femtosecond control of spin-polarization for electronic states at around the Dirac cone., National Science Foundation (U.S.) (DMR-1207469), United States. Office of Naval Research (N00014-13-1-0301), National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Award DMR-0819762), National Science Foundation (U.S.). Science and Technology Center for Integrated Quantum Materials (Grant DMR-1231319)

Time-resolved THz spectroscopy is employed to investigate the ultrafast electron dynamics in gaseous Ar, SF 6 , and an Ar–SF 6 mixture following ionization by an intense femtosecond laser pulse. The THz response of the free electrons can be described by the Drude model and yields the temporal evolution of the electron density and collision rate. The free-electron decay in the Ar plasma is accelerated enormously by adding small amounts of the electron scavenger SF 6 . This observation is assigned to electron attachment to SF 6 and allows us to infer an electronic temperature of about 20 000 K. The electron collision rate reflects the dynamics of the ion density showing that anions and cations neutralize on a 10-ps time scale.

The relaxation mechanisms in magnetic thin films studied in all-optical pump probe experiments involve electrons, spin and lattice as well as the different couplings in between those. With this technique, the evolution of the electron and spin dynamics can be studied directly in real time from 100 fs to ns timescale. We give a comprehensive view of the current understanding of the processes involved. The details of the spin relaxation-mechanisms on the ultrafast and Landau-Lifshitz-Gilbert time scales are still unknown. Time-resolved reflectivity measurements on ferromagnetic transition metal films give an insight into the specific electronic and lattice relaxation processes. The time-resolved Kerr rotation measurements address the demagnetization and relaxation of the spin system. The demagnetization of the spin system observed in general is strongly coupled to the relaxation mechanism of the electrons, thus follows almost instantaneously the dynamics of the electron system. On the longer time scale, coherent magnetization dynamics is described by the Landau-Lifshitz-Gilbert equation and results in a precession with periods of 50 to 200 ps typical for ferromagnets. The full understanding of the mechanisms will be only accessible by a complete analysis of the interaction between electrons, lattice and spin system. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Two concepts of ultrafast spin control at THz frequencies are presented: Exploiting a coherent phonon mode we transiently induce and destroy spin order in pnictides at a frequency as high as 5.5 THz. Strong THz magnetic fields control magnons in antiferromagnetic NiO coherently by direct Zeeman coupling.

We present examples of how terahertz (THz) electromagnetic transients can be used to control spin precession in antiferromagnets (through the THz Zeeman torque) and to probe spin transport in magnetic heterostructures (through the THz inverse spin Hall effect), on femtosecond time scales.

Terahertz radiation permits resonant and sensitive probing of electron transport, spin precession and ion vibration in solids. Recently developed sources of strong-field terahertz pulses even allow one to gain control over these fundamental modes.

Using a silicon slow-light photonic crystal waveguide, we demonstrate the operation of a dynamic delay line based on an ultrafast indirect photonic transition to alter the group velocity of a pulse. We show continuously tuneable delays of up to 20 ps, using a waveguide just 300 μm in length. Our approach is scalable, in that both the maximum delay and capacity of the buffer are proportional to the length of the waveguide, and flexible, in that individual pulses in a pulse stream can be controlled independently, which we demonstrate by operating on pulses separated by just 30 ps.

Ultrashort pulses in the terahertz (THz) spectral range allow us to study and control spin dynamics on time scales faster than a single oscillation cycle of light. In a first set of experiments, we harness an optically triggered coherent lattice vibration to induce a transient spin-density wave in BaFe2As2, the parent compound of pnictide superconductors. The time-dependent multi-THz response of the non-equilibrium phases shows that the ordering quasi-adiabatically follows a coherent lattice oscillation at a frequency as high as 5.5 THz. The results suggest important implications for unconventional superconductivity. In a second step, we utilize the magnetic field component of intense THz transients to directly switch on and off coherent spin waves in the antiferromagnetic nickel oxide NiO. A femtosecond optical probe traces the magnetic dynamics in the time domain and verifies that the THz field addresses spins selectively via Zeeman interaction. This concept provides a universal ultrafast handle on magnetic excitations in the electronic ground state.

We demonstrate the ultrafast tilting of the dispersion curve of a photonic crystal waveguide following the absorption of a femtosecond pump pulse. By shaping the pump cross section with a shadow mask, different waveguide eigenmodes have different spatial overlaps with the perturbation, leading to a local flattening of the dispersion by up to 11%. Such partial mode perturbation can be used to adiabatically compress the spectrum of a light pulse in the waveguide.

We use an indirect photonic transition to alter the group velocity of a pulse in a silicon photonic crystal waveguide. Delays of up to 20ps, with efficiencies of 30%, are achievable in a 300μm waveguide.

Intense THz electric and magnetic fields are exploited to drive extreme nonlinearities in semiconductors, magnetically ordered solids, and molecular systems. Electro-optic sampling allows us to perform field-sensitive two-dimensional spectroscopy, including four- and six-wave mixing in indium antimonide, as well as THz bias — optical probe experiments beyond static dielectric breakdown fields. Finally, we introduce a novel scheme for coherent spin control in antiferromagnetic nickel oxide mediated by the THz magnetic field component.

We propose a new design for compact tunable optical delay lines, based on adiabatic wavelength conversion and group velocity dispersion, in engineered silicon slow light photonic crystal waveguides. Actuation is performed over a small fraction of the device area, allowing for efficient operation in terms of switching power. We report on the experimental demonstration of variable delays up to 15 ps in a 300 µm long waveguide using this scheme, thus realising an ultrafast tunable delay line in an integrated format.