Phase-locked Pulse Pairs Research Articles

Vacuum-ultraviolet dispersive wave emission driven by phase-locked pulse pairs in a gas-filled hollow-core fiber: a numerical study

Vacuum-ultraviolet dispersive wave emission driven by phase-locked pulse pairs in a gas-filled hollow-core fiber: a numerical study

Rapid scan white light two-dimensional electronic spectroscopy with 100kHz shot-to-shot detection.

We demonstrate an approach to two-dimensional electronic spectroscopy (2DES) that combines the benefits of shot-to-shot detection at high-repetition rates with the simplicity of a broadband white light continuum input and conventional optical elements to generate phase-locked pump pulse pairs. We demonstrate this through mutual synchronization between the laser repetition rate, the acousto-optical deflector, the pump delay stage, and the CCD line camera, which allows for rapid scanning of pump optical delay synchronously with the laser repetition rate, while the delay stage is moved at a constant velocity. The resulting shot-to-shot detection scheme is repetition rate scalable and only limited by the CCD line rate and the maximum stage velocity. Using this approach, we demonstrate the measurement of an averaged 2DES absorptive spectrum in as much as 1.2s of continuous sample exposure per 2D spectrum. We achieve a signal-to-noise ratio of 6.8 for optical densities down to 0.05 with 11.6s of averaging at 100kHz laser repetition rate. Combining rapid scanning of mechanical delay lines with shot-to-shot detection as demonstrated here provides a viable alternative to acousto-optic pulse shaping approaches that is repetition-rate scalable, has comparable throughput and sensitivity, and minimizes sample exposure per 2D spectrum with promising micro-spectroscopy applications.

Development of interface-/surface-specific two-dimensional electronic spectroscopy.

Structures, kinetics, and chemical reactivities at interfaces and surfaces are key to understanding many of the fundamental scientific problems related to chemical, material, biological, and physical systems. These steady-state and dynamical properties at interfaces and surfaces require even-order techniques with time-resolution and spectral-resolution. Here, we develop fourth-order interface-/surface-specific two-dimensional electronic spectroscopy, including both two-dimensional electronic sum frequency generation (2D-ESFG) spectroscopy and two-dimensional electronic second harmonic generation (2D-ESHG) spectroscopy, for structural and dynamics studies of interfaces and surfaces. The 2D-ESFG and 2D-ESHG techniques were based on a unique laser source of broadband short-wave IR from 1200 nm to 2200 nm from a home-built optical parametric amplifier. With the broadband short-wave IR source, surface spectra cover most of the visible light region from 480 nm to 760 nm. A translating wedge-based identical pulses encoding system (TWINs) was introduced to generate a phase-locked pulse pair for coherent excitation in the 2D-ESFG and 2D-ESHG. As an example, we demonstrated surface dark states and their interactions of the surface states at p-type GaAs (001) surfaces with the 2D-ESFG and 2D-ESHG techniques. These newly developed time-resolved and interface-/surface-specific 2D spectroscopies would bring new information for structure and dynamics at interfaces and surfaces in the fields of the environment, materials, catalysis, and biology.

Coherent Dynamics in Quantum Emitters under Dichromatic Excitation

We characterize the coherent dynamics of a two-level quantum emitter driven by a pair of symmetrically detuned phase-locked pulses. The promise of dichromatic excitation is to spectrally isolate the excitation laser from the quantum emission, enabling background-free photon extraction from the emitter. While excitation is not possible without spectral overlap between the exciting pulse and the quantum emitter transition for ideal two-level systems due to cancellation of the accumulated pulse area, we find that any additional interactions that interfere with cancellation of the accumulated pulse area may lead to a finite stationary population inversion. Our spectroscopic results of a solid-state two-level system show that, while coupling to lattice vibrations helps to improve the inversion efficiency up to 50% under symmetric driving, coherent population control and a larger amount of inversion are possible using asymmetric dichromatic excitation, which we achieve by adjusting the ratio of the intensities between the red- and blue-detuned pulses. Our measured results, supported by simulations using a real-time path-integral method, offer a new perspective toward realizing efficient, background-free photon generation and extraction.

Interface-Specific Two-Dimensional Electronic Sum Frequency Generation Spectroscopy.

High even-order surface/interface specific spectroscopy has the potential to provide more structural and dynamical information about surfaces and interfaces. In this work, we developed a novel fourth-order interface-specific two-dimensional electronic sum frequency generation (2D-ESFG) for structures and dynamics at surfaces and interfaces. A translating wedge-based identical pulses encoding system (TWINs) was introduced to generate phase-locked pulse pairs for coherent pump beams in 2D-ESFG. As a proof-of-principle experiment, fourth-order 2D-ESFG spectroscopy was used to demonstrate couplings of surface states for both n-type and p-type GaAs (100). We found surface dark state within the bandgap of the GaAs in 2D-ESFG spectra, which could not be observed in one-dimensional ESFG spectra. To our best knowledge, this is a first demonstration of interface-specific two-dimensional electronic spectroscopy. The development of the 2D-ESFG spectroscopy will provide new structural probes of spectral diffusion, conformational dynamics, energy transfer, and charge transfer for surfaces and interfaces.

Supercontinuum generation without residual pump peak through multiple coherent pump seeds

We report an enhanced supercontinuum generation (SCG) in a conventional highly nonlinear fiber through injecting double bound-state solitons, which eliminates the residual pump peak existing in conventional SCG. The use of these phase-locked pulse pairs yields a novel multiple coherent pump technique. We further compare the SCGs pumped by conventional bound-state soliton and single-soliton. It confirms that the effective elimination of the residual pump peak in supercontinuum owes to higher transferring efficiency of the pump energy to newly generated frequencies in the multiple coherent pump scheme. The obtained results provide a new and simple method to obtain a flat supercontinuum source.

Diffractive shear interferometry for extreme ultraviolet high-resolution lensless imaging.

We demonstrate a novel imaging approach and associated reconstruction algorithm for far-field coherent diffractive imaging, based on the measurement of a pair of laterally sheared diffraction patterns. The differential phase profile retrieved from such a measurement leads to improved reconstruction accuracy, increased robustness against noise, and faster convergence compared to traditional coherent diffractive imaging methods. We measure laterally sheared diffraction patterns using Fourier-transform spectroscopy with two phase-locked pulse pairs from a high-harmonic source. Using this approach, we demonstrate spectrally resolved imaging at extreme ultraviolet wavelengths between 28 and 35 nm.

Phase control in coherent population distribution in molecules

A chirped laser pulse transfers population from one level to another level accessible by one photon dipole transition. We have used a pair of phase-locked chirped pulses of same frequency instead of a single chirped pulse to achieve phase control over the population transfer and thus creating coherent population distribution in hydrogen molecule. Simultaneous actions of the phase controlled interference and rapid adiabatic passages due to chirped pulses lead to the control in population transfer from the ground X(v = 0, j = 0) level to the C(v = 2, j = 1) level. We have extended this two-level system to a three-level 1 + 1 ladder system for population transfer from the X level to the J(v = 2, j = 2) level via the C intermediate level using two pairs of phase-locked laser chirped pulses and have achieved laudable control over the coherent population distribution.

Ionization enhancement and suppression by phase-locked ultrafast pulse pairs

We present the results of a study of ionization of Xe atoms by a pair of phase-locked pulses, which is characterized by interference produced by the twin peaks. Two types of interference are considered: ordinary optical interference, which changes the intensity of the composite pulse and thus the ion yield, and a quantum interference, in which the excited electron wave packets interfere. We use the measured ${\mathrm{Xe}}^{+}$ yield as a function of the temporal delay and/or relative phase between the peaks to monitor the interferences and compare their relative strengths. We model the interference with a pulse intensity function and by calculating the ionization yield with the time-dependent Schr\odinger equation. Our results provide insight into optimal control pulses generated with learning algorithms. The results also show that the relative phase between peaks of a control pulse, along with small features such as distortions and imperfections in the wings of an ideal shape, play a significant role in the control process.

Long-term mutual phase locking of picosecond pulse pairs generated by a semiconductor nanowire laser

The ability to generate phase-stabilized trains of ultrafast laser pulses by mode-locking underpins photonics research in fields, such as precision metrology and spectroscopy. However, the complexity of conventional mode-locked laser systems has hindered their realization at the nanoscale. Here we demonstrate that GaAs-AlGaAs nanowire lasers are capable of emitting pairs of phase-locked picosecond laser pulses with a repetition frequency up to 200 GHz when subject to incoherent pulsed optical excitation. By probing the two-pulse interference spectra, we show that pulse pairs remain mutually coherent over timescales extending to 30 ps, much longer than the emitted laser pulse duration (≤3 ps). Simulations performed by solving the optical Bloch equations produce good quantitative agreement with experiments, revealing how the phase information is stored in the gain medium close to transparency. Our results open the way to phase locking of nanowires integrated onto photonic circuits, optical injection locking and applications, such as on-chip Ramsey comb spectroscopy.

Excitation-emission Fourier-transform spectroscopy based on a birefringent interferometer

The correlation of molecular excitation and emission events provides a powerful multidimensional spectroscopy tool, by relating transitions from electronic ground and excited states through two-dimensional excitation-emission maps. Here we present a compact, fast and versatile Fourier-transform spectrometer, combining absorption and excitation-emission fluorescence spectroscopy in the visible. We generate phase-locked excitation pulse pairs via an inherently stable birefringent wedge-based common-path interferometer, retaining all the advantages of Fourier-transform spectroscopy but avoiding active stabilization or auxiliary tracking beams. We employ both coherent and incoherent excitation sources on dye molecules in solution, with data acquisition times in the range of seconds and minutes, respectively.

Two-dimensional electronic spectroscopy in the ultraviolet by a birefringent delay line.

We introduce a 2D electronic spectroscopy setup in the UV spectral range in the partially collinear pump-probe geometry. The required interferometrically phase-locked few-optical-cycle UV pulse pair is generated by combining a passive birefringent interferometer in the visible and nonlinear phase transfer. This is achieved by sum-frequency generation between the phase-locked visible pulse pair and narrowband infrared pulses. We demonstrate a pair of 16-fs, 330-nm pulses whose delay is interferometrically stable with an accuracy better than λ/450. 2DUV maps of pyrene solution probed in the UV and visible spectral ranges are demonstrated.

Coherent control of interfering wave packets in dissociating HD+ molecules: the role of phase and delay time

The coherent control of interference between dissociating wave packets of the HD+ molecules generated by a pair of time-delayed and phase-locked femtosecond laser pulses is theoretically studied by using the time-dependent quantum wave packet method. The density function in both coordinate and momentum representation are presented and discussed. It is demonstrated that the interference pattern is observed in both coordinate and momentum density functions. The interference undergoes a π-phase shift when the delay time between the two phase-locked femtosecond laser pulses is changed by half an optical period. In particular, the number of interference fringes, the fringe spacing in the R-dependent density distribution |ψ(R)|2, and the modulation period of the energy-dependent distribution of the fragments P(E) can be tuned by two phase-locked femtosecond pulses.

In-line femtosecond common-path interferometer in reflection mode.

An innovative method to perform femtosecond time-resolved interferometry in reflection mode is proposed. The experiment consists in the combined use of a pump-probe setup and of a fully passive in-line femtosecond common-path interferometer. The originality of this interferometer relies on the use of a single birefringent crystal first to generate a pair of phase-locked pulses and second to recombine them to interfere. As predicted by analytical modeling, this interferometer measures the temporal derivative of the ultrafast changes of the complex optical reflection coefficient of the sample. Working conditions are illustrated through picosecond opto-acoustic experiments on a thin film.

Ultra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium.

We investigate the excitation energy transfer (EET) pathways in the photosynthetic light harvesting 1 (LH1) complex of purple bacterium Rhodospirillum rubrum with ultra-broadband two-dimensional electronic spectroscopy (2DES). We employ a 2DES apparatus in the partially collinear geometry, using a passive birefringent interferometer to generate the phase-locked pump pulse pair. This scheme easily lends itself to two-color operation, by coupling a sub-10 fs visible pulse with a sub-15-fs near-infrared pulse. This unique pulse combination allows us to simultaneously track with extremely high temporal resolution both the dynamics of the photoexcited carotenoid spirilloxanthin (Spx) in the visible range and the EET between the Spx and the B890 bacterio-chlorophyll (BChl), whose Qx and Qy transitions peak at 585 and 881 nm, respectively, in the near-infrared. Global analysis of the one-color and two-color 2DES maps unravels different relaxation mechanisms in the LH1 complex: (i) the initial events of the internal conversion process within the Spx, (ii) the parallel EET from the first bright state S2 of the Spx towards the Qx state of the B890, and (iii) the internal conversion from Qx to Qy within the B890.

2D IR spectroscopy with phase-locked pulse pairs from a birefringent delay line.

We introduce a new scheme for two-dimensional IR spectroscopy in the partially collinear pump-probe geometry. Translating birefringent wedges allow generating phase-locked pump pulses with exceptional phase stability, in a simple and compact setup. A He-Ne tracking scheme permits to scan continuously the acquisition time. For a proof-of-principle demonstration we use lithium niobate, which allows operation up to 5 μm. Exploiting the inherent perpendicular polarizations of the two pump pulses, we also demonstrate signal enhancement and scattering suppression.

Modeling and correction of distorted two-dimensional Fourier transform spectra from pixelated pulse shaping devices

Two-dimensional Fourier transform spectra of a three level model system are simulated using a non-perturbative density matrix formalism. The electric field distortions resultant from using pixelated pulse shaping devices to produce phase-locked pulse pairs are modeled and the effects on the recovered spectra are examined. To minimize spectral distortions, a temporal filtering scheme is employed which eliminates contributions from spurious sample polarizations.

High sensitivity transient infrared spectroscopy: a UV/Visible transient grating spectrometer with a heterodyne detected infrared probe

We describe here a high sensitivity means of performing time resolved UV/Visible pump, infrared probe spectroscopy using optically Heterodyne Detected UV-IR Transient Gratings. The experiment design employed is simple, robust and includes a novel means of generating phase locked pulse pairs that relies on only mirrors and a beamsplitter. A signal to noise ratio increase of 24 compared with a conventional pump-probe arrangement is demonstrated.

Quantum complementarity of cavity photons coupled to a three-level system

Recently a device enabling the ultrafast all-optical control of the wave-particle duality of light was proposed [Ridolfo et al., Phys. Rev. Lett. 106, 013601 (2011)]. It is constituted by a three-level quantum emitter strongly coupled to a microcavity and can be realized by exploiting a great variety of systems ranging from atomic physics and semiconductor quantum dots to intersubband polaritons and Cooper pair boxes. Control pulses with specific arrival times, performing which-path and quantum-eraser operations, are able to destroy and recover interference almost instantaneously. Here we show that the coherence sudden death implies the sudden birth of a higher order correlation function storing coherence. Such storing enables coherence rebirth after the arrival of an additional suitable control pulse. We derive analytical calculations describing the all-optical control of the wave-particle duality and the entanglement-induced switch-off of the strong coupling regime. We also present analytical calculations describing a homodynelike method exploiting pairs of phase locked pulses with precise arrival times to probe the optical control of wave-particle duality of this system. Within such a method the optical control of wave-particle duality can be directly probed by just detecting the photons escaping the microcavity.

Test of the all-optical control of wave–particle duality of cavity photons by ordinary photodetection

The principle of complementarity refers to the ability of quantum entities to behave as particles or waves under different experimental conditions. We present a proposal for the experimental observation of the ultrafast all-optical control of the wave-particle duality of light. The device is constituted by a three-level quantum emitter strongly coupled to a microcavity (MC) and can be realized by exploiting a great variety of systems, ranging from atomic physics and semiconductor quantum dots to intersubband polaritons and Cooper pair boxes. The wavelike or particlelike behavior of MC photons can be probed by simply measuring the cavity output photon rate after excitation with pairs of phase-locked weak pulses with precise arrival times.