Generation of a single-cycle optical pulse

Giving entangled photons new colors

A fiber-based modulator shifts photon frequency while preserving quantum correlations.

Deep- to near-ultraviolet Raman frequency conversion pumped by femtosecond pulses in a hollow-core waveguide

Broadband vibrational/rotational Raman generation ranging from deep ultraviolet (DUV) to blue wavelengths is demonstrated by using molecular hydrogen in a hollow-core waveguide as a Raman-active medium pumped by a femtosecond DUV laser. We find the high-order transient stimulated Raman scattering is drastically enhanced for input beams including a circularly polarized component; a circularly polarized input beam achieves the highest conversion efficiency. Coherent vibrational anti-Stokes Raman emission is observed only for a circularly polarized pump beam, indicating that the waveguide effect also contributes to the upconversion of a DUV pulse via transient stimulated Raman scattering.

High-harmonic-driven inverse Raman scattering

Spectral analysis of high-order harmonics generated by ultrashort mid-infrared pulses in molecular nitrogen reveals well-resolved signatures of inverse Raman scattering, showing up near the frequencies of prominent vibrational transitions of nitrogen molecules. When tuned on a resonance with the v^'=0→v^''=0 pathway within the B³Π_g→C³Π_u second positive system of molecular nitrogen, the eleventh harmonic of a 3.9 µm, 80 fs driver is shown to acquire a distinctive antisymmetric spectral profile with red-shifted bright and blue-shifted dark features as indicators of stimulated Raman gain and loss. This high-harmonic setting extends the inverse Raman effect to a vast class of strong-field light-matter interaction scenarios.

Few-cycle optical pulse characterization under phase-mismatching

The phase-matching bandwidth of nonlinear crystal is of great significance in ultrashort laser pulse characterization. In order to satisfy the phase-matching bandwidth, ultra-thin nonlinear crystals are generally required. However, the significantly reduced conversion efficiency, as well as the machining difficulties, limits its applications. Here, we show that sufficient spectrum bandwidth response can be achieved for a thick crystal when the phase-matching wavelength is tuned outside of the spectral window of the measured pulse. By applying this phenomenon to a single-shot second-harmonic generation frequency resolved optical gating (SHG-FROG) device, we successfully characterized a few-cycle pulse using a 150µmβ-barium borate (BBO) crystal. The accuracy of the method was verified by comparing the conventional pulse retrieving approach with a 5µm BBO crystal, which has a sufficient phase-matching bandwidth.

Sub-half-cycle field transients from shock-wave-assisted soliton self-compression

We identify an unusual regime of ultrafast nonlinear dynamics in which an optical shock wave couples to soliton self-compression, steepening the tail of the pulse, thus yielding self-compressing soliton transients as short as the field sub-half-cycle. We demonstrate that this extreme pulse self-compression scenario can help generate sub-half-cycle mid-infrared pulses in a broad class of anomalously dispersive optical waveguide systems.

Prospects for continuous-wave molecular modulation in Raman-active microresonators

We propose the extension of existing molecular modulation techniques for continuous-wave optical modulation to Raman-active microresonators. Intense pump and Stokes modes inside a microresonator prepare a high coherence of the Raman transition between two ro-vibrational states. With the coherence prepared, any laser in the optical region can be coupled to the microresonator and be modulated. We perform numerical simulations which predict that these "microresonator-based molecular modulators" could have modulation efficiencies on the order of 1% at 10 THz-scale frequencies for any optical wavelength.

Steering the outcome of a photochemical reaction-An in silico experiment on the H2CSO sulfine using few-femtosecond dump pulses

We propose a pump-dump control scheme using sub-10 fs pulses to enhance the photochemical formation of the three-membered C-S-O ring oxathiirane from the parent H₂CSO sulfine molecule. The ultrashort nature of the pulses is essential to promptly alter the photoinduced dynamics, e.g., while a bond is elongating, which is key to selectively form the oxathiirane by radiative dumping. We carried out an in silico pump-dump experiment with excited-state dynamics simulations that include the interaction with electric field of the pump and dump pulses. By applying the dump pulse when the CS bond is elongating, the population transferred to the ground state will form the oxathiirane with a branching ratio of 4, much higher than the one solely due to nonradiative relaxation (0.66). The overall oxathiirane yield can be increased by up to 17% when the 6 fs IR dump pulse is applied at a delay time of 47 fs.

Sub-Femtosecond Stark Control of Molecular Photoexcitation with Near Single-Cycle Pulses

Electric fields can tailor molecular potential energy surfaces by interaction with the electronic state-dependent molecular dipole moment. Recent developments in optics have enabled the creation of ultrashort few-cycle optical pulses with precise control of the carrier envelope phase (CEP) that determines the offset of the maxima in the field and the pulse envelope. This opens news ways of controlling ultrafast molecular dynamics by exploiting the CEP. In this work, we show that the photoabsorption efficiency of oriented H₂CSO (sulfine) can be controlled by tuning the CEP. We further show that this control emanates from a resonance condition related to Stark shifting of the electronic energy levels.

Solid-State Source of Subcycle Pulses in the Midinfrared

We demonstrate a robust, all-solid-state approach for the generation of microjoule subcycle pulses in the midinfrared through a cascade of carefully optimized parametric-amplification, difference-frequency-generation, spectral-broadening, and chirp-compensation stages. This method of subcycle waveform generation becomes possible due to an unusual, ionization-assisted solid-state pulse self-compression dynamics, where highly efficient spectral broadening is enabled by ultrabroadband four-wave parametric amplification phase matched near the zero-group-velocity wavelength of the material.

Generation of five phase-locked harmonics by implementing a divide-by-three optical frequency divider

We report the generation of five phase-locked harmonics, f₁:2403  nm, f₂:1201  nm, f₃:801  nm, f₄:600  nm, and f₅:480  nm with an exact frequency ratio of 1:2:3:4:5 by implementing a divide-by-three optical frequency divider in the high harmonic generation process. All five harmonics are generated coaxially with high phase coherence in time and space, which are applicable for various practical uses.

Generation of intense subcycle optical pulses in a gas

The generation of intense subcycle laser pulses during the propagation of two-color femtosecond pulses in a gas medium is investigated theoretically and experimentally. Four-wave mixing induced by the laser pulses in a gas medium generates multi-octave laser radiation from the ultraviolet to the infrared, which forms stable subcycle laser pulses after a certain propagation distance in a gas medium with group-velocity dispersion. The intense subcycle laser pulses would allow the coherent control of the waveforms of soft-x-rays generated via high-harmonic generation.

Single nanoparticle detection using split-mode microcavity Raman lasers

Ultrasensitive nanoparticle detection holds great potential for early-stage diagnosis of human diseases and for environmental monitoring. In this work, we report for the first time, to our knowledge, single nanoparticle detection by monitoring the beat frequency of split-mode Raman lasers in high-Q optical microcavities. We first demonstrate this method by controllably transferring single 50-nm-radius nanoparticles to and from the cavity surface using a fiber taper. We then realize real-time detection of single nanoparticles in an aqueous environment, with a record low detection limit of 20 nm in radius, without using additional techniques for laser noise suppression. Because Raman scattering occurs in most materials under practically any pump wavelength, this Raman laser-based sensing method not only removes the need for doping the microcavity with a gain medium but also loosens the requirement of specific wavelength bands for the pump lasers, thus representing a significant step toward practical microlaser sensors.

Ultrafast waveform synthesis and characterization using coherent Raman sidebands in a reflection scheme

Coherent Raman sidebands have the potential to serve as a source of single cycle pulses. We generate these sidebands by crossing two-color femtosecond laser pulses in a Raman-active crystal. We design a reflection scheme using spherical mirrors to combine coherent Raman sidebands. The sidebands and the driving pulses are refocused back to the Raman crystal and the relative spectral phases are retrieved from an interferogram based on the nonlinear Raman interaction. Furthermore, using a deformable mirror to adjust the spectral phases, we demonstrate that our setup is capable of synthesizing ultrafast waveforms using coherent Raman sidebands.

Spectral broadening and compression of sub-millijoule laser pulses in hollow-core fibers filled with sulfur hexafluoride

Spectral broadening in gas-filled hollow-core fibers is discussed for sulfur hexafluoride, a molecular gas with Raman activity. Experimental results for compressed pulses are presented for input pulses longer than the Raman period and shorter than the dephasing time at a central wavelength of 800 nm and 400 nm, respectively. For both wavelengths we compress the pulses by a factor of three and maintain a good pulse quality. The obtained results are of interest for compressing pulses generated with Yb doped lasers.

Broadband spectrum generation using continuous-wave Raman scattering

We experimentally demonstrate a continuous-wave ro-vibrational Raman spectrum that is two octaves wide with spectral components ranging from 0.8 to 3.2 μm in wavelength. The spectrum is produced in low pressure molecular deuterium inside a high finesse cavity.

Formation of a single attosecond pulse via interaction of resonant radiation with a strongly perturbed atomic transition

We propose a technique to form a single few-cycle attosecond pulse from vacuum ultraviolet or extreme ultraviolet radiation via resonant interaction with hydrogenlike atoms, irradiated by a high-intensity far-off-resonant laser field. The laser field strongly perturbs excited atomic energy levels via the Stark effect and ionizes atoms from the excited states. We show that an isolated attosecond pulse can be formed using either a short incident femtosecond pulse of the resonant radiation or a steep front edge of the laser field. We propose an experimental realization of a single subfemtosecond pulse formation at 121.6 nm in atomic hydrogen and a single sub-100 as pulse formation at 13.5 nm in Li(2+) plasma.

Single-cycle radio-frequency pulse generation by an optoelectronic oscillator

We demonstrate experimentally passive mode-locking of an optoelectronic oscillator which generates a single-cycle radio-frequency pulse train. The measured pulse to pulse jitter was less than 5 ppm of the round-trip duration. The pulse waveform was repeated each round-trip. This result indicates that the relative phase between the pulse envelope and the carrier wave is autonomously locked. The results demonstrate, for the first time, that single-cycle pulses can be directly generated by a passive mode-locked oscillator. The passive mode-locked optoelectronic oscillator is important for developing novel radars and radio-frequency pulsed sources and it enables studying directly the physics of single-cycle pulse generation.

Few-cycle attosecond pulses via periodic resonance interaction with hydrogenlike atoms

We show that it is possible to produce nearly bandwidth-limited few-cycle attosecond pulses based on periodic resonance interaction of a quasi-monochromatic radiation with the bound states of hydrogenlike atoms. A periodic resonance is provided by a far-off-resonant laser field with intensity much below the atomic ionization threshold via periodic tunnel ionization from the excited states and adiabatic Stark splitting of the excited energy levels. Without external synchronization of the spectral components, it is possible to produce 135 as pulses at 13.5 nm in Li²⁺-plasma controlled by radiation of a mode-locked Nd:YAG laser, as well as 1.25 fs pulses at 122 nm in atomic hydrogen controlled by radiation of a CO₂ laser.

Continuous-wave, multiple-order rotational Raman generation in molecular deuterium

We demonstrate the generation of ≈10 rotational sidebands using continuous-wave stimulated Raman scattering in molecular deuterium. The generation occurs inside a high-finesse cavity at molecular gas pressures of ≈0.1 atm.

Octave-spanning carrier-envelope phase stabilized visible pulse with sub-3-fs pulse duration

The visible second harmonic of the idler output from a noncollinear optical parametric amplifier was compressed using adaptive dispersion control with a deformable mirror. The amplifier was pumped by and seeded in the signal path by a common 400 nm second-harmonic pulse from a Ti:sapphire regenerative amplifier. Thus, both the idler output and the second harmonic of the idler were passively carrier-envelope phase stabilized. The shortest pulse duration achieved was below 3 fs.

Quantum-fluctuation-initiated coherence in multioctave Raman optical frequency combs

We show experimentally and theoretically that the spectral components of a multioctave frequency comb spontaneously created by stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber exhibit strong self-coherence and mutual coherence within each 12 ns driving laser pulse. This coherence arises in spite of the field's initiation being from quantum zero-point fluctuations, which causes each spectral component to show large phase and energy fluctuations. This points to the possibility of an optical frequency comb with nonclassical correlations between all comb lines.

Amplification of impulsively excited molecular rotational coherence

We propose a scheme for preparation of high-coherence molecular dynamics which are phase stable with respect to ultrashort pulses. We experimentally demonstrate an example of this scheme using a phase-independent, nanosecond-duration, pump pulse to prepare a rotational coherence in molecular hydrogen. This rotational coherence is made phase stable with respect to a separate source of ultrashort pulses by seeding. The coherence is used to generate spectral broadening of femtosecond probe radiation by molecular phase modulation.

Line-by-line control of 10-THz-frequency-spacing Raman sidebands

We report line-by-line control of a coherent discrete spectrum (Raman sidebands) with a frequency spacing of 10.6 THz that is produced by an adiabatic Raman process. We show that the spectral phase of the Raman sidebands is finely controlled to the target (flat relative-spectral-phase). This is achieved by employing a combination of a spatial phase controller and a spectral interferometer, which are specifically designed for a high-power discrete spectrum. We also show that such spectral-phase control produces a train of Fourier transform limited pulses with an ultrahigh repetition rate of 10.6 THz in the time domain.

Continuous-wave high-power rotational Raman generation in molecular deuterium

We report the generation of more than 300 mW of rotational Stokes output power in a CW Raman laser. The generation is achieved in low-pressure molecular deuterium inside a high-finesse cavity.

Arbitrary waveform synthesis by multiple harmonics generation and phasing in aperiodic optical superlattices

The process of generating periodic optical waveforms includes the generation and phasing of several harmonics of a fundamental frequency. In this work, we show that simultaneous generation and phasing of the harmonics can be performed in a monolithic aperiodic optical superlattice (AOS). Stable periodic waveforms can thus be delivered to a predetermined location by simply sending a laser beam through a properly designed and fabricated AOS crystal. A detailed mathematical description for generating the domain pattern in such an AOS crystal is given and the process is numerically demonstrated. The waveform that is generated from a monolithic AOS is highly reproducible and phase stable. We also use propagation in air as an example to show how any predictable phase and amplitude modifications such as air dispersion that will alter the desired waveform can be pre-compensated in the design phase of the AOS crystal.

Characteristics of relativistic electron mirrors generated by an ultrashort nonadiabatic laser pulse from a nanofilm

For controllable generation of an isolated attosecond relativistic electron bunch [relativistic electron mirror (REM)] with nearly solid-state density, we proposed [V. V. Kulagin, Phys. Rev. Lett. 99, 124801 (2007)] to use a solid nanofilm illuminated normally by an ultraintense femtosecond laser pulse having a sharp rising edge (nonadiabatic laser pulse). In this paper, the REM characteristics are investigated in a regular way for a wide range of parameters. With the help of two-dimensional (2D) particle-in-cell (PIC) simulations, it is shown that, in spite of Coulomb forces, all of the electrons in the laser spot can be synchronously accelerated to ultrarelativistic velocities by the first half-cycle of the field, which has large enough amplitude. For the process of the REM generation, we also verify a self-consistent one-dimensional theory, which we developed earlier (cited above) and which takes into account Coulomb forces, radiation of the electrons, and laser amplitude depletion. This theory shows a good agreement with the results of the 2D PIC simulations. Finally, the scaling of the REM dynamical parameters with the field amplitude and the nanofilm thickness is analyzed.

Generation of ultrashort optical pulses in the 10 fs regime using multicolor Raman sidebands in KTaO3

We demonstrated Fourier synthesis of a new type of multiple coherent anti-Stokes Raman scatterings in KTaO(3) crystal. The signals with a wavelength range of 500-750 nm were generated by two femtosecond pulses whose frequency difference was set to be a two-phonon Raman frequency. Angle dispersion of the signals was compensated into one white-continuum beam by spherical mirrors and a prism. The spectral phase, measured by spectral phase interferometry for direct electric-field reconstruction, was compensated for by carefully aligning the angle and the position of the optical components so that 13 fs isolated pulses were generated. This result shows the robustness of our scheme to produce ultrashort optical pulses.

Controlling the carrier-envelope phase of Raman-generated periodic waveforms

We demonstrate control of the carrier-envelope phase of ultrashort periodic waveforms that are synthesized from a Raman-generated optical frequency comb. We generated the comb by adiabatically driving a molecular vibrational coherence with a beam at a fundamental frequency plus its second harmonic. Heterodyne measurements show that full interpulse phase locking of the comb components is realized. The results set the stage for the synthesis of periodic arbitrary waveforms in the femtosecond and subfemtosecond regimes with full control.

Acceleration of quantum optimal control theory algorithms with mixing strategies

We propose the use of mixing strategies to accelerate the convergence of the common iterative algorithms utilized in quantum optimal control theory (QOCT). We show how the nonlinear equations of QOCT can be viewed as a "fixed-point" nonlinear problem. The iterative algorithms for this class of problems may benefit from mixing strategies, as it happens, e.g., in the quest for the ground-state density in Kohn-Sham density-functional theory. We demonstrate, with some numerical examples, how the same mixing schemes utilized in this latter nonlinear problem may significantly accelerate the QOCT iterative procedures.

Wavelength-tunable, multicolored femtosecond-laser pulse generation in fused-silica glass

Wavelength-tunable multicolored femtosecond laser pulses were generated simultaneously through cascade four-wave mixing in a fused-silica glass plate using two crossing femtosecond laser beams. The wavelength of the sidebands can be continuously tuned from UV to IR. The pulse duration, spatial mode, spectrum, and energy stability of the sidebands indicated that they were good enough for various multicolor femtosecond laser experiments. As many as 15 spectral upshifted pulses and 2 spectral downshifted pulses were obtained with a spectral bandwidth broader than 1.8 octaves.

Coherent ultrafast pulse synthesis between an optical parametric oscillator and a laser

We have demonstrated coherent pulse synthesis between the carrier-envelope, phase-locked, second-harmonic pulses from a synchronously pumped femtosecond optical parametric oscillator and those from its self-mode-locked Ti:sapphire pump laser. By using a single nonlinear crystal for parametric and second-harmonic generation, we maximized the common-mode rejection of environmental noise, obtaining a temporal overlap between the pulses with a precision of 30 as (1% of the optical period) in an observation time of 20 ms. Mutual coherence between the two parent pulses was verified optically by spectral interferometry, and synthesis was tested by measuring the autocorrelation of the combined pulses, with and without carrier-envelope phase locking.

Tuning the frequency of few-cycle femtosecond laser pulses by molecular phase modulation

We demonstrate theoretically how the time-dependent phase modulation induced by molecular alignment can be used to tune the frequency of few-cycle femtosecond laser pulses continuously. Using impulsively excited alignment in N(2), the central wavelength of an initial 800 nm, 5 fs Gaussian pulse can be tuned from 324.6 to 4237.3 nm. The aligned N(2) molecules are obtained by pretransmitting another 800 nm, 100 fs linearly polarized laser pulse of intensity 3.5x10(13) Wcm(-2). The number of optical cycles contained in the frequency-tuned pulse is almost unchanged after ideal chirp compensation.

Characterization of Fourier-synthesized optical waveforms from optically phase-locked femtosecond multicolor pulses

For characterization of Fourier-synthesized optical waveforms of femtosecond multicolor phase-coherent pulses, we report relative-phase measurements among Fourier components from optically phase-locked two-color mode-locked lasers. The interference of two simultaneous second-order frequency-mixing processes in a common nonlinear crystal was utilized. The relative phases among three-color components with a frequency ratio of 2omega:3omega:4omega were measured by observing the interference fringes of two simultaneous frequency-mixing outputs. The inner field structure of the synthesized waveforms can be determined except for the ambiguity of its temporal shift with respect to the synthesized envelope, which corresponds to the carrier-envelope phase slip of one of the source lasers.

Octave-spanning Raman comb with carrier envelope offset control

We report that adiabatic manipulation of a Raman process allows us to produce an optical-frequency comb from single-frequency lasers. We realize an octave-spanning Raman comb with carrier-envelope-offset frequency control, by using dual-frequency laser radiation locked on a single laser cavity and simultaneously its second harmonic. It is shown that in both the temporal and spectral domains, locking the dual frequencies on a single laser cavity provides control of the carrier-envelope-offset frequency at integer multiples of the free spectral range of the laser cavity.

Spectral phase measurements for broad Raman sidebands by using spectral interferometry

We report a method of spectral phase measurement for a femtosecond pulse train composed of a discrete Raman spectrum. The method is based on an idea of spectral interference. Making use of a small portion of two Raman pump laser radiations, we produce two sum-frequency spectra that spectrally interfere with each other. Based on this interfering sum-frequency spectra, we successfully derive the spectral phase and reconstruct the temporal profile. The reliability of this method is also confirmed by measuring the spectral phase changes caused by intentionally inserted silica plates of various thicknesses and comparing them to theoretical predictions.

Broadband coherent anti-Stokes Raman scattering light generation in BBO crystal by using two crossing femtosecond laser pulses

As broad as 12000 cm(-1) coherent anti-Stokes Raman scattering (CARS) light from ultraviolet to infrared was generated in a BBO crystal by using two crossing femtosecond laser pulses with 30% conversion efficiency. More than fifteenth-order anti-Stokes and second-order Stokes Raman sidebands were observed with nice Gaussian spatial mode. The effect of the crossing angle between two input beams on the spectrum and emitting angle of the Raman sidebands was studied in detail. Calculation shows that the phase-matching condition determines the frequencies and angles of the sidebands.

Ultraviolet femtosecond laser ionization mass spectrometry

For this study, multiphoton ionization/mass spectrometry using an ultraviolet (UV) femtosecond laser was employed for the trace analysis of organic compounds. Some of the molecules, such as dioxins, contain several chlorine atoms and have short excited-state lifetimes due to a "heavy atom" effect. A UV femtosecond laser is, then, useful for efficient resonance excitation and subsequent ionization. A technique of multiphoton ionization using an extremely short laser pulse (e.g., <10 fs), referred to as "impulsive ionization," may have a potential for use in fragmentation-free ionization, thus providing information on molecular weight in mass spectrometry.

Sub-single-cycle optical pulse train with constant carrier envelope phase

We describe the synthesis of periodic waveforms consisting of a train of pulses that are 0.83 cycles long and have an electric field pulse width of 0.44 fs using 7 Raman sidebands generated by molecular modulation in H2. We verify by optical correlation that the carrier-envelope phase is constant in these waveforms when they are synthesized from commensurate sidebands. The estimated overall shift of the carrier-envelope phase is less than 0.18 cycles from the first to the last pulse of nearly 10(6) pulses in the pulse train.

Theoretical investigation of controlled generation of a dense attosecond relativistic electron bunch from the interaction of an ultrashort laser pulse with a nanofilm

For controllable generation of an isolated attosecond relativistic electron bunch [relativistic electron mirror (REM)] with nearly solid-state density, we propose using a solid nanofilm illuminated normally by an ultraintense femtosecond laser pulse having a sharp rising edge. With two-dimensional (2D) particle-in-cell (PIC) simulations, we show that, in spite of Coulomb forces, all of the electrons in the laser spot can be accelerated synchronously, and the REM keeps its surface charge density during evolution. We also developed a self-consistent 1D theory, which takes into account Coulomb forces, radiation of the electrons, and laser amplitude depletion. This theory allows us to predict the REM parameters and shows a good agreement with the 2D PIC simulations.

Coherent synthesis using carrier-envelope phase-controlled pulses from a dual-color femtosecond optical parametric oscillator

By using a dual-color femtosecond optical parametric oscillator (OPO), a coherent waveform was synthesized from two coresonant near-infrared signal pulses whose center wavelengths had a separation of 100 nm. Immediately after the OPO cavity the pulses had independent carrier-envelope phase-slip frequencies, and synthesis was achieved by shifting these frequencies using an acousto-optic modulator driven by an internally generated difference frequency. Soliton self-frequency shifted pulses from a photonic crystal fiber and a cross-correlation frequency-resolved optical gating (XFROG) measurement were used to analyze the result of the synthesis experiment and revealed that the synthesized waveform was a train of high-contrast 30 fs pulses.

Chirp and compress: toward single-cycle biphotons

The Letter describes a technique for the spontaneous generation of chirped time-energy entangled photons. Transmitting either photon through an appropriate dispersive medium results in a temporally compressed, transform limited biphoton. At maximum bandwidth, the biphoton is a single cycle in length, with a waveform that has the same characteristic shape as a classical single-cycle pulse.

Ultrafast electron pulses from a tungsten tip triggered by low-power femtosecond laser pulses

We present an experimental and numerical study of electron emission from a sharp tungsten tip triggered by sub-8-fs low-power laser pulses. This process is nonlinear in the laser electric field, and the nonlinearity can be tuned via the dc voltage applied to the tip. Numerical simulations of this system show that electron emission takes place within less than one optical period of the exciting laser pulse, so that an 8 fs 800 nm laser pulse is capable of producing a single electron pulse of less than 1 fs duration. Furthermore, we find that the carrier-envelope phase dependence of the emission process is smaller than 0.1% for an 8 fs pulse but is steeply increasing with decreasing laser pulse duration.

Molecular modulation in a hollow fiber

We report the extension of the technique of molecular modulation to a deuterium-filled optical fiber. Using driving lasers at 807 and 1064 nm, each with a pulse energy of several millijoules and a 200 microm diameter fiber with a length of 22.5 cm, we generate 12 sidebands with wavelengths spanning 1.56 microm to 254 nm.