Carrier-envelope Phase Stabilization Research Articles

Robust generation of isolated attosecond pulse against the variation of carrier envelope phase of driving laser pulses

We propose a scheme for generating isolated attosecond pulse (IAP) via high-order harmonic generation in gases using a chirped two-color laser field of multicycle duration. In contrast to previous techniques where the stable carrier-envelope phase (CEP) of the driving laser pulses is a prerequisite for IAP generation, the proposed scheme is robust against the large variation of CEP. We show the generation of IAP with an intensity fluctuation less than $50%$ and an intensity contrast ratio higher than $5:1$ when the CEP shift is as large as $1.35$$\ensuremath{\pi}$.

Sub-cycle strong-field interferometry

A nonlinear interferometry scheme is described theoretically to induce and resolve electron wavefunction beating on time scales shorter than the optical cycle of the time-delayed pump and probe pulses. By employing two moderately intense few-cycle laser fields with a stable carrier-envelope phase, a large range of the entire electronic level structure of a quantum system can be retrieved. In contrast to single-photon excitation schemes, the retrieved electronic states include levels that are both dipole- and non-dipole-accessible from the ground electronic state. The results show that strong-field interferometry can reveal both high-resolution and broad-band spectral information at the same time with important consequences for quantum-beat spectroscopy on attosecond time scales.

High-fidelity front-end for high-power, high temporal quality few-cycle lasers

A 80 μJ, 6 fs, CEP-stable high-contrast injector is demonstrated. The device relies on standard pulse post-compression in hollow-core fiber followed by a temporal filter based on cross-polarized wave generation. Pulses with a Gaussian spectrum over 350 nm, centered at 750 nm, are generated. Temporal measurements show that the contrast of the few-cycle pulses is enhanced on a femtosecond and picosecond time scale. The carrier-envelope phase stability is preserved (0.3 rad RMS). These performances make the system an ideal seed laser for high-power, high-contrast OPCPA systems.

Infrared Two-Color Multicycle Laser Field Synthesis for Generating an Intense Attosecond Pulse

We propose and demonstrate the generation of a continuum high-order harmonic spectrum by mixing multicycle two-color (TC) laser fields with the aim of obtaining an intense isolated attosecond pulse. By optimizing the wavelength of a supplementary infrared pulse in a TC field, a continuum harmonic spectrum was created around the cutoff region without carrier-envelope phase stabilization. The obtained harmonic spectra clearly show the possibility of generating isolated attosecond pulses from a multicycle TC laser field, which is generated by an 800 nm, 30 fs pulse mixed with a 1300 nm, 40 fs pulse. Our proposed method enables us not only to relax the requirements for the pump pulse duration but also to reduce ionization of the harmonic medium. This concept opens the door to create an intense isolated attosecond pulse using a conventional femtosecond laser system.

Carrier-Envelope Phase Control of Few-Cycle Parametric Chirped-Pulse Amplifier

We demonstrate the carrier-envelope phase (CEP) stabilization of the 5-fs, multi-mJ parametric chirped-pulse amplification system. The slow CEP drift induced in the parametric chirped-pulse amplifier was precompensated in the phase-control loop of the seed oscillator, and arbitrary CEP control of the whole system was realized over a few hours. We discuss several possible origins that induce CEP noise of the amplified pulses.

Complete real-time temporal waveform characterization of single-shot few-cycle laser pulses

A method for complete characterization of the waveform of individual few-cycle laser pulses is presented. By analyzing the ``left'' and ``right'' asymmetries of high-energy photoelectrons along the polarization axis using the recently developed quantitative rescattering theory, we show that the carrier-envelope phase (CEP), pulse duration, and peak intensity of each single-shot pulse can be readily retrieved. By CEP tagging each laser shot, the method permits the study of waveform-dependent processes be extended to relativistic beams and to wavelengths, where CEP stabilization is not yet possible.

1-mJ, sub-5-fs carrier–envelope phase-locked pulses

We report the routine generation of sub-5-fs laser pulses with 1-mJ energy and stable carrier–envelope phase at 1-kHz repetition rate, obtained by compressing the multi-mJ output from a phase-locked Ti:sapphire amplifier in a rare-gas-filled hollow fiber. The dual-stage amplifier features a hybrid transmission grating/chirped mirror compressor providing 2.2-mJ, 26-fs pulses at 1 kHz with standard phase deviation of 190 mrad rms. We demonstrate hour-long phase stability without feedback control of grating position or rigorous control of the laser environment, simply by using small pulse stretching factors in the amplifier, which minimize the beam pathway in the compressor. The amplifier also integrates a versatile AOPDF (acousto-optic programmable dispersive filter) for closed-loop spectral phase optimization. The various factors influencing the overall phase stability of the system are discussed in detail. Using the optimized output, 1-mJ, 4.5-fs pulses are generated by seeding the neon gas filled hollow fiber with a circularly polarized input beam. A standard phase deviation of 230 mrad after the HCF is obtained by direct f-to-2f detection and slow-loop feedback to the oscillator locking electronics without any additional spectral broadening.

Closed-loop carrier-envelope phase stabilization with an acousto-optic programmable dispersive filter

We demonstrate arbitrary carrier-envelope (CE) phase control of femtosecond laser pulses by an acousto-optic programmable dispersive filter (AOPDF), with an accuracy better than pi/100 at a repetition rate of 1 kHz. We also demonstrate, for the first time to the best of our knowledge, 15 Hz closed-loop CE phase stabilization using an AOPDF inside a 1 kHz chirped pulse amplifier to correct for slow CE phase drifts.

Carrier-envelope phase stabilization of a multi-millijoule, regenerative-amplifier-based chirped-pulse smplifier dystem

This article reports on the successful stabilization of the carrier-envelope phase of a 1-kHz laser system that includes a large grating stretcher, a regenerative amplifier, a multipass amplifier and a grating compressor. Phase stability for pulse energies up to 6 mJ is demonstrated using electronic feedback to the oscillator locking electronics as well as feedback via an acousto-optic programmable dispersive filter.

Carrier-envelope phase stabilization and control of 1 kHz, 6 mJ, 30 fs laser pulses from a Ti:sapphire regenerative amplifier

Carrier-envelope (CE) phase stabilization of a two-stage chirped pulse amplifier laser system with regenerative amplification as the preamplifier is demonstrated. The CE phase stability of this laser system is found to have a 90 mrad rms error averaged over 50 laser shots for a locking period of 4.5 h. The CE phase locking was confirmed unambiguously by experimental observation of the 2pi periodicity of the high-order harmonic spectrum generated by double optical gating.

Temperature feedback control for long-term carrier-envelope phase locking

We report a double feedback loop for the improvement of the carrier-envelope phase stabilization of a chirped mirror based femtosecond laser oscillator. By combining the control of the Ti:sapphire crystal temperature and the modulation of the pump power, the carrier envelope offset frequency, fCEO, was locked for close to 20 h, which is much longer than the typical phase stabilization time with only pump power modulation.

Tunable phase-stabilized infrared optical parametric amplifier for high-order harmonic generation

We demonstrate what we believe to be a novel tunable IR optical parametric amplifier (OPA) with the passively stabilized carrier-envelope phase (CEP), in which a hollow fiber is used to improve the output beam quality and to overcome the spatial chirp issue. Pumped by an 800 nm pump source, the output pulses are tunable from 1.2 to 2.4 microm with the CEP stabilization. The maximum output average energy can reach approximately (1.2 W/40 fs)/1 kHz with the total of (6.8 W/40 fs)/1 kHz pump energy. Further, the high-order harmonic generation driven by the tunable phase-stabilized OPA has been demonstrated.

Femtosecond continuum generation in bulk laser host materials with sub-μJ pump pulses

We report a comprehensive investigation of femtosecond continuum generation in single crystals of several common laser host materials. The absolute spectral energy density, pulse-to-pulse stability, pump threshold, and beam profile are studied in dependence on the focusing conditions, crystal thickness, pump pulse energy, and pump wavelength (775–1600 nm). Continuum generation is shown at repetition rates of up to 80 MHz and for pump pulse durations of up to 350 fs. In yttrium aluminum garnet (YAG), yttrium vanadate (YVO4), gadolinium vanadate (GdVO4), and potassium-gadolinium tungstate (KGW) thresholds below 50 nJ, plateau-like visible and infrared spectra, and higher infrared photon flux as compared to conventional materials like sapphire are found. We discuss the particular advantages of these materials for application in parametric amplification, femtosecond spectroscopy, and carrier-envelope phase stabilization.

Carrier-envelope phase-dependent field-free molecular orientation

We present a strategy to achieve carrier-envelope phase-dependent field-free molecular orientation with the use of carrier-envelope phase (CEP) stabilization and asymmetric few-cycle terahertz (THz) laser pulses. The calculations are performed on the LiH molecule by an exact solution of the full time-dependent Schr\odinger equation including both the vibrational and the rotational degrees of freedom. Our calculations show that an efficient field-free molecular orientation can be obtained even at considerable temperatures. Moreover, we find a simple dependence of the field-free orientation on the CEP, which implies that the CEP becomes an important parameter for control of molecular orientation. More importantly, the realization of this scenario is appealing based on the fact that the intense few-cycle THz pulse with duration as short as a few optical cycles is available as a research tool.

Carrier–envelope phase stabilization of 5-fs, 0.5-mJ pulses from adaptive phase modulator

We compressed high-power laser pulses to 5 fs and 0.5 mJ using a neon-filled hollow-core fiber and a high-throughput 4f system. The carrier–envelope phase of the two-cycle pulses was measured directly by using their over-one-octave output spectrum. The carrier–envelope phase was stabilized by feedback controlling the grating separation of a stretcher in a chirped pulse amplifier. To the best of our knowledge, this is the first time that carrier–envelope phase locked few-cycle pulses were generated by using an adaptive phase modulator.

Carrier-envelope phase stabilization and control using a transmission grating compressor and an AOPDF

Carrier-envelope phase (CEP) stabilization of a femtosecond chirped-pulse amplification system featuring a compact transmission grating compressor is demonstrated. The system includes two amplification stages and routinely generates phase-stable (approximately 250 mrad rms) 2 mJ, 25 fs pulses at 1 kHz. Minimizing the optical pathway in the compressor enables phase stabilization without feedback control of the grating separation or beam pointing. We also demonstrate for the first time to the best of our knowledge, out-of-loop control of the CEP using an acousto-optic programmable dispersive filter inside the laser chain.

Implementation of the direct locking method for long-term carrier-envelope-phase stabilization of a grating-based kHz femtosecond laser

We have stabilized the carrier-envelope phase (CEP) of amplified femtosecond laser pulses from a grating-based chirped-pulse amplification femtosecond laser by the direct locking method. Long-term CEP stabilization in the oscillator was achieved by employing a double-feedback loop to control both the pumping power and the cavity dispersion. Large CEP drift, induced during amplification, was compensated by adjusting the grating separation in the pulse compressor, and the CEP stabilization was maintained for four hours with a phase jitter of about 180 mrad. After pulse compression to 5.5-fs pulses in a filamentation pulse compressor, CEP-stabilized laser pulses were applied for high-harmonic generation to confirm the CEP stabilization.

Performance comparison of interferometer topologies for carrier-envelope phase detection

Performance and noise immunity of different interferometer set-ups for carrier-envelope phase detection are compared. The frequently used Mach–Zehnder interferometer is found to be easily corrupted by acoustic noise contributions and air streaks, whereas a quasi-common-path variant of the f-to-2f interferometer exhibits a 40% reduction of residual noise. This comparative analysis also provides deeper insight into additional mechanisms that are currently limiting the performance of carrier-envelope phase stabilization schemes.

Measurement of the carrier-envelope phase stability of infrared femtosecond laser pulses by two-path interferometer

We describe a self-referencing two-path interferometer designed to measure the carrier-envelope phase stability. In experiment, we measure the carrier-envelope phase （CEP） stability of a home-made infrared tunable OPA laser pulses with the self-referencing two-path interferometer. When the wavelength of the incident pulses is 1.6 μm, the CEP fluctuation is 115 mrad （rms） in 100 seconds. The interferometer can provide an accurate and quick measurement of the pulse CEP.

Octave-spanning, dual-output 2166 GHz Ti:sapphire laser

A self-referenced octave-spanning Ti:sapphire laser with 2.166 GHz repetition rate is demonstrated. The laser features both direct generation of octave-spanning spectra and a dual-output design for non-intrusive carrier-envelope (CE) phase-stabilization. Only a few percent of total power containing 1f and 2f spectral components is coupled out through a specially designed laser mirror and generates a >50 dB CE beat note in 100 kHz resolution bandwidth without perturbing the main output that still delivers octave-spanning spectra and 750 mW of output power.