M. Görbe

Bandwidth-independent linear method for detection of the carrier-envelope offset phase.

We propose and demonstrate a novel linear procedure for measurement of the carrier-envelope offset (CEO) phase of femtosecond oscillators. The technique is based on a Mach-Zehnder interferometer, a ring resonator, and a spectrograph. In this scheme, interference between subsequent pulses from a pulse train may frustrate the interference between identical pulses in the Mach-Zehnder, resulting in a modification of interference contrast depending on the CEO phase. We suggest spectrally and spatially resolved interferometry for robust detection of the fringe visibility. It is shown by numerical simulations and experimentally demonstrated that the visibility of such fringes uniquely depends on the CEO phase of the pulse train. Since the method relies only on linear interactions and does not require any nonlinear conversion, it allows characterizing the CEO frequency of mode-locked oscillators with virtually arbitrarily low bandwidth and power levels.

Isochronic carrier-envelope phase-shift compensator

A concept for orthogonal control of phase and group delay inside a laser cavity by a specially designed compensator assembly is discussed. Similar to the construction of variable polarization retarder, this assembly consists of two thin wedge prisms made from appropriately chosen optical materials. Being shifted as a whole, the assembly allows changing the phase delay with no influence on the cavity round-trip time, whereas relative shifting of the prisms enables adjustment of the latter. This scheme is discussed theoretically and verified experimentally, indicating a factor 30 reduction of the influence on the repetition rate compared to the commonly used silica wedge pair. For a 2pi adjustment of the carrier-envelope phase shift, single-pass timing differences are reduced to the single-femtosecond regime. With negligible distortions of timing and dispersion, the described compensator device greatly simplifies carrier-envelope phase control and experiments in extreme nonlinear optics.

Independent Control of Arbitrary Dispersion Order of High Intensity Laser Pulses

We report on wedge pairs made of different materials, which are capable of tuning exclusively one dispersion coefficient of laser pulses. Contrary to conventional dispersion controlling devices, these wedges can be used with high intensities.

A bandwidth independent linear method for detection of carrier envelope phase drift

Measurement and control of the carrier-envelope phase (CEP) has opened the route to attoscience and to applications of femtosecond pulses in metrology. It is common belief that CEP measurement schemes have to involve a nonlinear optical conversion step and that they require octave coverage of the input spectrum, as is the case for the widespread f to-2f interferometers. Here we will show that neither is required and discuss a linear optical interferometric method that allows for direct measurements of the CEP slippage rate of pulses with arbitrarily narrow spectrum and low power level.

Measurement of the group-delay dispersion of a pulse stretcher-compressor system with two-dimensional spectral interferometry

In this work, we present a two-dimensional extension of the stationary phase point (SPP) method which is suitable for measuring the group-delay dispersion (GDD) of a stretcher or a compressor. The light path in the chirped-pulse amplification (CPA) laser is completed to form a Mach-Zehnder type interferometer, and only the stretcher is placed in the sample arm. The recombined pulses from the interferometer are sent to the entrance slit of an imaging spectrograph. The group delay as a function of wavelength can be determined from the position of the center of the spectrally resolved interference (SRI) fringes.

A simple linear technique for measuring the carrier-envelope offset phase of ultrashort pulses

A spectrally resolved multiple beam interferometer is capable for measuring the carrier envelope offset phase of ultrashort laser pulses with an accuracy of 70 mrad. The performance has been cross-calibrated with a conventional f-to-2f interferometer.

A linear optical method for measuring the carrier envelope offset phase

A linear optical method is demonstrated for extracting the carrier-envelope offset phase via the fringe visibility in a combined two-path multi-path interferometer. This method is applicable to a wider class of lasers than f-to-2f interferometry.

Dispersion of femtosecond pulses in ambient and low pressure air

To measure the pressure dependence of dispersion, the Mach-Zender interferometer illuminated by 800nm, 16 fs pulses from a Ti:S oscillator working at 71 MHz repetition rate. The outcoming pulses from both arms were unified and sent to the entrance slit of an imaging spectrograph. The spectrally resolved interference fringes were then captured and evaluated, which provides directly the values of GDD, TOD and even higher order dispersion terms. When the tube was in air, the evaluation of the fringes provided the base dispersion values. Starting evacuating the tube, the spectrally resolved fringes were captured again at certain pressures. The dispersion falls exponentially with an exponent of 0.00149 mbar/sup -1/ but still exhibits a surprisingly high value of 4.7 fs/sup 2//m at more than four order of magnitude lower level than the standard pressure. The air conditioning system maintained constant the room temperature at 23 /spl deg/C and the relative humidity at 60 %.

A table-top high contrast TW laser system

The seed pulses of the laser system is generated in a Kerr-lens-mode-locked Ti:sapphire oscillator pumped with 3.2 W power of a frequency doubled cw Nd:YVO/sub 4/ laser. The produced pulses exhibit 16 fs duration at 800 nm with a mean output power of 200 mW at a repetition rate of 72 MHz. The pulses are stretched in an all reflective stretcher consisted of a pair of 1200 mm/sup -1/ gratings and a spherical mirror, which allows the spectral transmission as broad as 200 nm.