Adam Borzsonyi

Dispersion measurement of inert gases and gas mixtures at 800 nm

Dispersion of femtosecond laser pulses propagating in Ar, He, Kr, N(2), Ne, Xe, and their mixtures is measured by spectrally and spatially resolved interferometry. By varying the gas pressure in a 4.5 m long tube between 0.05 mbar and ambient pressure, the first, second, and third order phase derivatives of broadband laser pulses are determined at 800 nm under standard conditions. The dispersion of gases and gas mixtures obeys the Lorentz-Lorenz formula with an accuracy of 0.7%. Based on the measured pressure dependent dispersion values in the near infrared and the refractive indices available from the literature for the ultraviolet and visible, a pressure dependent Sellmeier-type formula is fitted for each gas. These common form, two-term dispersion equations provide an accuracy between 4.1x10(-9) (Ne) and 4.3x10(-7) (Xe) for the refractive indices, from UV to near IR.

Agile linear interferometric method for carrier-envelope phase drift measurement

A bandwidth-independent and linear interferometric method for the measurement of the carrier-envelope phase drift of ultrashort pulse trains is demonstrated. The pulses are temporally overlapped in a resonant multiple-beam interferometer. From the position of the spectral interference pattern, the relative carrier-envelope phase between two subsequent oscillator pulses is obtained at data acquisition rates up to 200 Hz. Cross calibration has been performed by f-to-2f interferometry in two independent experiments. The optical length of the interferometer has been actively stabilized, leading to a phase jitter of 117 mrad (rms). These results indicate a reduced noise and quicker data acquisition in comparison with previous linear methods for measuring the carrier-envelope phase drift.

Preservation of the carrier envelope phase during cross-polarized wave generation

The preservation of carrier envelope phase (CEP) during Cross-Polarized Wave Generation (XPWG) is demonstrated through two independent experiments based on the spatially and spectrally resolved interference fringes formed by the XPW beam and its fundamental. In a first measurement, we found that the vertical fringe position on the spatial detector was maintained over many consecutive laser shots, implying practically no change in relative CEP between the XPW and the fundamental. In a second experiment, we measured the change in relative CEP between the XPW and fundamental beam by systematically varying the amount of material dispersion inside the XPW arm of the interferometer. The recorded rate of relative phase change was in excellent agreement with the theoretical value.

Two-dimensional single-shot measurement of angular dispersion for compressor alignment

Misalignment of the stretcher-compressor stages of chirped pulse amplification (CPA) lasers can aggravate the spatiotemporal shape of ultrashort pulses. We demonstrate a simple technique for angular dispersion measurement, which offers real-time single-shot two-dimensional characterization across the entire beam profile. The accuracy of our pilot experiment approaches its current theoretical limit of 0.1 μrad/nm. Unlike the current one-dimensional techniques working in the near field, the method works in the far field; hence, it is especially appropriate for assisting the most accurate alignment of a CPA laser compressor ensuring the maximum intensity on the target.

Thermal Effects and Structural Changes of Photosynthetic Reaction Centers Characterized by Wide Frequency Band Hydrophone: Effects of Carotenoids and Terbutryn.

Photothermal characteristics and light‐induced structural (volume) changes of carotenoid‐containing and noncontaining photosynthetic reaction centers (RCs) were investigated by wide frequency band hydrophone. We found that the presence of carotenoid either does not play considerable role in the light‐induced conformational movements, or these rearrangements are too slow for inducing a photoacoustic (PA) signal. The kinetic component with a few tens of microseconds, exhibited by the carotenoid‐less RCs, appears to be similar to that of triplet state lifetimes, identified by other methods. The binding of terbutryn to the acceptor side is shown to affect the dynamics of the RC. Our results do not confirm large displacements or volume changes induced by the charge movements and by the charge relaxation processes in the RCs in few hundreds of microseconds time scale that accompanies the electron transfer between the primary and secondary electron acceptor quinones.

Measurement Of The Spectral Phase Shift And The Residual Angular Dispersion Of An AOPDF

The spectral phase shift and both types of angular dispersion introduced by an acousto‐optic programmable dispersive filter (AOPDF) into a femtosecond laser beam at 800 nm have been measured with high precision. With the use of spectrally and spatially resolved interferometry we experimentally proved that the AOPDF controls the group delay dispersion (GDD) and third‐order dispersion with an accuracy of better than 1% and 3% of the preset values within the range of 2 fs2–1000 fs2 and 1000 fs3–40000 fs3, respectively. Both the angular deviation as well as the angular dispersion values are primarily dependent on the set absolute value of GDD of the continuously operating AOPDF. Besides of a small offset value, there is no added angular dispersion at 0 fs2, while this can be as large as 0.2 μrad/nm at 10000 fs2.

Drift and noise of the carrier–envelope phase in a Ti:sapphire amplifier

We report on the drift and noise measurement of the carrier–envelope phase (CEP) of ultrashort pulses in a three-pass Ti:sapphire-based amplifier. Spectrally and spatially resolved interferometry makes it possible to investigate the absolute CEP changes due exclusively to the amplifier, that is, entirely separated from the incidental phase fluctuations of the oscillator. We found that propagation through the amplifier crystal could result in an increase up to 30 mrad noise depending on the repetition rate, cooling, and pumping conditions. Most of this noise is related to mechanical vibrations and thermal instabilities. The absolute CEP drift of thermal origin can be as large as 11 mrad/°C for each mm of the amplifier crystal, originating from inefficient heat conduction during the absorption of pump pulses. The noise of the thermal CEP drift is inversely proportional to the repetition rate, as was shown experimentally and proven by simulations.

Real-time two-dimensional measurement of angular dispersion of broadband laser beams

We demonstrate a simple technique for angular dispersion measurement, which allows two-dimensional detection in one shot and can be used in real-time acquisition. These make our method especially suitable for CPA compressor alignment. Experimental accuracy found to be close to common 1D techniques.

Measurement of pressure dependent nonlinear refractive index of inert gases

Nonlinear refractive index of Ar, Kr, N 2 Ne, Xe, and air has been determined from the spatially dependent nonlinear spectral phase of weak femtosecond pulses propagating in sample gases under pressure between 0.05mbar and 1bar.

Preservation of CEP upon generation of XPW pulses

Upon efficient generation of cross-polarized wave (XPW) in a cubic crystal via achromatic χ(3) process, the XPW pulses are polarized in the orthogonal direction. XPW generation has demonstrated its ability to filter amplified spontaneous emission out of a high power femtosecond pulse, thereby increasing its temporal contrast and also to broaden the pulse spectrum by more than a factor of two [1,2]. Furthermore, in case of energetic few-cycle pulses, the laser-matter interaction depends on the carrier envelope phase (CEP) of the pulses. Hence it is essential to stabilize the intrinsic CEP drift between successive pulses from the laser. If the XPW filter is used in the laser chain it is important to demonstrate that it does not deteriorate the CEP stability of the system. In this presentation, we give clear experimental evidence that the CEP is preserved upon the XPW process.