Cz. Radzewicz

A poor man's FROG

In this communication we present a new method for recording a two-dimensional second harmonic spectrogram of a femtosecond laser pulse. Filtering of the second harmonic signal due to phase matching in a thick nonlinear crystal is used to spectrally resolve the second harmonic autocorrelation. Amplitude and phase of a pulse can be retrieved from the spectrogram using a standard frequency resolved optical gating iterative algorithm.

Cavity ring-down spectroscopy of the oxygen B-band with absolute frequency reference to the optical frequency comb

Absolute positions of several oxygen B-band lines were measured with the Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectrometer. The frequency axis of spectra was linked to the optical frequency comb. Achieved uncertainties of line positions are between 0.9 and 2.9 MHz. Self-pressure shifts coefficients are also reported.

Time behaviour of diffuse band emission in Na2 and K2

Abstract The C states of sodium and potassium dimers were excited with short laser pulses (about 500 ps) and time evolution of the diffuse bands in Na2 (413–456 nm) and K2 (550–583 nm) was observed in fluorescence. The measured decay times were interpreted as lifetimes of unidentified triplet states giving origin to the diffuse bands. Our results contradict the values reported before.

Two-wavelength single mode grazing incidence dye laser

Abstract Two-wavelength single mode operation of a N2-laser pumped dye laser is described. The proper choice of a grazing incidence grating and highly selective cavity elements provided a stable operation of the laser. A single mode spectrum of 310 ± 50 MHz is measured and both wavelengths are independently tunable over the entire gain profile of the R6G DN dye.

A femtosecond snapshot of crystalline order in molecular liquids

A theoretical model of ultrafast dynamics in the optical Kerr effect in molecular liquids is developed. It assumes that for short times there exist dynamic quasicrystalline structures including a central molecule and its nearest neighbors. The interaction of such structures with a femtosecond laser pulse leads to excitation of vibrational modes (local phonons) which are responsible for subpicosecond nonlinear polarizability of the liquid. The results of numerical calculations performed for benzene show a very good agreement with the experimental data. The lifetime of the dynamic quasicrystalline structures in benzene, at room temperature, is estimated to be about 200 fs.

Excitation mechanisms and spectral shape of the diffuse violet emission band in Na2

A dense sodium vapour (T=450°C) has been illuminated with a laser light tuned across the whole visible region. For any laser wavelength the diffuse violet band of Na2 molecule (peaking at 436.5 nm) has been found in fluorescence spectrum. Several mechanisms are proposed for excitation of the diffuse band, including collisional energy transfer and ionization-recombination processes. New observations of a spectral shape of the diffuse band are reported.

Efficient high repetition rate synchronous amplification of a passively mode-locked femtosecond dye laser.

We demonstrate reliable operation of a stable synchronously pumped dye amplifier for femtosecond pulses from a passively mode-locked dye laser. Conversion efficiencies of 8% are obtained with output powers of 40 mW and 50-fs pulse widths at repetition rates of up to 10 kHz with pulse energy stability of 3% rms. Synchronization is achieved by driving the frequency-modulated mode-locked seed oscillator for the regenerative amplifier pump laser directly from the dye laser oscillator. Low timing jitter between the dye oscillator and seed laser of less than 1 ps leads to efficient amplification and low amplified spontaneous emission (1%) from the amplifier.

Ultrafast optical Kerr effect spectroscopy of water confined in nanopores of the gelatin gel

We report on the investigation of a short-time collective dynamics of water confined in the pores of the gelatin gel, using the femtosecond optical Kerr effect spectroscopy. The ultrafast responses of water molecules obtained in bulk liquid and in three concentrations of gelatin gels are explained theoretically, both in a long time and in a short time regime, taking into account all molecular motions. We prove that the contribution of molecules involved in tetrahedral, strongly H-bonded structures stabilizing the gel network increases with the gel concentration. On the other hand the long-time relaxation of water molecules is significantly slowed down in the gel pores.

High efficient system for studying multiphoton absorption

An optical arrangement for studying two-photon absorption in liquids is presented. The main feature of this new arrangement is fuller utilization of fluorescence light. This makes possible application of very low power cw laser in such experiments.

Characterization of an FM mode-locked Nd : YLF laser synchronized with a passively mode-locked dye laser

Abstract We have demonstrated stable, long-term operation of a diode-pumped FM mode-locked Nd: YLF laser, which is synchronized to a possively mode-locked dye laser (CPM). Relative jitter between the lasers is measured to be less than 1 ps. The operation of the FM mode-locked laser near threshold agrees well with the Kuizenga-Siegman theory, however deviations are observed well above threshold.