Transient coherent Raman scattering in the time and frequency domain

A new type of Raman spectroscopy is presented: After transient excitation of molecular modes coherently scattered Raman spectra are investigated in a depayed probing experiment. The spectral position of the Raman mode is observed after long delay times. The dephasing time is obtained from the time dependence of the scattered amplitudes. Frequency disturbing non-resonant susceptibilities are eliminated. We report on first experimental results of transient coherent Raman spectroscopy of liquid CH3CCl3

A new Raman technique of superior spectral resolution

Raman-active vibrational modes are coherently excited by the transient stimulated Raman process. A subsequent delayed probe of relatively long duration interacts with the freely relaxing vibrations. Raman spectra are generated with higher resolution and more accurate peak positions than in conventional Raman spectroscopy. In liquid cyclohexane four new Raman lines were readily detected in the frequency range 2870–2920 cm−1

Terahertz quantum beats in molecular liquids

With ultrashort pulses of less than 100 fs it is possible to excite coherently several vibrational modes of polyatomic molecules simultaneously. The femtosecond time resolution of the experiment allows the study of pronounced high-frequency beat phenomena up to 10 THz. The frequency difference between vibrational modes separated by more than 300 cm−1 may be determined with high precision

Influence of Fluctuating Pulse Durations on the Time Resolution of Probing Experiments

Fluctuating pulse durations considerably influence the time resolution of probing experiments. The commonly used arithmetic averaging the experimental data changes the shape of the signal curves and gives longer decay times in the wings. Methods are presented to reduce the effect of fluctuating pulse durations

Generation of frequency shifted picosecond pulses with low temporal jitter

Transient stimulated Raman scattering is used for the generation of a frequency shifted picosecond light pulse; part of this Raman shifted pulse is subsequently coherently scattered at a material excitation of a second Raman cell. Starting with the second harmonic pulse (tp = 4 ps) of a mode-locked Nd : glass laser system, both the stimulated and the coherently produced pulses have durations of 2.3 ps at different wavelengths. By the appropriate choice of the Raman medium pulses between 13 000 and 21 000 cm-1 can be generated. The coherent generation process minimizes the temporal jitter between the two pulses and allows to obtain a high time resolution of better than 0.3 ps in excite and probe experiments

Narrowing of spectral lines beyond the natural or dephasing line width

Transient excitation and gated or delayed observation provides a narrowing of the inherent line width of the transition. Possible experimental one- and two-photon systems are discussed and the loss of signal with line narrowing is calculated. The general case of lines broadened by dephasing processes is treated. Contact is made with the line narrowing in recent Raman type experiments

The interplay of electron doping and chemical pressure in Ba(Fe(1-y)Coy)2(As(1-x)Px)2

The effects of internal chemical pressure on electron doped iron arsenide superconductors are studied in the series Ba(Fe(1-y)Coy)2(As(1-x)Px)2. Combinations of both dopants induce superconductivity also in such areas where only one would not suffice, and can likewise move the system into an overdoped state, while no higher critical temperature than 31 K in BaFe2(As(1-x)Px)2 was found. The phase diagram gives no evidence of holes in BaFe2(As(1-x)Px)2 as suggested by recent photoemission experiments. Chemical and physical pressure act similarly in Ba(Fe(1-y)Coy)2(As(1-x)Px)2, but our data reveal that the most important control parameter is the length of the Fe-As bond and not the unit cell volume. This emphasizes that differences between chemical and physical pressure which manifest oneself as the non-linear reduction of the Fe-As distance in BaFe2(As(1-x)Px)2 are strongly linked to the superconducting properties also in the Co doped compounds.Comment: 11 pages, 10 figure

Theoretical and Experimental Investigations of a Passively Mode-Locked Nd" Glass Laser

The presented theoretical model for a mode-locked Nd-glass laser simultaneously takes into account dynamics of the mode-locking dye, amplification saturation and radiation background. A systematic variation of laser parameters gives insight into the pulse formation process and allows to improve the laser design. The calculations show that it should be possible to decrease considerably the duration of light pulses of a mode-locked Nd-glass laser. Using a new mode-locking dye with a switching time of τ=2.7×10−12 s we obtained stable laser operation and a pulse duration of 1.7×10−12s

Frequency shifts in stimulated Raman scattering

The nonresonant contributions to the nonlinear susceptibility χ(3) produce a frequency chirp during stimulated Raman scattering. In the case of transient stimulated Raman scattering, the spectrum of the generated Stokes pulse is found at higher frequencies than expected from spontaneous Raman data. The frequency difference can be calculated from the theory of stimulated Raman scattering