A. A. Babin

Femtosecond energy transfer within the LH2 peripheral antenna of the photosynthetic purple bacteria Rhodobacter sphaeroides and Rhodopseudomonas palustris LL

Abstract The ultrafast energy transfer among the pigments of the B800–850 membrane antenna pigment—protein complex of the photosynthetic purple bacteria Rhodobacter sphaeroides and Rhodopseudomonas palustris LL has been studied with ≈ 100 fs tunable infrared pulses at room temperature and 77 K. It is shown that the B800→B850 transfer time is similar in both species and occurs with a characteristic time constant of 0.6–0.8 ps at room temperature and 2.4–2.6 ps at 77 K. Measurements of absorption anisotropy in the 800 nm band shows that the depolarizing energy transfer among B800 molecules is slower than the B800→B850 transfer. At room temperature such a transfer occurs with a time constant of 0.8–1.6 ps and at 77 K with a time constant much longer than the excited state lifetime. A fast ≈ 300 fs non-depolarizing, almost temperature-independent, relaxation process is also observed within the B800 band. Energy transfer between a pair of almost parallel B800 molecules and possibly also vibrational relaxation are discussed as the possible origins of this process.

Second-Harmonic Generation of Super Powerful Femtosecond Pulses Under Strong Influence of Cubic Nonlinearity

A theoretical model of second-harmonic generation (SHG) under strong influence of cubic nonlinearity was verified in experiment. Effective energy conversion in thin potassium dihydrogen phosphate crystals at peak intensity up to 5 TW/cm2 (B-integral equaled 6.4) was demonstrated and no crystal damage was observed. Comparative analysis of SHG of radiation at the fundamental wavelengths of 910 and 800 nm showed the major advantages of the first one. The double-pass geometry of SHG in an ultrathin crystal on a substrate is discussed in detail. Additional correction of parabolic spectral phase of the SH radiation allows pulse duration to be shortened from 20 to 9 fs for 910 nm fundamental wavelength and from 20 to 12 fs for 800 nm.

Shock-wave generation upon axicon focusing of femtosecond laser radiation in transparent dielectrics

It is shown experimentally that the axicon focusing of intense femtosecond laser pulses in transparent dielectrics leads to efficient excitation of shock waves. A method is developed for measuring the dynamics of shock waves, which uses a frequency-chirped probe pulse and has high spatial (∼1 μm) and time (∼10 ps) resolutions. The initial stage of the evolution of an intense (up to 10 GPa) shock wave is studied by this method.

Spectroscopy of supersmall absorption using the technique of a phase-contrast thermal lens

The problem of measuring supersmall light absorption in materials led to the development of a high-sensitivity optothermal laser technique, thermal lens and interferometer technique being the most widely-known. An optimum combination of the two above methods has been implemented where high sensitivity of optothermal phase-contrast technique (which reached for liquid media 10 -9 cm -1 at the pump energy 3 J) was demonstrated. The technique suggested here is quite competitive with other optothermal methods due to its simplicity of performing, absorption linearity of the measured signal and independence of the signal on absorption at the windows of the cell containing the medium under investigation.

Three-dimensional optical data recording and reading in polymer media with dyes

Investigations on 3D optical data recording in polymethylmethacrylate with spiropyran molecules by means of femtosecond Ti:Sapphire laser have been performed. The possibility for modification of polymer optical properties in volumes with sizes of 2 micrometers and recording time of < 1 ms has been demonstrated. A high image contrast of the recorded data allows to use amplitude methods of reading by both transmitted and reflected light, including parallel readout at a high speed.

Experimental investigation of the interaction of subterawatt femtosecond laser radiation with transparent dielectrics using axicon focusing

A subterawatt fs laser complex with a power in a pulse P less than or equal to 0.15 TW is constructed. Our experiments show that axicon focusing of such laser light in transparent dielectric leads to formation of a long hollow channel with micron-order transverse dimensions. It is found that effective (approximately 10-3) generation of harmonics of incident light takes place in plasma appearing under axicon focusing. The discussion of the results obtained is presented.

Nonreciprocities in modification and etching of polymer films by Nd laser fifth-harmonic radiation

The threshold-like formation of strongly modified (nonsolvable) layer in PMMA and other nonreciprocal effects of Nd:YAG laser fifth harmonic radiation on PMMA and PI films are discovered and discussed.

Highly sensitive optothermal phase-contrast IR spectrometer

The automated IR-spectrometer based on the pulsed tunable (1.5 divided by 3.7 micrometers ) optical parametrical oscillator with a spectral resolution of 3 cm-1 and the optothermal phase-contrast detection system is created. A minimal detectable absorption level is as small as (alpha) equals 10-6 cm-1 at the heating energy of 10 mJ.

Self-starting femtosecond pulse generation from a Ti:sapphire laser synchronously pumped by a pointing-stabilized mode-locked Nd:YAG laser

We have constructed a self-starting Kerr-lens mode-locked Ti:sapphire laser pumped synchronously by a mode-locked, LBO-doubled Nd:YAG laser. Using a home-built beam- pointing stabilizer, beam wander of the 532 nm pump is reduced by a factor of 25, thus enabling long term operation of TEM00 nearly transform limited pulses with amplitude, repetition rate, and pulsewidth fluctuations comparable to or better than those of Ar-pumped Ti3+:Al2O3 lasers. Interferometric autocorrelation using second harmonic in reflection from GaAs yielded a pulse width of 30 fs, limited by the dispersion of wide bandwidth cavity optics that permit tunability from 0.7 to 1.0 micrometers .

Solid state tunable laser for space-and-time-domain holography

Application of Ti:sapphire femtosecond laser for 3-D image holographic recording of superfast processes in its temporal development is offered. Pulse shortening leads to time resolution improvement of the systems.