Anton Trifonov

Increasing the speed limit for hole transport in DNA

Transport of positive charge or holes in DNA occurs via a thermally activated multi-step hopping mechanism. The fastest hopping rates reported to date are those for repeating poly(purine) sequences in which hopping occurs via a random walk mechanism with rate constants of k(hop) = 4.3 × 10(9) s(-1) for poly(dG) and 1.2 × 10(9) s(-1) for poly(dA). We report here the dynamics of charge separation in DNA conjugates possessing repeating 7-deazaadenine (dzA) sequences. These data provide an estimated value of k(hop) = 4.2 × 10(10) s(-1) for poly(dzA), an order of magnitude faster than for poly(dG).

Dynamics and Efficiency of Hole Transport in LNA:DNA Hybrid Diblock Oligomers

We report here the effect of replacing one or both of the purine or pyrimidine blocks of a diblock stilbene donor-acceptor capped hairpin with locked nucleic acid (LNA) bases on the dynamics and efficiency of hole transport. The structures of the DNA and LNA:DNA hybrids are tentatively assigned to B- or A-type structures on the basis of their circular dichroism spectra. Replacing the bases in either the A-block or the G-block of the diblock DNA hairpin with LNA bases results in a modest decrease in the base-to-base hopping rate constant and quantum yield for charge separation. Somewhat larger decreases are observed when all of the purine or pyrimidine bases are replaced by LNA bases.

Effect of Mg2+ Cations on the Dynamics and Efficiency of Hole Transport in DNA

The effect of Mg(2+) cations on the electronic spectra and dynamics and efficiency of hole transport has been determined by means of femtosecond time-resolved transient absorption spectroscopy for DNA hairpins possessing stilbene electron acceptor and donor chromophores. The results are compared with those obtained previously for the same hairpins in the presence of Na(+) cations and for one hairpin with no added salt. Quantum yields and rate constants for charge separation are smaller in the presence of Mg(2+) than Na(+), the largest differences being observed for the hairpins with the largest number of base pairs. Slower charge separation is attributed to minor groove binding by Mg(2+), which results in a stiffer duplex structure rather than a change in ground state geometry. Reduction in the Na(+) concentration has little effect on either the dynamics or efficiency of hole transport.

52-mJ, kHz-Nd:YAG laser with diffraction limited output

We present Nd:YAG, diode pumped amplifier system emitting up to 52-mJ pulse energy with 1.6-ns pulse duration and near diffraction limited beam, operating at 0.75-kHz repetition rate.

Near diffraction limited pulses with 52-mJ, 1.2 ns at 0.5 kHz, generated by Nd-based MOPA

In this work, we report the amplification of laser pulses from a near diffraction limited, passively Q-switched Nd:YAG master oscillator (0.58 mJ, 1.2 ns at 0.5 kHz) up to 52-mJ in a Nd:YVO4 preamplifier and two diode pumped boost YAG-amplifiers, whilst preserving pulse duration, beam quality and linear polarization.

Picosecond energy scalable kHz OPO/OPA tunable in 3–3.5 μm mid-IR spectral range

We demonstrate 740 ps, 4.1-mJ tunable mid-IR PPSLT based OPO/OPA pumped by 38-mJ, 800 ps, Nd-laser system operated at 0.5–1kHz repetition rate.

χ (2) -Lens Mode-Locking of a High Average Power Nd:YVO 4 Laser

We report over 20 W, 6 ps, 170 MHz, passive mode-locking of a Nd:YVO₄ laser using χ⁽²⁾-lens formation in a LBO frequency doubling crystal. The laser is pumped at 808 nm with optical efficiency of 38%.

13-mJ, single frequency, sub-nanosecond Nd:YAG laser at kHz repetition rate with near diffraction limited beam quality

Near diffraction limited, single frequency, passively Q-switched Nd:YAG laser (240-μJ, 830-ps at 0.5-kHz) is amplified up to 13-mJ in a three-stage diode pumped amplifier whilst preserving pulse duration, beam quality and linear polarization.

Single Frequency Multi Milijoule Sub-nanosecond Nd:YAG Laser at kHz Repetition Rate

We report up to 13 mJ at 0.5 kHz, linearly polarized output with 830 ps pulse duration from a single frequency amplified Nd:YAG microchip laser at 1064 nm

Towards measuring structural dynamics in complex molecules by excited state circular dichroism

We demonstrate a new approach to broad band circular dichroism spectroscopy using polarization controlled femtosecond white-light generation which allows measurement of the differential absorption of right and left circular polarized light across the entire white light spectrum.