ABSTRACT
In this paper we report on the active stabilization of the carrier envelope phase (CEP) of a Yb:KGW chirped pulse amplifier laser system seeded by a Yb-doped solid-state Kerr-lens mode-locked oscillator. The regenerative amplifier delivers 180 fs CEP stable pulses of 30 µJ-1 mJ energy at a repetition rate tunable from 1 to 200 kHz. The bandwidth of the feedback loop was extended by a factor of 5 using a specially designed high-pass filter, which resulted in a dramatic decrease of CEP jitter below 0.45 rad after the amplifier.
ABSTRACT
BACKGROUND DATA: Research on the damaging effect of ultraviolet (UV) laser irradiation on the DNA of live organisms is still scarce, although UV lasers are increasingly being used in therapeutics and surgical treatment. OBJECTIVE: In this study we investigated the effect of new-generation 205-nm femtosecond solid-state laser irradiation on the DNA of murine bone marrow cells in vitro. MATERIALS AND METHODS: Mouse bone marrow cells in distinct plates were exposed to different doses of 205-nm femtosecond laser irradiation. Single-cell gel electrophoresis, or comet, assay was used for DNA damage measurement. RESULTS: Our study revealed intensity-dependent genotoxic, genotoxic-cytotoxic, or cytotoxic impact of laser irradiation. The lowest doses we used (0.0175-0.105 J/cm(2)) induced DNA photodamage in irradiated cells directly, medial doses (0.175 and 0.35 J/cm(2)) caused both direct damage of genetic material and irreversible injury of cell's structure whereas the highest doses (1.05-4.2 J/cm(2)) caused the death of most irradiated cells. It is worrisome that even comparatively low doses of irradiation were genotoxic. Exposure to the lowest-intensity irradiation (0.0175 J/cm(2)) caused a highly significant (p < 0.0001) increase in DNA strand breaks of bone marrow cells: the mean ± SEM %DNA score in the comet tail was 9.96 ± 0.56 compared with 3.58 ± 0.80 for controls. Investigation of the effects of low and medial intensities of irradiation showed a dosage-effect relationship of R(2) = 0.84, P < 0.01. CONCLUSION: New-generation 205-nm femtosecond laser irradiation produced a genotoxic effect by inducing strand breaks in the DNA of murine bone marrow cells in vitro. Research on the possible genotoxic effects of this laser on corneal and skin epithelial cells in vivo is needed.