Effects of pulse width and repetition rate of pulsed laser on kinetics and production of singlet oxygen luminescence

Pulsed and continuous-wave(CW)lasers have been widely used as the light sources for photodynamic therapy(PDT)treatment.Singlet oxygen(^(1)O_(2))is known to be a major cytotoxic agent in type-II PDT and can be directly detected by its near-infrared luminescence at 1270 nm.As compared to CW laser excitation,the effiects of pulse width and repetition rate of pulsed laser on the kinetics and production of^(1)O_(2)luminescence were quantitatively studied during photosensitization of Rose Bengal.Significant di®erence in kinetics of^(1)O_(2)luminescence was found under the excitation with various pulse widths of nanosecond,microsecond and CW irradiation with power of 20mW.The peak intensity and duration of^(1)O_(2)production varied with the pulse widths for pulsed laser excitation,while the^(1)O_(2)was generated continuously and its production reached a steady state with CW excitation.However,no significant di®erence(P>0:05)in integral^(1)O_(2)production was observed.The results suggest that the PDT efficacy using pulsed laser may be identical to the CW laser with the same wavelength and the same average°uence rate below a threshold in solution.

1.2 kW all-fiber narrow-linewidth picosecond MOPA system

Achieving an all-fiber ultra-fast system with above kW average power and mJ pulse energy is extremely challenging.This paper demonstrated a picosecond monolithic master oscillator power amplifier system at a 25 MHz repetition frequency with an average power of approximately 1.2 kW,a pulse energy of approximately 48μJ and a peak power of approximately 0.45 MW.The nonlinear effects were suppressed by adopting a dispersion stretched seed pulse(with a narrow linewidth of 0.052 nm)and a multi-mode master amplifier with an extra-large mode area;then an ultimate narrow bandwidth of 1.32 nm and a moderately broadened pulse of approximately 107 ps were achieved.Meanwhile,the great spatio-temporal stability was verified experimentally,and no sign of transverse mode instability appeared even at the maximum output power.The system has shown great power and energy capability with a sacrificed beam propagation product of 5.28 mm·mrad.In addition,further scaling of the peak power and pulse energy can be achieved by employing a lower repetition and a conventional compressor.

Design of coherent wideband radiation process in a Nd3+-doped high entropy glass system

We discover that the spatially coherent radiation within a certain frequency range can be obtained without a common nonlinear optical process.Conventionally,the emission spectra were obtained by de-exciting excited centers from real excited energy levels to the ground state.Our findings are achieved by deploying a high-entropy glass system(HEGS)doped with neodymium ions.The HEGS exhibits a much broader infrared absorption than common glass systems,which can be attributed to be high-frequency optical branch phonons or allowable multi-phonon processes caused by phonon broadening in the system.A broadened phonon-assisted wideband radiation(BPAWR)is induced if the pump laser is absorbed by the system.The subsequent low-threshold self-absorption coherence modulation(SACM)can be controlled by changing excitation wavelengths,sample size,and doping concentrations.The SACM can be red-shifted through the emission of phonons of the excited species and be blue-shifted by absorbing phonons before they are de-excited.There is a time delay up to 1.66 ns between the pump pulse and the BPAWR when measured after traveling through a 35 mm long sample,which is much longer than the Raman process.The BPAWR-SACM can amplify the centered non-absorption band with a gain up to 26.02 dB.These results reveal that the shift of the novel radiation is determined by the frequency of the non-absorption band near the absorption region,and therefore the emission shifts can be modulated by changing the absorption spectrum.When used in fiber lasers,the BPAWR-SACM process may help to achieve tunability.

152 W high-power blue diode laser operated at 447 nm

We demonstrate a high-power blue diode laser operated at 447 nm combining laser diodes using an optical fiber bundle. As many as 127 diode lasers at 447 nm were coupled into 400 μm/0.22 NA fibers using an aspherical lens group with different focus lengths. The bare fibers were mechanically bundled through high temperature ultraviolet adhesive after the coatings of the 127 fibers were stripped. The diameter of the fiber bundle was 6 mm. The total output power of such a bundle was 152 W with electro-optical conversion efficiency of 27.56%and the RMS power instability was less than ±1% within 3 h.

Experimental investigation of the stimulated Raman scattering effect in high-power nanosecond superfluorescent fiber source

In this work,we experimentally investigate the dependence of the stimulated Raman scattering(SRS)effect on the seed linewidth of a high-power nanosecond superfluorescent fiber source(ns-SFS).The results reveal that the SRS in the ns-SFS amplifier is significantly influenced by the full width at half maximum(FWHM)of the ns-SFS seed,and there is an optimal FWHM linewidth of 2 nm to achieve the lowest SRS in our case.The first-order SRS power ratio increases rapidly when the seed’s linewidth deviates from the optimal FWHM linewidth.By power scaling the ns-SFS seed with the optimal FWHM linewidth,a narrowband all-fiberized ns-SFS amplifier is achieved with a maximum average power of 602 W,pulse energy of 24.1 mJ and corresponding peak power of 422.5 kW.This is the highest average power and pulse energy achieved for all-fiberized ns-SFS amplifiers to the best of our knowledge.