Calibration of micro-channel plate detector in a Thomson spectrometer for protons and carbon ions with energies below 1 MeV.

The calibration of an ion detection system was carried out for protons and carbon ions from a few tens of keV up to about 1 MeV energies. A Thomson spectrometer deflecting the particle beam accelerated from a laser plasma creates the ion spectra on a phosphor screen behind a micro-channel plate (MCP), which are recorded by a camera. During calibration, the ion spectra simultaneously hit the slotted CR-39 track detector installed in front of the MCP and, passing through the adjacent CR-39 stripes, the MCP. The calibration provides the ratio of the interpolated values between two consecutive stripes of the camera signal and the total number of particles recorded on the corresponding stripe of CR-39. The efficiency of proton detection by CR-39 was also measured in a conventional accelerator beam and found to drop by 20% below 100 keV.

Low divergent MeV-class proton beam with micrometer source size driven by a few-cycle laser pulse.

Spatial characterization of 0.5 MeV proton beam, driven by 12 fs, 35 mJ, 1019 W/cm2 intense laser-foil interaction is presented. The accelerated proton beam has been applied to obtain a high-resolution, point-projection static radiograph of a fine mesh using a CR-39 plate. The reconstruction of mesh edge blurring and particle ray tracing suggests that these protons have an effective source size (FWHM) of just 3.3 ± 0.3 µm. Furthermore, the spatial distribution of the proton beam recorded on the CR-39 showed that the divergence of these particles is less than 5-degree (FWHM). The low divergence and small source size of the proton beam resulted in an ultralow transverse emittance of 0.00032 π-mm-mrad, which is several orders of magnitude smaller than that of a conventional accelerator beam.

Nanographene oxide as a switch for CW/pulsed NIR laser triggered drug release from liposomes.

The application of pulsed and continuous wave (CW) lasers in nanomedicine has increased significantly over the last decade. Near infrared (NIR) lasers can be used for the precise control of drug release at the target site in a non-invasive manner. In this study, we have prepared nanographene oxide (nGO, size ~40nm) integrated liposomes (size ~900nm). The nGOs were not simply adsorbed onto the liposome surface but was embedded inside the liposomes as characterized by cryo-TEM, selected area electron diffraction (SAED), and fluorescence quenching studies. The embedded nGOs could act as a molecular switch for NIR light controlled drug release from the liposomes. Calcein was encapsulated into the liposome as a model drug to evaluate the efficiency of light controlled release. An on-demand pulsatile drug release was achieved by irradiation of CW/pulsed NIR lasers into the nGO-liposome suspension. Triggering with a pulsed laser resulted in larger release of calcein with a minimal temperature increase (~2°C) of the liposome solution, compared to lower release rate and a significant temperature increase (~8°C) by a CW laser with the same light energy, suggesting two separate mechanisms and different potential applications depending on the laser type.

Application of pulsed buffer gas jets for the signal enhancement of laser-induced breakdown spectroscopy.

We report a new simple method for the signal enhancement of laser-induced breakdown spectroscopy using a pulsed buffer gas jet. The signal is enhanced up to more than 10 fold by using argon gas jets, which are injected through a pulsed nozzle onto the sample area to be analyzed. By synchronizing the buffer gas pulse with the laser pulse and optimizing the spatial arrangements between the gas jet and the sample surface, we have successfully exploited the useful properties of the buffer gas in open atmosphere. The signal-enhancement mechanism in our buffer gas jet has been discussed. Also, applications to various samples (metal, glass, and paper) have been demonstrated.