S. Kawanishi

High temporal and spatial quality petawatt-class Ti:sapphire chirped-pulse amplification laser system

Optical parametric chirped-pulse amplification (OPCPA) operation with low gain by seeding with high-energy, clean pulses is shown to significantly improve the contrast to better than 10(-10) to 10(-11) in a high-intensity Ti:sapphire laser system that is based on chirped-pulse amplification. In addition to the high-contrast broadband, high-energy output from the final amplifier is achieved with a flat-topped spatial profile of filling factor near 77%. This is the result of pump beam spatial profile homogenization with diffractive optical elements. Final pulse energies exceed 30 J, indicating capability for reaching peak powers in excess of 500 TW.

Measurement of relative biological effectiveness of protons in human cancer cells using a laser-driven quasimonoenergetic proton beamline

Human cancer cells are irradiated by laser-driven quasimonoenergetic protons. Laser pulse intensities at the 5×1019 W/cm2 level provide the source and acceleration field for protons that are subsequently transported by four energy-selective dipole magnets. The transport line delivers 2.25 MeV protons with an energy spread of 0.66 MeV and a bunch duration of 20 ns. The survival fraction of in vitro cells from a human salivary gland tumor is measured with a colony formation assay following proton irradiation at dose levels of up to 8 Gy, for which the single bunch dose rate is 1×107 Gy/s and the effective dose rate is 0.2 Gy/s for 1 Hz repetition of irradiation. Relative biological effectiveness at the 10% survival fraction is measured to be 1.20±0.11 using protons with a linear energy transfer of 17.1 keV/μm.

High-spatiotemporal-quality petawatt-class laser system

We have developed a femtosecond high-intensity laser system that combines both Ti:sapphire chirped-pulse amplification (CPA) and optical parametric CPA (OPCPA) techniques and produces more than 30 J broadband output energy, indicating the potential for achieving peak powers in excess of 500 TW. With a cleaned high-energy seeded OPCPA preamplifier as a front end in the system, for the compressed pulse without pumping the final amplifier, we found that the temporal contrast in this system exceeds 10(10) on the subnanosecond time scales, and is near 10(12) on the nanosecond time scale prior to the peak of the main femtosecond pulse. Using diffractive optical elements for beam homogenization of a 100 J level high-energy Nd:glass green pump laser in a Ti:sapphire final amplifier, we have successfully generated broadband high-energy output with a near-perfect top-hat-like intensity distribution.

The progress in the laser-driven proton acceleration experiment JAEA with table-tip Ti:Sappire laser system

This paper presents the experimental investigation of laser-driven proton acceleration using a table top Ti:Sapphire laser system interacting with the thin-foil targets during the course of medical application of the laser-driven proton beam. The proton beam with maximum energy of upto 14~MeV is generated in 60 TW mode. The number of protons at ~10 MeV is estimated to be over 105 proton/sr/MeV/shot with beam having half divergence angle of 5~degree. If 10 Hz operation is assumed 2 Gy dose is possible to irradiate during 10 min onto a ~1 mm tumor just under the skin. In contrast to the previous condition of our apparatus with which we demonstrated the DNA double-strand breaking by irradiating the laser-driven proton beam onto the human cancer cells in-vitro test, the result reported here has significant meaning in the sense that pre-clinical in-vivo test can be started by irradiating the laser-driven proton beam onto the skin of the mouse, which is unavoidable step before the real radiation therapy.

Toward laser driven proton medical accelerator

Towards our final goal, such as to establish the laser-driven proton accelerator for the medical application, one of the most important things to establish is to develop the proton transport system. In this continuous work, we demonstrate the focusing system of the laser-driven proton beam with permanent magnet qadrupoles (PMQs), with which a 2.4 MeV laser-driven proton beam, having a divergence angle of ~10 degrees at birth, is focused to a spot whose size is 3×8mm2 at 640mm downstream from the target.

Hundred mJ level, high contrast OPCPA/Yb:YAG hybrid laser system

Yb:YAG CPA have a potential to develop a compact, high peak power at high repetition rates. For high energy pulses of short duration Yb:YAG regenerative amplifiers have mainly been studied for which significant prepulse and amplified spontaneous emission (ASE). In laser proton acceleration studies it is very important to suppress the prepulse and ASE levels, because a preplasma is generated before the peak of the laser pulse, therefore the maximum proton energy is limited. To overcome this problem, the OPCPA can efficiently provide high gain for the main pulse while suppressing prepulse amplification. Here we have first demonstrated a hundred mJ level, femtosecond of an OPCPA/Yb:YAG hybrid laser system with a contrast level of 10−9 at −150 ps.

Radiobiology with laser-accelerated quasi-monoenergetic proton beams

Human cancer cells are irradiated by laser-driven quasi-monoenergetic protons. Laser pulse intensities at the 5×1019-W/cm2 level provide the source and acceleration field for protons that are subsequently transported by four energy-selective dipole magnets. The transport line delivers 2.25 MeV protons with an energy spread of 0.66 MeV and a bunch duration of 20 ns. The survival fraction of in-vitro cells from a human salivary gland tumor is measured with a colony formation assay following proton irradiation at dose levels up to 8 Gy, for which the single bunch does rate is 1 × 107 Gy/s and the effective dose rate is 0.2 Gy/s for 1-Hz repetition of irradiation. Relative biological effectiveness at the 10% survival fraction is measured to be 1.20 ± 0.11 using protons with a linear energy transfer of 17.1 ± 2.8 keV/μm.

Ion Acceleration in Subcritical Density Plasma via Interaction of Intense Laser Pulse with Cluster-Gas Target

We present substantial enhancement of the accelerated ion energies up to 10–20 MeV per nucleon by utilizing the unique properties of the cluster-gas target irradiated with 40-fs laser pulses of only 150 mJ energy, corresponding to approximately tenfold increase in the ion energies compared to previous experiments using thin foil targets. A particle-in-cell simulation infers that the high energy ions are generated at the rear side of the target due to the formation of a strong dipole vortex structure in subcritical density plasmas. The demonstrated method can be important in the development of efficient laser ion accelerators for hadron therapy and other applications.

High-energy, high-efficiency second-harmonic generation from a Nd-doped laser with high-quality CsB 3 O 5 crystal

Frequency doubling of high-energy Nd-doped laser emission yields harmonically converted laser energy (532-nm) of 1.2-J with 60 % conversion efficiency using a high optical quality top-seeded solution growth CsB3O5crystal.

Demonstration of high peak power, high contrast OPCPA/Ti:sapphire hybrid laser system

We have demonstrated over 30 J broadband output energy based on optical parametric chirped-pulse amplification (OPCPA) and Ti:sapphire chirped-pulse amplification (CPA), indicating potential for peak power of 500 TW with extremely high temporal contrast.