1. N. Yugami, Utsunomiya University, Japan Generation of Short Electromagnetic Wave via Laser Plasma Interaction Experiments US-Japan Workshop on Heavy Ion Fusion and High Energy Density Physics Sep. 28-30,2005 Department of Energy and Environmental Science, Graduate School of Engineering, Utsunomiya University 7-1-2 Yoto, Utsunomiya, Tochigi 321-8585, JAPAN, TEL: +81-28-689-6083, FAX: +81-28-689-7030

2. Outline A proof-of-principle experiment demonstrates the generation of the radiation from the Cerenkov wake excited by a ultra short and ultra high power pulse laser in a perpendicularly magnetized plasma. The frequency of the radiation is in the millimeter range(up to 200 GHz). The intensity of the radiation is proportional to the magnetic field intensity as the theory expected. Polarization of the emitted radiation is also detected. The difference in the frequency of the emitted radiation between the experiments and previous theory can be explained by the electrons' oscillation in the electric field of a narrow column of ions in the focal region.

3. Oscillating Current in Plasma Wave Electron Current Frequency ;    p (plasma freq.) n=1.0x10 16 cm -3 f=0.9 THz Skin depth ;   c/  p n 0 = 10 16 cm  3 p = 300  m   50  m [1] J. Yoshii et al., Phys. Rev. Lett. 79, 4194 (1997).

4. Experimental Setup for Radiation

5. Typical Example of Emitted Radiation Expected Pulse Width Laser Power: 0.5 TW B 0 : 8.5 kG, He 375 mTorr Experimental condition

6. Radiation intensity was proportional to the strength of B field Laser Power ; 0.5 TW N 2 750 mTorr

7. Plasma cavity for radiation plasma boundary Plasma column works as “cavity” for radiation boundary Wavelength of the radiation is satisfied the matching condtion, Strong radiation is expected to observe. The data suggests the wavelength(frequency) depends on the strength of B field.

8. Damping at the plasma-vacuum surface boundary Ratio

9. Typical Waveform of Radiation --- 2 peaks were observed --- Cut-off freq. of waveguide f c = 31.4 GHz Pulse width 200-250 ps

10. Each peak of radiation has different polarization

11. Two kinds of radiation in GHz region

12. Freq. Spectrum measured by TOF method --- Each peak has different freq. --- Flight length L = 1.2 m 1st peak~74 GHz 2nd peak~40 GHz

13. Freq. of 1st peak does NOT depend on B field. Freq. of 2nd peak depends on B field.

14. 1st peak of Radiation Freq. : 74 GHz ． Polarization of radiation // B field Frequency of radiation dose not depend on the strength of B field Electrons' oscillation in the electric field of a narrow column of ions in the focal region. ion column + + + + + + + + + + + + + + + + + E B Electron w z x

15. 2nd peak pulse Bernstein mode 1 2 4 3 12340 Freq. : ~40 GHz ． Polarization of radiation B field Frequency of radiation depends on the strength of B field

16. Conclusion The radiation from the interaction between laser and magnetized plasma was observed. Higher freq. and lower freq. components were observed. Higher Freq. Component Freq : 74 GHz Polarization …. Parallel to B field Frequency does not depend on the strength of B field. Due to the electron motion parallel to the B field. Lower Freq. Component Polarization …. Perpendicular to B field Frequency does depends on the strength of B field. Bernstein mode?