Laser-induced amplification and visualization of β-ray ionized tracks in dense gases

We describe some experiments on Bremsstrahlung energy transfer from an intense laser light towards electrons sorrounded by a dense gas. The electrons gain eventually enough energy to radiate light and to excite and ionize the surrounding atoms. We have measured the spectra of the light emitted in these conditions and the electron number multiplication factor resulting from successive ionization. In krypton we observe that a static field enhances significantly the rate of energy transfer from light to electrons. At the pressure of 200 bar we obtained controllable electron multiplication factors up to 10 ⁶. At this level of amplification the ionized track of a ⁹⁰Yβ-ray becomes visible. This latent electronic image development takes place in 10 ^-8s.