Abstract
When a laser is focused by a lens or mirror array the field acquires a longitudinal component. Under certain conditions this longitudinal laser field could be used to accelerate an injected particle to high energies.
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References
J. Blewett: In Linear Accelerators, ed. by P. Lapostolle, A. Septier (North-Holland, Amsterdam 1970)
C. Pellegrini, P. Sprangle, W. Zacowicz: In Proc. XII Conf. Part. Accel. Fermilab. ed. by F. Cole, R. Donaldson (1983) 473
R. Palmer: Part. Accel. 11, 81 (1980);
N. Kroll: In Proc. 1985 Laser Accel. Conf., ed. by C. Joshi, T. Katsouleas, AIP Conf. Proc. 130
G. Fontana, R. Pantell: J. Appl. Phys. 54, 4285 (1983)
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J. Lawson: Rutherford Lab. Report RL 83-057 (1983)
M. Feldman, R. Chacio: Phys. Rev. A 4, 352 (1971), see also R. Rossmannith, in Proc. 1985 Laser Accel. Conf., ed. by C. Joshi, T. Katsouleas, AIP Conf. Proc. 130. Consider the possibility of accelerating particles transvers to the laser propagation direction within a single half cycle
The fact that a focused light beam has a longitudinal component was shown for example by W. Carter: J. Opt. Soc. Am. 62, 1195 (1972); Expression (1) was derived by Louisell using a perturbation analysis in Phys. of Quant. Elec. Vol. III, ed. by S. Jacobs, M. Scully, M. Sargent, C. Cantrell, p. 378. See also M. Lax, W. Louisell, W. McKnight: Phys. Rev. A 41, 3727 (1975). In their paper they concentrated on the importance of the longitudinal components of a laser beam interacting with a plasma to accelerate electrons. In the present paper we consider the case of fast electrons interacting with a laser pulse. Equation (12b) follows from the works of Carter and of Cicchitelli et al. by using the asymptotic expression for Bessel functions in the limit kz ≫ 1, which is the case in our problem
See for example M. Sargent, M. Scully, W. Lamb: Laser Physics. The phase velocity associated with (2) is very slightly greater than c (by an amount cλ/R). This will cause no serious problem and can be compensated for by, for example, the phase shifters of Fig.4
S. Humphries: Principles of Charged Particle Acceleration (Wiley, New York 1986)
See Eqs.(23) and (48) of H. Kogelnik, R. Li: Appl. Opt. 5, 1550 (1966)
J. Slater: Rev. Mod. Phys. 20, 473 (1948)
For a good discussion of this point see R. Helm, R. Miller: In Linear Accelerators, ed. by P. Lapostolle, A. Septier (North-Holland, Amsterdam 1970)
Transverse instabilities are not a problem in RF linacs due to the extreme relativistic nature of the particle. The same would tend to be true in the present problem. But the transverse variation in the laser could lead to new beam instabilities, and this point will be discussed elsewhere. We note, however, that there are many well-known ways to compensate for transverse perturbation, e.g. the application of a longitudinal magnetic field
The field strength at a lens would be much smaller (where the beam is spread over a large area) than at the focus. Nevertheless it may prove advantagous to use mirrors instead of lenses