US 4,740,973 A · Free electron laser

Abstract

The invention envisages control devices acting on the laser to vary in time the electron/photon interaction, means proceeding to a State I in which they alter the optimal conditions for laser amplification; and a State II in which that reestablish said optimal conditions, which control devices permit the improvement of the peak amplitude and stability of the laser pulses and the rate and stability of the pulse period. According to another aspect of this invention, the two states are alternated, preferably periodically or almost periodically. The duration of State I should be selected by comparison with the characteristics of the electron packet and, in particular of the relaxation time observed for said packet. If the duration of State II is set to a value to be comparable to or longer than the electron relaxation time, the peak amplitude of the laser pulses is increased. The duration of State II should be selected by comparison with the natural macropulse width. If the duration of the State II is set to a value shorter than the natural duration of the laser macropulses, the repetition rate of the laser pulses can be increased.

Claims46

Dependent claims

A method of stabilizing the operation of a free electron laser in which a relativistic electron beam exchanges energy with a photon beam comprising the steps of:

establishing laser operation, the laser operation being inherently characterized by a gain which decays as the laser amplitude grows, thereby causing the optical field first to grow to a maximum and then to decay;
and
reducing the net gain, that is the value of gain minus the value of loss, prior to the time that the optical field reaches its minimum value following its initial growth.

A storage ring free electron laser comprising:

undulator means defining a laser section in which a relativistic electron beam consisting of a number of one or more electron packets is caused to undergo periodic transverse deflections, said electron beam being characerized by an electron energy distribution and an electron spatial distribution;
optical cavity means for propagating an electromagnetic wave consisting of a number of one or more photon pulses in the vicinity of said laser section, said optical cavity means being characterized by an optical axis and a round-trip time, said electromagnetic wave being characerized by an optical amplitude, a photon spectral width, a photon temporal width, and a photon spatial distribution;
storage ring means for extracting said electron beam from said laser section and reinjecting said electron beam into said laser section to cause a succession of electron packet passes through said laser section;
the intervals between successive electron packet passes through said laser section being synchronized with said round-trip time so that at least a portion of said electron beam periodically overlaps with at least a portion of said electromagnetic wave on passage through said laser section, the result of which is an interaction in which a portion of the energy of said electron beam is converted to light with an optical gain G;
said gain being a function of the periodic overlap, said optical amplitude, and a set of parameters including said electron energy distribution, said electron spatial distribution, and said photon temporal and spectral widths, said gain having a maximum value during operation;
said interaction altering at least one of said set of parameters so as to cause said gain to decrease on successive electron packet passes from said maximum value, said interaction resulting in the formation of a train of optical pulses;
and
control means for alternately varying said gain between first and second states of respectively lower and higher gain so as to permit control over the temporal profile and peak power of said train of optical pulses.

5 more elements

A storage ring free electron laser comprising:

undulator means defining a laser section in which a relativistic electron beam consisting of a number of one or more electron packets is caused to undergo periodic transverse deflections, said electron beam being characterized by an electron energy distribution and an electron spatial distribution;
optical cavity means for propating an electromagnetic wave consisting of a number of one or more photon pulses in the vicinity of said laser section, said optical cavity means being characterized by an optical axis, round-trip time, and a loss coefficient p, said electromagnetic wave being characterized by an optical amplitude, a photon spectral width, a photon temporal width, and a photon spatial distribution;
storage ring means for extracting said electron beam from said laser section and reinjecting said electron beam into said laser section to cause a succession of electron packet passes through said storage ring means;
the intervals between successive electron packet passes of said electron beam through said laser section being synchronized with said round-trip time so that at least a portion of said electron beam periodically overlaps with at least a portion of said electromagnetic wave on passage through said laser section, the result of which is an interaction in which a portion of the energy of said electron beam is converted to light with an optical gain G;
said gain being a function of the periodic overlap, said optical amplitude, and a set of parameters including said electron energy distribution, said electron spatial distribution, and said photon temporal and spectral widths, said gain having a maximum value during operation;
said interaction altering at least one of said set of parameters so as to cause said gain to decrease on successive electron packet passes from said maximum value, said interaction resulting in the formation of a train of optical pulses;
and
control means for alternately varying said loss coefficient between first and second states or respectively higher and lower loss so as to permit control over the temporal profile and peak power of said train of optical pulses.

5 more elements

A free electron laser comprising:

means for providing a relativistic electron beam consisting of a series of electron packets, said electron packets being characterized by an electron energy distribution and an electron spatial distribution;
undulator means defining a laser section in which said electron packets are caused to undergo periodic transverse deflections;
optical cavity means for propagating an electromagnetic wave consisting of a number of one or more photon pulses in the vicinity of said laser section, said optical cavity means being characterized by an optical axis and a round-trip time, said electromagnetic wave being characterized by an optical amplitude, a photon spectral width, a photon temporal width, and a photon spatial distribution;
the intervals at which said electron packets enter said laser section being synchronized with said round-trip time so that at least one of said number of photon pulses periodically overlaps with the electron packet that has entered said laser section, the result of which is an interaction in which a portion of the energy of said electron beam is converted to light with an optical gain G;
said gain being a function of the periodic overlap;
said optical amplitude, and a set of a parameters including said electron energy distribution, said electron spatial distribution, and said photon temporal and spectral widths, said gain having a maximum value during operation;
said interaction altering at least one of said set of parameters so as to cause said gain to decrease on successive electron passes from said maximum value, said interaction resulting in the formation of a train of optical pulses;
and
control means for alternately varying said gain between first and seocnd states of respectively lower and higher gain so as to permit control over the temporal profile and peak power of said train of optical pulses.

6 more elements

A free electron laser comprising:

means for providing a relativistic electron beam consisting of a series of electron packets, said electron packets being characterized by an electron energy distribution and an electron spatial distribution;
undulator means defining a laser section in which said electron packets are caused to undergo periodic transverse deflections;
optical cavity means for propagating an electromagnetic wave consisting of a number of one or more photon pulses in the vicinity of said laser section, and said optical cavity means being characterized by an optical axis, a round-trip time and a loss coefficient, said electromagnetic wave being characterized by an optical amplitude, a photon spectral width, a photon temporal width, and a photon spatial distribution;
the intervals at which said electron packets enter said laser section being synchronized with said round-trip time so that at least of portion of said photon pulses periodically overlaps with the electron packet that has entered said laser section, the result of which is an interaction in which a portion of the energy of said electron beam is converted to light with an optical gain G;
said gain being a function of the periodic overlap, said optical amplitude, and a set of parameters including said electron energy distribution, said electron spatial distribution, and said photon temporal and spectral widths, said gain having a maximum value during operation;
said interaction altering at least one of said set of parameters so as to cause said gain to decrease on successive elctron packets from said maximum value, said interaction resulting in the formation of a train of optical pulses;
and
control means for alternately varying said loss coefficient between first and second states of respectively higher and lower loss so as to permit control over the temporal profile and peak power of said train of optical pulses.

5 more elements

Dependencies are inferred from the claim text.

Free electron laser

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Free electron laser

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Abstract

Claims46