Method for separating FEL output beams from long wavelength radiation

Patent metadata

Field	Value
Publication number	US-9325145-B2
Application number	US-201514708551-A
Country	US
Kind code	B2
Filing date	May 11, 2015
Priority date	May 12, 2014
Publication date	Apr 26, 2016
Grant date	Apr 26, 2016

Abstract

A method for improving the output beam quality of a free electron laser (FEL) by reducing the amount of emission at wavelengths longer than the electron pulse length and reducing the amount of edge radiation. A mirror constructed of thermally conductive material and having an aperture therein is placed at an oblique angle with respect to the beam downstream of the bending magnet but before any sensitive use of the FEL beam. The aperture in the mirror is sized to deflect emission longer than the wavelength of the FEL output while having a minor impact on the FEL output beam. A properly sized aperture will enable the FEL radiation, which is coherent and generally at a much shorter wavelength than the bending radiations, to pass through the aperture mirror. The much higher divergence bending radiations will subsequently strike the aperture mirror and be reflected safely out of the way.

First claim

What is claimed is:

1. A method for improving the quality of the output of a free electron laser (FEL) having an optical wavelength and a bending magnet deflecting electrons from the output laser beam, comprising:
a. providing a mirror with an aperture therein;
b. sizing the aperture to deflect emission longer than the wavelength of the FEL output;
c. inserting the mirror at an oblique angle downstream of the bending magnet but before any sensitive use of the FEL beam;
d. determining the output wavelength of the FEL radiation by solving the equation

λ
s

=

λ
w

2
⁢

⁢

γ
2

⁢

(

1
+

K
2

)

where:
λ s is the output wavelength;
λ w is the wiggler wavelength;
γ is the relativistic parameter of the electrons=1+E/0.511 where E is the electrons' kinetic energy in units of mega-electron volts;
K is the wiggler strength parameter,

K
=

e
⁢

⁢
B

k
0

⁢

⁢
m
⁢

⁢

c
2

where e is the electron charge, B is the magnetic field strength of the wiggler, k 0 =2π/λ w , m is the electron rest mass and c is the speed of light;
e. determining the radius of the optical mode of the FEL beam by solving the equation

ω
=

ω
0

⁢

1
+

(

z
⁢

⁢

λ
s

π
⁢

⁢

ω
0
2

)

2

where:
ω 0 is the radius of the FEL optical mode in the wiggler; and
z is the distance from the wiggler where the radius is to be determined; and
f. setting the radius of the aperture to greater than 3 times the FEL optical mode at the insertion point of the mirror.

2. The method of claim 1 , wherein the aperture is substantially circular or elliptical and includes a radius.

3. The method of claim 2 , wherein the radius of the aperture as projected on the FEL optical mode is larger than the radius of the FEL optical mode at the insertion point of the mirror.

4. The method of claim 1 , further comprising constructing the mirror of thermally conductive material.

5. The method of claim 1 , further comprising constructing the mirror of thermally conductive metal.

6. The method of claim 1 , further comprising selecting the material of construction of the mirror from the group including molybdenum and copper.

7. The method of claim 1 , further comprising constructing the mirror of copper.

8. The method of claim 1 , further comprising
providing an upstream surface on the mirror; and
polishing the upstream surface to form a mirror finish.

9. The method of claim 1 , further comprising
providing an upstream surface on the mirror;
polishing the upstream surface to form a mirror finish; and
coating the mirror surface to enhance the mirror reflectivity at wavelengths longer than the primary FEL lasing wavelength.

10. The method of claim 9 , further comprising selecting the material of construction of the mirror coating from the group including gold and silver.

Assignees

• Jefferson Science Ass Llc

Inventors

• Neil George
• Shinn Michelle D
• Gubeli Joseph

Classifications

• H01S3/0805

  by apertures, e.g. pin-holes or knife-edges · CPC title

• H01S3/08068

  Holes; Stepped surface; Special cross-section · CPC title

• H01S3/0903 Primary

  Free-electron laser · CPC title

• H01S5/18375

  based on metal reflectors · CPC title

• H01S5/0286

  Coatings with a reflectivity that is not constant over the facets, e.g. apertures · CPC title