Abstract

Due to its low gain, the Orsay storage ring free-electron laser necessitates the use of high reflectivity mirrors. Three techniques for measuring the mirror losses are presented, based on cavity decay time measurements using either an external laser, the synchrotron radiation stored in the cavity, or the free-electron laser itself. The high signal-to-noise ratio allowed the detection of loss variations as low as 10−7/sec1/2. From these diagnostics three distinct processes of UV-induced degradation of TiO2/SiO2 dielectric mirrors were identified. One was a surface absorption of the upper SiO2–air interface; it was not affected by annealing. The other two corresponded to a volume absorption of the layers which completely recovered after annealing.

© 1985 Optical Society of America

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References

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  1. M. Billardon et al., “First Operation of a Storage Ring Free-Electron Laser,” Phys. Rev. Lett. 51, 1652 (1983).
    [CrossRef]
  2. P. Elleaume, D. A. G. Deacon, M. Billardon, J. M. Ortega, “UV and VUV Degradation of Very High Reflectivity Mirrors for Use in a Storage-Ring Free-Electron Laser,” in Technical Digest, Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 1983), paper THJ3.
  3. M. Billardon et al., “Recent Results of the ACO Storage Ring FEL Experiment,” J. Phys. Paris Colloq. 44, Cl-73 (1983).
  4. J. M. Herbelin et al., “Sensitive Measurement of Photon Lifetime and True Reflectances in an Optical Cavity by a Phase-Shift Method,” Appl. Opt. 19, 144 (1980).
    [CrossRef] [PubMed]
  5. N. A. Vinokurov, U. N. Litvinenko, “Method for Measuring Reflection Coefficients Near Unity,” Preprint INP 79–24 (Institute of Nuclear Physics, 630090 Novosibirsk, U.S.S.R.).
  6. W. G. Driscoll, W. Vaughan, Eds. Handbook of Optics, (McGraw-Hill, New York, 1978), gives values for the absorption and scattering losses in air. At 6328 Å at sea level, aerosol scattering dominates all other loss mechanisms. The propagation distance to be expected in the laboratory depends on the concentration of dust, forepump vapor, and other aerosols in the air but should clearly lie between the values quoted for clear air (37.6 km) and hazy air (1.2 km).
  7. A. Yariv, Quantum Electronics (Wiley, New York, 1975), Chap. 7.
  8. Ojai Research, 11554 Ventura Ave., Ojai, Calif. 93023.
  9. W. B. Colson, P. Elleaume, “Transverse Mode Dynamics in a Free-Electron Laser,” Appl. Phys. B 29, 101 (1982).
    [CrossRef]

1983 (2)

M. Billardon et al., “First Operation of a Storage Ring Free-Electron Laser,” Phys. Rev. Lett. 51, 1652 (1983).
[CrossRef]

M. Billardon et al., “Recent Results of the ACO Storage Ring FEL Experiment,” J. Phys. Paris Colloq. 44, Cl-73 (1983).

1982 (1)

W. B. Colson, P. Elleaume, “Transverse Mode Dynamics in a Free-Electron Laser,” Appl. Phys. B 29, 101 (1982).
[CrossRef]

1980 (1)

Billardon, M.

M. Billardon et al., “First Operation of a Storage Ring Free-Electron Laser,” Phys. Rev. Lett. 51, 1652 (1983).
[CrossRef]

M. Billardon et al., “Recent Results of the ACO Storage Ring FEL Experiment,” J. Phys. Paris Colloq. 44, Cl-73 (1983).

P. Elleaume, D. A. G. Deacon, M. Billardon, J. M. Ortega, “UV and VUV Degradation of Very High Reflectivity Mirrors for Use in a Storage-Ring Free-Electron Laser,” in Technical Digest, Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 1983), paper THJ3.

Colson, W. B.

W. B. Colson, P. Elleaume, “Transverse Mode Dynamics in a Free-Electron Laser,” Appl. Phys. B 29, 101 (1982).
[CrossRef]

Deacon, D. A. G.

P. Elleaume, D. A. G. Deacon, M. Billardon, J. M. Ortega, “UV and VUV Degradation of Very High Reflectivity Mirrors for Use in a Storage-Ring Free-Electron Laser,” in Technical Digest, Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 1983), paper THJ3.

Elleaume, P.

W. B. Colson, P. Elleaume, “Transverse Mode Dynamics in a Free-Electron Laser,” Appl. Phys. B 29, 101 (1982).
[CrossRef]

P. Elleaume, D. A. G. Deacon, M. Billardon, J. M. Ortega, “UV and VUV Degradation of Very High Reflectivity Mirrors for Use in a Storage-Ring Free-Electron Laser,” in Technical Digest, Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 1983), paper THJ3.

Herbelin, J. M.

Litvinenko, U. N.

N. A. Vinokurov, U. N. Litvinenko, “Method for Measuring Reflection Coefficients Near Unity,” Preprint INP 79–24 (Institute of Nuclear Physics, 630090 Novosibirsk, U.S.S.R.).

Ortega, J. M.

P. Elleaume, D. A. G. Deacon, M. Billardon, J. M. Ortega, “UV and VUV Degradation of Very High Reflectivity Mirrors for Use in a Storage-Ring Free-Electron Laser,” in Technical Digest, Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 1983), paper THJ3.

Vinokurov, N. A.

N. A. Vinokurov, U. N. Litvinenko, “Method for Measuring Reflection Coefficients Near Unity,” Preprint INP 79–24 (Institute of Nuclear Physics, 630090 Novosibirsk, U.S.S.R.).

Yariv, A.

A. Yariv, Quantum Electronics (Wiley, New York, 1975), Chap. 7.

Appl. Opt. (1)

Appl. Phys. B (1)

W. B. Colson, P. Elleaume, “Transverse Mode Dynamics in a Free-Electron Laser,” Appl. Phys. B 29, 101 (1982).
[CrossRef]

J. Phys. Paris Colloq. (1)

M. Billardon et al., “Recent Results of the ACO Storage Ring FEL Experiment,” J. Phys. Paris Colloq. 44, Cl-73 (1983).

Phys. Rev. Lett. (1)

M. Billardon et al., “First Operation of a Storage Ring Free-Electron Laser,” Phys. Rev. Lett. 51, 1652 (1983).
[CrossRef]

Other (5)

P. Elleaume, D. A. G. Deacon, M. Billardon, J. M. Ortega, “UV and VUV Degradation of Very High Reflectivity Mirrors for Use in a Storage-Ring Free-Electron Laser,” in Technical Digest, Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 1983), paper THJ3.

N. A. Vinokurov, U. N. Litvinenko, “Method for Measuring Reflection Coefficients Near Unity,” Preprint INP 79–24 (Institute of Nuclear Physics, 630090 Novosibirsk, U.S.S.R.).

W. G. Driscoll, W. Vaughan, Eds. Handbook of Optics, (McGraw-Hill, New York, 1978), gives values for the absorption and scattering losses in air. At 6328 Å at sea level, aerosol scattering dominates all other loss mechanisms. The propagation distance to be expected in the laboratory depends on the concentration of dust, forepump vapor, and other aerosols in the air but should clearly lie between the values quoted for clear air (37.6 km) and hazy air (1.2 km).

A. Yariv, Quantum Electronics (Wiley, New York, 1975), Chap. 7.

Ojai Research, 11554 Ventura Ave., Ojai, Calif. 93023.

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Figures (11)

Fig. 1
Fig. 1

Schematic experimental setup of the measurement of 1 − R using an external laser.

Fig. 2
Fig. 2

Inverse cavity decay time is plotted against the inverse mirror separation during one of the measurements in air of mirror set 3 prior to UV exposure. The curve should be linear with the slope related to the mirror losses and the intercept given by the losses in air.

Fig. 3
Fig. 3

Schematic experimental setup of the measurement of 1 − R using synchrotron radiation.

Fig. 4
Fig. 4

Optical pulses transmitted through a mirror of the FEL cavity: (a) a tuned cavity (b) and (c) a detuned cavity with δ = −3 and +3 mm, respectively.

Fig. 5
Fig. 5

Vertical magnetic field of the optical klystron calculated for a magnetic gap = 33.00 mm and the corresponding calculated trajectory for an energy of 240 MeV.

Fig. 6
Fig. 6

Calculated values of the intensities of the odd harmonics of an ideal undulator are plotted for several values of the magnetic field parameter K. The electron energy is adjusted as shown so that the wavelength of the emitted radiation is constant. In these conditions, the undulator emitted 6328-Å or 1.9-eV photons in the fundamental.

Fig. 7
Fig. 7

Mirror degradation after exposure to UV synchrotron radiation. T is the transmission. Points (a) and (a′) correspond to a measurement of 1 − R with the helium–neon laser before and after insertion into the vacuum. Curve (b) corresponds to an exposure several minutes at 150 MeV and curve (c) to 1000-mA hours at 166 MeV.

Fig. 8
Fig. 8

Penetration of the light intensity |E|2 inside a multilayer dielectric mirror at three wavelengths λ1 < λ2 < λ3. The intensity |E2)|2 at the mirror central wavelength λ2 presents a node at interfaces 1, 2, 4, 6,….

Fig. 9
Fig. 9

Auger electron spectrum of a forward mirror before and after exposure to UV synchrotron radiation. Before exposure, one clearly sees the silicion and oxygen peaks constituting the upper SiO2 layer. After exposure the oxygen peak has disappeared and a strong carbon peak is present.

Fig. 10
Fig. 10

Average mirror degradation after exposure to 200-mA hours at 540 MeV of electron energy [curve (d)] compared with the initial state [curve (c)].

Fig. 11
Fig. 11

Losses per reflection of the forward mirror as a function of position on the surface after exposure of 200-mA hours at 540 MeV of electron energy. One clearly sees a narrow horizontal bump which completely disappeared after annealing in air at 250° C for 12 h.

Tables (2)

Tables Icon

Table I Characteristics of the Different Dielectric Mirrors Used in the Experiments

Tables Icon

Table II Characteristics of the Three Processes of Degradation Observed on TiO2/SiO2 Dielectric Mirrors

Equations (27)

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d c τ = P 2 1 R .
R = R 1 + R 2 2 .
tan δ ϕ = 2 π ν τ .
1 τ = 1 τ a + c d ( 1 R ) .
w 0 = λ d π [ ( 2 d R c ) d R c ] 1 / 4 .
R ¯ = 1 2 [ T 1 ( x ) R 1 ( x ) d x I 1 ( x ) d x + I 2 ( x ) R 2 ( x ) d x I 2 ( x ) d x ] ,
S ( t ) = p = 0 f ( t + 2 p δ ) R p ,
1 R = δ c τ .
tan [ ϕ ( δ ) ϕ ( 0 ) ] = 2 π m ν 0 δ c ( 1 R ) ,
A = A ( δ = 0 ) | cos [ ϕ ( δ ) ϕ ( 0 ) ] | .
d δ , ν m ν
ϕ ( δ 1 ) ϕ ( δ 2 ) = 2 π m ν 0 c ( 1 R ) ( δ 1 δ 2 ) .
λ n = λ 0 2 n γ 2 ( 1 + K 2 2 ) ,
Δ ( λ n ) λ n ( 1 n N ) 2 + Δ i 2 ,
I ( photons / sec / cm 2 / mA ) = F ( γ ) G ( K , n ) ,
F ( λ ) = N e , ( d 2 ) 2 h c I ¯ γ 2 = 1 . 02 × 10 10 γ 2 photons / sec / cm 2 / mA ,
G ( K , n ) = n K 2 ( 1 + K 2 2 ) 2 [ J n 1 / 2 ( n K 2 4 + 2 K 2 ) J n + 1 / 2 ( n K 2 4 + 2 K 2 ) ] 2 ,
θ x H 2 2 + K 2 2 γ 2 + σ x 2 ,
θ z H 2 2 + σ z 2 ,
H = 0 . 58 λ / λ c ,
λ c ( Å ) = 7 . 15 × 10 7 B [ T ] γ 2 .
θ x 1 2 K γ ,
θ z H 2 θ x .
1 = R + T + A + D ,
1 R A .
Δ x 2 θ x d 2 = d K 2 γ = 8 . 6 mm .
λ ( Å ) = 2 . 13 × 10 8 B ( T ) ( Δ z 2 w 0 2 d 2 σ z 2 ) ,

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