Abstract

Laser induced damage characteristics have been studied for twelve, multiple-layer dielectric, 95% reflecting mirrors irradiated with single ruby laser pulses of 20-nsec and 20-psec duration and Gaussian beam radii ranging from 0.06 mm to 0.24 mm. During measurements to determine damage threshold the pulse energy, an oscilloscope trace of the pulse, and the beam’s transverse energy density profile at the surface being damaged are recorded for each shot. In a separate set of experiments, the temporal development of coating breakup and plasma formation is investigated. The experimental results are discussed in the context of possible damage mechanisms.

© 1973 Optical Society of America

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References

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  1. E. S. Bliss, D. Milam, AFCRL Report 72-0233 (1972). Available from the Defense Documentation Center, the National Technical Information Center, or the authors.
  2. D. Milam, IEEE J. Quantum Electron. QE-7, 319 (1971).
    [CrossRef]
  3. E. S. Bliss, Proc. 2nd ASTM Symp. Damage in Laser Materials, NBS Spec. Publ. 341, 105 (1970); also Optoelectron. 3, 99 (1971).
  4. E. S. Bliss, D. Milam, R. A. Bradbury, AFCRL Report 72-0423 (1972). Available from the Defense Documentation Center, the National Technical Information Center, or the authors; also 4th ASTM Symp. Damage in Laser Materials, to be published (1972).
  5. D. C. Burnham, Appl. Opt. 9, 1482 (1970).
    [CrossRef] [PubMed]
  6. I. M. Winer, Appl. Opt. 5, 1437 (1966).
    [CrossRef] [PubMed]
  7. B. E. Newman, L. G. DeShazer, 4th ASTM Symp. Damage in Laser Materials, to be published (1972).
  8. C. R. Giuliano, IEEE J. Quantum Electron. QE-8, 749 (1972).
    [CrossRef]
  9. N. L. Boling, Proc. 4th ASTM Symp. Damage in Laser Materials, to be published (1972).
  10. M. Bass, H. H. Barrett, 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

1972 (1)

C. R. Giuliano, IEEE J. Quantum Electron. QE-8, 749 (1972).
[CrossRef]

1971 (1)

D. Milam, IEEE J. Quantum Electron. QE-7, 319 (1971).
[CrossRef]

1970 (2)

E. S. Bliss, Proc. 2nd ASTM Symp. Damage in Laser Materials, NBS Spec. Publ. 341, 105 (1970); also Optoelectron. 3, 99 (1971).

D. C. Burnham, Appl. Opt. 9, 1482 (1970).
[CrossRef] [PubMed]

1966 (1)

Barrett, H. H.

M. Bass, H. H. Barrett, 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

Bass, M.

M. Bass, H. H. Barrett, 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

Bliss, E. S.

E. S. Bliss, Proc. 2nd ASTM Symp. Damage in Laser Materials, NBS Spec. Publ. 341, 105 (1970); also Optoelectron. 3, 99 (1971).

E. S. Bliss, D. Milam, R. A. Bradbury, AFCRL Report 72-0423 (1972). Available from the Defense Documentation Center, the National Technical Information Center, or the authors; also 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

E. S. Bliss, D. Milam, AFCRL Report 72-0233 (1972). Available from the Defense Documentation Center, the National Technical Information Center, or the authors.

Boling, N. L.

N. L. Boling, Proc. 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

Bradbury, R. A.

E. S. Bliss, D. Milam, R. A. Bradbury, AFCRL Report 72-0423 (1972). Available from the Defense Documentation Center, the National Technical Information Center, or the authors; also 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

Burnham, D. C.

DeShazer, L. G.

B. E. Newman, L. G. DeShazer, 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

Giuliano, C. R.

C. R. Giuliano, IEEE J. Quantum Electron. QE-8, 749 (1972).
[CrossRef]

Milam, D.

D. Milam, IEEE J. Quantum Electron. QE-7, 319 (1971).
[CrossRef]

E. S. Bliss, D. Milam, AFCRL Report 72-0233 (1972). Available from the Defense Documentation Center, the National Technical Information Center, or the authors.

E. S. Bliss, D. Milam, R. A. Bradbury, AFCRL Report 72-0423 (1972). Available from the Defense Documentation Center, the National Technical Information Center, or the authors; also 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

Newman, B. E.

B. E. Newman, L. G. DeShazer, 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

Winer, I. M.

Appl. Opt. (2)

IEEE J. Quantum Electron. (2)

D. Milam, IEEE J. Quantum Electron. QE-7, 319 (1971).
[CrossRef]

C. R. Giuliano, IEEE J. Quantum Electron. QE-8, 749 (1972).
[CrossRef]

Proc. 2nd ASTM Symp. Damage in Laser Materials (1)

E. S. Bliss, Proc. 2nd ASTM Symp. Damage in Laser Materials, NBS Spec. Publ. 341, 105 (1970); also Optoelectron. 3, 99 (1971).

Other (5)

E. S. Bliss, D. Milam, R. A. Bradbury, AFCRL Report 72-0423 (1972). Available from the Defense Documentation Center, the National Technical Information Center, or the authors; also 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

B. E. Newman, L. G. DeShazer, 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

N. L. Boling, Proc. 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

M. Bass, H. H. Barrett, 4th ASTM Symp. Damage in Laser Materials, to be published (1972).

E. S. Bliss, D. Milam, AFCRL Report 72-0233 (1972). Available from the Defense Documentation Center, the National Technical Information Center, or the authors.

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Figures (23)

Fig. 1
Fig. 1

Spatially integrated temporal profile of three Q-switched pulses from a series of 220 shots: (○) shot 11, (□) shot 89, (—) shot 217.

Fig. 2
Fig. 2

(a) Multiple exposure-level photograph showing the radial energy distribution in the damage plane for a 20-psec pulse. The dimension of the scale marker is 1 mm. (b) Microdensitometer trace of a multiple exposure-level photograph for a 20-psec pulse. Adjacent exposures differ in energy density by a factor of 1.83.

Fig. 3
Fig. 3

Scanning electron microscope (SEM) photograph of a damage site produced by a Q-switched pulse on mirror A-1. The site dimension is 250μm from left to right.

Fig. 4
Fig. 4

SEM photograph of the edge of a damage site on mirror A-1. The entire photo is 57 μm wide.

Fig. 5
Fig. 5

SEM photograph of the ring structure produced by a Q-switched pulse on mirror C-7. The width of the photo is approximately 100 μm.

Fig. 6
Fig. 6

SEM photograph of the bright spot seen below and to the left of center in Fig. 3. The width of the photo is 11 μm.

Fig. 7
Fig. 7

Crater produced in mirror C-7 by a Q-switched pulse. The width of the photo is approximately 20 μm.

Fig. 8
Fig. 8

SEM photograph of a damage site produced by a 20-psec pulse on mirror A-1. The width of the photo is 436 μm.

Fig. 9
Fig. 9

SEM photograph of a site damaged by a less energetic 20-psec pulse on mirror A-1. An irregular pattern of material removal is evident in the central portion. The width of the photo is 456 μm.

Fig. 10
Fig. 10

SEM photograph of a damage site produced on mirror A-l by a 20-psec pulse having an energy density only slightly above threshold. The width of the photo is 98 μm.

Fig. 11
Fig. 11

Optical microscope photograph of the scattering site type of damage (lower row) caused by 20-psec pulses on mirror E-1. For this mirror Q-switched pulses produced mostly ring type damage (upper row). The spacing between the two sites in the right side of the lower row is 1 mm.

Fig. 12
Fig. 12

Pitting damage caused by 20 psec pulse on mirror C-7. The width of the photo is approximately 50 μm.

Fig. 13
Fig. 13

Optical microscope photographs of (a) a damaged unfogged mirror, (b) the same mirror after fogging with breath, (c) (d) higher magnification view of some sites that were damaged 20 h before the fogged photograph and 1 h before the photograph, respectively.

Fig. 14
Fig. 14

Damage site diameter vs Q-switched pulse energy density on axis for mirror A-4. Shots causing no detectable damage are indicated by (●), those causing only randomly located small scattering centers by (△), and sites with well defined diameters by (○) at finite diameter values. A curve is drawn through the data points to intersect the axis at the practical damage threshold. The second curve gives the damage site diameter predicted on the assumption that any place on the coating will damage when subjected to an energy density of 30 J/cm2.

Fig. 15
Fig. 15

Damage site diameter vs Q-switched pulse energy density on axis for six mirrors.

Fig. 16
Fig. 16

Damage site diameter vs 20-psec pulse energy density on axis for mirrors A-1 and C-7. Shots causing no detectable damage on mirror A-1 are indicated by (X). The error bars shown are typical. Two other curves give the damage site diameter predicted on the assumption that any place on the coating will damage when subjected to energy densities of 1.6 J/cm2 or 2.0 J/cm2. The diameter at which the maximum stress due to thermal expansion is predicted, assuming that the heating is done by excited electrons is also shown.

Fig. 17
Fig. 17

Damage site diameter vs 20-psec pulse energy density on axis for eight mirrors.

Fig. 18
Fig. 18

Q-switched damage threshold vs the beam diameter at half the on-axis energy density for mirror A-6. Shots causing no detectable damage are indicated by (○), those causing only randomly located small scattering centers by (△), and sites with well defined diameters by (●). The solid curve indicates the best estimate for the variation of the perfect coating threshold and the dashed curve the best estimate for the variation of the practical threshold.

Fig. 19
Fig. 19

Single pulse damage threshold vs pulse duration for mirrors A-1 and A-4. The curves are drawn to fit the functional form suggested by theoretical considerations discussed in Sec. V.D.

Fig. 20
Fig. 20

Experimental arrangement for studying the properties of high reflectivity mirrors during 20 psec pulse damage.

Fig. 21
Fig. 21

Oscilloscope trace showing the low level train before and after the damaging pulse. The single pulse at the far left is the trigger pulse.

Fig. 22
Fig. 22

Oscilloscope trace of the damaging pulse showing that after passing through the apparatus of Fig. 20, the damaging pulse is indistinguishable from the predamage pulse shown in Fig. 21.

Fig. 23
Fig. 23

Oscilloscope traces showing the growth and decay of the plasma produced by 20-psec pulses on a 95% TiO2/SiO2 mirror.

Tables (3)

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Table I Characteristics of Laser Sources Used in Damage Experiments

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Table II Mirrors Used for Damage Tests

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Table III Measured Threshold Values

Equations (2)

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N = N 0 2 t / t α exp ( d / K ) ,
1 + p R 2 + p 2 R 4 = exp ( p R 2 )

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