Abstract

Spatial filters are essential components for maintaining high beam quality in high-energy pulsed laser systems. The long-duration (21 ns) high-energy pulses envisioned for future inertial-confinement fusion drive systems, such as the U.S. National Ignition Facility (NIF), are likely to lead to increased plasma generation and closure effects within the pinholes in the spatial filters. The design goal for the pinhole spatial filter for the NIF design is to remove small-angle scatter in the beam to as little as a ±100-μrad divergence. It is uncertain whether this design requirement can be met with a conventional pinhole design. We propose a new pinhole architecture that addresses these issues by incorporating features intended to reduce the rate of plasma generation. Initial experiments with this design have verified its performance improvement relative to a conventional pinhole design.

© 1998 Optical Society of America

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References

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  1. W. W. Simmons, J. S. Guch, F. Rainer, J. E. Murray, “A high energy spatial filter for removal of small scale beam instabilities in high power solid state lasers,” Internal Rep. No. UCRL-76873 (University of California, Lawrence Livermore Laboratory, Berkeley, Calif., 1975).
  2. J. S. Pearlman, J. P. Anthes, “Closure of pinholes under intense laser radiation,” Appl. Opt. 16, 2328–2331 (1977).
    [CrossRef] [PubMed]
  3. S. A. Dimakov, S. I. Zavgorodneva, L. V. Koval’chuk, A. Y. Rodionov, V. P. Yashukov, “Investigation of the threshold of formation of a plasma screening radiation in a plasma spatial filter,” Sov. J. Quantum Electron. 19, 803–805 (1989).
    [CrossRef]
  4. J. M. Auerbach, N. C. Holmes, J. T. Hunt, G. J. Linford, “Closure phenomena in pinholes irradiated by Nd laser pulses,” Appl. Opt. 18, 2495–2499 (1979).
    [CrossRef] [PubMed]
  5. C. L. M. Ireland, “A pinhole plasma shutter for optical isolation in high power glass lasers,” J. Phys. D 13, 9–16 (1980).
    [CrossRef]
  6. V. L. Ginzburg, The Propagation of Electromagnetic Waves in Plasmas (Pergamon, Oxford, 1964).
  7. T. W. Johnston, J. M. Dawson, “Correct values for high-frequency power absorption by inverse bremsstrahlung in plasmas,” Phys. Fluids 16, 722 (1973).
    [CrossRef]
  8. G. B. Zimmerman, W. L. Kruer, “Numerical simulation of laser-initiated fusion,” Comments Plasma Phys. Controlled Fusion 2, 51–61 (1975).
  9. A. E. Siegman, “New developments in laser resonators,” in Laser Resonators, D. A. Holmes, ed., Proc. SPIE1224, 2–14 (1990).
  10. A. E. Siegman, “Defining the effective radius of curvature for a nonideal optical beam,” IEEE J. Quantum Electron. 27, 1146–1148 (1991).
    [CrossRef]

1991

A. E. Siegman, “Defining the effective radius of curvature for a nonideal optical beam,” IEEE J. Quantum Electron. 27, 1146–1148 (1991).
[CrossRef]

1989

S. A. Dimakov, S. I. Zavgorodneva, L. V. Koval’chuk, A. Y. Rodionov, V. P. Yashukov, “Investigation of the threshold of formation of a plasma screening radiation in a plasma spatial filter,” Sov. J. Quantum Electron. 19, 803–805 (1989).
[CrossRef]

1980

C. L. M. Ireland, “A pinhole plasma shutter for optical isolation in high power glass lasers,” J. Phys. D 13, 9–16 (1980).
[CrossRef]

1979

1977

1975

G. B. Zimmerman, W. L. Kruer, “Numerical simulation of laser-initiated fusion,” Comments Plasma Phys. Controlled Fusion 2, 51–61 (1975).

1973

T. W. Johnston, J. M. Dawson, “Correct values for high-frequency power absorption by inverse bremsstrahlung in plasmas,” Phys. Fluids 16, 722 (1973).
[CrossRef]

Anthes, J. P.

Auerbach, J. M.

Dawson, J. M.

T. W. Johnston, J. M. Dawson, “Correct values for high-frequency power absorption by inverse bremsstrahlung in plasmas,” Phys. Fluids 16, 722 (1973).
[CrossRef]

Dimakov, S. A.

S. A. Dimakov, S. I. Zavgorodneva, L. V. Koval’chuk, A. Y. Rodionov, V. P. Yashukov, “Investigation of the threshold of formation of a plasma screening radiation in a plasma spatial filter,” Sov. J. Quantum Electron. 19, 803–805 (1989).
[CrossRef]

Ginzburg, V. L.

V. L. Ginzburg, The Propagation of Electromagnetic Waves in Plasmas (Pergamon, Oxford, 1964).

Guch, J. S.

W. W. Simmons, J. S. Guch, F. Rainer, J. E. Murray, “A high energy spatial filter for removal of small scale beam instabilities in high power solid state lasers,” Internal Rep. No. UCRL-76873 (University of California, Lawrence Livermore Laboratory, Berkeley, Calif., 1975).

Holmes, N. C.

Hunt, J. T.

Ireland, C. L. M.

C. L. M. Ireland, “A pinhole plasma shutter for optical isolation in high power glass lasers,” J. Phys. D 13, 9–16 (1980).
[CrossRef]

Johnston, T. W.

T. W. Johnston, J. M. Dawson, “Correct values for high-frequency power absorption by inverse bremsstrahlung in plasmas,” Phys. Fluids 16, 722 (1973).
[CrossRef]

Koval’chuk, L. V.

S. A. Dimakov, S. I. Zavgorodneva, L. V. Koval’chuk, A. Y. Rodionov, V. P. Yashukov, “Investigation of the threshold of formation of a plasma screening radiation in a plasma spatial filter,” Sov. J. Quantum Electron. 19, 803–805 (1989).
[CrossRef]

Kruer, W. L.

G. B. Zimmerman, W. L. Kruer, “Numerical simulation of laser-initiated fusion,” Comments Plasma Phys. Controlled Fusion 2, 51–61 (1975).

Linford, G. J.

Murray, J. E.

W. W. Simmons, J. S. Guch, F. Rainer, J. E. Murray, “A high energy spatial filter for removal of small scale beam instabilities in high power solid state lasers,” Internal Rep. No. UCRL-76873 (University of California, Lawrence Livermore Laboratory, Berkeley, Calif., 1975).

Pearlman, J. S.

Rainer, F.

W. W. Simmons, J. S. Guch, F. Rainer, J. E. Murray, “A high energy spatial filter for removal of small scale beam instabilities in high power solid state lasers,” Internal Rep. No. UCRL-76873 (University of California, Lawrence Livermore Laboratory, Berkeley, Calif., 1975).

Rodionov, A. Y.

S. A. Dimakov, S. I. Zavgorodneva, L. V. Koval’chuk, A. Y. Rodionov, V. P. Yashukov, “Investigation of the threshold of formation of a plasma screening radiation in a plasma spatial filter,” Sov. J. Quantum Electron. 19, 803–805 (1989).
[CrossRef]

Siegman, A. E.

A. E. Siegman, “Defining the effective radius of curvature for a nonideal optical beam,” IEEE J. Quantum Electron. 27, 1146–1148 (1991).
[CrossRef]

A. E. Siegman, “New developments in laser resonators,” in Laser Resonators, D. A. Holmes, ed., Proc. SPIE1224, 2–14 (1990).

Simmons, W. W.

W. W. Simmons, J. S. Guch, F. Rainer, J. E. Murray, “A high energy spatial filter for removal of small scale beam instabilities in high power solid state lasers,” Internal Rep. No. UCRL-76873 (University of California, Lawrence Livermore Laboratory, Berkeley, Calif., 1975).

Yashukov, V. P.

S. A. Dimakov, S. I. Zavgorodneva, L. V. Koval’chuk, A. Y. Rodionov, V. P. Yashukov, “Investigation of the threshold of formation of a plasma screening radiation in a plasma spatial filter,” Sov. J. Quantum Electron. 19, 803–805 (1989).
[CrossRef]

Zavgorodneva, S. I.

S. A. Dimakov, S. I. Zavgorodneva, L. V. Koval’chuk, A. Y. Rodionov, V. P. Yashukov, “Investigation of the threshold of formation of a plasma screening radiation in a plasma spatial filter,” Sov. J. Quantum Electron. 19, 803–805 (1989).
[CrossRef]

Zimmerman, G. B.

G. B. Zimmerman, W. L. Kruer, “Numerical simulation of laser-initiated fusion,” Comments Plasma Phys. Controlled Fusion 2, 51–61 (1975).

Appl. Opt.

Comments Plasma Phys. Controlled Fusion

G. B. Zimmerman, W. L. Kruer, “Numerical simulation of laser-initiated fusion,” Comments Plasma Phys. Controlled Fusion 2, 51–61 (1975).

IEEE J. Quantum Electron.

A. E. Siegman, “Defining the effective radius of curvature for a nonideal optical beam,” IEEE J. Quantum Electron. 27, 1146–1148 (1991).
[CrossRef]

J. Phys. D

C. L. M. Ireland, “A pinhole plasma shutter for optical isolation in high power glass lasers,” J. Phys. D 13, 9–16 (1980).
[CrossRef]

Phys. Fluids

T. W. Johnston, J. M. Dawson, “Correct values for high-frequency power absorption by inverse bremsstrahlung in plasmas,” Phys. Fluids 16, 722 (1973).
[CrossRef]

Sov. J. Quantum Electron.

S. A. Dimakov, S. I. Zavgorodneva, L. V. Koval’chuk, A. Y. Rodionov, V. P. Yashukov, “Investigation of the threshold of formation of a plasma screening radiation in a plasma spatial filter,” Sov. J. Quantum Electron. 19, 803–805 (1989).
[CrossRef]

Other

V. L. Ginzburg, The Propagation of Electromagnetic Waves in Plasmas (Pergamon, Oxford, 1964).

W. W. Simmons, J. S. Guch, F. Rainer, J. E. Murray, “A high energy spatial filter for removal of small scale beam instabilities in high power solid state lasers,” Internal Rep. No. UCRL-76873 (University of California, Lawrence Livermore Laboratory, Berkeley, Calif., 1975).

A. E. Siegman, “New developments in laser resonators,” in Laser Resonators, D. A. Holmes, ed., Proc. SPIE1224, 2–14 (1990).

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Figures (9)

Fig. 1
Fig. 1

(a) Diagram of the conventional washer-type pinhole operation. Rejected rays are highly absorbed at near-normal incidence and ablate the pinhole surface to form an expanding plasma. (b) Diagram of the conical pinhole design.

Fig. 2
Fig. 2

Snapshot of the simulated plasma electron-density distribution for (a) a conventional pinhole design made of Au at a time of 0.91 ns after the start of the laser pulse and (b) a conical pinhole structure made of Au at 2.00 ns after the start of the laser pulse. An incident energy of 250 J in a 5-ns pulse was used for these simulations. The gray scale and contour intervals are mapped logarithmically; the contour interval is one decade in density with the first contour located at 1018 cm-3 (0.001 × critical density).

Fig. 3
Fig. 3

Experimental arrangement for the measurement of incident transmitted and backscattered beams from the pinhole. Details are explained in the text.

Fig. 4
Fig. 4

Image of the far-field intensity distribution as recorded on the CCD detector in the far-field imager, mapped on a logarithmic gray scale; the contour interval spacing is 0.5.

Fig. 5
Fig. 5

(a) Horizontal (dotted) and vertical (dash-dot) lineouts of the far-field intensity distribution in Fig. 4 as well as the azimuthally averaged (solid curve) distribution. (b) Integrated energy (azimuthally averaged) as a function of radius from the spot center.

Fig. 6
Fig. 6

Streaked images of the near-field beam imaged at the output lens of the spatial filter with (a) no pinhole installed, (b) a 500-μm-diameter Ta pinhole, (c) a 500/900-μm Au conical pinhole.

Fig. 7
Fig. 7

Streaked images of the near-field beam imaged at the output lens of the spatial filter with (a) a 1-mm-diameter CH pinhole, (b) a 500-μm-diameter CH pinhole, (c) a 500/900-μm CH conical pinhole.

Fig. 8
Fig. 8

Incident (solid curves), transmitted (dashed curves), and backscattered (dotted curves) signals from (a) a 500-μm-diameter Ta washer-type pinhole and (b) a 500-μm-diameter CH washer-type pinhole. The average incident power level during the 5-ns pulse was 30 GW.

Fig. 9
Fig. 9

Incident (solid curves), transmitted (dashed curves), and backscattered (dotted curves) signals from (a) a 500/900-μm-diameter Au conical pinhole and (b) a 500/900-μm-diameter CH conical pinhole.

Tables (1)

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Table 1 Pinhole Closure Timesa

Equations (2)

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δ = π λ 0 L   n / n c d z ,
ϕ d = 1 2 0 L d n / n c d x d z ,

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