Abstract

We describe the design and performance of large-aperture (>30 cm × 30 cm) optical switches that have demonstrated, for the first time to our knowledge, active switching of a high-energy (>5 kJ) optical pulse in an inertial-confinement fusion laser. These optical switches, which consist of a plasma-electrode Pockels cell (PEPC) and a passive polarizer, permit the design of efficient, multipass laser amplifiers. In a PEPC, plasma discharges on the faces of a thin (1-cm) electro-optic crystal (KDP or KD*P) act as highly conductive and transparent electrodes. These plasma electrodes facilitate rapid (<100 ns) and uniform charging of the crystal to the half-wave voltage and discharging back to 0 V. We discuss the operating principles, design, optical performance, and technical issues of a 32 cm × 32 cm prototype PEPC with both KDP and KD*P crystals, and a 37 cm × 37 cm PEPC with a KDP crystal for the Beamlet laser. This PEPC recently switched a 6-kJ, 3-ns pulse in a four-pass cavity.

© 1995 Optical Society of America

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References

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  1. J. R. Murray, J. H. Campbell, D. N. Frank, J. T. Hunt, J. B. Trenholme, “The Nova Upgrade Beamlet Demonstration Project,” ICF Q. Rep. 1 (3), 89–107 (1991).
  2. L. L. Steinmetz, T. W. Pouliot, B. C. Johnson, “Cylindrical, ring-electrode KD*P electro-optic modulator,” Appl. Opt. 12, 1468–1471 (1973).
    [CrossRef] [PubMed]
  3. M. D. Skeldon, M. S. Jin, D. J. Smith, S. T. Bui, “Performance of longitudinal mode KD*P Pockels cells with transparent conductive coatings,” in Solid State Lasers II, G. Dube, ed., Proc. Soc. Photo-Opt. Instrum. Eng.1410, 116–124 (1991).
  4. J. Goldhar, M. A. Henesian, “Large-aperture electro-optical switches with plasma electrodes,” IEEE J. Quantum Electron. QE-22, 1137–1147 (1986).
    [CrossRef]
  5. B. M. van Wonterghem, J. R. Murray, D. R. Speck, J. H. Campbell, “Performance of the NIF Prototype Beamlet,” Fusion Technol. 26, 702–707 (1994).
  6. D. Eimerl, “Electro-optic, linear and nonlinear optical properties of KDP and its isomorphs,” Ferroelectrics 77, 95–139 (1987).
    [CrossRef]
  7. M. A. Rhodes, J. J. De Yoreo, B. W. Woods, L. J. Atherton, “Large-aperture optical switches for high-energy, multipass laser amplifiers,” ICF Q. Rep. 2 (1), 23–26 (1991).
  8. N. A. Krall, A. W. Trivelpiece, Principles of Plasma Physics (McGraw-Hill, New York), pp. 319–321.
  9. D. E. Golden, H. W. Bandel, “Absolute total electron-helium-atom scattering cross sections for low electron energies,” Phys. Rev. 138, 14–21 (1965).
    [CrossRef]
  10. C. A. Ebbers, J. Happe, N. Nilson, S. P. Velsko, “Optical absorption at 1.06 μm in highly deuterated potassium dihydrogen phosphate,” Appl. Opt. 31, 1960–1964 (1992).
    [CrossRef] [PubMed]
  11. J. J. DeYoreo, B. W. Woods, “A study of residual stress and the stress-optic effect in mixed crystals of K(DxH1−x)2PO4,” J. Appl. Phys. 73, 7780–7789 (1993).
    [CrossRef]
  12. I. M. Thomas, “Optical coatings by the sol-gel process,” Opt. News 12, (8), 18–22 (1986).
    [CrossRef]
  13. R. K. Waits, “Planar magnetron sputtering,” J. Vac. Sci. Technol. 15, 179–187 (1978).
    [CrossRef]
  14. M. A. Rhodes, J. Taylor, “Pulse power requirements for large-aperture optical switches based on plasma-electrode Pockels cells,” in Twentieth Power Modulator Symposium (Institute of Electrical and Electronics Engineer, Piscataway, N.J., 1992), pp. 380–382.
    [CrossRef]
  15. D. Rosen, G. K. Wehner, “Sputtering yields for low energy He+−, Kr+−, and Xe+− ion bombardment,” J. Appl. Phys. 33, 1842–1845 (1962).
    [CrossRef]

1994 (1)

B. M. van Wonterghem, J. R. Murray, D. R. Speck, J. H. Campbell, “Performance of the NIF Prototype Beamlet,” Fusion Technol. 26, 702–707 (1994).

1993 (1)

J. J. DeYoreo, B. W. Woods, “A study of residual stress and the stress-optic effect in mixed crystals of K(DxH1−x)2PO4,” J. Appl. Phys. 73, 7780–7789 (1993).
[CrossRef]

1992 (1)

1991 (2)

M. A. Rhodes, J. J. De Yoreo, B. W. Woods, L. J. Atherton, “Large-aperture optical switches for high-energy, multipass laser amplifiers,” ICF Q. Rep. 2 (1), 23–26 (1991).

J. R. Murray, J. H. Campbell, D. N. Frank, J. T. Hunt, J. B. Trenholme, “The Nova Upgrade Beamlet Demonstration Project,” ICF Q. Rep. 1 (3), 89–107 (1991).

1987 (1)

D. Eimerl, “Electro-optic, linear and nonlinear optical properties of KDP and its isomorphs,” Ferroelectrics 77, 95–139 (1987).
[CrossRef]

1986 (2)

J. Goldhar, M. A. Henesian, “Large-aperture electro-optical switches with plasma electrodes,” IEEE J. Quantum Electron. QE-22, 1137–1147 (1986).
[CrossRef]

I. M. Thomas, “Optical coatings by the sol-gel process,” Opt. News 12, (8), 18–22 (1986).
[CrossRef]

1978 (1)

R. K. Waits, “Planar magnetron sputtering,” J. Vac. Sci. Technol. 15, 179–187 (1978).
[CrossRef]

1973 (1)

1965 (1)

D. E. Golden, H. W. Bandel, “Absolute total electron-helium-atom scattering cross sections for low electron energies,” Phys. Rev. 138, 14–21 (1965).
[CrossRef]

1962 (1)

D. Rosen, G. K. Wehner, “Sputtering yields for low energy He+−, Kr+−, and Xe+− ion bombardment,” J. Appl. Phys. 33, 1842–1845 (1962).
[CrossRef]

Atherton, L. J.

M. A. Rhodes, J. J. De Yoreo, B. W. Woods, L. J. Atherton, “Large-aperture optical switches for high-energy, multipass laser amplifiers,” ICF Q. Rep. 2 (1), 23–26 (1991).

Bandel, H. W.

D. E. Golden, H. W. Bandel, “Absolute total electron-helium-atom scattering cross sections for low electron energies,” Phys. Rev. 138, 14–21 (1965).
[CrossRef]

Bui, S. T.

M. D. Skeldon, M. S. Jin, D. J. Smith, S. T. Bui, “Performance of longitudinal mode KD*P Pockels cells with transparent conductive coatings,” in Solid State Lasers II, G. Dube, ed., Proc. Soc. Photo-Opt. Instrum. Eng.1410, 116–124 (1991).

Campbell, J. H.

B. M. van Wonterghem, J. R. Murray, D. R. Speck, J. H. Campbell, “Performance of the NIF Prototype Beamlet,” Fusion Technol. 26, 702–707 (1994).

J. R. Murray, J. H. Campbell, D. N. Frank, J. T. Hunt, J. B. Trenholme, “The Nova Upgrade Beamlet Demonstration Project,” ICF Q. Rep. 1 (3), 89–107 (1991).

De Yoreo, J. J.

M. A. Rhodes, J. J. De Yoreo, B. W. Woods, L. J. Atherton, “Large-aperture optical switches for high-energy, multipass laser amplifiers,” ICF Q. Rep. 2 (1), 23–26 (1991).

DeYoreo, J. J.

J. J. DeYoreo, B. W. Woods, “A study of residual stress and the stress-optic effect in mixed crystals of K(DxH1−x)2PO4,” J. Appl. Phys. 73, 7780–7789 (1993).
[CrossRef]

Ebbers, C. A.

Eimerl, D.

D. Eimerl, “Electro-optic, linear and nonlinear optical properties of KDP and its isomorphs,” Ferroelectrics 77, 95–139 (1987).
[CrossRef]

Frank, D. N.

J. R. Murray, J. H. Campbell, D. N. Frank, J. T. Hunt, J. B. Trenholme, “The Nova Upgrade Beamlet Demonstration Project,” ICF Q. Rep. 1 (3), 89–107 (1991).

Golden, D. E.

D. E. Golden, H. W. Bandel, “Absolute total electron-helium-atom scattering cross sections for low electron energies,” Phys. Rev. 138, 14–21 (1965).
[CrossRef]

Goldhar, J.

J. Goldhar, M. A. Henesian, “Large-aperture electro-optical switches with plasma electrodes,” IEEE J. Quantum Electron. QE-22, 1137–1147 (1986).
[CrossRef]

Happe, J.

Henesian, M. A.

J. Goldhar, M. A. Henesian, “Large-aperture electro-optical switches with plasma electrodes,” IEEE J. Quantum Electron. QE-22, 1137–1147 (1986).
[CrossRef]

Hunt, J. T.

J. R. Murray, J. H. Campbell, D. N. Frank, J. T. Hunt, J. B. Trenholme, “The Nova Upgrade Beamlet Demonstration Project,” ICF Q. Rep. 1 (3), 89–107 (1991).

Jin, M. S.

M. D. Skeldon, M. S. Jin, D. J. Smith, S. T. Bui, “Performance of longitudinal mode KD*P Pockels cells with transparent conductive coatings,” in Solid State Lasers II, G. Dube, ed., Proc. Soc. Photo-Opt. Instrum. Eng.1410, 116–124 (1991).

Johnson, B. C.

Krall, N. A.

N. A. Krall, A. W. Trivelpiece, Principles of Plasma Physics (McGraw-Hill, New York), pp. 319–321.

Murray, J. R.

B. M. van Wonterghem, J. R. Murray, D. R. Speck, J. H. Campbell, “Performance of the NIF Prototype Beamlet,” Fusion Technol. 26, 702–707 (1994).

J. R. Murray, J. H. Campbell, D. N. Frank, J. T. Hunt, J. B. Trenholme, “The Nova Upgrade Beamlet Demonstration Project,” ICF Q. Rep. 1 (3), 89–107 (1991).

Nilson, N.

Pouliot, T. W.

Rhodes, M. A.

M. A. Rhodes, J. J. De Yoreo, B. W. Woods, L. J. Atherton, “Large-aperture optical switches for high-energy, multipass laser amplifiers,” ICF Q. Rep. 2 (1), 23–26 (1991).

M. A. Rhodes, J. Taylor, “Pulse power requirements for large-aperture optical switches based on plasma-electrode Pockels cells,” in Twentieth Power Modulator Symposium (Institute of Electrical and Electronics Engineer, Piscataway, N.J., 1992), pp. 380–382.
[CrossRef]

Rosen, D.

D. Rosen, G. K. Wehner, “Sputtering yields for low energy He+−, Kr+−, and Xe+− ion bombardment,” J. Appl. Phys. 33, 1842–1845 (1962).
[CrossRef]

Skeldon, M. D.

M. D. Skeldon, M. S. Jin, D. J. Smith, S. T. Bui, “Performance of longitudinal mode KD*P Pockels cells with transparent conductive coatings,” in Solid State Lasers II, G. Dube, ed., Proc. Soc. Photo-Opt. Instrum. Eng.1410, 116–124 (1991).

Smith, D. J.

M. D. Skeldon, M. S. Jin, D. J. Smith, S. T. Bui, “Performance of longitudinal mode KD*P Pockels cells with transparent conductive coatings,” in Solid State Lasers II, G. Dube, ed., Proc. Soc. Photo-Opt. Instrum. Eng.1410, 116–124 (1991).

Speck, D. R.

B. M. van Wonterghem, J. R. Murray, D. R. Speck, J. H. Campbell, “Performance of the NIF Prototype Beamlet,” Fusion Technol. 26, 702–707 (1994).

Steinmetz, L. L.

Taylor, J.

M. A. Rhodes, J. Taylor, “Pulse power requirements for large-aperture optical switches based on plasma-electrode Pockels cells,” in Twentieth Power Modulator Symposium (Institute of Electrical and Electronics Engineer, Piscataway, N.J., 1992), pp. 380–382.
[CrossRef]

Thomas, I. M.

I. M. Thomas, “Optical coatings by the sol-gel process,” Opt. News 12, (8), 18–22 (1986).
[CrossRef]

Trenholme, J. B.

J. R. Murray, J. H. Campbell, D. N. Frank, J. T. Hunt, J. B. Trenholme, “The Nova Upgrade Beamlet Demonstration Project,” ICF Q. Rep. 1 (3), 89–107 (1991).

Trivelpiece, A. W.

N. A. Krall, A. W. Trivelpiece, Principles of Plasma Physics (McGraw-Hill, New York), pp. 319–321.

van Wonterghem, B. M.

B. M. van Wonterghem, J. R. Murray, D. R. Speck, J. H. Campbell, “Performance of the NIF Prototype Beamlet,” Fusion Technol. 26, 702–707 (1994).

Velsko, S. P.

Waits, R. K.

R. K. Waits, “Planar magnetron sputtering,” J. Vac. Sci. Technol. 15, 179–187 (1978).
[CrossRef]

Wehner, G. K.

D. Rosen, G. K. Wehner, “Sputtering yields for low energy He+−, Kr+−, and Xe+− ion bombardment,” J. Appl. Phys. 33, 1842–1845 (1962).
[CrossRef]

Woods, B. W.

J. J. DeYoreo, B. W. Woods, “A study of residual stress and the stress-optic effect in mixed crystals of K(DxH1−x)2PO4,” J. Appl. Phys. 73, 7780–7789 (1993).
[CrossRef]

M. A. Rhodes, J. J. De Yoreo, B. W. Woods, L. J. Atherton, “Large-aperture optical switches for high-energy, multipass laser amplifiers,” ICF Q. Rep. 2 (1), 23–26 (1991).

Appl. Opt. (2)

Ferroelectrics (1)

D. Eimerl, “Electro-optic, linear and nonlinear optical properties of KDP and its isomorphs,” Ferroelectrics 77, 95–139 (1987).
[CrossRef]

Fusion Technol. (1)

B. M. van Wonterghem, J. R. Murray, D. R. Speck, J. H. Campbell, “Performance of the NIF Prototype Beamlet,” Fusion Technol. 26, 702–707 (1994).

ICF Q. Rep. (2)

M. A. Rhodes, J. J. De Yoreo, B. W. Woods, L. J. Atherton, “Large-aperture optical switches for high-energy, multipass laser amplifiers,” ICF Q. Rep. 2 (1), 23–26 (1991).

J. R. Murray, J. H. Campbell, D. N. Frank, J. T. Hunt, J. B. Trenholme, “The Nova Upgrade Beamlet Demonstration Project,” ICF Q. Rep. 1 (3), 89–107 (1991).

IEEE J. Quantum Electron. (1)

J. Goldhar, M. A. Henesian, “Large-aperture electro-optical switches with plasma electrodes,” IEEE J. Quantum Electron. QE-22, 1137–1147 (1986).
[CrossRef]

J. Appl. Phys. (2)

J. J. DeYoreo, B. W. Woods, “A study of residual stress and the stress-optic effect in mixed crystals of K(DxH1−x)2PO4,” J. Appl. Phys. 73, 7780–7789 (1993).
[CrossRef]

D. Rosen, G. K. Wehner, “Sputtering yields for low energy He+−, Kr+−, and Xe+− ion bombardment,” J. Appl. Phys. 33, 1842–1845 (1962).
[CrossRef]

J. Vac. Sci. Technol. (1)

R. K. Waits, “Planar magnetron sputtering,” J. Vac. Sci. Technol. 15, 179–187 (1978).
[CrossRef]

Opt. News (1)

I. M. Thomas, “Optical coatings by the sol-gel process,” Opt. News 12, (8), 18–22 (1986).
[CrossRef]

Phys. Rev. (1)

D. E. Golden, H. W. Bandel, “Absolute total electron-helium-atom scattering cross sections for low electron energies,” Phys. Rev. 138, 14–21 (1965).
[CrossRef]

Other (3)

N. A. Krall, A. W. Trivelpiece, Principles of Plasma Physics (McGraw-Hill, New York), pp. 319–321.

M. D. Skeldon, M. S. Jin, D. J. Smith, S. T. Bui, “Performance of longitudinal mode KD*P Pockels cells with transparent conductive coatings,” in Solid State Lasers II, G. Dube, ed., Proc. Soc. Photo-Opt. Instrum. Eng.1410, 116–124 (1991).

M. A. Rhodes, J. Taylor, “Pulse power requirements for large-aperture optical switches based on plasma-electrode Pockels cells,” in Twentieth Power Modulator Symposium (Institute of Electrical and Electronics Engineer, Piscataway, N.J., 1992), pp. 380–382.
[CrossRef]

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Figures (22)

Fig. 1
Fig. 1

Diagram of an optical switch that enables a multipass laser–amplifier architecture. The switch deflects the optical pulse out of the cavity after multiple gain passes. Amp, amplifier.

Fig. 2
Fig. 2

Cross-sectional view of a PEPC and the associated electronic circuit. The plasma pulsers produce the plasma electrodes by high-current discharge in helium; the switch pulser then applies the switching voltage across the KDP crystal.

Fig. 3
Fig. 3

Circuit model of the PEPC used to determine the relation between the peak switch-pulse current and the plasma current (results shown in Fig. 4, below).

Fig. 4
Fig. 4

(a) Current (based on the circuit shown in Fig. 3) in the crystal capacitance for plasma currents of 2 and 0.5 kA. For currents less than 2 kA, the charging current clamps at the plasma current, extending the charging time. (b) Corresponding voltage waveforms. The voltage rise time is longer for the 0.5-kA plasma current.

Fig. 5
Fig. 5

Strain-depolarization maps for (a) a 32-cm KD*P crystal and (b) a 32-cm KDP crystal.

Fig. 6
Fig. 6

PEPC assembly showing the sandwich structure.

Fig. 7
Fig. 7

(a) Side cut-away view and (b) top view of the magnet layout for the planar magnetron cathodes used in the PEPC. The magnetron cathodes provide a uniform discharge without thermionic emission.

Fig. 8
Fig. 8

Schematic diagram of the plasma-pulse generator. A thyratron switches a charged capacitor across the discharge electrodes to produce a plasma current of up to 5 kA.

Fig. 9
Fig. 9

Plasma current for a 2-kA pulse, and relative timing of the switch pulse.

Fig. 10
Fig. 10

Schematic diagram of the switch-pulse generator. Sections of coaxial cable act as a pulse-forming network (PFN) to produce a nominally rectangular pulse shape. Multiple cables are connected in parallel to achieve the low impedance required for charging of the crystal.

Fig. 11
Fig. 11

Voltage across the PEPC during normal operation and times at which the optical pulse traverses the cell (twice when the voltage is on and once after the cell is discharged).

Fig. 12
Fig. 12

Schematic diagram of the experimental setup used to evaluate the optical-switching performance of the prototype PEPC.

Fig. 13
Fig. 13

Typical Son efficiency image from the prototype PEPC with a 32-cm KDP crystal. A 30-cm-diameter central view is shown.

Fig. 14
Fig. 14

(a) Beamlet PEPC before installation into the Beamlet laser. (b) Beamlet PEPC integrated into the Beamlet laser.

Fig. 15
Fig. 15

Experimental setup used to evaluate the switching performance of the PEPC in the Beamlet laser at low fluence. An optical pulse from the Beamlet front-end laser is directed toward L1 by a small injection mirror (not shown) near the focus of the spatial filter before it propagates through the PEPC and polarizer. A high-resolution CCD video camera images the light transmitted by the PEPC–polarizer combination.

Fig. 16
Fig. 16

Switching efficiency across the 35 cm × 35 cm aperture of the Beamlet PEPC. The lower switching efficiency in the corners is due to strain-induced birefringence arising from vacuum loading in the silica windows.

Fig. 17
Fig. 17

Quartz-crystal microbalance data showing the helium–oxygen mixture removing carbon deposited by a pure helium plasma.

Fig. 18
Fig. 18

Time-dependent ER decrease arising from crystal heating (data normalized to the ER at the start of the run). The heating is greatly reduced when the average discharge power is lowered by the use of a gated simmer discharge.

Fig. 19
Fig. 19

Magnetically induced bright spot in the lower-anode PEPC quadrant.

Fig. 20
Fig. 20

Diagram showing how the magnetic field from wires carrying the discharge current can interfere with electron transport, thereby causing nonuniform switching.

Fig. 21
Fig. 21

(a) Plasma discharges for side 1 and side 2 are fed from the same side. The resulting magnetic field causes strong bright-spot formation. (b) Feeding discharges from opposite sides minimizes bright-spot formation.

Fig. 22
Fig. 22

Baffles mounted in the dc (DC) breaks increase the path length and break up a line of sight for electron flow. The baffles effectively eliminate switch-pulse leakage current to the grounded vacuum system.

Tables (2)

Tables Icon

Table 1 Switching Performance of the Prototype PEPC with KD*P and KDP Crystalsa

Tables Icon

Table 2 Heating (in degrees Celsius) as a Result of Plasma Discharge at Five Locations Inside the Prototype PEPC, Measured with Thermistors

Equations (10)

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η en = 8.93 × 10 11 n n n e [ m e σ en q 2 ( k T e m e ) 1 / 2 ] ,
S eff = 1 1 ER .
V π = V sw C sheath C KDP + C sheath ,
ϕ ( x ) = ϕ 0 exp ( x / λ D ) ,
λ D = 740 ( T ev n e ) 1 / 2 ,
E = d ϕ d x = ϕ 0 λ D exp ( x / λ D ) .
W = 0 2 E 2 d v = A 0 2 ϕ 0 2 λ D 2 0 exp ( 2 x / λ D ) d x = A 0 ϕ 0 2 4 λ D ,
W = ½ C sheath ϕ 0 2 .
C sheath = A 0 2 λ D ,
n e = 3.3 × 10 11 T e .

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