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Intensity measurements of a quasi-monochromatic X-ray beam formed by a spherically bent crystal
Volume 77. number 2,3
OPTICS COMMUNICATIONS
15 June 1990
INTENSITY MEASUREMENTS OF A QUASI-MONOCHROMATIC F O R M E D BY A S P H E R I C A L L Y B E N T C R Y S T A L
X-RAY B E A M
A.V. RODI~, A.M. MAKSIMCHUK, G.V. SKLIZKOV PN Lebedev Physical Institute, USSR
A. RIDGELEY, C. DANSON, N. RIZVI, R. BANN Rutherford Appleton Laboratory, UK
E. F O R S T E R and I. U S C H M A N N Friedrich Schiller University .lena, Jena, GDR
Received 26 October 1989: revised manuscript received 12 February 1990
A quasi-monochromatic backlighting scheme f o r the diagnosis of laser-produced plasmas using spherically curved crystals to produce the monochromatic beam is proposed. Comparative flux measurements have been made of a variety of candidate backlighting materials using a spherically bent quartz [ 10|0] crystal as the monochromaticising component. It is demonstrated that very bright quasi-monochromatic beams can be obtained with this crystal in the narrow spectral range 8.43 A + 0.03 A using Lshell emitters with z=29-33 or M-shell emitters with z= 64-68.
I. Introduction
B1 B 2
C
B
X-ray backlighting techniques are now well established as a m e t h o d o f diagnosing laser-produced plasmas. N o r m a l l y a wide band o f X-ray emission from the backlighter source is used as the probing radiation. This m e a n s that an analysis o f the recorded opacity profiles requires a knowledge o f relative spectral brightness for the backlighter plasma. If the backlighter source can be m a d e m o n o c h r o matic then this p r o b l e m can be overcome. The use o f m o n o c h r o m a t i c or q u a s i - m o n o c h r o m a t i c backlighting b e a m s has been investigated in previous works: Lewis and Mc Glinchey [1 ] have d e m o n strated the use o f a fiat Bragg crystal to m o n o c h r o maticise the beam, and Ahlstrom [2] has d e m o n strated the use o f a Fresnel zone plate plus X-ray muitilayer mirror. Goetz et al. [ 3 ] have originally proposed the quasim o n o c h r o m a t i c X-ray backlighting scheme investigated in this work and this scheme is shown in fig. 1. The " p o i n t " backlighter source B~ is used to il-
E}I
BACKLIGHTING
B2
DIAGNOSED PLASMA
C
SPHERICALLY
P
PINHOLE
B ', - BACKLIGHTING
SOURCE CURVED CRYSTAL
SOURCE IMAGE
1 132 - DIAGNOSED PLASMA IMAGE
Fig. 1. Schematic diagram of backlighting scheme proposed by Kalashnikov et al., using a spherically curved crystal. luminate the implosion plasma B2 and a spherically curved crystal C focusses the backlighting source onto a pinhole at P. The pinhole size is m a t c h e d to the backlighting source image size to m a x i m i s e the relative brightness o f backlightcr to diagnosed plasmas in the selected spectral range, which d e p e n d s on the Bragg angle and geometry o f the experiment [4]. The m e t h o d gives a bright backlighting beam due to the
0030-4018/90/$03.50 © Elsevier Science Publishers B.V. ( North-Holland )
163
Volume 77, number 2.3
(.)PTI('S COMMUNI('-~TII)NS
large collecting angle of the spherical crystal. If the spectral range of the reflected beam coincides with the line emission from the backlighter source then the brightness of the backlighter can be large enough for the investigation of low' intensity, short lifetime effects and high spatial resolution effects in the dense plasma. The analysis of absorption and refraction of the Xray transmitted beam in the dense plasma [4J indicates that the spectral range 7-10 ,& is optimal tot diagnostics of the plasma regions close to solid densit3. A transmitted beam of wavelength ~ 10 ,\ is transmitted essentially unabsorbed in a plasma with density 10-'-'-10.,-3cm 3 but refraction may reach 0. I By using the tbcusing crystal's selective ability to refract in a narrow spectral range, it is possible to obtain an investigated plasma image which is formed only in the backlighting source beam, refracted in the dense N a s m a regions. The feasibility of this backlighting method depends on the ability to produce a bright enough quasimonochromatic beam. As a preliminary step in the optimisation of the "'focussing-crystal X-ray backlight source" a series of experiments was conducted at the Central Laser Facility, RAL. The aim of these experiments was the optimisation of the focusing cry'sial/X-ray backlighter source combination by selecting the target material in the backlighting scheme. A comparison of K-. L - , M-spectrum intensities of the plasma radiation in the narrow spectral range was made. The brightness of an X-ray quasi-monochromatic beam formed by the spherically-bent focusing crystal using a variety of target elements was determined.
15 June 1990 sphoNc,ll
•
'L rnlr +or
.D
"x
phi ,t)ql ,maqt!
I
//
,m
f la~e,
<
.........
\
\X, '\\
[/
~lle¢ I r O9 r ;llnr'm r-.
".._-"
d(Jubl~
cr ySt,ll
~p¢.c t t oral,liar
Fig. 2. lhc experimental scheme for X-ray beam inlensit.~ measurements.
L M1 g2 8.42
32
Ge
r~ 11.20 8,40 8A3
i,!
,
~,I',
8.45 8.50
4 I ~As33
l 7.50
2. Experimental conditions The experimental scheme is given in fig. 2. The radiation from a Nd : laser with energy of ~ 10 J and duration of 0.6 ns was focused on the target surface, the flux density being 5 × 10 ~3 W / c m 2. The X-ray quasi-monochromatic beam was formed by a spherically-bent crystal of quartz [1010], 2 d = 8 . 5 0 9 /k. with diameter 24 m m and curvature radius of 300 mm. The spectral range of X-ray radiation reflected at a crystal and then focused depends on the c~'stal curvature radius, crystal di164
8.40
8A6
8.50
Fig.3.X-rayspectraof magnesium,germaniumandarsenic.The spectralrangeof 8.41-8.46,Jr.wherethe X-rayquantummonochromaticbeam is formed, is marked. ( lnlensity scales are nol consislent ). ameter, the magnification of the scheme and radiation incident angle [5]. The wavelength range 8.41-8.46.2k was chosen to measure the beam brightness in the image plane comparing different target materials. This range was chosen as the Ly, MgXII lines and the corresponding dielectronic satellite lines are in this range. The Bragg angle was 82:, and the
Volume 77, number 2,3
OPTICS C O M M U N I C A T I O N S
magnification was equal to 2. The monitoring of spectral line alignment in the focusing crystal reflection range was achieved by means of the double-crystal quartz spectrometer which offers the possibility of absolute measurements of X-ray spectral wavelengths [6]. For instance fig. 3 shows the K-spectrum of magnesium and the L-spectrum of germanium and arsenic, in which is marked the spectral width of the monochromatic beam. The plasma radiation lines contained in the given range are clearly seen. The spectral interval positon may be changed [5] by scanning the focusing crystal Bragg angle and its width is varied with the aperture diaphragm or by changing the magnification. The intensity measurements are carried out in the source image plane using DEF-2 film which was developed in a Kodak-Dl9 developer.
3. Results Fig. 4 shows the results of intensity measurements of a quasi-monochromatic beam in the laser plasma image plane when diffcrcnt target materials are used as a target. The targets compared were K-spectrum (magnesium, aluminium, silicon): L-spectrum (copper, germanium, arsenic, selenium, bromine): M-spectrum (samarium, europium, gadolinium, terbium, dysposium, holmium, erbium).
I ~- ),:841=846A
M
1
15 June 1990
Based on the results mentioned above the following observations are made concerning the intcnsity of different target radiation within the range of 8.418.46 A: The X-ray intensity of magnesium K-spectrum is twice or three times as much as that of aluminium and silicon, because the Mg(XII ) Ly,-line is aligned in the spectral range registered, whereas aluminium and silicon form a beam only in the continuum radiation. The beam intensity when L-spectra of elements with Z = 29-33 or M-spectra with Z = 64-68 are used is an order of magnitude higher than that obtained with the MgXII K-shell spectrum. For targets for which there are no spectral lines in the wavelength range of the crystal the quasi-monochromatic beam is formed in the recombination continuum, and similar intensities are obtained regardless of whether the target materials is a K-, L-, or M-shell emitter. This is seen from the comparison of All3, Sil4, Br35, Sm62 and Eu63.
4. Conclusions A spherically curved crystal can be used to obtain a bright backlighting source. Use of suitable L- or Mshell emitters is an order of magnitude more effective than use of a K-shell emitter even when the wavelength band of the crystal is turned to the line emission from the K-shell emitting target in the conditions obtained using an incident laser flux density
of l014 W / c m 2.
L
References
K-
10
12 1314
29
32333435
62 636465666768
2
Fig. 4. Relative intensities of X-ray monochromatic beams in the plasma image plane, comparing different materials being used a s a target.
[ 1 ] C.L.S. Lewis and J. McGlinchey, Optics Comm 53 (1985) 179. [2 ] H.G. Ahlstrom, X-ray radiography of Laser Fusion Targets, in: Physics of Laser Fusion, II, Univ of California LLL, UCRL-53106 (1979) p. 129. [3] K. Goetz, M. Dick, M.P. Kalashnikov, A.M. Maksimchuk, Y.A. Mikhailov, A.V. Rode. G.V. Sklizkov, 1. Uschmann and E. Forster, Preprint of the Lebedev Physical Institute, no 143, Moscow, (1989), J. Soy. Las. Res. no 3 (1990) (in press). [4] M.P. Kalashnikov, G. Korn, M.Yu. Mazur, A.M. Maksimchuk, Y.A. Mikhailov, A.V. Rode, G.V. Sklizkov, V.P. Shevelko, E. Forster and I. Uschmann, Preprint of the
165
Volume 77, number 2.3
OPTICS COMMI.INICATIONS
Lebedev Physical Inst, no 70 C1989 ) 48; J. Soy. Las. Res. no 3 (1990) (in press). [ 5] N.G. Basov, Yu.A. Mikhailov and A.V. Rod6. G.V. Sklizkov. Annual Reporl to the Laser Facility Committee 1988 RAI,88-042 (1988).
166
15 June 199(I
[6] A.V. Rode. A.M. Maksimchuk, (i.V. Sklizkov. A. Ridgele), C. Danson. R. Bann, E. Forster. K. Goetz and 1. Uschmann. Measurements of X-ray spectral line wavelengths by using two Bragg reflections, J. X-ray Sci. and Tech. (submitted).
OPTICS COMMUNICATIONS
15 June 1990
INTENSITY MEASUREMENTS OF A QUASI-MONOCHROMATIC F O R M E D BY A S P H E R I C A L L Y B E N T C R Y S T A L
X-RAY B E A M
A.V. RODI~, A.M. MAKSIMCHUK, G.V. SKLIZKOV PN Lebedev Physical Institute, USSR
A. RIDGELEY, C. DANSON, N. RIZVI, R. BANN Rutherford Appleton Laboratory, UK
E. F O R S T E R and I. U S C H M A N N Friedrich Schiller University .lena, Jena, GDR
Received 26 October 1989: revised manuscript received 12 February 1990
A quasi-monochromatic backlighting scheme f o r the diagnosis of laser-produced plasmas using spherically curved crystals to produce the monochromatic beam is proposed. Comparative flux measurements have been made of a variety of candidate backlighting materials using a spherically bent quartz [ 10|0] crystal as the monochromaticising component. It is demonstrated that very bright quasi-monochromatic beams can be obtained with this crystal in the narrow spectral range 8.43 A + 0.03 A using Lshell emitters with z=29-33 or M-shell emitters with z= 64-68.
I. Introduction
B1 B 2
C
B
X-ray backlighting techniques are now well established as a m e t h o d o f diagnosing laser-produced plasmas. N o r m a l l y a wide band o f X-ray emission from the backlighter source is used as the probing radiation. This m e a n s that an analysis o f the recorded opacity profiles requires a knowledge o f relative spectral brightness for the backlighter plasma. If the backlighter source can be m a d e m o n o c h r o matic then this p r o b l e m can be overcome. The use o f m o n o c h r o m a t i c or q u a s i - m o n o c h r o m a t i c backlighting b e a m s has been investigated in previous works: Lewis and Mc Glinchey [1 ] have d e m o n strated the use o f a fiat Bragg crystal to m o n o c h r o maticise the beam, and Ahlstrom [2] has d e m o n strated the use o f a Fresnel zone plate plus X-ray muitilayer mirror. Goetz et al. [ 3 ] have originally proposed the quasim o n o c h r o m a t i c X-ray backlighting scheme investigated in this work and this scheme is shown in fig. 1. The " p o i n t " backlighter source B~ is used to il-
E}I
BACKLIGHTING
B2
DIAGNOSED PLASMA
C
SPHERICALLY
P
PINHOLE
B ', - BACKLIGHTING
SOURCE CURVED CRYSTAL
SOURCE IMAGE
1 132 - DIAGNOSED PLASMA IMAGE
Fig. 1. Schematic diagram of backlighting scheme proposed by Kalashnikov et al., using a spherically curved crystal. luminate the implosion plasma B2 and a spherically curved crystal C focusses the backlighting source onto a pinhole at P. The pinhole size is m a t c h e d to the backlighting source image size to m a x i m i s e the relative brightness o f backlightcr to diagnosed plasmas in the selected spectral range, which d e p e n d s on the Bragg angle and geometry o f the experiment [4]. The m e t h o d gives a bright backlighting beam due to the
0030-4018/90/$03.50 © Elsevier Science Publishers B.V. ( North-Holland )
163
Volume 77, number 2.3
(.)PTI('S COMMUNI('-~TII)NS
large collecting angle of the spherical crystal. If the spectral range of the reflected beam coincides with the line emission from the backlighter source then the brightness of the backlighter can be large enough for the investigation of low' intensity, short lifetime effects and high spatial resolution effects in the dense plasma. The analysis of absorption and refraction of the Xray transmitted beam in the dense plasma [4J indicates that the spectral range 7-10 ,& is optimal tot diagnostics of the plasma regions close to solid densit3. A transmitted beam of wavelength ~ 10 ,\ is transmitted essentially unabsorbed in a plasma with density 10-'-'-10.,-3cm 3 but refraction may reach 0. I By using the tbcusing crystal's selective ability to refract in a narrow spectral range, it is possible to obtain an investigated plasma image which is formed only in the backlighting source beam, refracted in the dense N a s m a regions. The feasibility of this backlighting method depends on the ability to produce a bright enough quasimonochromatic beam. As a preliminary step in the optimisation of the "'focussing-crystal X-ray backlight source" a series of experiments was conducted at the Central Laser Facility, RAL. The aim of these experiments was the optimisation of the focusing cry'sial/X-ray backlighter source combination by selecting the target material in the backlighting scheme. A comparison of K-. L - , M-spectrum intensities of the plasma radiation in the narrow spectral range was made. The brightness of an X-ray quasi-monochromatic beam formed by the spherically-bent focusing crystal using a variety of target elements was determined.
15 June 1990 sphoNc,ll
•
'L rnlr +or
.D
"x
phi ,t)ql ,maqt!
I
//
,m
f la~e,
<
.........
\
\X, '\\
[/
~lle¢ I r O9 r ;llnr'm r-.
".._-"
d(Jubl~
cr ySt,ll
~p¢.c t t oral,liar
Fig. 2. lhc experimental scheme for X-ray beam inlensit.~ measurements.
L M1 g2 8.42
32
Ge
r~ 11.20 8,40 8A3
i,!
,
~,I',
8.45 8.50
4 I ~As33
l 7.50
2. Experimental conditions The experimental scheme is given in fig. 2. The radiation from a Nd : laser with energy of ~ 10 J and duration of 0.6 ns was focused on the target surface, the flux density being 5 × 10 ~3 W / c m 2. The X-ray quasi-monochromatic beam was formed by a spherically-bent crystal of quartz [1010], 2 d = 8 . 5 0 9 /k. with diameter 24 m m and curvature radius of 300 mm. The spectral range of X-ray radiation reflected at a crystal and then focused depends on the c~'stal curvature radius, crystal di164
8.40
8A6
8.50
Fig.3.X-rayspectraof magnesium,germaniumandarsenic.The spectralrangeof 8.41-8.46,Jr.wherethe X-rayquantummonochromaticbeam is formed, is marked. ( lnlensity scales are nol consislent ). ameter, the magnification of the scheme and radiation incident angle [5]. The wavelength range 8.41-8.46.2k was chosen to measure the beam brightness in the image plane comparing different target materials. This range was chosen as the Ly, MgXII lines and the corresponding dielectronic satellite lines are in this range. The Bragg angle was 82:, and the
Volume 77, number 2,3
OPTICS C O M M U N I C A T I O N S
magnification was equal to 2. The monitoring of spectral line alignment in the focusing crystal reflection range was achieved by means of the double-crystal quartz spectrometer which offers the possibility of absolute measurements of X-ray spectral wavelengths [6]. For instance fig. 3 shows the K-spectrum of magnesium and the L-spectrum of germanium and arsenic, in which is marked the spectral width of the monochromatic beam. The plasma radiation lines contained in the given range are clearly seen. The spectral interval positon may be changed [5] by scanning the focusing crystal Bragg angle and its width is varied with the aperture diaphragm or by changing the magnification. The intensity measurements are carried out in the source image plane using DEF-2 film which was developed in a Kodak-Dl9 developer.
3. Results Fig. 4 shows the results of intensity measurements of a quasi-monochromatic beam in the laser plasma image plane when diffcrcnt target materials are used as a target. The targets compared were K-spectrum (magnesium, aluminium, silicon): L-spectrum (copper, germanium, arsenic, selenium, bromine): M-spectrum (samarium, europium, gadolinium, terbium, dysposium, holmium, erbium).
I ~- ),:841=846A
M
1
15 June 1990
Based on the results mentioned above the following observations are made concerning the intcnsity of different target radiation within the range of 8.418.46 A: The X-ray intensity of magnesium K-spectrum is twice or three times as much as that of aluminium and silicon, because the Mg(XII ) Ly,-line is aligned in the spectral range registered, whereas aluminium and silicon form a beam only in the continuum radiation. The beam intensity when L-spectra of elements with Z = 29-33 or M-spectra with Z = 64-68 are used is an order of magnitude higher than that obtained with the MgXII K-shell spectrum. For targets for which there are no spectral lines in the wavelength range of the crystal the quasi-monochromatic beam is formed in the recombination continuum, and similar intensities are obtained regardless of whether the target materials is a K-, L-, or M-shell emitter. This is seen from the comparison of All3, Sil4, Br35, Sm62 and Eu63.
4. Conclusions A spherically curved crystal can be used to obtain a bright backlighting source. Use of suitable L- or Mshell emitters is an order of magnitude more effective than use of a K-shell emitter even when the wavelength band of the crystal is turned to the line emission from the K-shell emitting target in the conditions obtained using an incident laser flux density
of l014 W / c m 2.
L
References
K-
10
12 1314
29
32333435
62 636465666768
2
Fig. 4. Relative intensities of X-ray monochromatic beams in the plasma image plane, comparing different materials being used a s a target.
[ 1 ] C.L.S. Lewis and J. McGlinchey, Optics Comm 53 (1985) 179. [2 ] H.G. Ahlstrom, X-ray radiography of Laser Fusion Targets, in: Physics of Laser Fusion, II, Univ of California LLL, UCRL-53106 (1979) p. 129. [3] K. Goetz, M. Dick, M.P. Kalashnikov, A.M. Maksimchuk, Y.A. Mikhailov, A.V. Rode. G.V. Sklizkov, 1. Uschmann and E. Forster, Preprint of the Lebedev Physical Institute, no 143, Moscow, (1989), J. Soy. Las. Res. no 3 (1990) (in press). [4] M.P. Kalashnikov, G. Korn, M.Yu. Mazur, A.M. Maksimchuk, Y.A. Mikhailov, A.V. Rode, G.V. Sklizkov, V.P. Shevelko, E. Forster and I. Uschmann, Preprint of the
165
Volume 77, number 2.3
OPTICS COMMI.INICATIONS
Lebedev Physical Inst, no 70 C1989 ) 48; J. Soy. Las. Res. no 3 (1990) (in press). [ 5] N.G. Basov, Yu.A. Mikhailov and A.V. Rod6. G.V. Sklizkov. Annual Reporl to the Laser Facility Committee 1988 RAI,88-042 (1988).
166
15 June 199(I
[6] A.V. Rode. A.M. Maksimchuk, (i.V. Sklizkov. A. Ridgele), C. Danson. R. Bann, E. Forster. K. Goetz and 1. Uschmann. Measurements of X-ray spectral line wavelengths by using two Bragg reflections, J. X-ray Sci. and Tech. (submitted).