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Optics Letters

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  • Editor: Alan E. Willner
  • Vol. 37, Iss. 15 — Aug. 1, 2012
  • pp: 3033–3035
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Investigating the interaction of x-ray free electron laser radiation with grating structure

Jérôme Gaudin, Cigdem Ozkan, Jaromír Chalupský, Saša Bajt, Tomáš Burian, Ludĕk Vyšín, Nicola Coppola, Shafagh Dastjani Farahani, Henry N. Chapman, Germano Galasso, Vĕra Hájková, Marion Harmand, Libor Juha, Marek Jurek, Rolf A. Loch, Stefan Möller, Mitsuru Nagasono, Michael Störmer, Harald Sinn, Karel Saksl, Ryszard Sobierajski, Joachim Schulz, Pavol Sovak, Sven Toleikis, Kai Tiedtke, Thomas Tschentscher, and Jacek Krzywinski  »View Author Affiliations


Optics Letters, Vol. 37, Issue 15, pp. 3033-3035 (2012)
http://dx.doi.org/10.1364/OL.37.003033


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Abstract

The interaction of free electron laser pulses with grating structure is investigated using 4.6 ± 0.1 nm radiation at the FLASH facility in Hamburg. For fluences above 63.7 ± 8.7 mJ / cm 2 , the interaction triggers a damage process starting at the edge of the grating structure as evidenced by optical and atomic force microscopy. Simulations based on solution of the Helmholtz equation demonstrate an enhancement of the electric field intensity distribution at the edge of the grating structure. A procedure is finally deduced to evaluate damage threshold.

© 2012 Optical Society of America

The experiment was performed at the FLASH facility in Hamburg [2

2. W. Ackermann, G. Asova, V. Ayvazyan, A. Azima, N. Baboi, J. Bähr, V. Balandin, B. Beutner, A. Brandt, A. Bolzmann, R. Brinkmann, O. I. Brovko, M. Castellano, P. Castro, L. Catani, E. Chiadroni, S. Choroba, A. Cianchi, T. Costello, D. Cubaynes, J. Dardis, W. Decking, H. Delsim-Hashemi, A. Delserieys, G. Di Pirro, M. Dohlus, S. Düsterer, A. Eckhardt, T. Edwards, B. Faatz, J. Feldhaus, K. Flöttmann, J. Frisch, L. Fröhlich, T. Garvey, U. Gensch, Ch. Gerth, M. Görler, N. Golubeva, H.-J. Grabosch, M. Grecki, O. Grimm, K. Hacker, U. Hahn, J. H. Han, K. Honkavaara, T. Hott, M. Hüning, Y. Ivanisenko, E. Jaeschke, W. Jalmuzna, T. Jezynski, R. Kammering, V. Katalev, K. Kavanagh, E. T. Kennedy, S. Khodyachykh, K. Klose, V. Kocharyan, M. Körfer, M. Kollewe, W. Koprek, S. Korepanov, D. Kostin, M. Krassilnikov, G. Kube, M. Kuhlmann, C. L. S. Lewis, L. Lilje, T. Limberg, D. Lipka, F. Löhl, H. Luna, M. Luong, M. Martins, M. Meyer, P. Michelato, V. Miltchev, W. D. Möller, L. Monaco, W. F. O. Müller, O. Napieralski, O. Napoly, P. Nicolosi, D. Nölle, T. Nuñez, A. Oppelt, C. Pagani, R. Paparella, N. Pchalek, J. Pedregosa-Gutierrez, B. Petersen, B. Petrosyan, G. Petrosyan, L. Petrosyan, J. Pflüger, E. Plönjes, L. Poletto, K. Pozniak, E. Prat, D. Proch, P. Pucyk, P. Radcliffe, H. Redlin, K. Rehlich, M. Richter, M. Roehrs, J. Roensch, R. Romaniuk, M. Ross, J. Rossbach, V. Rybnikov, M. Sachwitz, E. L. Saldin, W. Sandner, H. Schlarb, B. Schmidt, M. Schmitz, P. Schmüser, R. Schneider, A. Schneidmiller, S. Schnepp, S. Schreiber, M. Seidel, D. Sertore, V. Shabunov, C. Simon, S. Simrock, E. Sombrowski, A. Sorokin, P. Spanknebel, R. Spesyvtsev, L. Staykov, B. Steffen, F. Stephan, F. Stulle, H. Thom, K. Tiedtke, M. Tischer, S. Toleikis, R. Treusch, D. Trines, I. Tsakov, E. Vogel, T. Weiland, H. Weise, M. Wellhöfer, M. Wendt, I. Will, A. Winter, K. Wittenburg, W. Wurth, P. Yeates, V. Yurkov, I. Zagorodnov, and K. Zapfe, Nat. Photon. 1, 336 (2007). [CrossRef]

]. The sample was placed, under vacuum, in the focus of a 2 m focal length mirror. The pulse duration was in the 80–150 fs range, and the radiation wavelength was measured to be 4.6±0.1nm. This error bar corresponds to the uncertainty on the absolute value of the wavelength and not to the pulse to pulse jittering, which has also be measured and found to be negligible (1e3nm). The beam was impinging the sample at the grazing angle α=2°±0.1, following a procedure described in [3

3. J. Chalupský, V. Hájková, V. Altapova, T. Burian, A. J. Gleeson, L. Juha, M. Jurek, H. Sinn, M. Störmer, R. Sobierajski, K. Tiedtke, S. Toleikis, T. Tschentscher, L. Vyšín, H. Wabnitz, and J. Gaudin, Appl. Phys. Lett. 95, 031111 (2009). [CrossRef]

]. The 200l/mm (5 μm periods) grating sample was produced by ion etching of a 1 mm thick Si wafer, with a duty ratio of 0.4. The groove depth was measured to be 13.5 nm. These parameters reproduce a real grating currently used in the Soft X-Ray beamline at the Linac Coherent Light Source (LCLS) [4

4. P. Heimann, O. Krupin, W. F. Schlotter, J. Turner, J. Krzywinski, F. Sorgenfrei, M. Messerschmidt, D. Bernstein, J. Chalupský, V. Hájková, S. Hau-Riege, M. Holmes, L. Juha, N. Kelez, J. Lüning, D. Nordlund, M. F. Perea, A. Scherz, R. Soufli, W. Wurth, and M. Rowen, Rev. Sci. Instrum. 82, 093104 (2011). [CrossRef]

]. The etched wafer was then coated with 45 nm of amorphous carbon (a-C), which is a typical coating for XFEL optics. Atomic force microscopy (AFM) measurement confirms that the coating exactly reproduces the ion etched profile. The grating sample, as well as a mirrorlike flat sample also made of 45 nm thick a-C coated on Si substrate, was exposed to single pulses with varying pulse energy. For each pulse, the pulse energy was measured with a gas detector monitor. The pulse energy monitor was located upstream from all optical components; e.g., the beamline transmission should be evaluated so the real pulse energy impinging on the sample can be known. As already stated, the radiation’s wavelength was known with an accuracy of ±0.1nm. The beamline consists of two plane Ni coated mirrors and three (2plane+1ellipsoidal) a-C coated mirrors (grazing incidence at 2 and 3 deg, respectively). In this wavelength domain, the beamline transmission is evaluated, taking into account the mirrors setting, to range from 0.20 (at 4.50 nm) to 0.46 (at 4.70 nm). This large variation is primarily due to the two upstream carbon coated mirrors present in the beamline, which are very sensitive around the carbon K-edge (at 4.37 nm). In this analysis, we assume therefore a wavelength of 4.60 nm corresponding to a beamline transmission of 0.39.

The exposed samples were analyzed ex situ by optical differential interference contrast (DIC) microscopy, which is sensitive to variations of optical refractive index, hence to any phase change, evidenced by a change of color. For each irradiated sample region, the area showing a color change (encircled areas shown in Fig. 1) in the microscope image was measured. For both the flat and the grating sample, the energy damage threshold (Eth) was determined by plotting the damaged area versus pulse energy, as shown in Fig. 2. Due to the non-Gaussian shape of the beam, only the very first data points should be fitted, as described in [5

5. J. Chalupský, J. Krzywinski, L. Juha, V. Hájková, J. Cihelka, T. Burian, L. Vyšín, J. Gaudin, A. Gleeson, M. Jurek, A. R. Khorsand, D. Klinger, H. Wabnitz, R. Sobierajski, M. Störmer, K. Tiedtke, and S. Toleikis, Opt. Express 18, 27836 (2010). [CrossRef]

]. A line fit through the point gives a threshold for grating EthG=0.40±0.04μJ and EthM=1.17±0.16μJ for the flat sample. The error bars correspond to the confidence on the fit, at the 4.60 nm wavelength. We then calculate the ratio EthM/EthG=2.92±0.69, which will be used for comparison with the model later, and is independent of the beamline transmission value.

Fig. 1. Top: schematic of the interaction of the experiment. Below: DIC microscopy (left) and AFM (right) measurements for three different fluences 356 (A), 806 (B), and 1115mJ/cm2 (C).
Fig. 2. Damaged area on flat mirrorlike sample (red dots, right vertical scale) and grating (black square, left vertical scale).

The damage fluence threshold (Fth) is retrieved from the values of Eth and by making the following assumption. The beam profile was carefully characterized using imprints in the PMMA sample and following the procedure described in [5

5. J. Chalupský, J. Krzywinski, L. Juha, V. Hájková, J. Cihelka, T. Burian, L. Vyšín, J. Gaudin, A. Gleeson, M. Jurek, A. R. Khorsand, D. Klinger, H. Wabnitz, R. Sobierajski, M. Störmer, K. Tiedtke, and S. Toleikis, Opt. Express 18, 27836 (2010). [CrossRef]

]. The effective area is found to be Aeff=22±2μm2. We assumed that the beam footprint in case of grazing incidence is equal to the projected area, e.g., Aeff/sin(2). We obtained FthG=63.7±8.7mJ/cm2 for the grating and FthM=186.6±29.9mJ/cm2 for the flat sample.

Figure 1A, obtained with DIC microscopy, shows the onset of the damage on the edge of the grating structure. The AFM measurements confirm this observation, and show the extension of the damage first on the top of the groove as the fluence is increasing. The damage in the bottom part of the grating structure happens at higher fluence, as can be seen in Fig. 1B. At the highest fluence values (see Fig. 1C), black dots become visible due to the complete removal of the a-C coating and melting of the Si substrate.

To gain deeper insight in the understanding of the beam–grating interaction, an accurate model has to be used. As stated in the introduction, the electric field distribution at the surface of a grating can be highly nonhomogeneous, especially while dealing with a coherent laser beam. We simulated the deposited energy distribution in the grating by solving the Helmholtz equation in a paraxial approximation. Assuming that the refractive index of the medium is nearly equal to 1 (which is true for the photon energy considered here), then the propagation of the scalar field ψ can be expressed as
Ψ(r^,z^)z^=i2·2Ψ(r^,z^)r^2+δε(r^,z^)·Ψ(r^,z^),r^=rk,r2=x2+y2,z^=zk,k=2·π/λ.
(1)

Fig. 3. X-ray intensity distribution |ψ(r,z)|2 close to the grating surface. The beam comes from the left. Inset: energy distribution absorbed in the grating. Both color scales are normalized intensity to the impinging beam.

In conclusion, we have investigated the interaction of 4.60 nm XFEL radiation with grating structure. An accurate description based on the Helmholtz equation shows that the specific field distribution at the surface leads to an enhancement of the absorbed energy at the edge of the laminar grating structure. The model provides a good qualitative and quantitative description of the experimental results. From a practical point of view, when designing a soft x-ray monochromator for an XFEL beamline, it is crucial to consider the fluence damage threshold values. We propose to first extrapolate FthM(α) for a flat mirrorlike surface using published data (for example, [3

3. J. Chalupský, V. Hájková, V. Altapova, T. Burian, A. J. Gleeson, L. Juha, M. Jurek, H. Sinn, M. Störmer, R. Sobierajski, K. Tiedtke, S. Toleikis, T. Tschentscher, L. Vyšín, H. Wabnitz, and J. Gaudin, Appl. Phys. Lett. 95, 031111 (2009). [CrossRef]

]). Next, simulations should be performed taking into account the exact geometry of the grating, to obtain γ. Finally the damage threshold on grating is deduced from the relation FthG(α)=FthM(α)/γ.

This work was financially supported by the Czech Science Foundation (projects P108/11/1312, P205/11/0571, and P208/10/2302) and the Czech Ministry of Education (projects CZ.1.05/1.1.00/483/02.0061, CZ.1.07/ 2.3.00/483/20.0087, LA08024, and ME10046).

References

1.

S. Hocquet, J. Neauport, and N. Bonod, Appl. Phys. Lett. 99, 061101 (2011). [CrossRef]

2.

W. Ackermann, G. Asova, V. Ayvazyan, A. Azima, N. Baboi, J. Bähr, V. Balandin, B. Beutner, A. Brandt, A. Bolzmann, R. Brinkmann, O. I. Brovko, M. Castellano, P. Castro, L. Catani, E. Chiadroni, S. Choroba, A. Cianchi, T. Costello, D. Cubaynes, J. Dardis, W. Decking, H. Delsim-Hashemi, A. Delserieys, G. Di Pirro, M. Dohlus, S. Düsterer, A. Eckhardt, T. Edwards, B. Faatz, J. Feldhaus, K. Flöttmann, J. Frisch, L. Fröhlich, T. Garvey, U. Gensch, Ch. Gerth, M. Görler, N. Golubeva, H.-J. Grabosch, M. Grecki, O. Grimm, K. Hacker, U. Hahn, J. H. Han, K. Honkavaara, T. Hott, M. Hüning, Y. Ivanisenko, E. Jaeschke, W. Jalmuzna, T. Jezynski, R. Kammering, V. Katalev, K. Kavanagh, E. T. Kennedy, S. Khodyachykh, K. Klose, V. Kocharyan, M. Körfer, M. Kollewe, W. Koprek, S. Korepanov, D. Kostin, M. Krassilnikov, G. Kube, M. Kuhlmann, C. L. S. Lewis, L. Lilje, T. Limberg, D. Lipka, F. Löhl, H. Luna, M. Luong, M. Martins, M. Meyer, P. Michelato, V. Miltchev, W. D. Möller, L. Monaco, W. F. O. Müller, O. Napieralski, O. Napoly, P. Nicolosi, D. Nölle, T. Nuñez, A. Oppelt, C. Pagani, R. Paparella, N. Pchalek, J. Pedregosa-Gutierrez, B. Petersen, B. Petrosyan, G. Petrosyan, L. Petrosyan, J. Pflüger, E. Plönjes, L. Poletto, K. Pozniak, E. Prat, D. Proch, P. Pucyk, P. Radcliffe, H. Redlin, K. Rehlich, M. Richter, M. Roehrs, J. Roensch, R. Romaniuk, M. Ross, J. Rossbach, V. Rybnikov, M. Sachwitz, E. L. Saldin, W. Sandner, H. Schlarb, B. Schmidt, M. Schmitz, P. Schmüser, R. Schneider, A. Schneidmiller, S. Schnepp, S. Schreiber, M. Seidel, D. Sertore, V. Shabunov, C. Simon, S. Simrock, E. Sombrowski, A. Sorokin, P. Spanknebel, R. Spesyvtsev, L. Staykov, B. Steffen, F. Stephan, F. Stulle, H. Thom, K. Tiedtke, M. Tischer, S. Toleikis, R. Treusch, D. Trines, I. Tsakov, E. Vogel, T. Weiland, H. Weise, M. Wellhöfer, M. Wendt, I. Will, A. Winter, K. Wittenburg, W. Wurth, P. Yeates, V. Yurkov, I. Zagorodnov, and K. Zapfe, Nat. Photon. 1, 336 (2007). [CrossRef]

3.

J. Chalupský, V. Hájková, V. Altapova, T. Burian, A. J. Gleeson, L. Juha, M. Jurek, H. Sinn, M. Störmer, R. Sobierajski, K. Tiedtke, S. Toleikis, T. Tschentscher, L. Vyšín, H. Wabnitz, and J. Gaudin, Appl. Phys. Lett. 95, 031111 (2009). [CrossRef]

4.

P. Heimann, O. Krupin, W. F. Schlotter, J. Turner, J. Krzywinski, F. Sorgenfrei, M. Messerschmidt, D. Bernstein, J. Chalupský, V. Hájková, S. Hau-Riege, M. Holmes, L. Juha, N. Kelez, J. Lüning, D. Nordlund, M. F. Perea, A. Scherz, R. Soufli, W. Wurth, and M. Rowen, Rev. Sci. Instrum. 82, 093104 (2011). [CrossRef]

5.

J. Chalupský, J. Krzywinski, L. Juha, V. Hájková, J. Cihelka, T. Burian, L. Vyšín, J. Gaudin, A. Gleeson, M. Jurek, A. R. Khorsand, D. Klinger, H. Wabnitz, R. Sobierajski, M. Störmer, K. Tiedtke, and S. Toleikis, Opt. Express 18, 27836 (2010). [CrossRef]

6.

O. K. Ersoy, Diffraction, Fourier Optics and Imaging(Wiley, 2007).

7.

H. J. W. M. Hoekstra, Opt. Quantum Electron. 29, 157 (1997). [CrossRef]

8.

B. L. Henke, E. M. Gullikson, and J. C. Davis, At. Data Nucl. Data Tables 54, 181 (1993). [CrossRef]

OCIS Codes
(050.0050) Diffraction and gratings : Diffraction and gratings
(140.2600) Lasers and laser optics : Free-electron lasers (FELs)
(340.7480) X-ray optics : X-rays, soft x-rays, extreme ultraviolet (EUV)
(350.1820) Other areas of optics : Damage

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: April 23, 2012
Revised Manuscript: May 31, 2012
Manuscript Accepted: May 31, 2012
Published: July 16, 2012

Citation
Jérôme Gaudin, Cigdem Ozkan, Jaromír Chalupský, Saša Bajt, Tomáš Burian, Ludĕk Vyšín, Nicola Coppola, Shafagh Dastjani Farahani, Henry N. Chapman, Germano Galasso, Vĕra Hájková, Marion Harmand, Libor Juha, Marek Jurek, Rolf A. Loch, Stefan Möller, Mitsuru Nagasono, Michael Störmer, Harald Sinn, Karel Saksl, Ryszard Sobierajski, Joachim Schulz, Pavol Sovak, Sven Toleikis, Kai Tiedtke, Thomas Tschentscher, and Jacek Krzywinski, "Investigating the interaction of x-ray free electron laser radiation with grating structure," Opt. Lett. 37, 3033-3035 (2012)
http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-37-15-3033


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References

  1. S. Hocquet, J. Neauport, N. Bonod, Appl. Phys. Lett. 99, 061101 (2011). [CrossRef]
  2. W. Ackermann, G. Asova, V. Ayvazyan, A. Azima, N. Baboi, J. Bähr, V. Balandin, B. Beutner, A. Brandt, A. Bolzmann, R. Brinkmann, O. I. Brovko, M. Castellano, P. Castro, L. Catani, E. Chiadroni, S. Choroba, A. Cianchi, T. Costello, D. Cubaynes, J. Dardis, W. Decking, H. Delsim-Hashemi, A. Delserieys, G. Di Pirro, M. Dohlus, S. Düsterer, A. Eckhardt, T. Edwards, B. Faatz, J. Feldhaus, K. Flöttmann, J. Frisch, L. Fröhlich, T. Garvey, U. Gensch, Ch. Gerth, M. Görler, N. Golubeva, H.-J. Grabosch, M. Grecki, O. Grimm, K. Hacker, U. Hahn, J. H. Han, K. Honkavaara, T. Hott, M. Hüning, Y. Ivanisenko, E. Jaeschke, W. Jalmuzna, T. Jezynski, R. Kammering, V. Katalev, K. Kavanagh, E. T. Kennedy, S. Khodyachykh, K. Klose, V. Kocharyan, M. Körfer, M. Kollewe, W. Koprek, S. Korepanov, D. Kostin, M. Krassilnikov, G. Kube, M. Kuhlmann, C. L. S. Lewis, L. Lilje, T. Limberg, D. Lipka, F. Löhl, H. Luna, M. Luong, M. Martins, M. Meyer, P. Michelato, V. Miltchev, W. D. Möller, L. Monaco, W. F. O. Müller, O. Napieralski, O. Napoly, P. Nicolosi, D. Nölle, T. Nuñez, A. Oppelt, C. Pagani, R. Paparella, N. Pchalek, J. Pedregosa-Gutierrez, B. Petersen, B. Petrosyan, G. Petrosyan, L. Petrosyan, J. Pflüger, E. Plönjes, L. Poletto, K. Pozniak, E. Prat, D. Proch, P. Pucyk, P. Radcliffe, H. Redlin, K. Rehlich, M. Richter, M. Roehrs, J. Roensch, R. Romaniuk, M. Ross, J. Rossbach, V. Rybnikov, M. Sachwitz, E. L. Saldin, W. Sandner, H. Schlarb, B. Schmidt, M. Schmitz, P. Schmüser, R. Schneider, A. Schneidmiller, S. Schnepp, S. Schreiber, M. Seidel, D. Sertore, V. Shabunov, C. Simon, S. Simrock, E. Sombrowski, A. Sorokin, P. Spanknebel, R. Spesyvtsev, L. Staykov, B. Steffen, F. Stephan, F. Stulle, H. Thom, K. Tiedtke, M. Tischer, S. Toleikis, R. Treusch, D. Trines, I. Tsakov, E. Vogel, T. Weiland, H. Weise, M. Wellhöfer, M. Wendt, I. Will, A. Winter, K. Wittenburg, W. Wurth, P. Yeates, V. Yurkov, I. Zagorodnov, K. Zapfe, Nat. Photon. 1, 336 (2007). [CrossRef]
  3. J. Chalupský, V. Hájková, V. Altapova, T. Burian, A. J. Gleeson, L. Juha, M. Jurek, H. Sinn, M. Störmer, R. Sobierajski, K. Tiedtke, S. Toleikis, T. Tschentscher, L. Vyšín, H. Wabnitz, J. Gaudin, Appl. Phys. Lett. 95, 031111 (2009). [CrossRef]
  4. P. Heimann, O. Krupin, W. F. Schlotter, J. Turner, J. Krzywinski, F. Sorgenfrei, M. Messerschmidt, D. Bernstein, J. Chalupský, V. Hájková, S. Hau-Riege, M. Holmes, L. Juha, N. Kelez, J. Lüning, D. Nordlund, M. F. Perea, A. Scherz, R. Soufli, W. Wurth, M. Rowen, Rev. Sci. Instrum. 82, 093104 (2011). [CrossRef]
  5. J. Chalupský, J. Krzywinski, L. Juha, V. Hájková, J. Cihelka, T. Burian, L. Vyšín, J. Gaudin, A. Gleeson, M. Jurek, A. R. Khorsand, D. Klinger, H. Wabnitz, R. Sobierajski, M. Störmer, K. Tiedtke, S. Toleikis, Opt. Express 18, 27836 (2010). [CrossRef]
  6. O. K. Ersoy, Diffraction, Fourier Optics and Imaging(Wiley, 2007).
  7. H. J. W. M. Hoekstra, Opt. Quantum Electron. 29, 157 (1997). [CrossRef]
  8. B. L. Henke, E. M. Gullikson, J. C. Davis, At. Data Nucl. Data Tables 54, 181 (1993). [CrossRef]

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