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Optics Express

Optics Express

  • Editor: J. H. Eberly
  • Vol. 9, Iss. 1 — Jul. 2, 2001
  • pp: 2–6
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A spatial light modulator based on fused-silica plates for adaptive feedback control of intense femtosecond laser pulses

Akira Suda, Yu Oishi, Keigo Nagasaka, Pengqian Wang, and Katsumi Midorikawa  »View Author Affiliations


Optics Express, Vol. 9, Issue 1, pp. 2-6 (2001)
http://dx.doi.org/10.1364/OE.9.000002


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Abstract

A novel spatial light modulator (SLM) made of an array of fused-silica plates was developed for the purpose of feedback control for intense femtosecond laser pulses over a wide spectral range. Dispersion compensation for 20-fs pulses from a Ti:sapphire oscillator was successfully demonstrated using the SLM with an adaptive feedback control system. The SLM was also applied to the output pulses from a Ti:sapphire amplifier for compensation of material.

© Optical Society of America

1. Introduction

The spatial light modulator (SLM) is a powerful tool for pulse shaping of femtosecond lasers [1

1. A. M. Weiner, D. E. Leaird, J. S. Patel, and J. R. Wullert, “Programmable femtosecond pulse shaping by use of a multielement liquid-crystal phase modulator,” Opt. Lett. 15, 326–328 (1990). [CrossRef] [PubMed]

4

4. A. M. Weiner, “Femtosecond pulse shaping using spatial light modulators,” Rev. Sci. Instrum. 71, 1929–1960 (2000). [CrossRef]

], dispersion compensation in chirped pulse amplification [5

5. C. Dorrer, F. Salin, F. Verluise, and J. P. Huignard, “Programmable phase control of femtosecond pulses by use of a nonpixelated spatial light modulator,” Opt. Lett. 23, 709–711 (1998). [CrossRef]

8

8. F. Verluise, V. Laude, Z. Cheng, Ch. Spielmann, and P. Tournois, “Amplitude and phase control of ultrashort pulses by use of an acousto-optic programmable dispersive filter: pulse compression and shaping,” Opt. Lett. 25, 575–577 (2000). [CrossRef]

], and feedback control of various physical and chemical phenomena [9

9. C. J. Bardeen, V. V. Yakovlev, K. R. Wilson, S. D. Carpenter, P. M. Weber, and W. S. Warren, “Feedback quantum control of molecular electronic population transfer,” Chem. Phys. Lett. 280151–158 (1997). [CrossRef]

11

11. T. Hornung, R. Meier, D. Zeidler, K. L. Kompa, D. Proch, and M. Motzkus, “Optimal control of one- and two-photon transitions with shaped femtosecond pulses and feedback,” Appl. Phys. B 71, 277–284 (2000). [CrossRef]

]. However, in conventional SLM’s made of liquid crystal there is a possibility of optical damage induced by intense laser pulses, which restricts their application to relatively low intensities. In order to use an SLM after chirped pulse amplification of the Ti:sapphire laser and for pulse compression after spectral broadening by self-phase modulation in a gas-filled hollow fiber [12

12. M. Nisoli, S. De Silvestri, and O. Svelto, “Generation of high energy 10 fs pulses by a new pulse compression technique,” Appl. Phys. Lett. 68, 2793–2795 (1996). [CrossRef]

] a novel SLM which can withstand high-intensity laser pulses is required. For the purpose of controlling high-field physical phenomena such as high-order harmonic generation [13

13. Z. Chang, A. Rundquist, H. Wang, M. M. Murnane, and H. C. Kapteyn, “Generation of coherent soft X rays at 2.7 nm using high harmonics,” Phys Rev. Lett. 79, 2967–2970 (1997). [CrossRef]

,14

14. M. Schnürer, Ch. Spielmann, P. Wobrauschek, C. Streli, N. H. Burnett, C. Kan, K. Ferencz, R. Koppitsch, Z. Cheng, T. Brabec, and F. Krausz, “Coherent 0.5keV X-ray emission from helium driven by a sub-10-fs laser,” Phys. Rev. Lett. 80, 3236–3239 (1998). [CrossRef]

], we have developed an SLM made of a one-dimensional array of fused-silica glass plates. The fused silica has an optical damage threshold in excess of 1 J/cm2 [15

15. A.-C. Tien, S. Backus, H. Kapteyn, M. Murnane, and G. Mourou, “Short-pulse laser damage in transparent materials as a function of pulse duration,” Phys. Rev. Lett. 82, 3883–3886 (1999). [CrossRef]

]. Another application covers the transparency range from vacuum ultraviolet to mid infrared, which enables us to use the fused-silica SLM not only for the fundamental pulses of the Ti:sapphire laser but also for the third harmonic pulses and their amplified pulses in the KrF laser. It is reported that deformable-mirror-based modulators can also solve the above problems [7

7. E. Zeek, K. Maginnis, S. Backus, U. Russek, M. Murnane, G. Mourou, H. Kapteyn, and G. Vdovin, “Pulse compression by use of deformable mirrors,” Opt. Lett. 24, 493–495 (1999). [CrossRef]

].

In this paper, we show the design and construction of a novel SLM made of fused-silica plates, and we demonstrate feedback control of dispersion compensation for femtosecond laser pulses from Ti:sapphire lasers using the SLM with an adaptive feedback control system.

2. Setup of Fused-Silica Spatial Light Modulator

The principle of the fused-silica SLM is quite simple. Figure 1 shows a schematic view of the SLM. For a beam passing through a fused-silica plate with thickness d, the phase delay introduced by the plate is 2πd(n-1)/λ, where n is the refractive index of fused silica at wavelength λ. When the plate is tilted at an angle θ, the optical path length inside the plate increases. Then, the phase shift ϕ(θ) is expressed as

ϕ(θ)=2πdλ(n2sin2θcosθ)
(1)

For example, the phase changes by ±7.5 rad, when the angle of a fused-silica plate with a thickness of 1 mm is changed by ±1 deg at around 10 deg of tilt for a wavelength of 800 nm.

This can readily be accomplished by changing the angle using bimorphous piezo actuators, whose tip displacement is typically 1 mm for an applied voltage of 100 V.

Fig. 1. Schematic view of the fused-silica spatial light modulator.

We constructed an SLM from an array of 48 fused-silica plates with broad-band (600–1000 nm) antireflection coatings. Each plate has dimensions of 2 mm in width, 1 mm in thickness, and 20 mm in length. Since the fused-silica plates were prepared by cutting them from a large piece of fused-silica plate after polishing, the surface figure was better than λ/10 over almost all area. The parallelism was less than 15 mrad, and difference in thickness from piece to piece was within 3 µm. Each plate was set in a holder made of steel, which also held a bearing cylinder inside. The tip of the holder contacts with the bimorphous piezo actuator, which has a width of 1.8 mm. A total of 48 pixels were connected and aligned by using a shaft passing through the center of the bearing cylinders. The size of the gap between neighboring pixels was 0.18 mm, which was set by putting a plain washer between each of them on the shaft. Therefore the total width of the SLM active area was 104 mm. Although the dead space between the pixels introduces pre- and post pulses, those intensities are two orders of magnitude lower than the main pulse intensity in the SLM, which allows to use the processed pulse as it is in many nonlinear applications such as high-order harmonics generation. The change in the beam path after passing through the tilted plate in upward or downward direction can be compensated by reflecting the beam using a folding mirror installed at a position on the Fourier plane, as shown in Fig. 2. Although the plates are positioned a few mm away from the Fourier plane, the SLM performance is not degraded because of the wide Fourier plane and of the long focal length of the 4f optical configuration, which is constructed by a grating with 1200 groove/mm installed just below the folding mirror and a concave mirror with a radius of curvature of 1 m. In this case the spectral resolution is 3.4 nm/pixel. The corresponding separation of pre- and post pulses from the main pulse is approximately 600 fs.

Fig. 2. Experimental setup.

3. Experiments

In a preliminary experiment, we confirmed the amount of phase shift obtained by installing the SLM without the folding mirror in one of the arms of a Mach-Zehnder interferometer. Fringe patterns generated by an expanded HeNe laser beam after passing through the interferometer were observed with a CCD camera. The angle of each fused-silica plate was changed at around a reference point of 10 deg. This resulted in a maximum phase shift of ±5 rad at a wavelength of 633 nm for a maximum applied voltage of ±60 V. We were able to increment the voltage in 0.1 V steps, which corresponded to a phase shift of 5 mrad, though it was hard to confirm this value. However, within the resolution of the instruments, the minimum phase shift observed was 50 mrad. It should be noted that the maximum phase shift observed in the actual setup with the Ti:sapphire laser at 800 nm is ±12 rad because of the double-pass configuration using the folding mirror. The reproducibility of the phase shift was not complete because of hysteresis (~15%) inherent in the piezo actuators. However, this does not matter in a feedback control system, because we do not need to control the absolute position but rather the relative positions of the actuators, as is described later.

Fig. 3. Autocorrelation traces (a) before and (b) after the compensation of material dispersion. (c) SHG peak intensity as a function of the number of iterations.

Since the initial positioning of the 48 actuators can not be completely aligned, the SLM system initially gives a random phase function. In order to compensate for this characteristics, we have carried out a couple of experiments. First, the random phase shift due to the initial condition of the fused-silica plates was compensated by the SLM system itself. Next, the pulse was stretched by inserting a block and the dispersion was compensated by the SLM system again. Figures 3(a) and (b) respectively are the autocorrelation traces before and after compensation for the material dispersion. The pulse was successfully compressed to nearly the Fourier transform limit, i.e., 20 fs assuming a sech2 pulse shape. Figure 3(c) shows the SHG peak intensity as a function of the number of iterations. It took several minutes for convergence to take place. In another series, the random phase shift due to the SLM itself and dispersion caused by the block were compensated simultaneously. The result obtained by this process was also satisfactory. In both cases, the update time per pixel was about 0.9 s, with the limitation being the creeping of the bimorphous piezo actuators. This slow response can be improved by over a factor of more than 10 by means of an impact drive force method using piezo actuators [17

17. T. Morita, R. Yoshida, Y. Okamoto, M. K. Kurosawa, and T. Higuchi, “A smooth impact rotation motor using a multi-layered torsional piezoelectric actuator,” IEEE Trans. Ultrasonics Ferroelectronics and Frequency Control 46, 1439–1445 (1999).

], which is now under development. Another point to be addressed is that the transmittance of the beam was about 60%, including the grating efficiency (82%/reflection). The intrinsic transmission in a double pass through the fused-silica plates was estimated to be around 90%. The corresponding transmission loss of 10% is due to loss at the dead spaces between pixels. Is is noted that the dead spaces reduce the peak intensity of the main pulse by 18%, where the pre- and post pulses contain an additional 8%.

4. Conclusion

In conclusion, we have shown a novel SLM made of fused-silica plates for feedback control of intense femtosecond laser pulses. We have demonstrated the dispersion compensation of femtosecond pulses both from a Ti:sapphire oscillator and from an amplifier using the SLM. We have a plan to improve the SLM by applying an impact drive force method [17

17. T. Morita, R. Yoshida, Y. Okamoto, M. K. Kurosawa, and T. Higuchi, “A smooth impact rotation motor using a multi-layered torsional piezoelectric actuator,” IEEE Trans. Ultrasonics Ferroelectronics and Frequency Control 46, 1439–1445 (1999).

] in order to shorten the update time and to enable calibrated single-step control. The application of the SLM to ultraviolet femtosecond pulses is another area of interest because of the potential to compensate material dispersion including high-order terms, which is 5–10 times stronger than at 800 nm.

Acknowledgements

We would like to thank members of the Division of Research Instruments Development at RIKEN for manufacturing the SLM. We also acknowledge T. Inoshima for his technical assistance.

References and links

1.

A. M. Weiner, D. E. Leaird, J. S. Patel, and J. R. Wullert, “Programmable femtosecond pulse shaping by use of a multielement liquid-crystal phase modulator,” Opt. Lett. 15, 326–328 (1990). [CrossRef] [PubMed]

2.

D. Yelin, D. Meshulach, and Y. Silberberg, “Adaptive femtosecond pulse compression,” Opt. Lett. 22, 1793–1795 (1997). [CrossRef]

3.

T. Baumert, T. Brixner, V. Seyfried, M. Strehle, and G. Gerber, “Femtosecond pulse shaping by an evolutionary algorithm with feedback,” Appl. Phys. B 65, 779–782 (1997). [CrossRef]

4.

A. M. Weiner, “Femtosecond pulse shaping using spatial light modulators,” Rev. Sci. Instrum. 71, 1929–1960 (2000). [CrossRef]

5.

C. Dorrer, F. Salin, F. Verluise, and J. P. Huignard, “Programmable phase control of femtosecond pulses by use of a nonpixelated spatial light modulator,” Opt. Lett. 23, 709–711 (1998). [CrossRef]

6.

A. Efimov, M. D. Moores, N. M. Beach, J. L. Krause, and D. H. Reitze, “Adaptive control of pulse phase in a chirped-pulse amplifier,” Opt. Lett. 23, 1915–1917 (1998). [CrossRef]

7.

E. Zeek, K. Maginnis, S. Backus, U. Russek, M. Murnane, G. Mourou, H. Kapteyn, and G. Vdovin, “Pulse compression by use of deformable mirrors,” Opt. Lett. 24, 493–495 (1999). [CrossRef]

8.

F. Verluise, V. Laude, Z. Cheng, Ch. Spielmann, and P. Tournois, “Amplitude and phase control of ultrashort pulses by use of an acousto-optic programmable dispersive filter: pulse compression and shaping,” Opt. Lett. 25, 575–577 (2000). [CrossRef]

9.

C. J. Bardeen, V. V. Yakovlev, K. R. Wilson, S. D. Carpenter, P. M. Weber, and W. S. Warren, “Feedback quantum control of molecular electronic population transfer,” Chem. Phys. Lett. 280151–158 (1997). [CrossRef]

10.

T. Feurer, “Feedback-controlled optimization of soft-X-ray radiation from femtosecond laser-produced plasmas,” Appl. Phys. B 68, 55–60 (1999). [CrossRef]

11.

T. Hornung, R. Meier, D. Zeidler, K. L. Kompa, D. Proch, and M. Motzkus, “Optimal control of one- and two-photon transitions with shaped femtosecond pulses and feedback,” Appl. Phys. B 71, 277–284 (2000). [CrossRef]

12.

M. Nisoli, S. De Silvestri, and O. Svelto, “Generation of high energy 10 fs pulses by a new pulse compression technique,” Appl. Phys. Lett. 68, 2793–2795 (1996). [CrossRef]

13.

Z. Chang, A. Rundquist, H. Wang, M. M. Murnane, and H. C. Kapteyn, “Generation of coherent soft X rays at 2.7 nm using high harmonics,” Phys Rev. Lett. 79, 2967–2970 (1997). [CrossRef]

14.

M. Schnürer, Ch. Spielmann, P. Wobrauschek, C. Streli, N. H. Burnett, C. Kan, K. Ferencz, R. Koppitsch, Z. Cheng, T. Brabec, and F. Krausz, “Coherent 0.5keV X-ray emission from helium driven by a sub-10-fs laser,” Phys. Rev. Lett. 80, 3236–3239 (1998). [CrossRef]

15.

A.-C. Tien, S. Backus, H. Kapteyn, M. Murnane, and G. Mourou, “Short-pulse laser damage in transparent materials as a function of pulse duration,” Phys. Rev. Lett. 82, 3883–3886 (1999). [CrossRef]

16.

W. H. Press, B. P. Flannery, S. A. Teukolsky, and W. T. Vetterling, Numerical Recipes, 2nd Ed. (Cambridge Univ. Press, Cambridge, 1989), Chap. 10.

17.

T. Morita, R. Yoshida, Y. Okamoto, M. K. Kurosawa, and T. Higuchi, “A smooth impact rotation motor using a multi-layered torsional piezoelectric actuator,” IEEE Trans. Ultrasonics Ferroelectronics and Frequency Control 46, 1439–1445 (1999).

OCIS Codes
(230.6120) Optical devices : Spatial light modulators
(320.5520) Ultrafast optics : Pulse compression

ToC Category:
Research Papers

History
Original Manuscript: May 11, 2001
Published: July 2, 2001

Citation
Akira Suda, Yu Oishi, Keigo Nagasaka, Pengqian Wang, and Katsumi Midorikawa, "A spatial light modulator based on fused-silica plates for adaptive feedback control of intense femtosecond laser pulses," Opt. Express 9, 2-6 (2001)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-9-1-2


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References

  1. A. M. Weiner, D. E. Leaird, J. S. Patel, and J. R. Wullert, "Programmable femtosecond pulse shaping by use of a multielement liquid-crystal phase modulator," Opt. Lett. 15, 326-328 (1990). [CrossRef] [PubMed]
  2. D. Yelin, D. Meshulach, and Y. Silberberg, "Adaptive femtosecond pulse compression," Opt. Lett. 22, 1793-1795 (1997). [CrossRef]
  3. T. Baumert, T. Brixner, V. Seyfried, M. Strehle, and G. Gerber, "Femtosecond pulse shaping by an evolutionary algorithm with feedback," Appl. Phys. B 65, 779-782 (1997). [CrossRef]
  4. A. M. Weiner, "Femtosecond pulse shaping using spatial light modulators," Rev. Sci. Instrum. 71, 1929-1960 (2000). [CrossRef]
  5. C. Dorrer, F. Salin, F. Verluise, and J. P. Huignard, "Programmable phase control of femtosecond pulses by use of a nonpixelated spatial light modulator," Opt. Lett. 23, 709-711 (1998). [CrossRef]
  6. A. Efimov, M. D. Moores, N. M. Beach, J. L. Krause, and D. H. Reitze, "Adaptive control of pulse phase in a chirped-pulse amplifier," Opt. Lett. 23, 1915-1917 (1998). [CrossRef]
  7. E. Zeek, K. Maginnis, S. Backus, U. Russek, M. Murnane, G. Mourou, H. Kapteyn, and G. Vdovin, "Pulse compression by use of deformable mirrors," Opt. Lett. 24, 493-495 (1999). [CrossRef]
  8. F. Verluise, V. Laude, Z. Cheng, Ch. Spielmann, and P. Tournois, "Amplitude and phase control of ultrashort pulses by use of an acousto-optic programmable dispersive filter: pulse compression and shaping," Opt. Lett. 25, 575-577 (2000). [CrossRef]
  9. C. J. Bardeen, V. V. Yakovlev, K. R. Wilson, S. D. Carpenter, P. M. Weber, and W. S. Warren, "Feedback quantum control of molecular electronic population transfer," Chem. Phys. Lett. 280 151-158 (1997). [CrossRef]
  10. T. Feurer, "Feedback-controlled optimization of soft-X-ray radiation from femtosecond laser-produced plasmas," Appl. Phys. B 68, 55-60 (1999). [CrossRef]
  11. T. Hornung, R. Meier, D. Zeidler, K. L. Kompa, D. Proch, and M. Motzkus, "Optimal control of one- and two-photon transitions with shaped femtosecond pulses and feedback," Appl. Phys. B 71, 277-284 (2000). [CrossRef]
  12. M. Nisoli, S. De Silvestri, and O. Svelto, "Generation of high energy 10 fs pulses by a new pulse compression technique," Appl. Phys. Lett. 68, 2793-2795 (1996). [CrossRef]
  13. Z. Chang, A. Rundquist, H. Wang, M. M. Murnane, and H. C. Kapteyn, "Generation of coherent soft X rays at 2.7 nm using high harmonics," Phys Rev. Lett. 79, 2967-2970 (1997). [CrossRef]
  14. M. Schn.rer, Ch. Spielmann, P. Wobrauschek, C. Streli, N. H. Burnett, C. Kan, K. Ferencz, R. Koppitsch, Z. Cheng, T. Brabec, and F. Krausz, "Coherent 0.5keV X-ray emission from helium driven by a sub-10-fs laser," Phys. Rev. Lett. 80, 3236-3239 (1998). [CrossRef]
  15. A.-C. Tien, S. Backus, H. Kapteyn, M. Murnane, and G. Mourou, "Short-pulse laser damage in transparent materials as a function of pulse duration," Phys. Rev. Lett. 82, 3883-3886 (1999). [CrossRef]
  16. W. H. Press, B. P. Flannery, S. A. Teukolsky, W. T. Vetterling, Numerical Recipes, 2nd Ed. (Cambridge Univ. Press, Cambridge, 1989), Chap. 10.
  17. T. Morita, R. Yoshida, Y. Okamoto, M. K. Kurosawa, and T. Higuchi, "A smooth impact rotation motor using a multi-layered torsional piezoelectric actuator," IEEE Trans. Ultrasonics Ferroelectronics and Frequency Control 46, 1439-1445 (1999).

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