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  • Editor: Alan E. Willner
  • Vol. 37, Iss. 21 — Nov. 1, 2012
  • pp: 4407–4409
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Sub 25 fs pulses from solid-core nonlinear compression stage at 250 W of average power

Christoph Jocher, Tino Eidam, Steffen Hädrich, Jens Limpert, and Andreas Tünnermann  »View Author Affiliations


Optics Letters, Vol. 37, Issue 21, pp. 4407-4409 (2012)
http://dx.doi.org/10.1364/OL.37.004407


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Abstract

We report on a highpower femtosecond fiber chirped-pulse amplification system with an excellent beam quality ( M 2 = 1.2 ) operating at 250 MHz repetition rate. We demonstrate nonlinear compression in a solid-core photonic crystal fiber at unprecedented average power levels. By exploiting self-phase modulation with subsequent chirped-mirror compression we achieve pulse shortening by more than one order of magnitude to 23 fs pulses. The use of circular polarization allows higher than usual peak powers in the broadening fiber resulting in compressed 0.9 μJ pulse energy and a peak power of 34 MW at 250 W of average power ( M 2 = 1.3 ). This system is well suited for driving cavity-enhanced high-repetition rate high-harmonic generation.

© 2012 Optical Society of America

Here, we report on a femtosecond fiber chirped-pulse amplification (CPA) system operating at a 250 MHz repetition rate (footprint 2.2m×1.4m) with a solidcore nonlinear pulse-shortening technique achieving an unprecedented combination of repetition rate, average, and peak power, which makes this system suitable for both direct HHG and cavity enhancement.

The principle setup is illustrated in Fig. 1. A 250 MHz modelocked fiber oscillator (MenloSystems orange) with a pre-amplification unit and an isolator is integrated for seeding the highpower laser system. 18 ps pulses are emitted from the seed source with a broadband spectrum ranging from 1005 to 1055 nm and with an average output power of 2.5 W. Due to the dimensions of the optical components inside the grating stretcher (polarization depending low loss grating, 1740lines/mm) the bandwidth of the spectrum is 18 nm centered at 1040 nm. Consequently, the average power is reduced to 900 mW (pulse duration around 870 ps). After the stretcher the pulses are amplified to more than 50 W of average power in a preamplifier consisting of a 1.5 m long bendable photonic crystal fiber (PCF) with a cladding/core diameter of 170/40μm. An isolator between the pre- and main-amplifier protects the preamplifier against back reflections. In the main amplifier a PCF with a cladding/core diameter of 500/35μm is employed. The output power from this 12 m long fiber is limited to 480 W (B-Integral below 3 rad) due to the occurrence of mode instabilities at higher power levels [15

15. T. Eidam, C. Wirth, C. Jauregui, F. Stutzki, F. Jansen, H. Otto, O. Schmidt, T. Schreiber, J. Limpert, and A. Tünnermann, Opt. Express 19, 13218 (2011). [CrossRef]

]. Therefore, the gain factor of around 10 will not give rise to gain narrowing or spectral shifts. After the main-amplifier a polarization-dependent grating compressor, with the same gratings as inside the stretcher, is used to compress the pulses. The M2 after the compressor is measured to be smaller than 1.2 with a near-field pinhole reducing the residual cladding light (5%, which shows that only a small fraction of the output power is inside the cladding). Consequently, the corrected compressed output power has an excellent beam quality, which is 360 W. Even without the near-field pinhole hardly any cladding light can be seen in the near-field beam profile, which is shown in Fig. 2(a). By considering 5% cladding light the output power versus the pump power of the laser system is illustrated in Fig. 2(b). Figure 3(a) shows the spectrum after the compressor. The Fourier-limited pulse duration is 230 fs (autocorrelation width of 320 fs, deconvolution factor 0.72). The measured autocorrelation width of 370 fs of the compressed pulses [Fig. 3(b)] is longer, which is due to residual material dispersion in the amplifiers and aberrations/mismatches in the stretcher-compressor unit. Assuming that the de-convolution factor is 0.72 from the Fourier-limited pulse, then the measured pulse duration is 265 fs.

Fig. 1. Schematic setup of the fiber CPA with solid-core nonlinear compression stage.
Fig. 2. (a) Near-field beam profile without pinhole and (b) compressed output power of the laser system considering the near-field pinhole.
Fig. 3. (a) Spectrum measured after the compressor (b) measured autocorrelation trace.

As mentioned above, fibers are very suitable for observation of nonlinear effects. In our case we use a small piece of photonic crystal fiber based on the largepitch concept well known for its fundamental mode operations at large modefield diameters [16

16. F. Jansen, F. Stutzki, H.-J. Otto, M. Baumgartl, C. Jauregui, J. Limpert, and A. Tünnermann, Opt. Express 18, 26834 (2010). [CrossRef]

]. The mode-field diameter of the large-pitch fiber (LPF) used for the fundamental mode is 59 μm. The peak power, fiber length, and mode-field diameter determines the SPM broadened spectrum. Calculations based on the laser-system parameters show that the specified bandwidth of the chirped mirrors fit together with an obtained SPM spectrum using a 9 cm long flat, cleaved piece of the LPF. As noted above, self-focusing sets a limit for the peak power of the input pulses. The estimated peak power from the laser system is around 4 MW considering the pulse shape (see autocorrelation trace and simulations below). In order to operate below the critical power for self-focusing and to avoid damage to the nonlinear fiber we increased the selffocusing threshold to about 6 MW by converting the linear polarization into circular polarization using a quarter-wave plate (QWP) [14

14. A. Smith, B. Do, G. Hadley, and R. Farrow, IEEE J. Sel. Topics Quantum Electron. 15, 153 (2009). [CrossRef]

]. After propagation the polarization is converted back to linear by another QWP. Additionally, a half-wave plate (HWP) adapts the linearly polarized beam to the s-polarization of the chirped mirror compressor. Behind this HWP we reach a degree of linear polarization of over 95%. In order to measure the power inside the core of the nonlinear fiber we employed a near-field pinhole. The core-power content is measured to be 79%. With the use of the near-field

pinhole the M2 (after the LPF) is measured to be 1.3 (four-sigma), which is an excellent value for fibers with such large mode-field diameters. The SPM-broadened spectrum [Fig. 4(a)] allows for Fourier-limited pulse durations of 18.5 fs. In the logarithmic scale the measured spectrum contains a negligible amount of spectral components in the range of 1150 nm, which could be generated by other nonlinear effects such as Raman scattering or four-wave mixing. In order to compress the pulses we compensate the second-order dispersion with 24 bounces in a chirped-mirror compressor. Each mirror is specified with 100fs2 per bounce resulting in 2400fs2 for the complete compression stage. We measure an autocorrelation width of 31 fs for the compressed pulses pulses with a small pedestal due to not perfectly compensated dispersion [Fig. 4(b)]. The average power behind the mirror compressor is measured to be more than 250 W, after a concave lens, in order to cut the residual cladding light at the aperture of the power meter (Fig. 5).

Fig. 4. Pulse-shortening by nonlinear compression. (a) Measurement and calculation of SPM-broadened spectrum after 9 cm of nonlinear fiber. A broader-band spectral scan revealed no extra structure outside the wavelength range shown here. (b) Measured autocorrelation trace of the compressed pulses in comparison with the simulation.
Fig. 5. Output power versus pump power of the nonlinear compression stage.

In order to estimate the main pulse energy and the pulse peak power we compare our measurement results with simulations. For that purpose we numerically solve the nonlinear Schrödinger equation including nonlinear effects such as SPM, self-steepening, and the Raman effect [17

17. fiberdesk www.fiberdesk.com.

]. First, a post pulse with 12% of pulse energy is added to the main pulse (Fourier transform limit of the fiber CPA spectrum from Fig. 3(a)). This simple assumption has been made to explain the occurrence of the pre/post pulses in the autocorrelation traces [Figs. 3(b) and 4(b)]. In the second step we calculate the propagation of these laser pulses along the 9 cm long LPF by considering the power content inside the core and the surface reflection at the end facet of the fiber. The calculated spectrum is compared to the measured one in Fig. 4(a) showing a good agreement. In a last step we compensate the second order dispersion with 2340fs2 by compressing the pulse to 23 fs. The calculated autocorrelation trace duration (31 fs) fits to our measurement [Fig. 4(b)]. After the chirped-mirror compressor we estimate from simulation the peak power to 34 MW and the main pulse energy to 0.9 μJ.

In conclusion, we demonstrated a high-power fiber CPA system operating at 250 MHz repetition rate (360 W of average power) and providing 265 fs pulses with an M2 of 1.2. Subsequent nonlinear compression in a short piece of solid core photonic-crystal fiber (LPF) reduces the pulse duration by more than one order of magnitude to 23 fs. At the same time we achieve an average power of 250 W and an excellent beam quality (M2=1.3). The peak power of the compressed pulses is estimated to be 34 MW (0.9 μJ main pulse energy). This laser system is important for driving enhancement cavities with MW of average power [18

18. J. Kaster, I. Pupeza, T. Eidam, C. Jocher, E. Fill, J. Limpert, R. Holzwarth, B. Bernhardt, T. Udem, T. Hänsch, A. Tünnermann, and F. Krausz, “Towards MW average powers in ultrafast high-repetition-rate enhancement cavities,” presented at High-Intensity Lasers and High-Field Phenomena 2011, Istanbul, Turkey, February 16–18, 2011.

].

This work has been partly supported by the European Research Council (ERC) under grant No. 240460-PECS. We thank the attosecond group at the Max-Planck-Institut für Quantenoptik especially Ferenc Krausz, Ioachim Pupeza, Simon Holzberger, Henning Carstens, and Jan Kaster for the fruitful discussions.

References

1.

M. Ferray, A. L’Huillier, X. Li, L. Lomprk, G. Mainfray, and C. Manus, J. Phys. B 21, L31 (1988). [CrossRef]

2.

S. Mathias, M. Bauer, M. Aeschlimann, L. Miaja-Avila, H. Kapteyn, and M. Murnane, in Dynamics at Solid State Surface and Interfaces Vol. 1: Current Developments, U. Bovensiepen, H. Petek, and M. Wolf, eds. (Wiley-VCH, 2010).

3.

F. Krausz and M. Ivanov, Rev. Mod. Phys. 81, 163 (2009). [CrossRef]

4.

G. Lambert, T. Hara, D. Garzella, T. Tanikawa, M. Labat, B. Carre, H. Kitamura, T. Shintake, M. Bougeard, S. Inoue, Y. Tanaka, P. Salieres, H. Merdji, O. Chubar, O. Gobert, K. Tahara, and M. Couprie, Nat. Phys. 4, 296 (2008). [CrossRef]

5.

S. Hädrich, M. Krebs, J. Rothhardt, H. Carstens, S. Demmler, J. Limpert, and A. Tünnermann, Opt. Express 19, 19374 (2011). [CrossRef]

6.

C. Gohle, T. Udem, M. Herrmann, J. Rauschenberger, R. Holzwarth, H. Schuessler, F. Krausz, and T. Hänsch, Nature 436, 234 (2005). [CrossRef]

7.

R. Jones, K. Moll, M. Thorpe, and J. Ye, Phys. Rev. Lett. 94, 193201 (2005). [CrossRef]

8.

I. Pupeza, T. Eidam, J. Rauschenberger, B. Bernhardt, A. Ozawa, E. Fill, A. Apolonski, T. Udem, J. Limpert, Z. Alahmed, A. Azzeer, A. Tünnermann, T. Hänsch, and F. Krausz, Opt. Lett. 35, 2052 (2010). [CrossRef]

9.

T. Allison, A. Cingöz, D. Yost, and J. Ye, Phys. Rev. Lett. 107, 183903 (2011). [CrossRef]

10.

M. Nisoli, S. De Silvestri, and O. Svelto, Appl. Phys. Lett. 68, 2793 (1996). [CrossRef]

11.

S. Hädrich, H. Carstens, J. Rothhardt, J. Limpert, and A. Tünnermann, Opt. Express 19, 7546 (2011). [CrossRef]

12.

T. Eidam, F. Röser, O. Schmidt, J. Limpert, and A. Tünnermann, Appl. Phys. B 92, 9 (2008). [CrossRef]

13.

I. Fedotov, A. Lanin, A. Voronin, A. Fedotov, A. Zheltikov, O. Egorova, S. Semjonov, A. Pryamikov, and E. Dianov, J. Mod. Opt. 57, 1867 (2010). [CrossRef]

14.

A. Smith, B. Do, G. Hadley, and R. Farrow, IEEE J. Sel. Topics Quantum Electron. 15, 153 (2009). [CrossRef]

15.

T. Eidam, C. Wirth, C. Jauregui, F. Stutzki, F. Jansen, H. Otto, O. Schmidt, T. Schreiber, J. Limpert, and A. Tünnermann, Opt. Express 19, 13218 (2011). [CrossRef]

16.

F. Jansen, F. Stutzki, H.-J. Otto, M. Baumgartl, C. Jauregui, J. Limpert, and A. Tünnermann, Opt. Express 18, 26834 (2010). [CrossRef]

17.

fiberdesk www.fiberdesk.com.

18.

J. Kaster, I. Pupeza, T. Eidam, C. Jocher, E. Fill, J. Limpert, R. Holzwarth, B. Bernhardt, T. Udem, T. Hänsch, A. Tünnermann, and F. Krausz, “Towards MW average powers in ultrafast high-repetition-rate enhancement cavities,” presented at High-Intensity Lasers and High-Field Phenomena 2011, Istanbul, Turkey, February 16–18, 2011.

OCIS Codes
(140.3280) Lasers and laser optics : Laser amplifiers
(140.3510) Lasers and laser optics : Lasers, fiber
(140.4050) Lasers and laser optics : Mode-locked lasers
(140.7090) Lasers and laser optics : Ultrafast lasers
(190.4370) Nonlinear optics : Nonlinear optics, fibers
(140.3615) Lasers and laser optics : Lasers, ytterbium

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: August 6, 2012
Revised Manuscript: September 12, 2012
Manuscript Accepted: September 17, 2012
Published: October 19, 2012

Citation
Christoph Jocher, Tino Eidam, Steffen Hädrich, Jens Limpert, and Andreas Tünnermann, "Sub 25 fs pulses from solid-core nonlinear compression stage at 250 W of average power," Opt. Lett. 37, 4407-4409 (2012)
http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-37-21-4407


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References

  1. M. Ferray, A. L’Huillier, X. Li, L. Lomprk, G. Mainfray, and C. Manus, J. Phys. B 21, L31 (1988). [CrossRef]
  2. S. Mathias, M. Bauer, M. Aeschlimann, L. Miaja-Avila, H. Kapteyn, and M. Murnane, in Dynamics at Solid State Surface and Interfaces Vol. 1: Current Developments, U. Bovensiepen, H. Petek, and M. Wolf, eds. (Wiley-VCH, 2010).
  3. F. Krausz and M. Ivanov, Rev. Mod. Phys. 81, 163 (2009). [CrossRef]
  4. G. Lambert, T. Hara, D. Garzella, T. Tanikawa, M. Labat, B. Carre, H. Kitamura, T. Shintake, M. Bougeard, S. Inoue, Y. Tanaka, P. Salieres, H. Merdji, O. Chubar, O. Gobert, K. Tahara, and M. Couprie, Nat. Phys. 4, 296 (2008). [CrossRef]
  5. S. Hädrich, M. Krebs, J. Rothhardt, H. Carstens, S. Demmler, J. Limpert, and A. Tünnermann, Opt. Express 19, 19374 (2011). [CrossRef]
  6. C. Gohle, T. Udem, M. Herrmann, J. Rauschenberger, R. Holzwarth, H. Schuessler, F. Krausz, and T. Hänsch, Nature 436, 234 (2005). [CrossRef]
  7. R. Jones, K. Moll, M. Thorpe, and J. Ye, Phys. Rev. Lett. 94, 193201 (2005). [CrossRef]
  8. I. Pupeza, T. Eidam, J. Rauschenberger, B. Bernhardt, A. Ozawa, E. Fill, A. Apolonski, T. Udem, J. Limpert, Z. Alahmed, A. Azzeer, A. Tünnermann, T. Hänsch, and F. Krausz, Opt. Lett. 35, 2052 (2010). [CrossRef]
  9. T. Allison, A. Cingöz, D. Yost, and J. Ye, Phys. Rev. Lett. 107, 183903 (2011). [CrossRef]
  10. M. Nisoli, S. De Silvestri, and O. Svelto, Appl. Phys. Lett. 68, 2793 (1996). [CrossRef]
  11. S. Hädrich, H. Carstens, J. Rothhardt, J. Limpert, and A. Tünnermann, Opt. Express 19, 7546 (2011). [CrossRef]
  12. T. Eidam, F. Röser, O. Schmidt, J. Limpert, and A. Tünnermann, Appl. Phys. B 92, 9 (2008). [CrossRef]
  13. I. Fedotov, A. Lanin, A. Voronin, A. Fedotov, A. Zheltikov, O. Egorova, S. Semjonov, A. Pryamikov, and E. Dianov, J. Mod. Opt. 57, 1867 (2010). [CrossRef]
  14. A. Smith, B. Do, G. Hadley, and R. Farrow, IEEE J. Sel. Topics Quantum Electron. 15, 153 (2009). [CrossRef]
  15. T. Eidam, C. Wirth, C. Jauregui, F. Stutzki, F. Jansen, H. Otto, O. Schmidt, T. Schreiber, J. Limpert, and A. Tünnermann, Opt. Express 19, 13218 (2011). [CrossRef]
  16. F. Jansen, F. Stutzki, H.-J. Otto, M. Baumgartl, C. Jauregui, J. Limpert, and A. Tünnermann, Opt. Express 18, 26834 (2010). [CrossRef]
  17. fiberdesk www.fiberdesk.com .
  18. J. Kaster, I. Pupeza, T. Eidam, C. Jocher, E. Fill, J. Limpert, R. Holzwarth, B. Bernhardt, T. Udem, T. Hänsch, A. Tünnermann, and F. Krausz, “Towards MW average powers in ultrafast high-repetition-rate enhancement cavities,” presented at High-Intensity Lasers and High-Field Phenomena 2011, Istanbul, Turkey, February 16–18, 2011.

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