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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 11, Iss. 26 — Dec. 29, 2003
  • pp: 3550–3554
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Generation of 36-femtosecond pulses from a ytterbium fiber laser

F. Ö. Ilday, J. Buckley, L. Kuznetsova, and F. W. Wise  »View Author Affiliations


Optics Express, Vol. 11, Issue 26, pp. 3550-3554 (2003)
http://dx.doi.org/10.1364/OE.11.003550


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Abstract

By optimizing the cavity dispersion map, 1.5-nJ pulses as short as 36 fs are obtained from a Yb-doped fiber laser. Residual higher-order dispersion currently limits the pulse duration, and it should be possible to generate pulses as short as 25–30 fs with Yb-doped fiber.

© 2003 Optical Society of America

Mode-locked fiber lasers have the potential to supplant solid-state lasers in some applications owing to their excellent stability, freedom from misalignment, and compact size. These attributes have motivated a substantial development effort over the past decade. The majority of progress has been made with Er- (1.55 µm) and Nd-doped (1 µm) fibers. Applications ranging from telecommunication to nonlinear microscopy have motivated exploration of correspondingly wide ranges of modelocking techniques and parameters. In the context of photophysical applications such as nonlinear microscopy, there is greatest interest in pulse repetition rates of tens to hundreds of megahertz, pulse durations of ~100 fs, and maximum pulse energy. Pulse energies as high as 2.7 nJ have been produced by stretched-pulse fiber lasers [1

1. L. E. Nelson, S. B. Fleischer, G. Lenz, and E. P. Ippen, “Efficient frequency doubling of a femtosecond fiber laser,” Opt. Lett. 21, 1759–1761 (1996). [CrossRef] [PubMed]

], and pulses less than 100 fs in duration were generated.

Recently, ytterbium has attracted much attention as a gain ion because it offers several advantageous properties. Spectroscopic properties include high quantum efficiency, absence of ground-state and excited-state absorptions, a long upper-state lifetime, and broad gain spectrum. A practical feature is that Yb can be pumped in convenient absorption bands at 915 and 980 nm. As a result of these properties, Yb-doped fiber seems likely to supercede Nd-doped fiber among materials that emit near 1 µm.

The highest-power standard mode-locked Ti:sapphire lasers produce 20-nJ pulses, but 5–10 nJ is more typical. Extended-cavity Ti:sapphire lasers generate ~150-nJ pulses, at repetition rates ~5 MHz and with increased complexity [6

6. A. M. Kowalevicz, A. Tucay Zare, F. X. Kartner, J. G. Fujimoto, S. Dewald, U. Morgner, V. Scheuer, and G. Angelow, “Generation of 150-nJ pulses from a multiple-pass cavity Kerr-lens mode-locked Ti:Al2O3 oscillator,” Opt. Lett. 28, 1597–1599 (2003). [CrossRef] [PubMed]

]. Theoretical calculations show that pulse energies of tens of nanojoules should be possible through the suppression of wave-breaking in Yb fiber lasers [7

7. F. O. Ilday and F. W. Wise, “Similariton Laser,” Proceedings of the Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 2003), paper CTHPDA3.

]. Thus, it appears that fiber lasers will be able to supply pulse energies comparable to those of solid-state lasers.

Given the recent advances in pulse energy, it seems appropriate to turn attention to the pulse duration, another parameter in which fiber lasers have historically lagged behind solid-state lasers. The shortest pulses produced by an Er fiber laser had duration 63 fs [8

8. K. Tamura, E. P. Ippen, and H. A. Haus, “Pulse dynamics in stretched-pulse fiber lasers,” App. Phys. Lett. 67, 158–160 (1995). [CrossRef]

], while a Nd fiber laser generated pulses as short as 42 fs [4

4. M. H. Ober, M. Hofer, and M. E. Fermann, “42-fs pulse generation from a mode-locked fiber laser started with a moving mirror,” Opt. Lett. 18, 367–369 (1993). [CrossRef] [PubMed]

]. Here we report the results of an effort to minimize the pulse duration of a Yb fiber laser. By optimizing the group-velocity dispersion of the laser, pulses as short as 36 fs are generated. To date, these are the shortest pulses produced by a fiber laser. The pulse duration is limited by third-order dispersion (TOD), and ultimately it should be possible to generate pulses below 30 fs in duration.

Numerical simulations (details of which can be found in [2

2. H. Lim, F. O. Ilday, and F. W. Wise, “Generation of 2-nJ pulses from a femtosecond Yb fiber laser,” Opt. Lett. 28, 660–662 (2003). [CrossRef] [PubMed]

] and [3

3. F. O. Ilday, H. Lim, J. R. Buckley, F. W. Wise, and W. G. Clark, “Generation of 50-fs, 5-nJ pulses at 1.03 µm from a wave-breaking-free fiber laser,” Opt. Lett. 28, 1365–1367 (2003). [CrossRef] [PubMed]

]) guided the design of the Yb fiber laser. The laser is modeled as 3.5 m of single-mode fiber (SMF), followed by 20 cm of Yb-doped gain fiber, 20 cm of SMF (which represents a collimator), a transfer function for nonlinear polarization evolution, and a linear dispersive delay (which is implemented experimentally with diffraction gratings). The TOD of the fiber and gratings are included in the simulations. In addition, the gain is modeled as a complex Lorentzian susceptibility [9

9. S. Chi, C. W. Chang, and S. Wen, “Femtosecond soliton propagation in erbium-doped fiber amplifiers: the equivalence of two different models”, Opt. Comm. 106, 193–196 (1994). [CrossRef]

], in place of the simple parabolic-gain model employed previously. The calculations show that the pulse duration is minimized in a cavity with segments of normal and anomalous dispersion, and net anomalous dispersion. Under these conditions strong soliton-like pulse-shaping occurs, along with substantial pulse-stretching. That is, the laser should be operated in the stretched-pulse regime, not the wave-breaking-free [3

3. F. O. Ilday, H. Lim, J. R. Buckley, F. W. Wise, and W. G. Clark, “Generation of 50-fs, 5-nJ pulses at 1.03 µm from a wave-breaking-free fiber laser,” Opt. Lett. 28, 1365–1367 (2003). [CrossRef] [PubMed]

] or self-similar [7

7. F. O. Ilday and F. W. Wise, “Similariton Laser,” Proceedings of the Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 2003), paper CTHPDA3.

] regimes. The minimum pulse duration is obtained with net dispersion values between zero and -0.01 ps2. A representative stable solution is shown in Fig. 1. The power spectrum exhibits significant structure. The FWHM pulse duration is ~40 fs, and the intensity profile includes secondary pulses or wings that typically encompass ~20% of the pulse energy.

Fig. 1. Results of numerical simulations of the Yb fiber laser. Main figure: power spectrum plotted on logarithmic scale. Inset: temporal intensity profile of dechirped output pulse.

The experimental arrangement, which is similar to that described in [2

2. H. Lim, F. O. Ilday, and F. W. Wise, “Generation of 2-nJ pulses from a femtosecond Yb fiber laser,” Opt. Lett. 28, 660–662 (2003). [CrossRef] [PubMed]

], is illustrated in Fig. 2. The Yb fiber (NA=0.12, core diameter 6 µm, 23,600 ppm doping, Institut National d’Optique, Canada) is 23 cm long to minimize nonlinear effects during amplification. Coupling in and out of the fiber section is facilitated with fiber-pigtailed collimators (OFR, Inc.). A maximum of 300 mW pump light at 980 nm from a laser diode is delivered to the cavity with a 980/1030-nm wavelength division multiplexer (Lightel Technologies, Inc.). The GVD and TOD of the fibers are estimated to be ~23 fs2/mm and ~70 fs3/mm, respectively. An optical isolator (OFR, Inc.) ensures unidirectional operation. The repetition rate of the laser was set to ~50 MHz, which corresponds to a fiber length sufficiently short to keep nonlinear effects manageable and to minimize difficulties with initiation of modelocking associated with residual birefringence. Shorter cavity lengths are possible, but the energy stored in the cavity would not be sufficient for nanojoule output energies. Once the fiber length was chosen, the net cavity dispersion was optimized for shortest pulse duration by adjusting the grating separation (~45° angle of incidence, 600 lines/mm groove density, GVD of -1400 fs2/mm, and TOD of 2100 fs3/mm, Optometrics LLC). As the dispersion was varied from large anomalous values toward zero, shorter pulses were observed, as expected. As is typical for fiber lasers, several distinct mode-locked states are accessible for a given choice of cavity dispersion, by adjustment of the wave-plates that control the nonlinear polarization evolution (NPE) [10

10. M. Hofer, M. E. Fermann, F. Harberl, M. H. Ober, and A. J. Schmidt, Opt. Lett.16, 502 (1991). [CrossRef] [PubMed]

]. The variation of the spectral shape, pulse energy and duration among different mode-locked states is most significant for small anomalous dispersion values. Because of this variation, a complete characterization of the minimum pulse duration for varying dispersion is not possible. Experimentally, the shortest pulses were obtained for dispersion values close to -0.01 ps2. Increasing the dispersion further, so that the net dispersion was normal, produced longer pulses, and larger pulse energies could be supported. Highly-chirped pulses were switched out of the NPE rejection port and dechirped with a pair of diffraction gratings external to the cavity.

Measurements of the shortest pulses produced by the Yb fiber laser are shown in Fig. 3. The autocorrelation implies a FWHM pulse duration of 36 fs (assuming a gaussian pulse shape), which agrees with the pulse duration retrieved by fitting the measured interferometric autocorrelation and the power spectrum [11

11. J. W. Nicholson, J. Jasapara, W. Rudolph, F. G. Omenetto, and A. J. Taylor, “Full-field characterization of femtosecond pulses by spectrum and cross-correlation measurements,” Opt. Lett. 24, 1774–1776 (1999). [CrossRef]

]. With 270 mW pump power, the output-pulse energies before and after dechirping are 1.8 and 1.5 nJ, respectively. We estimate that ~30% of the pulse energy resides in the secondary lobe that is visible in the autocorrelation. The resulting peak power is thus ~25 kW. Some care in setting the waveplates that control the NPE is required to obtain the shortest pulses. However, slightly longer pulses (40–45 fs) can be obtained quite routinely.

Fig. 2. Schematic of the Yb fiber laser. w.p.: waveplate.
Fig. 3. Output of the Yb fiber laser. Measured interferometric autocorrelation (top left panel) along with the interferometric autocorrelation of the pulse retrieved by PICASO (top right panel). Bottom panel: retrieved intensity and phase profiles compared to the transform-limited pulse (dash-dotted line).

Fig. 4. Measured power spectrum plotted on semi-logarithmic scales. The component at 980 nm is unabsorbed pump light. The inset shows the spectrum on linear scales.

We believe that the bandwidths of components such as the collimators and wavelength-division multiplexing coupler used for pumping slightly limit the achievable pulse spectrum. With improvements in these components, and by reduction of third-order dispersion of the cavity, reduction of the pulse duration to ~30 fs may be possible. The power spectrum of the 36-fs pulses is already broader than the ~40-nm gain bandwidth of Yb-doped fiber. There is currently great interest in the development of ultra-broadband sources, and it is naturally desirable to extend the present performance to even broader spectra/shorter pulses. Larger spectral widths may be possible with stronger self-phase modulation, but the initiation and stability of mode-locked operation will be increasingly difficult. The structured spectrum of Fig. 4 is qualitatively similar to the spectra produced by mode-locked solid-state lasers operated close to the limitations of the gain bandwidth. Among solid-state lasers that emit near 1050 nm, we are not aware of pulse durations less than 60 fs, which are achieved by Nd:glass [13

13. J. Aus der Au, D. Kopf, F. Morier-Genoud, M. Moser, and U. Keller, “60-fs pulses from a diode-pumped Nd:glass laser,” Opt. Lett. 22, 307–309 (1997). [CrossRef]

] and Yb:glass [14

14. C. Honninger, F. Morier-Genoud, M. Moser, U. Keller, L. R. Brovelli, and C. Harder, “Efficient and tunable diode-pumped femtosecond Yb : glass lasers,” Opt. Lett. 23, 126–128 (1998). [CrossRef]

] lasers.

In conclusion, we have demonstrated a Yb fiber laser that produces 36-fs pulses. The laser is a stable instrument, so we expect that the short pulses demonstrated here will find applications in ultrafast science. Pulses as short as 25–30 fs should be obtained in the future.

Acknowledgments

This work was supported by the National Institutes of Health under grant EB002019 and Clark-MXR, Incorporated. J. R. Buckley acknowledges the support of the National Physical Science Consortium through a graduate research fellowship.

References and links

1.

L. E. Nelson, S. B. Fleischer, G. Lenz, and E. P. Ippen, “Efficient frequency doubling of a femtosecond fiber laser,” Opt. Lett. 21, 1759–1761 (1996). [CrossRef] [PubMed]

2.

H. Lim, F. O. Ilday, and F. W. Wise, “Generation of 2-nJ pulses from a femtosecond Yb fiber laser,” Opt. Lett. 28, 660–662 (2003). [CrossRef] [PubMed]

3.

F. O. Ilday, H. Lim, J. R. Buckley, F. W. Wise, and W. G. Clark, “Generation of 50-fs, 5-nJ pulses at 1.03 µm from a wave-breaking-free fiber laser,” Opt. Lett. 28, 1365–1367 (2003). [CrossRef] [PubMed]

4.

M. H. Ober, M. Hofer, and M. E. Fermann, “42-fs pulse generation from a mode-locked fiber laser started with a moving mirror,” Opt. Lett. 18, 367–369 (1993). [CrossRef] [PubMed]

5.

H. Lim, F. O. Ilday, and F. W. Wise, “Femtosecond ytterbium fiber laser with photonic crystal fiber for dispersion control,” Opt. Exp. 10, 1497–1502 (2002). [CrossRef]

6.

A. M. Kowalevicz, A. Tucay Zare, F. X. Kartner, J. G. Fujimoto, S. Dewald, U. Morgner, V. Scheuer, and G. Angelow, “Generation of 150-nJ pulses from a multiple-pass cavity Kerr-lens mode-locked Ti:Al2O3 oscillator,” Opt. Lett. 28, 1597–1599 (2003). [CrossRef] [PubMed]

7.

F. O. Ilday and F. W. Wise, “Similariton Laser,” Proceedings of the Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 2003), paper CTHPDA3.

8.

K. Tamura, E. P. Ippen, and H. A. Haus, “Pulse dynamics in stretched-pulse fiber lasers,” App. Phys. Lett. 67, 158–160 (1995). [CrossRef]

9.

S. Chi, C. W. Chang, and S. Wen, “Femtosecond soliton propagation in erbium-doped fiber amplifiers: the equivalence of two different models”, Opt. Comm. 106, 193–196 (1994). [CrossRef]

10.

M. Hofer, M. E. Fermann, F. Harberl, M. H. Ober, and A. J. Schmidt, Opt. Lett.16, 502 (1991). [CrossRef] [PubMed]

11.

J. W. Nicholson, J. Jasapara, W. Rudolph, F. G. Omenetto, and A. J. Taylor, “Full-field characterization of femtosecond pulses by spectrum and cross-correlation measurements,” Opt. Lett. 24, 1774–1776 (1999). [CrossRef]

12.

L. E. Nelson, D. J. Jones, K. Tamura, H. A. Haus, and E. P. Ippen, “Ultrashort-pulse fiber ring lasers,” Appl. Phys. B 65, 277–294 (1997). [CrossRef]

13.

J. Aus der Au, D. Kopf, F. Morier-Genoud, M. Moser, and U. Keller, “60-fs pulses from a diode-pumped Nd:glass laser,” Opt. Lett. 22, 307–309 (1997). [CrossRef]

14.

C. Honninger, F. Morier-Genoud, M. Moser, U. Keller, L. R. Brovelli, and C. Harder, “Efficient and tunable diode-pumped femtosecond Yb : glass lasers,” Opt. Lett. 23, 126–128 (1998). [CrossRef]

OCIS Codes
(140.3510) Lasers and laser optics : Lasers, fiber
(320.2250) Ultrafast optics : Femtosecond phenomena
(320.7090) Ultrafast optics : Ultrafast lasers

ToC Category:
Research Papers

History
Original Manuscript: November 14, 2003
Revised Manuscript: December 1, 2003
Published: December 29, 2003

Citation
F. Ilday, J. Buckley, L. Kuznetsova, and F. Wise, "Generation of 36-femtosecond pulses from a ytterbium fiber laser," Opt. Express 11, 3550-3554 (2003)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-11-26-3550


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References

  1. L. E. Nelson, S. B. Fleischer, G. Lenz, and E. P. Ippen, �??Efficient frequency doubling of a femtosecond fiber laser,�?? Opt. Lett. 21, 1759-1761 (1996). [CrossRef] [PubMed]
  2. H. Lim, F. O. Ilday, and F. W. Wise, �??Generation of 2-nJ pulses from a femtosecond Yb fiber laser,�?? Opt. Lett. 28, 660-662 (2003). [CrossRef] [PubMed]
  3. F. O. Ilday, H. Lim, J. R. Buckley, F. W. Wise, and W. G. Clark, �??Generation of 50-fs, 5-nJ pulses at 1.03 µm from a wave-breaking-free fiber laser,�?? Opt. Lett. 28, 1365-1367 (2003). [CrossRef] [PubMed]
  4. M. H. Ober, M. Hofer, and M. E. Fermann, �??42-fs pulse generation from a mode-locked fiber laser started with a moving mirror,�?? Opt. Lett. 18, 367-369 (1993). [CrossRef] [PubMed]
  5. H. Lim, F. O. Ilday, and F. W. Wise, "Femtosecond ytterbium fiber laser with photonic crystal fiber for dispersion control," Opt. Exp. 10, 1497-1502 (2002). [CrossRef]
  6. A. M. Kowalevicz, A. Tucay Zare, F. X. Kartner, J. G. Fujimoto, S. Dewald, U. Morgner, V. Scheuer, G. Angelow, �??Generation of 150-nJ pulses from a multiple-pass cavity Kerr-lens mode-locked Ti:Al2O3 oscillator,�?? Opt. Lett. 28, 1597-1599 (2003). [CrossRef] [PubMed]
  7. F. O. Ilday and F. W. Wise, �??Similariton Laser,�?? Proceedings of the Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 2003), paper CTHPDA3.
  8. K. Tamura, E. P. Ippen, and H. A. Haus, �??Pulse dynamics in stretched-pulse fiber lasers,�?? App. Phys. Lett. 67, 158-160 (1995). [CrossRef]
  9. S. Chi, C. W. Chang, and S. Wen, "Femtosecond soliton propagation in erbium-doped fiber amplifiers: the equivalence of two different models", Opt. Comm. 106, 193-196 (1994). [CrossRef]
  10. M. Hofer, M. E. Fermann, F. Harberl, M. H. Ober, and A. J. Schmidt, Opt. Lett. 16, 502 (1991) [CrossRef] [PubMed]
  11. J. W. Nicholson, J. Jasapara, W. Rudolph, F. G. Omenetto, and A. J. Taylor, �??Full-field characterization of femtosecond pulses by spectrum and cross-correlation measurements,�?? Opt. Lett. 24, 1774-1776 (1999). [CrossRef]
  12. L. E. Nelson, D. J. Jones, K. Tamura, H. A. Haus, and E. P. Ippen, �??Ultrashort-pulse fiber ring lasers,�?? Appl. Phys. B 65, 277-294 (1997). [CrossRef]
  13. J. Aus der Au, D. Kopf, F. Morier-Genoud, M. Moser, U. Keller, �??60-fs pulses from a diode-pumped Nd:glass laser,�?? Opt. Lett. 22, 307-309 (1997). [CrossRef]
  14. C. Honninger, F. Morier-Genoud, M. Moser, U. Keller, L. R. Brovelli, C. Harder, �??Efficient and tunable diode-pumped femtosecond Yb : glass lasers,�?? Opt. Lett. 23, 126-128 (1998). [CrossRef]

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