Abstract

We have obtained both extracavity and intracavity simultaneous second-harmonic generation and compression of signal pulses at 1.25 µm from a synchronously pumped RbTiOAsO4-based optical parametric oscillator with an aperiodically poled crystal of KTiOPO4. The 290-fs input pulses yield temporally compressed frequency-doubled pulses with durations of 120 fs and average output powers of as much as 120 mW. Experimental results are compared with a numerical model in which the temporal and spectral pulse shape and phase of the second-harmonic pulses are calculated with data obtained by characterization of the input pulses by use of the frequency-resolved optical gating technique. We also used the model to optimize the crystal parameters that would result in higher conversion efficiencies and that would enhance pulse compression.

© 1999 Optical Society of America

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References

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  1. J. A. Armstrong, N. Bloembergen, J. Ducuing, and P. S. Peshan, “Interactions between light waves in a nonlinear dielectric,” Phys. Rev. 127, 1918–1939 (1962).
    [CrossRef]
  2. D. E. Thompson, J. D. McMullen, and D. B. Anderson, “Second harmonic generation in GaAs ‘stack of plates’ using high power CO2 laser radiation,” Appl. Phys. Lett. 29, 113–115 (1976).
    [CrossRef]
  3. E. Lallier, M. Brevignon, and J. Lehoux, “Efficient second-harmonic generation of CO2 lasers with a quasi-phase-matched GaAs crystal,” Opt. Lett. 23, 1511–1513 (1998).
    [CrossRef]
  4. H. Karlsson, F. Laurell, P. Henriksson, and G. Arvidsson, “Frequency doubling in periodically poled RbTiOAsO4,” Electron. Lett. 32, 556–557 (1996).
    [CrossRef]
  5. E. J. Lim, M. M. Fejer, and R. L. Byer, “Second-harmonic generation of green light in periodically poled planar lithium niobate waveguide,” Electron. Lett. 25, 174–175 (1989).
    [CrossRef]
  6. G. Khanarian, M. A. Mortazavi, and A. J. East, “Phase-matched second-harmonic generation from freestanding periodically stacked polymer films,” Appl. Phys. Lett. 63, 1462–1464 (1993).
    [CrossRef]
  7. M. A. Mortazavi and G. Khanarian, “Quasi-phase-matched frequency doubling in bulk periodic polymeric structures,” Opt. Lett. 19, 1290–1292 (1994).
    [CrossRef] [PubMed]
  8. M. M. Fejer, G. A. Magel, D. H. Jundt, and R. L. Byer, “Quasi-phase-matched second-harmonic generation: tuning and tolerances,” IEEE J. Quantum Electron. 28, 2631–2654 (1992).
    [CrossRef]
  9. L. E. Myers, R. C. Eckardt, M. M. Fejer, R. L. Byer, W. R. Bosenberg, and J. W. Pierce, “Quasi-phase-matched optical parametric oscillators in bulk periodically poled LiNbO3,” J. Opt. Soc. Am. B 12, 2102–2116 (1995).
    [CrossRef]
  10. V. Pruneri, S. D. Butterworth, and D. C. Hanna, “Highly efficient green-light generation by quasi-phase-matched frequency doubling of picosecond pulses from an amplified mode-locked Nd:YLF laser,” Opt. Lett. 21, 390–392 (1996).
    [CrossRef] [PubMed]
  11. J. C. Diels and W. Rudolph, Ultrashort Laser Pulse Phenomena (Academic, New York, 1996).
  12. G. Imeshev, A. Galvanauskas, D. Harter, M. A. Arbore, M. Proctor, and M. M. Fejer, “Engineerable femtosecond pulse shaping by second-harmonic generation with Fourier synthetic quasi-phase-matching gratings,” Opt. Lett. 23, 864–866 (1998).
    [CrossRef]
  13. E. Sidick, A. Knoesen, and A. Dienes, “Ultrashort-pulsesecond-harmonic generation in quasi-phase-matched dispersive media,” Opt. Lett. 19, 266–268 (1994).
    [CrossRef] [PubMed]
  14. R. L. Fork, O. E. Martinez, and J. P. Gordon, “Negative dispersion using a pair of prisms,” Opt. Lett. 9, 150–152 (1984).
    [CrossRef] [PubMed]
  15. M. A. Arbore, M. M. Fejer, M. E. Fermann, A. Hariharan, A. Galvanauskas, and D. Harter, “Frequency doubling of femtosecond erbium-fiber soliton laser in periodically poled lithium niobate,” Opt. Lett. 22, 13–15 (1997).
    [CrossRef] [PubMed]
  16. M. A. Arbore, A. Galvanauskas, D. Harter, M. H. Chou, and M. M. Fejer, “Compression of ultrashort pulses using second-harmonic generation in aperiodically poled lithium niobate,” in Conference on Lasers and Electro-Optics, Vol. 11 of 1997 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1997), postdeadline paper CPD6–2.
  17. M. A. Arbore, A. Galvanauskas, D. Harter, M. H. Chou, and M. M. Fejer, “Engineerable compression of ultrashort pulses by use of second-harmonic generation in chirped-period-poled lithium niobate,” Opt. Lett. 22, 1341–1343 (1997).
    [CrossRef]
  18. A. Galvanauskas, D. Harter, M. A. Arbore, M. H. Chou, and M. M. Fejer, “Chirped-pulse amplification circuits for fiber amplifiers, based on chirped-period quasi-phase-matching gratings,” Opt. Lett. 23, 1695–1697 (1998).
    [CrossRef]
  19. M. A. Arbore, O. Marco, and M. M. Fejer, “Pulse compression during second-harmonic generation in aperiodic quasi-phase-matching gratings,” Opt. Lett. 22, 865–867 (1997).
    [CrossRef] [PubMed]
  20. D. T. Reid, C. McGowan, W. Sleat, M. Ebrahimzadeh, and W. Sibbett, “Compact, efficient 344-MHz repetition-rate femtosecond optical parametric oscillator,” Opt. Lett. 22, 525–527 (1997).
    [CrossRef] [PubMed]
  21. D. T. Reid, M. Padgett, C. McGowan, W. Sleat, M. Ebrahimzadeh, and W. Sibbett, “Light-emitting diodes as measurement devices for femtosecond laser pulses,” Opt. Lett. 22, 233–235 (1997).
    [CrossRef] [PubMed]
  22. D. T. Reid, P. Loza-Alvarez, M. Ebrahimzadeh, E. U. Rafailov, P. Faller, D. J. L. Birkin, W. Sibbett, H. Karlsson, and F. Laurell, “Femtosecond pulse compression by second-harmonic generation in aperiodically-poled KTP,” in Conference on Lasers and Electro-Optics, Vol. 6 of 1998 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1998), paper CME3.
  23. K. W. Delong, R. Trebino, J. Hunter, and W. E. White, “Frequency-resolved optical gating with the use of second-harmonic generation,” J. Opt. Soc. Am. B 11, 2206–2215 (1994).
    [CrossRef]
  24. D. T. Reid, C. McGowan, W. E. Sleat, and W. Sibbett, “A real-time FROG-trace acquisition system for non-amplified femtosecond oscillators,” Opt. Photon. News (Suppl.) 8(5), (1997).
  25. W. H. Press, S. A. Teukolosky, W. T. Vetterling, and B. P. Flannery, Numerical Recipes in Fortran, 2nd ed. (Cambridge U. Press, Cambridge, UK, 1994), Chap. 19, pp. 818–880.
  26. E. U. Rafailov, D. J. L. Birkin, E. A. Avrutin, and W. Sibbett, “High average power short-pulse generation from single-mode InGaAs/GaAs laser diodes,” IEE Proc. Optoelectron. (to be published).

1998 (3)

1997 (5)

1996 (2)

1995 (1)

1994 (3)

1993 (1)

G. Khanarian, M. A. Mortazavi, and A. J. East, “Phase-matched second-harmonic generation from freestanding periodically stacked polymer films,” Appl. Phys. Lett. 63, 1462–1464 (1993).
[CrossRef]

1992 (1)

M. M. Fejer, G. A. Magel, D. H. Jundt, and R. L. Byer, “Quasi-phase-matched second-harmonic generation: tuning and tolerances,” IEEE J. Quantum Electron. 28, 2631–2654 (1992).
[CrossRef]

1989 (1)

E. J. Lim, M. M. Fejer, and R. L. Byer, “Second-harmonic generation of green light in periodically poled planar lithium niobate waveguide,” Electron. Lett. 25, 174–175 (1989).
[CrossRef]

1984 (1)

1976 (1)

D. E. Thompson, J. D. McMullen, and D. B. Anderson, “Second harmonic generation in GaAs ‘stack of plates’ using high power CO2 laser radiation,” Appl. Phys. Lett. 29, 113–115 (1976).
[CrossRef]

1962 (1)

J. A. Armstrong, N. Bloembergen, J. Ducuing, and P. S. Peshan, “Interactions between light waves in a nonlinear dielectric,” Phys. Rev. 127, 1918–1939 (1962).
[CrossRef]

Anderson, D. B.

D. E. Thompson, J. D. McMullen, and D. B. Anderson, “Second harmonic generation in GaAs ‘stack of plates’ using high power CO2 laser radiation,” Appl. Phys. Lett. 29, 113–115 (1976).
[CrossRef]

Arbore, M. A.

Armstrong, J. A.

J. A. Armstrong, N. Bloembergen, J. Ducuing, and P. S. Peshan, “Interactions between light waves in a nonlinear dielectric,” Phys. Rev. 127, 1918–1939 (1962).
[CrossRef]

Arvidsson, G.

H. Karlsson, F. Laurell, P. Henriksson, and G. Arvidsson, “Frequency doubling in periodically poled RbTiOAsO4,” Electron. Lett. 32, 556–557 (1996).
[CrossRef]

Bloembergen, N.

J. A. Armstrong, N. Bloembergen, J. Ducuing, and P. S. Peshan, “Interactions between light waves in a nonlinear dielectric,” Phys. Rev. 127, 1918–1939 (1962).
[CrossRef]

Bosenberg, W. R.

Brevignon, M.

Butterworth, S. D.

Byer, R. L.

L. E. Myers, R. C. Eckardt, M. M. Fejer, R. L. Byer, W. R. Bosenberg, and J. W. Pierce, “Quasi-phase-matched optical parametric oscillators in bulk periodically poled LiNbO3,” J. Opt. Soc. Am. B 12, 2102–2116 (1995).
[CrossRef]

M. M. Fejer, G. A. Magel, D. H. Jundt, and R. L. Byer, “Quasi-phase-matched second-harmonic generation: tuning and tolerances,” IEEE J. Quantum Electron. 28, 2631–2654 (1992).
[CrossRef]

E. J. Lim, M. M. Fejer, and R. L. Byer, “Second-harmonic generation of green light in periodically poled planar lithium niobate waveguide,” Electron. Lett. 25, 174–175 (1989).
[CrossRef]

Chou, M. H.

Delong, K. W.

Dienes, A.

Ducuing, J.

J. A. Armstrong, N. Bloembergen, J. Ducuing, and P. S. Peshan, “Interactions between light waves in a nonlinear dielectric,” Phys. Rev. 127, 1918–1939 (1962).
[CrossRef]

East, A. J.

G. Khanarian, M. A. Mortazavi, and A. J. East, “Phase-matched second-harmonic generation from freestanding periodically stacked polymer films,” Appl. Phys. Lett. 63, 1462–1464 (1993).
[CrossRef]

Ebrahimzadeh, M.

Eckardt, R. C.

Fejer, M. M.

G. Imeshev, A. Galvanauskas, D. Harter, M. A. Arbore, M. Proctor, and M. M. Fejer, “Engineerable femtosecond pulse shaping by second-harmonic generation with Fourier synthetic quasi-phase-matching gratings,” Opt. Lett. 23, 864–866 (1998).
[CrossRef]

A. Galvanauskas, D. Harter, M. A. Arbore, M. H. Chou, and M. M. Fejer, “Chirped-pulse amplification circuits for fiber amplifiers, based on chirped-period quasi-phase-matching gratings,” Opt. Lett. 23, 1695–1697 (1998).
[CrossRef]

M. A. Arbore, O. Marco, and M. M. Fejer, “Pulse compression during second-harmonic generation in aperiodic quasi-phase-matching gratings,” Opt. Lett. 22, 865–867 (1997).
[CrossRef] [PubMed]

M. A. Arbore, A. Galvanauskas, D. Harter, M. H. Chou, and M. M. Fejer, “Engineerable compression of ultrashort pulses by use of second-harmonic generation in chirped-period-poled lithium niobate,” Opt. Lett. 22, 1341–1343 (1997).
[CrossRef]

M. A. Arbore, M. M. Fejer, M. E. Fermann, A. Hariharan, A. Galvanauskas, and D. Harter, “Frequency doubling of femtosecond erbium-fiber soliton laser in periodically poled lithium niobate,” Opt. Lett. 22, 13–15 (1997).
[CrossRef] [PubMed]

L. E. Myers, R. C. Eckardt, M. M. Fejer, R. L. Byer, W. R. Bosenberg, and J. W. Pierce, “Quasi-phase-matched optical parametric oscillators in bulk periodically poled LiNbO3,” J. Opt. Soc. Am. B 12, 2102–2116 (1995).
[CrossRef]

M. M. Fejer, G. A. Magel, D. H. Jundt, and R. L. Byer, “Quasi-phase-matched second-harmonic generation: tuning and tolerances,” IEEE J. Quantum Electron. 28, 2631–2654 (1992).
[CrossRef]

E. J. Lim, M. M. Fejer, and R. L. Byer, “Second-harmonic generation of green light in periodically poled planar lithium niobate waveguide,” Electron. Lett. 25, 174–175 (1989).
[CrossRef]

Fermann, M. E.

Fork, R. L.

Galvanauskas, A.

Gordon, J. P.

Hanna, D. C.

Hariharan, A.

Harter, D.

Henriksson, P.

H. Karlsson, F. Laurell, P. Henriksson, and G. Arvidsson, “Frequency doubling in periodically poled RbTiOAsO4,” Electron. Lett. 32, 556–557 (1996).
[CrossRef]

Hunter, J.

Imeshev, G.

Jundt, D. H.

M. M. Fejer, G. A. Magel, D. H. Jundt, and R. L. Byer, “Quasi-phase-matched second-harmonic generation: tuning and tolerances,” IEEE J. Quantum Electron. 28, 2631–2654 (1992).
[CrossRef]

Karlsson, H.

H. Karlsson, F. Laurell, P. Henriksson, and G. Arvidsson, “Frequency doubling in periodically poled RbTiOAsO4,” Electron. Lett. 32, 556–557 (1996).
[CrossRef]

Khanarian, G.

M. A. Mortazavi and G. Khanarian, “Quasi-phase-matched frequency doubling in bulk periodic polymeric structures,” Opt. Lett. 19, 1290–1292 (1994).
[CrossRef] [PubMed]

G. Khanarian, M. A. Mortazavi, and A. J. East, “Phase-matched second-harmonic generation from freestanding periodically stacked polymer films,” Appl. Phys. Lett. 63, 1462–1464 (1993).
[CrossRef]

Knoesen, A.

Lallier, E.

Laurell, F.

H. Karlsson, F. Laurell, P. Henriksson, and G. Arvidsson, “Frequency doubling in periodically poled RbTiOAsO4,” Electron. Lett. 32, 556–557 (1996).
[CrossRef]

Lehoux, J.

Lim, E. J.

E. J. Lim, M. M. Fejer, and R. L. Byer, “Second-harmonic generation of green light in periodically poled planar lithium niobate waveguide,” Electron. Lett. 25, 174–175 (1989).
[CrossRef]

Magel, G. A.

M. M. Fejer, G. A. Magel, D. H. Jundt, and R. L. Byer, “Quasi-phase-matched second-harmonic generation: tuning and tolerances,” IEEE J. Quantum Electron. 28, 2631–2654 (1992).
[CrossRef]

Marco, O.

Martinez, O. E.

McGowan, C.

McMullen, J. D.

D. E. Thompson, J. D. McMullen, and D. B. Anderson, “Second harmonic generation in GaAs ‘stack of plates’ using high power CO2 laser radiation,” Appl. Phys. Lett. 29, 113–115 (1976).
[CrossRef]

Mortazavi, M. A.

M. A. Mortazavi and G. Khanarian, “Quasi-phase-matched frequency doubling in bulk periodic polymeric structures,” Opt. Lett. 19, 1290–1292 (1994).
[CrossRef] [PubMed]

G. Khanarian, M. A. Mortazavi, and A. J. East, “Phase-matched second-harmonic generation from freestanding periodically stacked polymer films,” Appl. Phys. Lett. 63, 1462–1464 (1993).
[CrossRef]

Myers, L. E.

Padgett, M.

Peshan, P. S.

J. A. Armstrong, N. Bloembergen, J. Ducuing, and P. S. Peshan, “Interactions between light waves in a nonlinear dielectric,” Phys. Rev. 127, 1918–1939 (1962).
[CrossRef]

Pierce, J. W.

Proctor, M.

Pruneri, V.

Reid, D. T.

Sibbett, W.

Sidick, E.

Sleat, W.

Thompson, D. E.

D. E. Thompson, J. D. McMullen, and D. B. Anderson, “Second harmonic generation in GaAs ‘stack of plates’ using high power CO2 laser radiation,” Appl. Phys. Lett. 29, 113–115 (1976).
[CrossRef]

Trebino, R.

White, W. E.

Appl. Phys. Lett. (2)

D. E. Thompson, J. D. McMullen, and D. B. Anderson, “Second harmonic generation in GaAs ‘stack of plates’ using high power CO2 laser radiation,” Appl. Phys. Lett. 29, 113–115 (1976).
[CrossRef]

G. Khanarian, M. A. Mortazavi, and A. J. East, “Phase-matched second-harmonic generation from freestanding periodically stacked polymer films,” Appl. Phys. Lett. 63, 1462–1464 (1993).
[CrossRef]

Electron. Lett. (2)

H. Karlsson, F. Laurell, P. Henriksson, and G. Arvidsson, “Frequency doubling in periodically poled RbTiOAsO4,” Electron. Lett. 32, 556–557 (1996).
[CrossRef]

E. J. Lim, M. M. Fejer, and R. L. Byer, “Second-harmonic generation of green light in periodically poled planar lithium niobate waveguide,” Electron. Lett. 25, 174–175 (1989).
[CrossRef]

IEEE J. Quantum Electron. (1)

M. M. Fejer, G. A. Magel, D. H. Jundt, and R. L. Byer, “Quasi-phase-matched second-harmonic generation: tuning and tolerances,” IEEE J. Quantum Electron. 28, 2631–2654 (1992).
[CrossRef]

J. Opt. Soc. Am. B (2)

Opt. Lett. (12)

M. A. Arbore, M. M. Fejer, M. E. Fermann, A. Hariharan, A. Galvanauskas, and D. Harter, “Frequency doubling of femtosecond erbium-fiber soliton laser in periodically poled lithium niobate,” Opt. Lett. 22, 13–15 (1997).
[CrossRef] [PubMed]

D. T. Reid, M. Padgett, C. McGowan, W. Sleat, M. Ebrahimzadeh, and W. Sibbett, “Light-emitting diodes as measurement devices for femtosecond laser pulses,” Opt. Lett. 22, 233–235 (1997).
[CrossRef] [PubMed]

D. T. Reid, C. McGowan, W. Sleat, M. Ebrahimzadeh, and W. Sibbett, “Compact, efficient 344-MHz repetition-rate femtosecond optical parametric oscillator,” Opt. Lett. 22, 525–527 (1997).
[CrossRef] [PubMed]

M. A. Arbore, O. Marco, and M. M. Fejer, “Pulse compression during second-harmonic generation in aperiodic quasi-phase-matching gratings,” Opt. Lett. 22, 865–867 (1997).
[CrossRef] [PubMed]

M. A. Arbore, A. Galvanauskas, D. Harter, M. H. Chou, and M. M. Fejer, “Engineerable compression of ultrashort pulses by use of second-harmonic generation in chirped-period-poled lithium niobate,” Opt. Lett. 22, 1341–1343 (1997).
[CrossRef]

G. Imeshev, A. Galvanauskas, D. Harter, M. A. Arbore, M. Proctor, and M. M. Fejer, “Engineerable femtosecond pulse shaping by second-harmonic generation with Fourier synthetic quasi-phase-matching gratings,” Opt. Lett. 23, 864–866 (1998).
[CrossRef]

E. Lallier, M. Brevignon, and J. Lehoux, “Efficient second-harmonic generation of CO2 lasers with a quasi-phase-matched GaAs crystal,” Opt. Lett. 23, 1511–1513 (1998).
[CrossRef]

V. Pruneri, S. D. Butterworth, and D. C. Hanna, “Highly efficient green-light generation by quasi-phase-matched frequency doubling of picosecond pulses from an amplified mode-locked Nd:YLF laser,” Opt. Lett. 21, 390–392 (1996).
[CrossRef] [PubMed]

A. Galvanauskas, D. Harter, M. A. Arbore, M. H. Chou, and M. M. Fejer, “Chirped-pulse amplification circuits for fiber amplifiers, based on chirped-period quasi-phase-matching gratings,” Opt. Lett. 23, 1695–1697 (1998).
[CrossRef]

R. L. Fork, O. E. Martinez, and J. P. Gordon, “Negative dispersion using a pair of prisms,” Opt. Lett. 9, 150–152 (1984).
[CrossRef] [PubMed]

E. Sidick, A. Knoesen, and A. Dienes, “Ultrashort-pulsesecond-harmonic generation in quasi-phase-matched dispersive media,” Opt. Lett. 19, 266–268 (1994).
[CrossRef] [PubMed]

M. A. Mortazavi and G. Khanarian, “Quasi-phase-matched frequency doubling in bulk periodic polymeric structures,” Opt. Lett. 19, 1290–1292 (1994).
[CrossRef] [PubMed]

Phys. Rev. (1)

J. A. Armstrong, N. Bloembergen, J. Ducuing, and P. S. Peshan, “Interactions between light waves in a nonlinear dielectric,” Phys. Rev. 127, 1918–1939 (1962).
[CrossRef]

Other (6)

J. C. Diels and W. Rudolph, Ultrashort Laser Pulse Phenomena (Academic, New York, 1996).

M. A. Arbore, A. Galvanauskas, D. Harter, M. H. Chou, and M. M. Fejer, “Compression of ultrashort pulses using second-harmonic generation in aperiodically poled lithium niobate,” in Conference on Lasers and Electro-Optics, Vol. 11 of 1997 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1997), postdeadline paper CPD6–2.

D. T. Reid, P. Loza-Alvarez, M. Ebrahimzadeh, E. U. Rafailov, P. Faller, D. J. L. Birkin, W. Sibbett, H. Karlsson, and F. Laurell, “Femtosecond pulse compression by second-harmonic generation in aperiodically-poled KTP,” in Conference on Lasers and Electro-Optics, Vol. 6 of 1998 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1998), paper CME3.

D. T. Reid, C. McGowan, W. E. Sleat, and W. Sibbett, “A real-time FROG-trace acquisition system for non-amplified femtosecond oscillators,” Opt. Photon. News (Suppl.) 8(5), (1997).

W. H. Press, S. A. Teukolosky, W. T. Vetterling, and B. P. Flannery, Numerical Recipes in Fortran, 2nd ed. (Cambridge U. Press, Cambridge, UK, 1994), Chap. 19, pp. 818–880.

E. U. Rafailov, D. J. L. Birkin, E. A. Avrutin, and W. Sibbett, “High average power short-pulse generation from single-mode InGaAs/GaAs laser diodes,” IEE Proc. Optoelectron. (to be published).

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Figures (10)

Fig. 1
Fig. 1

Experimental setup for simultaneous SHG and pulse compression for the extracavity configuration: M1, highly reflecting curved mirror; M2, end mirror; L, lens.

Fig. 2
Fig. 2

(a) Interferometric autocorrelation and (b) pulse spectrum of the signal output from the RTA-based OPO showing frequency-chirped pulses of Δτ=286 fs, with a spectral bandwidth of 37 nm centered at 1.25 µm. The pulse-duration–bandwidth product is ΔνΔτ=2.00.

Fig. 3
Fig. 3

Pulse characterization of the extracavity SHG pulses from the AP-KTP crystal: (a) intensity autocorrelations showing pulses of Δτ=121 fs (solid curve) for the compression direction and of Δτ=240 (dashed curve) for the expansion direction, (b) interferometric autocorrelation for pulses in the compression direction, (c) spectra of the pulses (for both configurations) centered at 630 nm with a spectral bandwidth of Δλ=8.5 nm. The pulse-duration–bandwidth products obtained were ΔνΔτ=0.77 for the compression direction and ΔνΔτ=1.54 for the expansion direction.

Fig. 4
Fig. 4

Experimental setup for simultaneous SHG and pulse compression for the intracavity configuration: M1, M3, M4, highly reflecting curved mirrors; FM, 5% output coupler; M2, end mirror; L, lens.

Fig. 5
Fig. 5

FROG characterization of the signal output from the RTA-based OPO that shows pulse durations of Δτ=290 fs with positive quadratic phase and with pulse-duration–bandwidth products of ΔνΔτ=2.0: (a) FROG trace, (b) temporal intensity profile and phase of the retrieved pulses, (c) measured (solid curve) and retrieved (dashed curve) intensity autocorrelations, (d) measured (solid curve) and retrieved (dotted curve) spectra of the pulses centered at 1.25 µm and with a spectral bandwidth of 37 nm.

Fig. 6
Fig. 6

Schematic representation of the QPM crystal geometry used in the model.

Fig. 7
Fig. 7

Autocorrelations and spectral measurements of the intracavity SHG pulses generated with the AP-KTP crystal oriented in the expansion direction: (a) intensity and (b) interferometric autocorrelations showing pulse durations of Δτ=222 fs, (c) spectrum of the pulses centered at 620 nm with a spectral bandwidth of Δλ=6 nm. The pulse-duration–bandwidth product is ΔνΔτ=1.04.

Fig. 8
Fig. 8

Pulse characterization from the intracavity SHG, with the AP-KTP crystal oriented for compression, showing pulses as short as 124 fs with a nearly constant phase and a pulse-duration–bandwidth product of ΔνΔτ=0.48: (a) temporal intensity profile and phase obtained with the model, (b) measured (solid curve) and calculated spectra (heavy dashed curve) of the pulses centered at 622 nm with a spectral bandwidth of 5 nm, (c) measured (gray shading) and calculated (solid curves) interferometric autocorrelations, (d) measured (solid curve) and calculated (dashed curve) intensity autocorrelations.

Fig. 9
Fig. 9

Theoretical evolution of the SHG pulses inside the QPM crystal: (a) temporal intensity, (b) temporal phase, (c) FWHM.

Fig. 10
Fig. 10

Second-harmonic pulses predicted by the model by use of different QPM parameters: crystal length L; initial (Λi), final (Λf), and central (Λ0) grating periods; and crystal bandwidth ΔΛ=Λf-Λi. One parameter was varied each time as follows: (a) Λf, Λi constant, with L varied; (b) Λi, L constant, with Λf varied; (c) Λf, L constant, with Λi varied; (d) ΔΛ, L constant, with Λ0 varied; (e) Λ0, L constant, with ΔΛ varied; (f) same as (e), with ΔΛ optimized. In each case the results of the model are compared with the experimentally used crystal parameters (solid curve): L=630 µm, Λi=14.20 µm, Λf=15.45 µm, Λ0=14.835 µm, and ΔΛ=1.25 µm.

Equations (2)

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δA1(z, t)δz+1vg1δA1(z, t)δt=0,
δA2(z, t)δz+1vg2δA2(z, t)δt=Γs(z)A12(z,t)exp(iΔk0z),

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