OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 18 — Aug. 29, 2011
  • pp: 17127–17132
« Show journal navigation

Broadband conversion in an Yb:KYW-pumped ultrafast optical parametric oscillator with a long nonlinear crystal

Zhaowei Zhang, Jinghua Sun, Tom Gardiner, and Derryck T. Reid  »View Author Affiliations


Optics Express, Vol. 19, Issue 18, pp. 17127-17132 (2011)
http://dx.doi.org/10.1364/OE.19.017127


View Full Text Article

Acrobat PDF (1280 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We report the generation of 200-nm-bandwidth mid-infrared pulses at 3.5-µm from an optical parametric oscillator incorporating a 25-mm MgO:PPLN crystal and synchronously-pumped by chirped pulses from a fiber-amplified Yb:KYW laser. A long nonlinear crystal permits efficient transfer of the pump bandwidth into the idler pulses, achieves exceptional passive stability and enables pumping using chirped pulses directly from a fiber-amplifier, avoiding the need to use lossy pulse-compression optics.

© 2011 OSA

1. Introduction

Femtosecond lasers based on Yb-doped gain media are becoming established as serious competitors to Ti:sapphire in many applications because of their compatibility with high-gain Yb-fiber amplifiers, which enable their average powers to be scaled to several Watts. Most practical ultrafast fiber-amplifiers adopt a chirped-pulse amplification (CPA) approach [1

1. A. Galvanauskas, “Mode-scalable fiber-based chirped pulse amplification systems,” IEEE J. Sel. Top. Quantum Electron. 7(4), 504–517 (2001). [CrossRef]

] in which the seed pulses are stretched, amplified, then re-compressed after amplification. The final compression stage is normally unavoidably lossy – requiring a double-pass through a diffraction-grating pair – and even the best transmission gratings introduce 20 - 30% loss in this configuration. In this paper we present an optical parametric oscillator (OPO) which is directly pumped by the chirped 3-ps output of an Yb-fiber amplifier, seeded by a Yb:KYW laser, eliminating the need for post-amplification pulse compression. Our scheme exploits an inflexion point of the phase-matching curve in a long MgO:PPLN crystal, which allows efficient parametric transfer of the pump bandwidth into the idler pulses for a narrowband resonant signal pulse. Broadband idler pulses of the kind available from the OPO have immediate applications in femtosecond Fourier-transform infrared spectroscopy [2

2. K. A. Tillman, R. R. J. Maier, D. T. Reid, and E. D. McNaghten, “Mid-infrared absorption spectroscopy of methane using a broadband femtosecond optical parametric oscillator based on aperiodically poled lithium niobate,” J. Opt. A, Pure Appl. Opt. 7(6), S408–S414 (2005). [CrossRef]

,3

3. N. Gayraud, U. W. Kornaszewski, J. M. Stone, J. C. Knight, D. T. Reid, D. P. Hand, and W. N. MacPherson, “Mid-infrared gas sensing using a photonic bandgap fiber,” Appl. Opt. 47(9), 1269–1277 (2008). [PubMed]

].

2. Broadband Phasematching using a Long MgO:PPLN Crystal

It is well known that certain crystals possess unique phase-matching properties permitting efficient coupling between broadband and narrowband waves. Examples include Type-I BBO, used in broadband OPOs [4

4. G. M. Gale, M. Cavallari, T. J. Driscoll, and F. Hache, “Sub-20-fs tunable pulses in the visible from an 82-MHz optical parametric oscillator,” Opt. Lett. 20(14), 1562–1564 (1995). [CrossRef] [PubMed]

], and Type-II KDP, with applications in optical pulse characterization [5

5. D. T. Reid and I. G. Cormack, “Single-shot sonogram: a real-time chirp monitor for ultrafast oscillators,” Opt. Lett. 27(8), 658–660 (2002). [CrossRef] [PubMed]

,6

6. A. S. Radunsky, E. M. Kosik Williams, I. A. Walmsley, P. Wasylczyk, W. Wasilewski, A. B. U’Ren, and M. E. Anderson, “Simplified spectral phase interferometry for direct electric-field reconstruction by using a thick nonlinear crystal,” Opt. Lett. 31(7), 1008–1010 (2006). [CrossRef] [PubMed]

]. Quasi-phase-matched MgO:PPLN exhibits phasematching properties which permit broadband pump pulses to efficiently amplify narrowband signal pulses, even for long crystals. Figure 1(a)
Fig. 1 (a) Phase-matching map for a 25-mm MgO:PPLN crystal at 40°C with a 30-µm grating period. The color scale is linear with sinc2kL/2) and the map was calculated using the Sellmeier data of [7]. The solid white lines are sections along the dashed lines. (b) Group delay variation with wavelength in a 25-mm long MgO:PPLN crystal. Experimental pump, signal and idler wavelengths are indicated, showing near-perfect group-velocity matching of the pump and idler pulses, with a transit-time difference of < 500 fs after 25 mm propagation.
illustrates this scenario by showing the phase-matching map for a 25-mm-long MgO:PPLN crystal with a grating period of 30 µm and a temperature of 40°C.

3. Experiment

3.1 Pump Source

The pump was a master-oscillator-power-amplifier (MOPA) and is shown in Fig. 2
Fig. 2 Schematic of the OPO pump source. HWP, half-waveplate; L, lens; ISO, isolator.
. The seed laser was a single-mode-diode-pumped, semiconductor-saturable-absorber-mirror modelocked Yb:KYW laser, which produced pulses with FWHM (full-width at half-maximum) durations of 250 fs, and spectra centred at 1045 nm with FWHM bandwidths of 5 nm. The average output power was 150 mW and the repetition rate was 94 MHz. The seed was amplified by a cladding-pumped Yb-doped fiber amplifier, pumped by a 6-W, 915-nm multimode fiber-coupled diode laser. The amplifier fiber was a 6-m long, double-clad fiber with a single-mode and polarization-maintaining (PM) core. With 6 W pump power we obtained 2.5 W output power in a spectrum (Fig. 3(a)
Fig. 3 (a) Spectrum. and (b) IAC of the pump pulses.
) broadened to a FWHM bandwidth of 18 nm (4.82 THz) due to self-phase modulation effects in the amplifier, while the central wavelength of the output pulses was red-shifted to 1058 nm because of the large difference between the central wavelengths of the amplifier gain and seed laser. The output pulses were strongly chirped due to the normal dispersion of the amplifier fiber. With an interferometric autocorrelation (IAC) technique based on two-photon absorption (TPA) [10

10. D. T. Reid, M. Padgett, C. McGowan, W. E. Sleat, and W. Sibbett, “Light-emitting diodes as measurement devices for femtosecond laser pulses,” Opt. Lett. 22(4), 233–235 (1997). [CrossRef] [PubMed]

,11

11. D. T. Reid, W. Sibbett, J. M. Dudley, L. P. Barry, B. Thomsen, and J. D. Harvey, “Commercial semiconductor devices for two-photon absorption autocorrelation of ultrashort light pulses,” Appl. Opt. 37, 8142 (1998). [CrossRef]

], the durations of the amplified pulses were determined to be ~3.0 ps, corresponding to a duration-bandwidth-product (DBP) of 14.3. The IAC trace for the amplifier output pulses at the maximum pump power is shown in Fig. 3(b). By adjusting the half-wave plate so that the seed polarization was launched parallel to the slow axis of the PM amplifier fiber, a linearly polarized output was obtained.

3.2 OPO Cavity Configuration

The OPO crystal was 5-mol.% MgO:PPLN (HC Photonics) and was 25-mm long and 1-mm thick, with a grating period of 30 µm, and was housed in an aluminum heat-sink held at 30 °C. The cavity is shown in Fig. 4
Fig. 4 OPO layout: HWP, half-wave plate: ISO, isolator; L, lens. See text for other definitions.
, in which focusing mirrors M1 and M2 (radius of curvature 150 mm) and plane mirror M3 were coated on YAG substrates for high transmission at the pump and idler wavelengths (T >90% at 1020 – 1110 nm and 2.3 – 3.7 µm), and high reflectivity at the signal wavelength (R >99.8% at 1.4 – 1.8 µm). The OPO was singly resonant for the signal, which was extracted via a 2 – 20% output coupler (OC). The cavity length was adjusted for synchronism with the pump laser. The idler and depleted pump passed through M2 and were collimated by an anti-reflection (AR) coated CaF2 lens, following which an AR-coated Ge window was used to isolate the idler pulses prior to characterization.

3.3 Results and Discussion

With the 2% OC, the threshold pump power was 200 mW, and Fig. 5(a)
Fig. 5 (a) The output signal/idler power; (b) residual pump power exiting from the OPO; (c) spectra of the undepleted and depleted (dashed line) pump pulses at maximum pump power.
shows the measured signal / idler powers, and the idler power inferred from the signal power by using the Manley-Rowe relationship (assuming signal and idler wavelengths of 1503 nm and 3575 nm respectively). The discrepancy between the measured and derived idler power arises largely from the non-optimized anti-reflection coatings of the crystal at the idler wavelength, estimated to have R ≤ 40%. Figure 5(b) shows the residual pump power coupled from M2 versus the incident pump power. At the maximum incident pump power of 2.2 W, 603 mW signal and 144 mW idler were measured, while 252 mW idler power was inferred. The quantum conversion efficiencies for the signal and idler outputs were 39% and 22% respectively, and the pump conversion was 75%. When a 10% OC was used, the threshold and maximum signal power were 400 mW and 910 mW respectively. The signal quantum conversion efficiency was 59%. With a 20% OC, the threshold power and maximum signal output power were 800 mW and 510 mW respectively, with a signal quantum conversion efficiency of 33%. A 2% OC was used in all of the other results presented here. Figure 5(c) shows the spectra of the undepleted and depleted pump pulses at 2.2-W pump power. The intensity is normalized to the measured depletion ratio of 75% and the data show that the pump was depleted uniformly across most of its bandwidth, with negligible back-conversion.

The signal spectrum of the OPO, pumped at full power, is shown in Fig. 6(a)
Fig. 6 (a) Measured signal spectrum, and (b) corresponding interferometric autocorrelation. (c) Measured idler spectrum, and (d) corresponding interferometric autocorrelation.
. Its central wavelength is 1503 nm and its FWHM was measured to be 2.4 nm (0.32 THz). This bandwidth is much narrower than the pump bandwidth (4.8 THz), implying that a broadband idler can be obtained, because the pump spectrum is the convolution of the signal and idler spectra, and almost the full width of the pump spectrum was depleted in the OPO. Such a narrow signal bandwidth is mainly due to the relatively long MgO:PPLN grating. The origin of the satellite peak at 1527 nm is unclear, however this wavelength is phasematched to the edges of the pump spectrum by a +/− 50-nm domain error, which is within the tolerance of the crystal photomask design. The signal pulses at full pump power were measured using the IAC technique based on TPA by using a Si photodiode [11

11. D. T. Reid, W. Sibbett, J. M. Dudley, L. P. Barry, B. Thomsen, and J. D. Harvey, “Commercial semiconductor devices for two-photon absorption autocorrelation of ultrashort light pulses,” Appl. Opt. 37, 8142 (1998). [CrossRef]

], and the result shown in Fig. 6(b) implied a FWHM duration of ~1.4 ps. The DBP was calculated to be 0.45, showing that the signal pulses were moderately chirped.

Figure 6(c) presents the idler spectrum obtained at full pump power, measured with a scanning monochromator. Its central wavelength is 3573 nm and its FWHM bandwidth is 200 nm (4.70 THz), closely following the pump bandwidth of 4.82 THz and confirming effective parametric transfer, as expected from theory. The IAC of the idler pulse at full pump power was measured using TPA in an extended-InGaAs photodiode [11

11. D. T. Reid, W. Sibbett, J. M. Dudley, L. P. Barry, B. Thomsen, and J. D. Harvey, “Commercial semiconductor devices for two-photon absorption autocorrelation of ultrashort light pulses,” Appl. Opt. 37, 8142 (1998). [CrossRef]

] (see Fig. 6(d)) and implied a FWHM duration of ~3.0 ps and DBP of 14.1, nearly identical to that of the pump pulses.

The output power stability of the signal at 1503 nm was detected with an InGaAs photodiode and recorded in the time domain over a period of 16 seconds with a sampling rate of 256 kHz. The corresponding relative intensity noise (RIN) and cumulative power error were calculated and shown in Fig. 7
Fig. 7 Left axis: RIN of the pump laser (green) and OPO signal output (black). Right axis: the cumulative power fluctuations of the pump laser (green) and OPO signal output (black).
. For comparison, the pump power stability was also recorded and shown in Fig. 7. The cumulative power fluctuation of the OPO signal output was around 0.1%. This excellent power-stability is attributed to the use of the long nonlinear crystal, which introduces large dispersion in the OPO cavity and therefore reduces the sensitivity of the signal central wavelength to fluctuations in the OPO cavity length arising from mechanical vibrations or temperature variations. To demonstrate this, we recorded the signal central wavelength of the OPO as a function of the cavity length detuning. The OPO oscillated over a cavity-length detuning range of 0.12 mm, and over this tuning range, the variation of the signal wavelength was less than 3 nm.

4. Summary and Conclusions

We have presented a mid-infrared MgO:PPLN OPO synchronously-pumped by chirped pulses from a Yb:fiber amplifier and exhibiting a quantum conversion efficiency of up to 59%. With 2.2 W incident pump power, 144 mW average power of idler was directly measured at a central wavelength of 3573 nm and with a 200-nm FWHM bandwidth.

We attribute the broadband idler spectrum to the use of a long MgO:PPLN crystal, whose phasematching provides a narrow signal acceptance bandwidth when pumped near 1050 nm, facilitating accurate parametric transfer from the broadband pump to the idler. The principal advantages of this scheme are its compatibility with using chirped pump pulses, which eliminates the complexity and loss associated with compressing the pulses leaving the fiber amplifier, and low back-conversion because of the broad acceptance bandwidth at the pump wavelength.

Acknowledgments

The authors gratefully acknowledge financial support from the UK Engineering and Physical Sciences Research Council under grants EP/H018190/1 and EP/H000011/1, and from the United Kingdom's National Physical Laboratory under its Strategic Research Programme.

References and links

1.

A. Galvanauskas, “Mode-scalable fiber-based chirped pulse amplification systems,” IEEE J. Sel. Top. Quantum Electron. 7(4), 504–517 (2001). [CrossRef]

2.

K. A. Tillman, R. R. J. Maier, D. T. Reid, and E. D. McNaghten, “Mid-infrared absorption spectroscopy of methane using a broadband femtosecond optical parametric oscillator based on aperiodically poled lithium niobate,” J. Opt. A, Pure Appl. Opt. 7(6), S408–S414 (2005). [CrossRef]

3.

N. Gayraud, U. W. Kornaszewski, J. M. Stone, J. C. Knight, D. T. Reid, D. P. Hand, and W. N. MacPherson, “Mid-infrared gas sensing using a photonic bandgap fiber,” Appl. Opt. 47(9), 1269–1277 (2008). [PubMed]

4.

G. M. Gale, M. Cavallari, T. J. Driscoll, and F. Hache, “Sub-20-fs tunable pulses in the visible from an 82-MHz optical parametric oscillator,” Opt. Lett. 20(14), 1562–1564 (1995). [CrossRef] [PubMed]

5.

D. T. Reid and I. G. Cormack, “Single-shot sonogram: a real-time chirp monitor for ultrafast oscillators,” Opt. Lett. 27(8), 658–660 (2002). [CrossRef] [PubMed]

6.

A. S. Radunsky, E. M. Kosik Williams, I. A. Walmsley, P. Wasylczyk, W. Wasilewski, A. B. U’Ren, and M. E. Anderson, “Simplified spectral phase interferometry for direct electric-field reconstruction by using a thick nonlinear crystal,” Opt. Lett. 31(7), 1008–1010 (2006). [CrossRef] [PubMed]

7.

O. Paul, A. Quosig, T. Bauer, M. Nittmann, J. Bartschke, G. Anstett, and J. A. L’Huillier, “Temperature-dependent Sellmeier equation in the MIR for the extraordinary refractive index of 5% MgO doped congruent LiNbO3,” Appl. Phys. B 86(1), 111–115 (2006). [CrossRef]

8.

A. V. Smith, “Bandwidth and group-velocity effects in nanosecond optical parametric amplifiers and oscillators,” J. Opt. Soc. Am. B 22(9), 1953 (2005). [CrossRef]

9.

H. S. S. Hung, J. Prawiharjo, N. K. Daga, D. C. Hanna, and D. P. Shepherd, “Experimental investigation of parametric transfer in synchronously pumped optical parametric oscillators,” J. Opt. Soc. Am. B 24(12), 2998 (2007). [CrossRef]

10.

D. T. Reid, M. Padgett, C. McGowan, W. E. Sleat, and W. Sibbett, “Light-emitting diodes as measurement devices for femtosecond laser pulses,” Opt. Lett. 22(4), 233–235 (1997). [CrossRef] [PubMed]

11.

D. T. Reid, W. Sibbett, J. M. Dudley, L. P. Barry, B. Thomsen, and J. D. Harvey, “Commercial semiconductor devices for two-photon absorption autocorrelation of ultrashort light pulses,” Appl. Opt. 37, 8142 (1998). [CrossRef]

OCIS Codes
(140.7090) Lasers and laser optics : Ultrafast lasers
(190.4410) Nonlinear optics : Nonlinear optics, parametric processes
(190.4970) Nonlinear optics : Parametric oscillators and amplifiers
(190.7110) Nonlinear optics : Ultrafast nonlinear optics

ToC Category:
Nonlinear Optics

History
Original Manuscript: June 2, 2011
Revised Manuscript: July 29, 2011
Manuscript Accepted: July 29, 2011
Published: August 17, 2011

Citation
Zhaowei Zhang, Jinghua Sun, Tom Gardiner, and Derryck T. Reid, "Broadband conversion in an Yb:KYW-pumped ultrafast optical parametric oscillator with a long nonlinear crystal," Opt. Express 19, 17127-17132 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-18-17127


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. A. Galvanauskas, “Mode-scalable fiber-based chirped pulse amplification systems,” IEEE J. Sel. Top. Quantum Electron. 7(4), 504–517 (2001). [CrossRef]
  2. K. A. Tillman, R. R. J. Maier, D. T. Reid, and E. D. McNaghten, “Mid-infrared absorption spectroscopy of methane using a broadband femtosecond optical parametric oscillator based on aperiodically poled lithium niobate,” J. Opt. A, Pure Appl. Opt. 7(6), S408–S414 (2005). [CrossRef]
  3. N. Gayraud, U. W. Kornaszewski, J. M. Stone, J. C. Knight, D. T. Reid, D. P. Hand, and W. N. MacPherson, “Mid-infrared gas sensing using a photonic bandgap fiber,” Appl. Opt. 47(9), 1269–1277 (2008). [PubMed]
  4. G. M. Gale, M. Cavallari, T. J. Driscoll, and F. Hache, “Sub-20-fs tunable pulses in the visible from an 82-MHz optical parametric oscillator,” Opt. Lett. 20(14), 1562–1564 (1995). [CrossRef] [PubMed]
  5. D. T. Reid and I. G. Cormack, “Single-shot sonogram: a real-time chirp monitor for ultrafast oscillators,” Opt. Lett. 27(8), 658–660 (2002). [CrossRef] [PubMed]
  6. A. S. Radunsky, E. M. Kosik Williams, I. A. Walmsley, P. Wasylczyk, W. Wasilewski, A. B. U’Ren, and M. E. Anderson, “Simplified spectral phase interferometry for direct electric-field reconstruction by using a thick nonlinear crystal,” Opt. Lett. 31(7), 1008–1010 (2006). [CrossRef] [PubMed]
  7. O. Paul, A. Quosig, T. Bauer, M. Nittmann, J. Bartschke, G. Anstett, and J. A. L’Huillier, “Temperature-dependent Sellmeier equation in the MIR for the extraordinary refractive index of 5% MgO doped congruent LiNbO3,” Appl. Phys. B 86(1), 111–115 (2006). [CrossRef]
  8. A. V. Smith, “Bandwidth and group-velocity effects in nanosecond optical parametric amplifiers and oscillators,” J. Opt. Soc. Am. B 22(9), 1953 (2005). [CrossRef]
  9. H. S. S. Hung, J. Prawiharjo, N. K. Daga, D. C. Hanna, and D. P. Shepherd, “Experimental investigation of parametric transfer in synchronously pumped optical parametric oscillators,” J. Opt. Soc. Am. B 24(12), 2998 (2007). [CrossRef]
  10. D. T. Reid, M. Padgett, C. McGowan, W. E. Sleat, and W. Sibbett, “Light-emitting diodes as measurement devices for femtosecond laser pulses,” Opt. Lett. 22(4), 233–235 (1997). [CrossRef] [PubMed]
  11. D. T. Reid, W. Sibbett, J. M. Dudley, L. P. Barry, B. Thomsen, and J. D. Harvey, “Commercial semiconductor devices for two-photon absorption autocorrelation of ultrashort light pulses,” Appl. Opt. 37, 8142 (1998). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited