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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 13, Iss. 26 — Dec. 26, 2005
  • pp: 10882–10887
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Spectral phase optimization of femtosecond laser pulses for narrow-band, low-background nonlinear spectroscopy

Vadim V. Lozovoy, Janelle C. Shane, Bingwei Xu, and Marcos Dantus  »View Author Affiliations


Optics Express, Vol. 13, Issue 26, pp. 10882-10887 (2005)
http://dx.doi.org/10.1364/OPEX.13.010882


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Abstract

We use experimental search space mapping to examine the problem of selective nonlinear excitation with binary phase shaped femtosecond laser pulses. The search space maps represent a graphical view of all the possible solutions to the selective nonlinear excitation problem along with their experimental degrees of success. Using the information learned from these maps, we generate narrow lines with low background in second harmonic generation and stimulated Raman scattering spectra.

© 2005 Optical Society of America

1. Introduction

The ability to produce a narrow tunable peak in the nonlinear spectra of a femtosecond laser would allow nonlinear optical processes such as two-photon excitation and impulsive stimulated Raman excitation to be controlled with a single femtosecond source. Approaches guided empirically and by theory have shown remarkable progress toward this goal [1–5

1 . A. M. Weiner , D. E. Leaird , G. P. Wiederrecht , and K. A. Nelson , “ Femtosecond Pulse Sequences Used for Optical Manipulation of Molecular-Motion ,” Science 247 , 1317 – 1319 ( 1990 ). [CrossRef] [PubMed]

]. It is important not only to be able to generate a strong signal at a desired wavelength (Fig. 1 (a), but also to suppress background elsewhere in the nonlinear spectra (Fig. 1(b), the latter being the goal of this project.

Fig. 1. Nonlinear spectra of phase modulated pulses. The dashed line is the spectrum of a Gaussian transform-limited (flat spectral phase) pulse. (a) Maximization or minimization of nonlinear spectra at a selected frequency. (b) Generation of a narrow peak at a selected frequency with low background (the goal of this project).

2. Experimental section

We measured second harmonic generation (SHG) and simulated Raman scattering (SRS) spectra of pulses from a Ti: Sapphire oscillator (K&M Laboratories) capable of producing 10 fs pulses (110 nm FWHM) centered near 800 nm. The average power of the oscillator was 250 mW, with a repetition frequency of 97 MHz. The beam went through a folded pulse compressor consisting of a pair of SF10 prisms and then into a pulse shaper. The pulse shaper, consisting of a SF10 and a BK7 prism, a 200-mm focal length cylindrical mirror, and a dual-mask SLM (CRI, Inc., SLM-256), is based on the general design of Weiner [12

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

] in the folded geometry. To achieve accurate phase retardations, each pixel of the SLM was carefully calibrated by measuring the polarization-dependent transmission of light through each pixel. The multi-photon intra-pulse interference phase scan (MIIPS) method [13

13 . V. V. Lozovoy , I. Pastirk , and M. Dantus , “ Multiphoton intrapulse interference. IV. Ultrashort laser pulse spectral phase characterization and compensation ,” Opt. Lett. 29 , 775 – 777 ( 2004 ). [CrossRef] [PubMed]

, 14

14 . B. Xu , J. M. Gunn , J. M. DelaCruz , V. V. Lozovoy , and M. Dantus , “ Quantitative investigation of the MIIPS method for phase measurement and compensation of femtosecond laser pulses ,” J.Opt. Soc. Am. B , in press.

] was used for all the experiments to achieve TL pulses at the target within 0.05 radian precision. For SHG experiments, the beam was focused on a 10 μm β-BBO type I crystal and the signal was recorded with a spectrometer of spectral resolution ~0.3 nm. For SRS experiments, the beam was introduced into a balanced Michelson interferometer (FR-103PD, Femtochrome Research, Inc). SRS spectra were retrieved from Fourier transformation of autocorrelation traces obtained by a two-photon diode. Acquisition of a single spectrum requires 0.8 s for SHG and 4 s for SRS; therefore, the 65,536-phase mapping experiments described below lasted 15 hours for SHG and 70 hours for SRS. Significant speedup of acquisition times is possible, for example through use of a single pulse autocorrelator.

3. Results and discussion

3.1 Mapping of exhaustive experimental evaluation

In the first series of experiments we investigated all possible 16-bit binary phase functions for their ability to generate selective SHG and SRS excitation. We applied each phase to the center spectral region of our femtosecond laser pulses, using amplitude shaping to eliminate the signal outside of this spectral window. Each of the 16 logical bits covered 4 SLM pixels for SHG and 3 SLM pixels for SRS. For both SHG and SRS, we defined a window of spectral width 1.3 nm or 50 cm-1; the integrated intensity of the spectrum inside this window was defined as signal S, while the integrated intensity of the spectrum outside the window was defined as background B (Fig. 1). For SRS, we disregarded the spectral region below 150 cm-1, a region that is essentially unaffected by phase shaping. We assigned each phase function a fitness value S/B based on the ratio between integrated signal and integrated background.

Fig. 2. Experimental mapping of selective SHG (left) and SRS (right) at the center of the spectrum (see Fig. 1(b). X and y coordinates are the decimal representations of the left and right halves of the binary phase sequences, respectively, and color as z coordinate is the experimentally measured signal to background ratio of nonlinear excitation. Here, phase sequences with high S/B ratios are shown in red, while sequences with low S/B ratios are shown in black. Arrows point to the locations of the global maxima. [Media 1] [Media 2]

As the target signal wavelength is scanned across the nonlinear spectrum, the center of symmetry that maximizes this signal is scanned across the phase function. Movie 1 and movie 2 show the SHG or SRS maps when signal window is scanned from one end of the spectrum to the other. In each case, the phase functions with the highest S/B ratios are located on lines that contain only symmetric or antisymmetric phases, with the locations of the lines changing to reflect the changing location of the center or symmetry.

3.2 Experimental scanning of narrow peaks in SHG and SRS spectra

We examined not only phase functions to optimize nonlinear signal at the center of the spectrum produced by a TL pulse, but also functions that optimized signal at other locations in the nonlinear spectra. Symmetry provides maximization of the signal at a selected frequency. When this frequency is detuned from the center of the spectrum, the required center of symmetry is detuned as well, resulting in SLM pixels at the far end of the spectrum that do not contribute to the symmetry. These extra pixels only contribute to background, so for our experiments we eliminated signal from these locations using amplitude shaping.

Fig. 3. Experimental generation (dots) and simulation (red) of narrow-band and low-background nonlinear fields using optimized binary phase functions. (a) and (b) Phase (black) and amplitude (red) modulation was imprinted with the SLM on a broad fundamental pulse. (c) SHG spectrum measured with a nonlinear crystal. (d) SRS spectrum recorded as the Fourier transform of the autocorrelation trace using a collinear Michelson interferometer. [Media 3] [Media 4]

The ultimate goal for our shaped pulses is to apply them to a source producing ultrabroad bandwidth. The bandwidth of modern lasers with chirped mirrors or from continuum generation in fibers would allow spectral tuning from 300 to 550 nm for the two photon field and up to 5000 cm-1 for Raman scattering. Using a 640-pixel shaper with optical resolution of one pixel will improve the resolution down to few wave numbers and essentially eliminate the background.

4. Conclusion

Acknowledgments

References and Links

1 .

A. M. Weiner , D. E. Leaird , G. P. Wiederrecht , and K. A. Nelson , “ Femtosecond Pulse Sequences Used for Optical Manipulation of Molecular-Motion ,” Science 247 , 1317 – 1319 ( 1990 ). [CrossRef] [PubMed]

2 .

Z. Zheng and A. M. Weiner , “ Coherent control of second harmonic generation using spectrally phase coded femtosecond waveforms ,” Chem. Phys. 267 , 161 – 171 ( 2001 ). [CrossRef]

3 .

D. Meshulach and Y. Silberberg , “ Coherent quantum control of two-photon transitions by a femtosecond laser pulse ,” Nature 396 , 239 – 242 ( 1998 ). [CrossRef]

4 .

D. Oron , N. Dudovich , and Y. Silberberg , “ Femtosecond phase-and-polarization control for background-free coherent anti-Stokes Raman spectroscopy ,” Phys. Rev. Lett. 90 , 213902 ( 2003 ). [CrossRef] [PubMed]

5 .

J. M. Dela Cruz , I. Pastirk , V. V. Lozovoy , K. A. Walowicz , and M. Dantus , “ Multiphoton intrapulse interference 3: Probing microscopic chemical environments ,” J. Phys. Chem. A 108 , 53 – 58 ( 2004 ). [CrossRef]

6 .

H. A. Rabitz , M. M. Hsieh , and C. M. Rosenthal , “ Quantum optimally controlled transition landscapes ,” Science 303 , 1998 – 2001 ( 2004 ). [CrossRef] [PubMed]

7 .

M. Comstock , V. V. Lozovoy , I. Pastirk , and M. Dantus , “ Multiphoton intrapulse interference 6; binary phase shaping ,” Opt. Express 12 , 1061 – 1066 ( 2004 ). [CrossRef] [PubMed]

8 .

K. A. Walowicz , I. Pastirk , V. V. Lozovoy , and M. Dantus , “ Multiphoton intrapulse interference. 1. Control of multiphoton processes in condensed phases ,” J. Phys. Chem. A 106 , 9369 – 9373 ( 2002 ). [CrossRef]

9 .

V. V. Lozovoy , I. Pastirk , K. A. Walowicz , and M. Dantus , “ Multiphoton intrapulse interference. II. Control of two- and three-photon laser induced fluorescence with shaped pulses ,” J. Chem. Phys. 118 , 3187 – 3196 ( 2003 ). [CrossRef]

10 .

I. Pastirk , J. M. Dela Cruz , K. A. Walowicz , V. V. Lozovoy , and M. Dantus , “ Selective two-photon microscopy with shaped femtosecond pulses ,” Opt. Express 11 , 1695 – 1701 ( 2003 ). [CrossRef] [PubMed]

11 .

V. V. Lozovoy and M. Dantus , “ Systematic control of nonlinear optical processes using optimally shaped femtosecond pulses ,” Chem. Phys. Chem. 6 , 1952 – 1967 ( 2005 ). [CrossRef]

12 .

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

13 .

V. V. Lozovoy , I. Pastirk , and M. Dantus , “ Multiphoton intrapulse interference. IV. Ultrashort laser pulse spectral phase characterization and compensation ,” Opt. Lett. 29 , 775 – 777 ( 2004 ). [CrossRef] [PubMed]

14 .

B. Xu , J. M. Gunn , J. M. DelaCruz , V. V. Lozovoy , and M. Dantus , “ Quantitative investigation of the MIIPS method for phase measurement and compensation of femtosecond laser pulses ,” J.Opt. Soc. Am. B , in press.

15 .

V. V. Lozovoy , B. Xu , J. C. Shane , and M. Dantus , “ Selective nonlinear excitation with pseudorandom Galois fields ,” to be published ( 2005 ).

16 .

J. M. Dela Cruz , I. Pastirk , M. Comstock , V. V. Lozovoy , and M. Dantus , “ Use of coherent control methods through scattering biological tissue to achieve functional imaging ,” P. Natl. Acad. Sci. USA 101 , 16996 – 17001 ( 2004 ). [CrossRef]

17 .

I. Pastirk , M. Kangas , and M. Dantus , “ Multidimensional analytical method based on binary phase shaping of femtosecond pulses ,” J. Phys. Chem. A 109 , 2413 – 2416 ( 2005 ). [CrossRef]

18 .

J. M. Dela Cruz , V. V. Lozovoy , and M. Dantus , “ Quantitative mass spectrometric identification of isomers applying coherent laser control ,” J. Phys. Chem. A 109 , 8447 – 8450 ( 2005 ). [CrossRef]

OCIS Codes
(320.5540) Ultrafast optics : Pulse shaping
(320.7110) Ultrafast optics : Ultrafast nonlinear optics

ToC Category:
Research Papers

Citation
Vadim V. Lozovoy, Janelle C. Shane, Bingwei Xu, and Marcos Dantus, "Spectral phase optimization of femtosecond laser pulses for narrow-band, low-background nonlinear spectroscopy," Opt. Express 13, 10882-10887 (2005)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-13-26-10882


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References

  1. A. M. Weiner, D. E. Leaird, G. P. Wiederrecht, and K. A. Nelson, "Femtosecond pulse sequences used for optical manipulation of molecular-motion," Science 247, 1317-1319 (1990). [CrossRef] [PubMed]
  2. Z. Zheng, and A. M. Weiner, "Coherent control of second harmonic generation using spectrally phase coded femtosecond waveforms," Chem. Phys. 267, 161-171 (2001). [CrossRef]
  3. D. Meshulach, and Y. Silberberg, "Coherent quantum control of two-photon transitions by a femtosecond laser pulse," Nature 396, 239-242 (1998). [CrossRef]
  4. D. Oron, N. Dudovich, and Y. Silberberg, "Femtosecond phase-and-polarization control for background-free coherent anti-Stokes Raman spectroscopy," Phys. Rev. Lett. 90, 213902 (2003). [CrossRef] [PubMed]
  5. J. M. Dela Cruz, I. Pastirk, V. V. Lozovoy, K. A. Walowicz, and M. Dantus, "Multiphoton intrapulse interference 3: Probing microscopic chemical environments," J. Phys. Chem. A 108, 53-58 (2004). [CrossRef]
  6. H. A. Rabitz, M. M. Hsieh, and C. M. Rosenthal, "Quantum optimally controlled transition landscapes," Science 303, 1998-2001 (2004). [CrossRef] [PubMed]
  7. K. A. Walowicz, I. Pastirk, V. V. Lozovoy, and M. Dantus, "Multiphoton intrapulse interference. 1. Control of multiphoton processes in condensed phases," J. Phys. Chem. A 106, 9369-9373 (2002). [CrossRef]
  8. V. V. Lozovoy, I. Pastirk, K. A. Walowicz, and M. Dantus, "Multiphoton intrapulse interference. II Control of two- and three-photon laser induced fluorescence with shaped pulses," J. Chem. Phys. 118, 3187-3196 (2003). [CrossRef]
  9. I. Pastirk, J. M. Dela Cruz, K. A. Walowicz, V. V. Lozovoy, and M. Dantus, "Selective two-photon microscopy with shaped femtosecond pulses," Opt. Express 11, 1695-1701 (2003)<a href= http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-14-1695>http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-14-1695</a>. [CrossRef] [PubMed]
  10. V. V. Lozovoy, and M. Dantus, "Systematic control of nonlinear optical processes using optimally shaped femtosecond pulses," Chem. Phys. Chem. 6, 1952-1967 (2005). [CrossRef]
  11. A. M. Weiner, "Femtosecond pulse shaping using spatial light modulators," Rev. Sci. Instrum. 71, 1929-1960 (2000). [CrossRef]
  12. V. V. Lozovoy, I. Pastirk, and M. Dantus, "Multiphoton intrapulse interference. IV. Ultrashort laser pulse spectral phase characterization and compensation," Opt. Lett. 29, 775-777 (2004). [CrossRef] [PubMed]
  13. B. Xu, J. M. Gunn, J. M. DelaCruz, V. V. Lozovoy, and M. Dantus, "Quantitative investigation of the MIIPS method for phase measurement and compensation of femtosecond laser pulses," J.Opt. Soc. Am. B, in press.
  14. V. V. Lozovoy, B. Xu, J. C. Shane, and M. Dantus, "Selective nonlinear excitation with pseudorandom Galois fields," to be published (2005).
  15. J. M. Dela Cruz, I. Pastirk, M. Comstock, V. V. Lozovoy, and M. Dantus, "Use of coherent control methods through scattering biological tissue to achieve functional imaging," P. Natl. Acad. Sci. USA 101, 16996-17001 (2004). [CrossRef]
  16. I. Pastirk, M. Kangas, and M. Dantus, "Multidimensional analytical method based on binary phase shaping of femtosecond pulses," J. Phys. Chem. A 109, 2413-2416 (2005). [CrossRef]
  17. J. M. Dela Cruz, V. V. Lozovoy, and M. Dantus, "Quantitative mass spectrometric identification of isomers applying coherent laser control," J. Phys. Chem. A 109, 8447-8450 (2005). [CrossRef]

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