OSA/ CLEO 2011
QMC2.pdf
Single attosecond pulse generation using GDOG without the need to stabilize Carrier-Envelope phase Yi Wu1, Sabih D. Khan2, Steve Gilbertson2, Michael Chini1,2 and Zenghu Chang1,2 1
CREOL and Department of Physics, University of Central Florida, Orlando, Florida 32816, USA 2
Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA
Abstract: We demonstrate that CE phase stability is not required in GDOG method to generate single attosecond pulses when gate width is set smaller than optical cycle. Introduction Single attosecond pulses have been utilized in a variety of experiments with atoms, molecules and solids [1]. However, the requirement of carrier-envelope (CE) phase stability and single cycle pulses, have kept this technology accessible to a handful of laboratories worldwide. Furthermore, CE phase locking is a major bottleneck for pettawatt (PW) class lasers to generate single attosecond pulses, thus preventing scaling up the photon flux. Recently, double optical gating (DOG) was demonstrated to generate single attosecond pulses from multi-cycle lasers [2] and generalized double optical gating (GDOG) has demonstrated single attosecond pulses directly from a CE phase locked chirped pulse amplifier [3] , thereby opening possibilities to scale up the photon flux. In this paper, we report generation of single attosecond pulses from multi-cycle lasers without the need to lock the CE phase. We demonstrate that if a sufficiently narrow gate width is set then only single attosecond pulse is produced at any value of CE phase. Experimental Setup For this experiment, a 9 fs laser pulse was produced by compressing 2 mJ, 25 fs, 2 kHz, 800 nm pulses produced by a 14 pass CE-phase stabilized chirped pulse amplifier (Kansas Light Source) [4] and using a Neon filled hollow-core fiber and chirped mirrors compressor. To achieve a gate width of ~1.4 fs, 80% of a 9 fs beam is passed through the GDOG optics [3] which include a 530 µm quartz plate (T d = 5 optical cycles), a 0.5mm Brewster window, a 440 µm quartz plate and 141 µm barium borate crystal (BBO). This GDOG pulse is sent into the attosecond streak camera [3] to generate attosecond pulses in a 1.4mm long Argon filled gas cell and is streaked with linear polarized pulses on a Krypton filled gas jet, the details of the attosecond streak camera setup are given elsewhere [3]. Results and Discussion The photoelectron spectra obtained by changing the CE phase is presented in figure 1 (a). The spectrum is continuum for all values of CE phase, which satisfies the necessary condition for generating a single attosecond pulse. There may be two extreme cases, first is when electron is born in a linearly polarized field but recombines in an increasingly elliptical field, leading to a lower flux due to reduced recombination probability. In the second case, the electron spends all of its excursion time away from the nuclear core in a mainly linearly polarized field, which leads to maximized photon flux. The plot in figure 1(a) shows the signal of the CE phase integrated along the energy spectrum, which is related to the intensity of the spectrum. It is quite evident that the intensity of the attosecond pulse is a strong function of CE phase and the signal fluctuates between the two extreme cases. Figure 1(b) shows the streaked spectrogram when the CE phase is unlocked. The temporal intensity and phase as retrieved by the FROG-CRAB method [5] is presented in figure 1(c). The retrieved pulse duration is 182 as. Streaked spectrograms were also recorded for CE phases of 0, π/2, π and 3π/2 and reported elsewhere [6]. The retrieved pulse duration was 180 as when CE phase was 0 and π and was 182 as when it was π/2 and 3π/2. The ratio
OSA/ CLEO 2011
QMC2.pdf
between the main pulse and pre and post pulses is ~10-5 for each of the four cases. The photoelectron spectra for each of these values of CE phase is presented in figure 1(d). It can be seen that the spectral width in each of these cases is similar. It is important to note that although the CE phase of the driving laser pulse is locked, the absolute values are different in the generation and streaking leg of the streak camera because dispersion is not same in the two paths. The retrieved pulse duration of the locked and unlocked cases have less than 5% error, proving that CE phase stability is not needed to generate similar attosecond pulses when gate width is narrow enough.
Figure 1, Photoelectron spectra of attosecond pulses as a function of CE phase is given in (a). In (b) a streaked spectrogram is given when CE phase is unlocked and retrieved temporal profile (solid line) and phase (dashed line) is given in (c) using FROG-CRAB. The photoelectron energy spectrum when CE phase is locked at 0, π/2, π and 3π/2 is given in (d). [6]
Conclusion In conclusion, we have experimentally demonstrated that when gate width is set narrow enough, CE stability is not required to generate a single attosecond pulse using GDOG technique. The attosecond pulses produced with unlocked CE phase and for four different values of CE phase appear to be similar in profile and phase and furthermore, the pulse duration is the same within an error of 5%. We have also seen that the photon flux is a strong function of the CE phase. However, this result is still important as the GDOG method now gives the ability to produce single attosecond pulses from PW class lasers and scale up the photon flux and may lead to nonlinear attosecond science. References [1] A. Scrinzi et al., J. Phys. B, 39, R1 (2206) [2] H. Mashiko et al. Phys. Rev. Lett., 100, 103906 (2008) [3] X. Feng et al., Phys. Rev. Lett., 103, 183901 (2009) [4] H. Mashiko et al., Appl. Phys. Lett., 90, 161114 (2007) [5] Y. Mairesse and F. Quere, Phys. Rev. A, 71, 011401(R) (2005) [6] S. Gilbertson et al., Phys. Rev. Lett., 105, 093902 (2010)
QMC2.pdf
Single attosecond pulse generation using GDOG without the need to stabilize Carrier-Envelope phase Yi Wu1, Sabih D. Khan2, Steve Gilbertson2, Michael Chini1,2 and Zenghu Chang1,2 1
CREOL and Department of Physics, University of Central Florida, Orlando, Florida 32816, USA 2
Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA
Abstract: We demonstrate that CE phase stability is not required in GDOG method to generate single attosecond pulses when gate width is set smaller than optical cycle. Introduction Single attosecond pulses have been utilized in a variety of experiments with atoms, molecules and solids [1]. However, the requirement of carrier-envelope (CE) phase stability and single cycle pulses, have kept this technology accessible to a handful of laboratories worldwide. Furthermore, CE phase locking is a major bottleneck for pettawatt (PW) class lasers to generate single attosecond pulses, thus preventing scaling up the photon flux. Recently, double optical gating (DOG) was demonstrated to generate single attosecond pulses from multi-cycle lasers [2] and generalized double optical gating (GDOG) has demonstrated single attosecond pulses directly from a CE phase locked chirped pulse amplifier [3] , thereby opening possibilities to scale up the photon flux. In this paper, we report generation of single attosecond pulses from multi-cycle lasers without the need to lock the CE phase. We demonstrate that if a sufficiently narrow gate width is set then only single attosecond pulse is produced at any value of CE phase. Experimental Setup For this experiment, a 9 fs laser pulse was produced by compressing 2 mJ, 25 fs, 2 kHz, 800 nm pulses produced by a 14 pass CE-phase stabilized chirped pulse amplifier (Kansas Light Source) [4] and using a Neon filled hollow-core fiber and chirped mirrors compressor. To achieve a gate width of ~1.4 fs, 80% of a 9 fs beam is passed through the GDOG optics [3] which include a 530 µm quartz plate (T d = 5 optical cycles), a 0.5mm Brewster window, a 440 µm quartz plate and 141 µm barium borate crystal (BBO). This GDOG pulse is sent into the attosecond streak camera [3] to generate attosecond pulses in a 1.4mm long Argon filled gas cell and is streaked with linear polarized pulses on a Krypton filled gas jet, the details of the attosecond streak camera setup are given elsewhere [3]. Results and Discussion The photoelectron spectra obtained by changing the CE phase is presented in figure 1 (a). The spectrum is continuum for all values of CE phase, which satisfies the necessary condition for generating a single attosecond pulse. There may be two extreme cases, first is when electron is born in a linearly polarized field but recombines in an increasingly elliptical field, leading to a lower flux due to reduced recombination probability. In the second case, the electron spends all of its excursion time away from the nuclear core in a mainly linearly polarized field, which leads to maximized photon flux. The plot in figure 1(a) shows the signal of the CE phase integrated along the energy spectrum, which is related to the intensity of the spectrum. It is quite evident that the intensity of the attosecond pulse is a strong function of CE phase and the signal fluctuates between the two extreme cases. Figure 1(b) shows the streaked spectrogram when the CE phase is unlocked. The temporal intensity and phase as retrieved by the FROG-CRAB method [5] is presented in figure 1(c). The retrieved pulse duration is 182 as. Streaked spectrograms were also recorded for CE phases of 0, π/2, π and 3π/2 and reported elsewhere [6]. The retrieved pulse duration was 180 as when CE phase was 0 and π and was 182 as when it was π/2 and 3π/2. The ratio
OSA/ CLEO 2011
QMC2.pdf
between the main pulse and pre and post pulses is ~10-5 for each of the four cases. The photoelectron spectra for each of these values of CE phase is presented in figure 1(d). It can be seen that the spectral width in each of these cases is similar. It is important to note that although the CE phase of the driving laser pulse is locked, the absolute values are different in the generation and streaking leg of the streak camera because dispersion is not same in the two paths. The retrieved pulse duration of the locked and unlocked cases have less than 5% error, proving that CE phase stability is not needed to generate similar attosecond pulses when gate width is narrow enough.
Figure 1, Photoelectron spectra of attosecond pulses as a function of CE phase is given in (a). In (b) a streaked spectrogram is given when CE phase is unlocked and retrieved temporal profile (solid line) and phase (dashed line) is given in (c) using FROG-CRAB. The photoelectron energy spectrum when CE phase is locked at 0, π/2, π and 3π/2 is given in (d). [6]
Conclusion In conclusion, we have experimentally demonstrated that when gate width is set narrow enough, CE stability is not required to generate a single attosecond pulse using GDOG technique. The attosecond pulses produced with unlocked CE phase and for four different values of CE phase appear to be similar in profile and phase and furthermore, the pulse duration is the same within an error of 5%. We have also seen that the photon flux is a strong function of the CE phase. However, this result is still important as the GDOG method now gives the ability to produce single attosecond pulses from PW class lasers and scale up the photon flux and may lead to nonlinear attosecond science. References [1] A. Scrinzi et al., J. Phys. B, 39, R1 (2206) [2] H. Mashiko et al. Phys. Rev. Lett., 100, 103906 (2008) [3] X. Feng et al., Phys. Rev. Lett., 103, 183901 (2009) [4] H. Mashiko et al., Appl. Phys. Lett., 90, 161114 (2007) [5] Y. Mairesse and F. Quere, Phys. Rev. A, 71, 011401(R) (2005) [6] S. Gilbertson et al., Phys. Rev. Lett., 105, 093902 (2010)
