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Femtosecond all-optical synchronization of an X-ray free-electron laser.

Schulz S, Grguraš I, Behrens C, Bromberger H, Costello JT, Czwalinna MK, Felber M, Hoffmann MC, Ilchen M, Liu HY, Mazza T, Meyer M, Pfeiffer S, Prędki P, Schefer S, Schmidt C, Wegner U, Schlarb H, Cavalieri AL - Nat Commun (2015)

Bottom Line: To generate these pulses and to apply them in time-resolved experiments, synchronization techniques that can simultaneously lock all independent components, including all accelerator modules and all external optical lasers, to better than the delivered free-electron laser pulse duration, are needed.Here we achieve all-optical synchronization at the soft X-ray free-electron laser FLASH and demonstrate facility-wide timing to better than 30 fs r.m.s. for 90 fs X-ray photon pulses.Crucially, our analysis indicates that the performance of this optical synchronization is limited primarily by the free-electron laser pulse duration, and should naturally scale to the sub-10 femtosecond level with shorter X-ray pulses.

View Article: PubMed Central - PubMed

Affiliation: Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22607 Hamburg, Germany.

ABSTRACT
Many advanced applications of X-ray free-electron lasers require pulse durations and time resolutions of only a few femtoseconds. To generate these pulses and to apply them in time-resolved experiments, synchronization techniques that can simultaneously lock all independent components, including all accelerator modules and all external optical lasers, to better than the delivered free-electron laser pulse duration, are needed. Here we achieve all-optical synchronization at the soft X-ray free-electron laser FLASH and demonstrate facility-wide timing to better than 30 fs r.m.s. for 90 fs X-ray photon pulses. Crucially, our analysis indicates that the performance of this optical synchronization is limited primarily by the free-electron laser pulse duration, and should naturally scale to the sub-10 femtosecond level with shorter X-ray pulses.

No MeSH data available.


Optical locking of independent lasers.Optical cross-correlators measure the relative timing between two pulses. The principle of the device is illustrated in a. In the first stage, two input pulses with arbitrary timing are mixed in a nonlinear crystal resulting in an SFG signal with intensity that depends on their overlap. To determine which pulse arrived first, one of them is delayed by a fixed amount Δ, before they are overlapped again in the second SFG stage. The difference between the SFG intensities allows the exact input timing to be determined without sign ambiguity. A characteristic cross-correlator curve is traced, as illustrated, if the input timing is scanned continuously. A measured scan of the relative timing between the Ti:sapphire pump–probe laser and optical reference laser at FLASH results in the cross-correlator response plotted in b. Outside of the regions where the detector is limited (±1 V), the measured curve matches the curve calculated based on the input laser pulse durations. Once calibrated, the relative timing between the two pulses can be determined with sub-femtosecond accuracy within the ~400 fs dynamic range of the cross-correlator. Using this for feedback, the cavity length of the pump–probe oscillator is varied to lock the relative timing. The residual jitter between the external laser and reference is shown in c, as measured with an independent optical cross-correlator and is found to be (5±1) fs r.m.s., with accuracy given by the numerical fit to the corresponding distribution shown in d.
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f3: Optical locking of independent lasers.Optical cross-correlators measure the relative timing between two pulses. The principle of the device is illustrated in a. In the first stage, two input pulses with arbitrary timing are mixed in a nonlinear crystal resulting in an SFG signal with intensity that depends on their overlap. To determine which pulse arrived first, one of them is delayed by a fixed amount Δ, before they are overlapped again in the second SFG stage. The difference between the SFG intensities allows the exact input timing to be determined without sign ambiguity. A characteristic cross-correlator curve is traced, as illustrated, if the input timing is scanned continuously. A measured scan of the relative timing between the Ti:sapphire pump–probe laser and optical reference laser at FLASH results in the cross-correlator response plotted in b. Outside of the regions where the detector is limited (±1 V), the measured curve matches the curve calculated based on the input laser pulse durations. Once calibrated, the relative timing between the two pulses can be determined with sub-femtosecond accuracy within the ~400 fs dynamic range of the cross-correlator. Using this for feedback, the cavity length of the pump–probe oscillator is varied to lock the relative timing. The residual jitter between the external laser and reference is shown in c, as measured with an independent optical cross-correlator and is found to be (5±1) fs r.m.s., with accuracy given by the numerical fit to the corresponding distribution shown in d.

Mentions: The measurement principle of an optical cross-correlator3140 is shown in Fig. 3a. In the first stage, two pulses with arbitrary temporal overlap are mixed by sum-frequency generation in a nonlinear crystal. The strength of the mixed signal depends on the precise temporal overlap. To determine which pulse arrives first and to balance the cross-correlator, a second stage is used in which one pulse is delayed with respect to the other by a fixed amount. The rearranged pulses are mixed again, to generate another sum-frequency signal. By combining the two signals, the absolute delay between the pulses can be determined independently of intensity fluctuations, providing ideal feedback for locking the laser to the reference (see Methods for more details).


Femtosecond all-optical synchronization of an X-ray free-electron laser.

Schulz S, Grguraš I, Behrens C, Bromberger H, Costello JT, Czwalinna MK, Felber M, Hoffmann MC, Ilchen M, Liu HY, Mazza T, Meyer M, Pfeiffer S, Prędki P, Schefer S, Schmidt C, Wegner U, Schlarb H, Cavalieri AL - Nat Commun (2015)

Optical locking of independent lasers.Optical cross-correlators measure the relative timing between two pulses. The principle of the device is illustrated in a. In the first stage, two input pulses with arbitrary timing are mixed in a nonlinear crystal resulting in an SFG signal with intensity that depends on their overlap. To determine which pulse arrived first, one of them is delayed by a fixed amount Δ, before they are overlapped again in the second SFG stage. The difference between the SFG intensities allows the exact input timing to be determined without sign ambiguity. A characteristic cross-correlator curve is traced, as illustrated, if the input timing is scanned continuously. A measured scan of the relative timing between the Ti:sapphire pump–probe laser and optical reference laser at FLASH results in the cross-correlator response plotted in b. Outside of the regions where the detector is limited (±1 V), the measured curve matches the curve calculated based on the input laser pulse durations. Once calibrated, the relative timing between the two pulses can be determined with sub-femtosecond accuracy within the ~400 fs dynamic range of the cross-correlator. Using this for feedback, the cavity length of the pump–probe oscillator is varied to lock the relative timing. The residual jitter between the external laser and reference is shown in c, as measured with an independent optical cross-correlator and is found to be (5±1) fs r.m.s., with accuracy given by the numerical fit to the corresponding distribution shown in d.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4309427&req=5

f3: Optical locking of independent lasers.Optical cross-correlators measure the relative timing between two pulses. The principle of the device is illustrated in a. In the first stage, two input pulses with arbitrary timing are mixed in a nonlinear crystal resulting in an SFG signal with intensity that depends on their overlap. To determine which pulse arrived first, one of them is delayed by a fixed amount Δ, before they are overlapped again in the second SFG stage. The difference between the SFG intensities allows the exact input timing to be determined without sign ambiguity. A characteristic cross-correlator curve is traced, as illustrated, if the input timing is scanned continuously. A measured scan of the relative timing between the Ti:sapphire pump–probe laser and optical reference laser at FLASH results in the cross-correlator response plotted in b. Outside of the regions where the detector is limited (±1 V), the measured curve matches the curve calculated based on the input laser pulse durations. Once calibrated, the relative timing between the two pulses can be determined with sub-femtosecond accuracy within the ~400 fs dynamic range of the cross-correlator. Using this for feedback, the cavity length of the pump–probe oscillator is varied to lock the relative timing. The residual jitter between the external laser and reference is shown in c, as measured with an independent optical cross-correlator and is found to be (5±1) fs r.m.s., with accuracy given by the numerical fit to the corresponding distribution shown in d.
Mentions: The measurement principle of an optical cross-correlator3140 is shown in Fig. 3a. In the first stage, two pulses with arbitrary temporal overlap are mixed by sum-frequency generation in a nonlinear crystal. The strength of the mixed signal depends on the precise temporal overlap. To determine which pulse arrives first and to balance the cross-correlator, a second stage is used in which one pulse is delayed with respect to the other by a fixed amount. The rearranged pulses are mixed again, to generate another sum-frequency signal. By combining the two signals, the absolute delay between the pulses can be determined independently of intensity fluctuations, providing ideal feedback for locking the laser to the reference (see Methods for more details).

Bottom Line: To generate these pulses and to apply them in time-resolved experiments, synchronization techniques that can simultaneously lock all independent components, including all accelerator modules and all external optical lasers, to better than the delivered free-electron laser pulse duration, are needed.Here we achieve all-optical synchronization at the soft X-ray free-electron laser FLASH and demonstrate facility-wide timing to better than 30 fs r.m.s. for 90 fs X-ray photon pulses.Crucially, our analysis indicates that the performance of this optical synchronization is limited primarily by the free-electron laser pulse duration, and should naturally scale to the sub-10 femtosecond level with shorter X-ray pulses.

View Article: PubMed Central - PubMed

Affiliation: Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22607 Hamburg, Germany.

ABSTRACT
Many advanced applications of X-ray free-electron lasers require pulse durations and time resolutions of only a few femtoseconds. To generate these pulses and to apply them in time-resolved experiments, synchronization techniques that can simultaneously lock all independent components, including all accelerator modules and all external optical lasers, to better than the delivered free-electron laser pulse duration, are needed. Here we achieve all-optical synchronization at the soft X-ray free-electron laser FLASH and demonstrate facility-wide timing to better than 30 fs r.m.s. for 90 fs X-ray photon pulses. Crucially, our analysis indicates that the performance of this optical synchronization is limited primarily by the free-electron laser pulse duration, and should naturally scale to the sub-10 femtosecond level with shorter X-ray pulses.

No MeSH data available.