MIT, Cambridge, Massachusetts, USA
CFEL, Hamburg, Germany
Intense, ultrafast THz fields are of great interest for electron acceleration, beam manipulation and measurement, and pump-probe experiments with coherent soft/hard x-ray sources based on FELs or inverse Compton scattering sources. Acceleration at THz frequencies has an advantage over RF in terms of accessing high electric-field gradients (>100 MV/cm), while the beam delivery can be treated quasi-optically. However, high-field THz pulse generation is still demanding when compared with conventional RF generation. In this paper, we present highly efficient, single-cycle, 0.45 THz pulse generation by optical rectification of 1.03 μm pulses in cryogenically cooled lithium niobate (LN). Using a near-optimal duration of 680 fs and a pump energy of 1.2 mJ, we report conversion efficiencies above 3% [1], >10 times higher than previous report (0.24%) [2]. Cryogenic cooling of lithium niobate significantly reduces the THz absorption, which will enable the scaling of THz pulse energies to the mJ. We will also report on polarization and mode conversion using segmented THz waveplates to generate radially-polarized TEM01 modes, suitable for THz electron acceleration in dielectric waveguide.
[1] S.-W. Huang et al., Opt. Lett. 38, 796-798 (2013).
[2] J. A. Fülöp et al., Opt. Lett. 37, 557-559 (2012).
MIT, Cambridge, Massachusetts, USA
DESY, Hamburg, Germany
AdvR, Inc., Montana, USA
OFS Laboratories, New Jersey, USA
CFEL, Hamburg, Germany
Sub-fs X-ray pulse generation in kilometer-scale FEL facilities will require sub-fs long-term timing stability between optical sources over kilometer distances. We present here key developments towards a completely fiber-coupled, sub-fs optical timing distribution system. Our approach [*] is to lock a femtosecond pulsed laser to a microwave reference and distribute its pulse train through fiber links stabilized by balanced optical cross-correlators (BOCs) [**]. First, we verified that low-noise optical master oscillators for sub-fs timing distribution are available today; the measured jitter for two commercial femtosecond lasers is less than 70 as for frequencies above 1 kHz. Second, we developed a novel 1.2 km dispersion-compensated, polarization-maintaining fiber link to eliminate drifts induced by polarization mode dispersion. Link stabilization for 16 days showed 0.6 fs RMS timing drift and during a 3-day interval only 0.13 fs drift. Lastly, we fabricated a hybrid-integrated BOC using PPKTP waveguides [***] to eliminate alignment drifts and to reduce the link operation power by a factor of 10-100, which will reduce timing errors induced by fiber nonlinearities.
* J. Kim et al., Nat. Photon., 2, 12, 733–736, 2008.
** J. Kim et al., Opt. Lett., 32, 9, 1044–1046, 2007.
*** A. H. Nejadmalayeri et al., Opt. Lett., 34, 16, 2522–2524, 2009.
CFEL, Hamburg, Germany
MIT, Cambridge, Massachusetts, USA
The last decade has witnessed extensive research efforts to reduce the size of charged particle accelerators to achieve compact devices for providing relativistic particles. To this end, various methods such as laser plasma and dielectric wakefield acceleration are investigated and their pros and cons are studied. With the advent of efficient THz generation techniques based on optical rectification, THz waveguides are also considered to be proper candidates for compact accelerators. Sofar, the proposed schemes toward high power THz generation are capable of producing short pulses, which dictates the study of particle acceleration in the pulsed regime rather than continuous-wave regime. Therefore, THz waveguides are more suitable than cavities for the considered purpose*. Consequently, various effects such as group velocity mismatch and group velocity dispersion start to influence the acceleration scenario and impose limits on the maximum energy gain from the pulse. In this contribution, we investigate electron bunch acceleration and compression in dielectrically loaded metal waveguides for the THz wavelength range and present design methodologies to optimize their performance.
* Liang Jie Wong, Arya Fallahi, and Franz X. Kärtner. "Compact electron acceleration and bunch compression in THz waveguides." Optics Express 21, no. 8 (2013): 9792-9806.
KAIST, Daejeon, Republic of Korea
Idesta Quantum Electronics, New Jersey, USA
PSI, Villigen PSI, Switzerland
CFEL, Hamburg, Germany
PAL, Pohang, Kyungbuk, Republic of Korea
We present our recent progress in remote RF synchronization using an optical way at PAL. A 79.33-MHz, low-jitter fiber laser is used as an optical master oscillator (OMO), which is locked to the 2.856-GHz RF master oscillator (RMO) using a balanced optical-microwave phase detector (BOM-PD). The locked optical pulse train is then transferred via a timing-stabilized 610-m long optical fiber link. The output is locked to the 2.856 GHz voltage controlled oscillator (VCO) using the second BOM-PD, which results in remote synchronization between the RMO and the VCO. We measured the long-term phase drift between the input optical pulse train and the remote RF signals using an out-of-loop BOM-PD, which results in 2.7 fs (rms) drift maintained over 7 hours. We are currently working to measure the phase drift between the two RF signals and reduce the phase drift over longer measurement time.
SLAC, Menlo Park, California, USA
Idesta Quantum Electronics, New Jersey, USA
CFEL, Hamburg, Germany
MIT, Cambridge, Massachusetts, USA
PU, Princeton, New Jersey, USA
We present the design and progress of a femtosecond fiber timing distribution system for the Linac Coherent Light Source (LCLS) at SLAC to enable the machine diagnostic at the 10 fs level. The LCLS at the SLAC is the world’s first hard x-ray free-electron laser (FEL) with unprecedented peak brightness and pulse duration. The time-resolved optical/x-ray pump-probe experiments on this facility open the era of exploring the ultrafast dynamics of atoms, molecules, proteins, and condensed matter. However, the temporal resolution of current experiments is limited by the time jitter between the optical and x-ray pulses. Recently, sub-25 fs rms jitter is achieved from an x-ray/optical cross-correlator at the LCLS, and external seeding is expected to reduce the intrinsic timing jitter, which would enable full synchronization of the optical and x-ray pulses with sub-10 fs precision. Of such a technique, synchronization between seed and pump lasers would be implemented. Preliminary test results of the major components for a 4 link system will be presented. Currently, the system is geared towards diagnostics to study the various sources of jitter at the LCLS.
*P. Emma et al.,Nat. Photonics 4,641-647(2010).
*J. Kim et al.,Opt. Lett,, 31,3659(2006).
*J. Kim et al.,Opt. Lett,, 32,1044(2007).
*J.Kim et al.,Nat. Photonics 2,733-736(2008).
MIT, Cambridge, Massachusetts, USA
DESY, Hamburg, Germany
AdvR, Inc., Montana, USA
OFS Laboratories, New Jersey, USA
CFEL, Hamburg, Germany
Sub-fs X-ray pulse generation in kilometer-scale FEL facilities will require sub-fs long-term timing stability between optical sources over kilometer distances. We present here key developments towards a completely fiber-coupled, sub-fs optical timing distribution system. Our approach [*] is to lock a femtosecond pulsed laser to a microwave reference and distribute its pulse train through fiber links stabilized by balanced optical cross-correlators (BOCs) [**]. First, we verified that low-noise optical master oscillators for sub-fs timing distribution are available today; the measured jitter for two commercial femtosecond lasers is less than 70 as for frequencies above 1 kHz. Second, we developed a novel 1.2 km dispersion-compensated, polarization-maintaining fiber link to eliminate drifts induced by polarization mode dispersion. Link stabilization for 16 days showed 0.6 fs RMS timing drift and during a 3-day interval only 0.13 fs drift. Lastly, we fabricated a hybrid-integrated BOC using PPKTP waveguides [***] to eliminate alignment drifts and to reduce the link operation power by a factor of 10-100, which will reduce timing errors induced by fiber nonlinearities.
* J. Kim et al., Nat. Photon., 2, 12, 733–736, 2008.
** J. Kim et al., Opt. Lett., 32, 9, 1044–1046, 2007.
*** A. H. Nejadmalayeri et al., Opt. Lett., 34, 16, 2522–2524, 2009.
CFEL, Hamburg, Germany
MIT, Cambridge, Massachusetts, USA
The last decade has witnessed extensive research efforts to reduce the size of charged particle accelerators to achieve compact devices for providing relativistic particles. To this end, various methods such as laser plasma and dielectric wakefield acceleration are investigated and their pros and cons are studied. With the advent of efficient THz generation techniques based on optical rectification, THz waveguides are also considered to be proper candidates for compact accelerators. Sofar, the proposed schemes toward high power THz generation are capable of producing short pulses, which dictates the study of particle acceleration in the pulsed regime rather than continuous-wave regime. Therefore, THz waveguides are more suitable than cavities for the considered purpose*. Consequently, various effects such as group velocity mismatch and group velocity dispersion start to influence the acceleration scenario and impose limits on the maximum energy gain from the pulse. In this contribution, we investigate electron bunch acceleration and compression in dielectrically loaded metal waveguides for the THz wavelength range and present design methodologies to optimize their performance.
* Liang Jie Wong, Arya Fallahi, and Franz X. Kärtner. "Compact electron acceleration and bunch compression in THz waveguides." Optics Express 21, no. 8 (2013): 9792-9806.
MIT, Cambridge, Massachusetts, USA
Northern Illinois University, DeKalb, Illinois, USA
X-ray free electron laser studies are presented that rely on a nanostructured electron beam interacting with a “laser undulator” configured in the head-on inverse Compton scattering geometry. The structure in the electron beam is created by a nanoengineered cathode that produces a transversely modulated electron beam. Electron optics demagnify the modulation period and then an emittance exchange line translates the modulation to the longitudinal direction resulting in coherent bunching at x-ray wavelength. The predicted output radiation at 1 keV from a 7 MeV electron beam reaches 10 nJ or 6X108 photons per shot and is fully coherent in all dimensions, a result of the dominant mode growth transversely and the longitudinal coherence imposed by the electron beam nanostructure. This output is several orders of magnitude higher than incoherent inverse Compton scattering and occupies a much smaller phase space volume, reaching peak brilliance of 1027 and average brilliance of 1017 photons/(mm2 mrad2 0.1% sec).
SLAC, Menlo Park, California, USA
Idesta Quantum Electronics, New Jersey, USA
CFEL, Hamburg, Germany
MIT, Cambridge, Massachusetts, USA
PU, Princeton, New Jersey, USA
We present the design and progress of a femtosecond fiber timing distribution system for the Linac Coherent Light Source (LCLS) at SLAC to enable the machine diagnostic at the 10 fs level. The LCLS at the SLAC is the world’s first hard x-ray free-electron laser (FEL) with unprecedented peak brightness and pulse duration. The time-resolved optical/x-ray pump-probe experiments on this facility open the era of exploring the ultrafast dynamics of atoms, molecules, proteins, and condensed matter. However, the temporal resolution of current experiments is limited by the time jitter between the optical and x-ray pulses. Recently, sub-25 fs rms jitter is achieved from an x-ray/optical cross-correlator at the LCLS, and external seeding is expected to reduce the intrinsic timing jitter, which would enable full synchronization of the optical and x-ray pulses with sub-10 fs precision. Of such a technique, synchronization between seed and pump lasers would be implemented. Preliminary test results of the major components for a 4 link system will be presented. Currently, the system is geared towards diagnostics to study the various sources of jitter at the LCLS.
*P. Emma et al.,Nat. Photonics 4,641-647(2010).
*J. Kim et al.,Opt. Lett,, 31,3659(2006).
*J. Kim et al.,Opt. Lett,, 32,1044(2007).
*J.Kim et al.,Nat. Photonics 2,733-736(2008).