Abstract
The Novosibirsk Free Electron Laser (NovoFEL) facility is able to produce high-power tunable terahertz (THz) laser radiation in quasi-continuous mode. The ability to control/shape this THz radiation is required in a number of user experiments. In this work we propose a modulation approach suitable for free electron lasers based on recuperation design. It allows for generating THz macropulses of a desirable length, down to several microseconds (limited by a quality factor of FEL optical resonator). Using this approach, macropulses in the time window from several microseconds to several hundred microseconds have been shown for three possible frequency ranges: mid-infrared (~1100 cm−1), far-infrared (~200 cm−1) and THz (~40 cm−1). In each case, the observed rise and decay of the macropulse have been measured and interpreted. The advantage of using short macropulses at the maximum peak power available has been demonstrated with the time-resolved Electron Paramagnetic Resonance (EPR) spectroscopy.
Highlights
The Novosibirsk Free Electron Laser (NovoFEL) facility comprises three FELs, which use an energy recovery linac (ERL) as a source of electrons
In order to demonstrate the possibilities of an electronic modulation system (EMS), we recorded order to demonstrate the possibilities of anatelectronic system (EMS), recorded to the THz In macropulses with different pulse length all threemodulation
We developed and implemented the approach allowing one to create THz macropulses at NovoFEL with any repetition rate and almost any individual pulse length
Summary
The Novosibirsk Free Electron Laser (NovoFEL) facility comprises three FELs, which use an energy recovery linac (ERL) as a source of electrons. It operates in quasi-continuous (CW) mode and produces a periodic train of radiation pulses. Energy recovery allows one to achieve a very high average current of the electron beam, which results in high average power of radiation. This is crucial for some applications [2], in most of the experiments, such high average power is excessive and should be attenuated. The use of short macropulses is required which allows one to keep the peak power very high, while the average one can be reduced significantly [3]
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