Towards GV/m single-cycle THz pulses from undulators Vitaliy - PowerPoint PPT Presentation

Towards GV/m single-cycle THz pulses from undulators Vitaliy Goryashko 2016

Outline • Accelerator physics in Uppsala and FREIA Laboratory • Work on a linac-based THz source • Concept of generation of single-cycle pulses with undulators • Optimal tapering • Proposal for a THz Light at Uppsala 2 Vitaliy Goryashko Single-cycle THz pulses

Background: accelerator physics in Uppsala 1940's: The(odore) Svedberg proposes to build a cyclotron • Gustaf Werner synchro-cyclotron (1947 – present) – nuclear physics & cancer treatment • CELSIUS ring (1984 – 2005) – nuclear physics • External – CTF3/CLIC at CERN (since 2005) – FLASH/XFEL at DESY (since 2008) – ESS (since 2009) • FREIA laboratory (since 2011) • Skandion clinic (2015) – cancer treatment 3 Vitaliy Goryashko Single-cycle THz pulses

European Spallation Source (ESS), Sweden 4 Vitaliy Goryashko Single-cycle THz pulses

FREIA 5 Vitaliy Goryashko Single-cycle THz pulses

FREIA: Facility for Research Instrumentation & Accelerator Development State-of-the-art Equipment control room cryogenics - equipment controls - liquid helium - data acquisition - liquid nitrogen Competent and motivated staff collaboration of physics (IFA) and engineering (Teknikum). Funded by KAWS, vertical cryostat Government, Uppsala Univ. 3 bunkers with test stands horizontal radio-frequency (RF) cryostat power sources 6 Vitaliy Goryashko Single-cycle THz pulses

Low-energy excitations: D. N. Basov et al., Rev. of Mod. Phys. 2011 7 Vitaliy Goryashko Single-cycle THz pulses

Combined THz/X-ray source: old design 8 Vitaliy Goryashko Single-cycle THz pulses

How to generate GV/m single- cycle pulses with MeV bunches? 9 Vitaliy Goryashko Single-cycle THz pulses

Single-cycle synchrotron radiation 10 Vitaliy Goryashko Single-cycle THz pulses

Single-cycle radiation from a segmented undulator 11 Vitaliy Goryashko Single-cycle THz pulses

Single-cycle radiation from a segmented undulator: cont’d Magnetic field of segments 12 Vitaliy Goryashko Single-cycle THz pulses

Single-cycle radiation from a segmented undulator If instead of increasing the distance between the segments I will decrease it, I will recover Takashi’s tapered undulator. 13 Vitaliy Goryashko Single-cycle THz pulses

14 Vitaliy Goryashko Single-cycle THz pulses

What is the optimum taper profile? Can one generate just one cycle? 15 Vitaliy Goryashko Single-cycle THz pulses

Simple reasoning from Takashi total field is a convolution of the current density and the field of a single electron Suppose that the time profile of the current density is the same as the single-electron field profile The convolution boils down to the inverse Fourier transform of the spectral power. � via undulator tapering �(�) Let us optimize � in order to get as few cycles as possible. 16 Vitaliy Goryashko Single-cycle THz pulses

On-axis field in a tapered undulator / 0 /� � � (�′) sin # � � $ � � �� � � � � 2� � � � (� )* + , - .� $ � � 0, � = − � � 1 + ' � − �′ �2�� � �/ 0 /� � #� � 2 = 3 , 3 4 3 4 = 3 � 2� � E. Saldin et al. "A simple method for the determination of the structure of ultrashort relativistic electron bunches." NIMA 539.3 (2005): 499-526. 17 Vitaliy Goryashko Single-cycle THz pulses

Stationary phase method stationary point 2� � 1 + � � 3 = 3 � � (� 4 ) , 2 � � 18 Vitaliy Goryashko Single-cycle THz pulses

Optimal taper profile I equate the spectral power of radiation from a tapered undulator 5 � to that of the quasi-half-cycle pulse It turns out that the minimum number of cycles is 1.5. 19 Vitaliy Goryashko Single-cycle THz pulses

Radiation from the optimally-tapered undulator 20 Vitaliy Goryashko Single-cycle THz pulses

Proposal for a THz Light Source in Uppsala 21 Vitaliy Goryashko Single-cycle THz pulses

Wish list for intense THz radiation. Quasi-half-cycle Narrowband pulses for time- pulses for Parameter resolved frequency-resolved experiments experiments Spectral range (THz) 1.5-15 1.5-15 Pulse duration (ps) 0.1-1 1-10 Pulse energy (mJ) 1000 100 Peak electric field 1 0.1 (GV/m) Relative bandwidth 100% 10% FWHM Repetition rate (kHz) 1-100 1-100 + Polarization control, pump-probe configuration 22 Vitaliy Goryashko Single-cycle THz pulses

The source • it covers the spectral range from 5 to 15 THz, exceeding that of laser-based sources; • polarization variable from linear to circular or elliptical; • tunability of the central frequency and bandwidth; • mutli-kilohertz repetition rate; • light carrying orbital angular momentum. 23 Vitaliy Goryashko Single-cycle THz pulses

Source 1: quasi-half-cycle pulses 24 Vitaliy Goryashko Single-cycle THz pulses

Source 2: multi-cycle pump and single-cycle probe Source 2a Source 2b 25 Vitaliy Goryashko Single-cycle THz pulses