Exeter Time Resolved Magnetism Facility (EXTREMAG)
The EPSRC-funded EXTREMAG facility is open to external users through a proposal sytem and is supported by a Senior Scientific Officer. It houses two ultrafast fibre laser systems.
The first produces 140 fs pulses at 80 MHz repetition with an average power of 10 W and is intended for imaging experiments. The second produces an average power of 40W at 1 MHz and pumps an optical parametric amplifier (OPA) for use in two-colour pump-probe experiments.
The laboratory contains wide field and scanning probe magneto-optical microscopes, offers a range of mangetic field and temperature environments, and has high frequency electrical instrumentation for the generation and characterisation of waveforms that can be phase-locked to the laser systems.
Ultrafast Laser Lab
We use an amplified Ti:Sapphire Legend laser system to probe the electronic and phononic properties of semiconductors and graphene based systems. With a time averaged power of 3 W, produced in over one thousand ultrafast (100 fs) pulses per second, a range of time-resolved experiments are possible.
THz time domain spectroscopy is used in both collimating and focusing configurations to probe materials at low energies (approximately 4meV). Temperature controlled samples can be used within these time resolved measurements and the THz generation dynamics of different materials can also be measured. Time resolved (pump-probe) measurements are performed at visible and near-infrared frequencies, with bespoke chambers for in-situ measurements in ambient, vacuum or inert gas environments.
Within this ultrafast lab we can align up to five different laser sources, ranging from 700-1600 nm in wavelength, through two inverted microscopes to provide spatial resolution of approximately 1 micron at the sample. With picosecond and femtosecond operation, a wide range of optical measurements can be taken.
Multiphoton fluorescence, Second- and Third-Harmonic Generation (SHG & THG), Stimulated Raman Scattering (SRS),Coherent Anti-stokes Raman Scattering (CARS) and time-resolved pump-probe measurements are all taken within this single facility. With such a broad range of available wavelengths, coupled with the high spatial resolution of the microscope (with raster scanning capability), this lab offers researchers the ability to probe a variety of different biological and solid-state systems.
Time-resolved scanning magneto-optical microscopes
We operate several time-resolved (pump-probe) imaging systems offering a range of measurement modes. The systems are used for studies of electron, spin, and lattice dynamics in the time and space domains, with time resolution down to 50 fs and spatial resolution down to 300 nm. We image ultrafast dynamics excited in samples either optically or by pulsed or cw microwave magnetic fields. The measurements are performed at bias magnetic fields up to 1 Tesla (soon, up to 5 Tesla) and temperatures down to 6 K. The areas of investigations range from magnonics and ultrafast magnetic switching in magnetic nano-structures to phase change materials.
300 kHz ultrafast regenerative amplifier system
A 300 kHz regenerative amplifier system is used for pump-probe and other non-linear optical measurements. Micro-Joule pulses of less than 80 fs duration are generated at 800 nm wavelength. Visible and near-infrared optical parameteric amplifiers, a difference frequency generator, and various doubling units allow pulses to be generated with wavelength ranging from the ultraviolet to the infrared.
Spectrometers, beam profilers, autocorrelators, and a Spectral Phase Interferometry for Direct Electric-field Reconstruction (SPIDER) instrument are available for beam characterization. The seed oscillator is equipped with a synchrolock unit to facilitate phase locking to other instruments.
Microwave and magnetic measurement
Vibrating sample magnetometer (VSM)
Microsense EZ7 VSM system with magnetic field up to 2.15 T and sample temperature of 77 K and 10 - 1000 K
High frequency electrical measurements
We can perform high frequency electrical and electro-optical measurements on both contacted devices and at the wafer level using high frequency probe stations.
These experiments also utilise a 50 GHz spectrum analyzer, a 50 GHz sampling oscilloscope, a 40 GHz microwave synthesizer, and an assortment of smaller microwave frequency components.
We have made measurements upon both spin transfer oscillators and phase change random access memory devices at the wafer level.
A collimated beam acoustic apparatus for measuring the air-borne far-field response of test samples to high frequencies, in the frequency and time domain. A SONAR facility to similarly characterise the repsonse of samples underwater in the time-domain. A computer controlled 3D scanner provides the ability for mapping local pressure fields in air and underwater. A semi-anachoic chamber for airborne measurements.