Experiments – Summer 2020

All optical pump-probe measurements at variable temperature

Two-colour, all-optical pump-probe experiments will be available for measurements at room temperature, and will utilise the tuneable Opera-F OPA output (640 – 900 nm, 1200 – 2400 nm).  At room temperature separate electromagnets for in-plane or out-of-plane magnetic fields (<0.5 T) will be available.  The option for variable temperature (4 – 300 K) will be available in 2020 using either the Oxford Instruments MicrostatHe-R cryostat (with rectangular tail and optical access), MicrostatMO superconducting magnet with up to 5 T out-of-plane field, or Spectromag SM4000 superconducting magnet (mid-commissioning) with up to 10 T out-of-plane field.

MicrostatHe-R

The MicrostatHe is located in the Free Space Lab B2 so that it can be readily configured for all-optical pump probe experiments, or optically detected ferromagnetic resonance (FMR) experiments.  The cryostat probe was upgraded in January 2020 to accommodate an RF coaxial cable to the sample and an SMB RF feedthrough in addition to the original 10 pin DC sample connectors.  For FMR experiments, the coaxial cable will be soldered to an impedance matched PCB coplanar waveguide with ceramic filled, high thermal conductivity substrate (Arlon1000) onto which samples can be placed for RF field excitation.  Electrical connection to samples may be available for transport measurements on request using a Keithley 6221/2182A (AC and DC Current Source/Nanovoltmeter) Delta Mode System.

The MicrostatHe-R helium gas-flow cryostat with rectangular tail and optical access for all optical pump-probe or optically detected FMR at variable temperature.

MicrostatMO

The MicrostatMO is located in the Microscopy Lab B2 with the wide field Kerr microscope.  The ‘MO’ is oriented on its side for an all-optical pump probe set-up in the horizontal plane of the optical table.  The field direction is along the axis of the cylindrical body of the MO.  All-optical pump-probe will be available at variable temperatures from room temperature down to ~4 K, and fields up to ~5 T.

During 2020 a beam scanning optical set up will be constructed to add microscopy capability to the MO in all-optical pump probe experiments.

Electrical connection to samples may be available for transport measurements on request using a Keithley 6221/2182A (AC and DC Current Source/Nanovoltmeter) Delta Mode System.

The MicrostatMO 5T superconducting magnet during commissioning testing.

Spectromag SM4000

Commissioning of an Oxford Instruments Spectromag SM4000 is ongoing.  Once operational optical pump-probe will be available at temperatures from room temperature down to ~4 K, and fields up to ~10 T.

Electrical connection to samples may be available for transport measurements on request using a Keithley 6221/2182A (AC and DC Current Source/Nanovoltmeter) Delta Mode System.

Commissioning of the Spectromag SM4000 superconducting magnet.

Time-resolved scanning Kerr microscopy

Time-resolved scanning Kerr microscopy (TRSKM) is available for room temperature measurements with spatial resolution down to 100s of nanometers.  The microscope is equipped with a 3D projected field electromagnet capable of applying 0.2 T in any orientation, and a 65 GSa/s arbitrary waveform generator for user defined excitation waveforms appropriate for the type of sample/device under test.  Picosecond pulsed field excitation, microwave field excitation, or quasi-dc excitation are available.

Samples require either an integrated microscale waveguide device for efficient excitation, otherwise samples can be placed onto a PCB waveguide for weaker excitation.

The time-resolved scanning Kerr microscope for room temperature imaging of picosecond magnetisation dynamics.

The microscope features a piezoelectric scanning stage with 300 microns travel in x-, y-, and z-directions, and a quad-pass optical delay line for up to 8 ns of time delay.  The microscope uses the 520 nm second harmonic of the Fidelity laser (80 MHz repetition rate, 140 fs pulse duration), and can currently achieve a spatial resolution of ~400 nm.

Quad-pass, 8 ns optical delay optics.

In situ AFM and MFM capability can be added to the microscope on request for characterisation of the sample topography and equilibrium magnetic state at remanence.

Electrical connection to samples may also be used for transport measurements on request using a Keithley 6221/2182A (AC and DC Current Source/Nanovoltmeter) Delta Mode System.

THz spectroscopy and imaging

A THz spectrometer is being set up for use in the Free Space Lab B2. The system uses a novel trilayer THz emitter and a photoconductive antenna detector enabling access to a wavelength range of ~0.4 -1.5THz.  A pulsed beam is used to allow access to amplitude and phase information by temporally scanning a detection pulse. This method is suitable for characterising the THz response of samples.

The development of THz spectroscopy inside the laser enclosure. THz spectroscopy is now located in the Free Space Lab B2.

Longer term, the system will be converted to a near-field THz single pixel imaging system by incorporating a Digital Micromirror Device (DMD).  Micron-level spatial resolution is anticipated with an imaging time of under 1 minute.

THz emission at variable temperature (300 – 4 K) and high magnetic field (up to 10 T) will be available once the Spectromag SM400 has been fully commissioned.  THz emission at room temperature is currently available on request.

Wide field Kerr microscopy

High resolution wide field Kerr microscopy is available at room temperature, or at low temperature using the helium gas flow microscopy cryostat.  In-plane or out-of-plane magnetic fields may be applied to samples in each case.  The microscope can be equipped with a rotatable electromagnet for in-plane magnetic fields up to 1.3 T, or a polar electromagnet for out-of-plane magnetic fields up to 0.9 T.  Low temperature microscopy down to below 10 K can be performed in an out-of-plane field up to ~100 mT, or an in-plane field up to ~700 mT.  The microscope is sensitive to all three components of the sample magnetisation using longitudinal and polar Kerr effects.  The microscope features piezoelectric drift correction for optimised differential imaging, and spatially resolved magnetometry (hysteresis loop measurement) from user defined regions of interest.

Electrical connection to samples may be available for transport measurements on request using a Keithley 6221/2182A (AC and DC Current Source/Nanovoltmeter) Delta Mode System.  Note that piezoelectric drift correction is not be possible for fixed electrical probe connections.

The high resolution wide field Kerr microscope with low temperature capability using a helium gas flow microscopy cryostat.  A lower resolution overview wide field Kerr microscope is available for larger samples, or samples with large domain structure.

The system is also equipped with a lower resolution overview wide field Kerr microscope for larger samples or samples with large domains.

A pulsed laser optical pump with tuneable wavelength, or microscale electrical probes to devices are available for this instrument on request and subject to specific requirements.

In the longer term time-resolved wide field Kerr microscopy will be developed by using the femtosecond lasers as a light source for the wide field microscope.

The optical set up for optical pulse excitation of samples in the microscopy cryostat of the wide field Kerr microscope, equipped with polar field solenoid.