Instruments

The diamond samples are prepared by Alexander Kromka's group through chemical vapour deposition (CVD) technique utilising Seki Diamond Systems' SDS6K and AIXTRON's Focused Microwave Plasma Enhanced Chemical Vapour Deposition device. The lab is equipped to produce both monocrystalline and polycrystalline diamond layers containing colour centres, such as silicon-vacancy (SiV) and nitrogen-vacancy (NV) centres.

We use scanning electron microscopy (SEM) to investigate the morphological properties of prepared samples. The departmental scanning electron microscope (MAIA 3, Tescan) is equipped with detectors for both secondary and back-scattered electrons. At 15 kV, it can achieve a resolution of 1 nm.  We can also perform elemental analysis using energy-dispersive X-ray spectroscopy. 

Raman spectroscopy is used to evaluate the crystalline quality of the deposited diamond, while photoluminescence spectroscopy is used to characterise the luminescence properties of the embedded colour centres. The Raman and luminescence signals are measured using a Renishaw inVia Reflex micro-spectrophotometer in confocal geometry.  Three excitation wavelengths are available: 325 nm and 442 nm (Dual Wavelength HeCd laser, IK5651R-G, Kimmon), and 785 nm (Renishaw RL785 diode-pumped solid state).

In this photoluminescence setup, we use a broadband plasma light (EQ-99X, Energetiq) as the excitation source  (400 - 1100 nm) in combination with a monochromator (MSH-150, LOT-QuantumDesign).  The emission is collected via fibre optics, which is then dispersed by a spectrometer (SR-303i-B, Andor) onto a CCD camera (DU970P-UVB, Andor). The spectrometer is equipped with three gratings, and we could achieve a resolution down to 0.2 nm.

With this setup, we can also measure absorption in a single-beam configuration. Additionally, we have a commercial double-beam absorption spectrometer (Libra S60, Biochrom), which can measure in the range of 200 - 1200 nm.

Our closed-cycle helium cryostat (Cryostation s200, Montana Instruments) enables us to measure spectroscopic signatures down to 4 K. We use this cryostat to measure steady-state emission as well as time-resolved emission (using a streak camera for detection).

For cryogenic measurements, particularly those involving silicon vacancy centres (SiV) in diamond, a high spectral resolution is essential. The SR-500i-D1 spectrometer (Andor),  fitted with a 1200 lines/mm grating, allows us to achieve a resolution of 0.06 nm.

We measure time-resolved photoluminescence using our streak camera setup. This setup consists of a spectrometer (Acton SpectraPro SP-2300, Princeton Instruments), a streak tube (C10627, Hamamatsu), and a camera (C9300, Hamamatsu). It enables simultaneous measurement of temporal and spectral features. We are able to measure fluorescence lifetimes as short as 20 ps with a spectral resolution of 0.3 nm. For dynamics shorter than this, as well as to probe non-emissive excited states, we utilise femtosecond transient absorption spectroscopy (see below). We use one of two excitation sources: either a 532 nm picosecond laser (LDH-D-TA-530B, Picoquant; pulse width <80 ps, repetition rate up to 80 MHz) or a variable excitation femtosecond laser (Light Conversion), which is described in more detail below.

Our femtosecond laser is a yettrbium based on with a fundamental emission at 1030 nm (Pharos, Light Conversion). The optical parametric amplifier (Orpheus, Light Conversion) produces pump wavelengths ranging from 315 - 3000 nm, with a maximum repetition rate of 10 kHz. The direct harmonic generator (HIRO, Light Conversion) produces signals at 515 nm, 343 nm, and 257 nm with a repetition rate of 200 kHz. The optical parametric amplifier (OPA) output is used for both pump-probe spectroscopy and streak camera measurements, while the HIRO output is primarily used for streak camera measurements. Due to its high power and superior beam quality, the HIRO output is also occasionally used for pump-probe spectroscopy. 

Femtosecond pump probe spectroscopy enables the measurement of excited state process in ultrafast timescale. To probe the system, we generate broadband white light continuum spanning from 500 - 1000 nm using a nonlinear crystal (YAG). The probe signal (in transmission configuration) is measured with a CMOS linear sensor (Hamamatsu).  Using OPA, the samples can be pumped at any wavelength from 315 - 3000 nm, at a repetition rate of 3 kHz. With a temporal resolution of 200 fs, we could measure time resolved signals upto 2 ns delay.