Scientists develop laser

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A multinational collaborative effort has led to the discovery of a new laser-based diamond sensor that can measure magnetic fields up to 10 times better than what instruments do today, a university press release said.

Magnetic field measurements are used widely in the field of medicine today. Magnetic resonance imaging (MRI), which combines the use of a magnet and radio waves to look at organs and structures inside the body, has become a significant tool for examining the brain and spinal cord and looking for early signs of diseases.

On the other hand, with advancements in medical technology, we can now also measure the magnetic fields produced by the electrical currents inside our brains. Using a technique called magnetoencephalography (MEG), clinicians can now map the activity in the brain and look for locations that might be the source of epileptic seizures or spot malfunctioning neurons during normal activities in the brain.

While technologies like MEG are a boon to the medical community, installing and operating these machines is a major challenge. The instrument that can measure the magnetic field is costly and fills up an entire room that needs magnetic shielding. It also demands ultra-cold temperatures to keep the helium used in the instrument in the liquid state. Most difficult of all, it requires the patient to remain absolutely still while making these measurements.

Researchers at the Royal Melbourne Institute of Technology (RMIT) collaborated with Fraunhofer Institute for Applied Solid State Physics (IAF) in Germany to look for ways to improve the detection of these waves and found that the diamond used for these detections could be improved further.

Diamonds are part of the instruments used for magnetic field sensing today. The intensity of the light that comes from the quantum defects on the diamond changes with the strength of the magnetic field. The researchers, however, found that most of the light that the diamond gives out is lost.

By converting this light into a laser, the researchers were able to collect all of it and this led to a 10-fold increase in the detection of the magnetic field.

The researchers envision that a MEG instrument made with their laser-emitting diamond will be much smaller than today's instruments and could be made portable if required. Instead of sitting still, patients could practically walk with the MEG developed using this new technology. Since the instrument would not require liquid helium, it would operate at room temperature too.

The instrument, which could take up to five years to be built, will be useful in spotting early signs of diseases such as dementia, Alzheimer's disease, and epilepsy.

The researchers have published their findings in the journal Science Advances.

Abstract

Negatively charged nitrogen-vacancy (NV) centers in diamond are promising magnetic field quantum sensors. Laser threshold magnetometry theory predicts improved NV center ensemble sensitivity via increased signal strength and magnetic field contrast. Here, we experimentally demonstrate laser threshold magnetometry. We use a macroscopic high-finesse laser cavity containing a highly NV-doped and low absorbing diamond gain medium that is pumped at 532 nm and resonantly seeded at 710 nm. This enables a 64% signal power amplification by stimulated emission. We test the magnetic field dependency of the amplification and thus demonstrate magnetic field–dependent stimulated emission from an NV center ensemble. This emission shows an ultrahigh contrast of 33% and a maximum output power in the milliwatt regime. The coherent readout of NV centers pave the way for novel cavity and laser applications of quantum defects and diamond NV magnetic field sensors with substantially improved sensitivity for the health, research, and mining sectors.