Doctoral dissertation

Lasers targeting new wavelength ranges for nuclear medicine and quantum technology applications

Lasers revolutionized numerous fields, ranging from medicine and biology to telecommunications, sensing, and quantum technologies. Parameters of the laser light emission have to be precisely matching the requirements manifested by the particular laser application. Each laser platform differs in terms of flexibility and capability of tailoring the light emission parameters in accordance to the application requirements.

In this doctoral thesis, Kostiantyn Nechay aimed on development of optically-pumped vertical-external-cavity surface-emitting lasers (OP-VECSELs), or semiconductor disk lasers, one of the most flexible laser platform, targeting nuclear medicine and quantum technology applications.

OP-VECSELs constitute a very flexible laser platform, delivering high-power and high-brightness emission at a vast wavelength range. This laser combines advantages of solid-state lasers with the emission wavelength versatility typical for semiconductor lasers. Thus, by engineering the semiconductor part, which plays a role of light-emitting section, it is possible to obtain emission at different wavelengths (or colors), with easily tailorable parameters thanks to external resonator. However, due to specific laser architecture, this laser is a subject for certain limitations, which arise from the impossibility to manufacture certain semiconductor compounds. Therefore, emissions at certain wavelength are more challenging to achieve with VECSELs.

“The goal of this work was to demonstrate VECSELs with emission at the specific wavelength range, namely 700-800 nm, where development of VECSELs were not extensively addressed. On the other hand, potential applications for such high-brightness lasers in nuclear medicine (i.e. radioisotope separation), quantum technology or spectroscopy, would point to a large audience interested in the results,” says Nechay.

The research on the topic has followed two alternative directions: first is to develop VECSELs employing AlGaAs quantum wells, which would provide direct-emission at 750 nm (deep red color), second is to develop VECSELs with fundamental emission at 1.5 µm and then achieve efficient frequency doubling to 750 nm.

VECSELs have benefited the quantum technology field, where they have been successfully employed in ion cooling and ion trapping in order to create qubits, the building blocks of quantum computers. Moreover, VECSELs at this wavelength range are being proposed for application in nuclear medicine with an aim on radioisotope separation. The newly invented technique of medical radioisotope separation, with efficiency surpassing previous methods by a factor of 1000, is promised to revolutionize medical isotope manufacturing. Medical radioisotopes are one of the most expensive and rarest commodities on Earth, which are routinely used in tens of millions cancer treatments per year. The new method of separation relies on lasers with tunable, high-power, narrow-linewidth emission at the specific wavelengths, the requirements that can be easily delivered by VECSELs.

The doctoral dissertation of M. Sc. Kostiatyn Nechay in the field of Photonics titled High-power VECSELs operating at the 700-800 nm wavelength range will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University at 12 o’clock noon on Friday 22nd of November 2019 in Festia building auditorium Pieni Sali 1, Korkeakoulunkatu 8. The Opponent will be professor Harri Lipsanen from Aalto University, Finland. The custos will be professor Mircea Guina, Optoelectronics Research Centre, Faculty of Engineering and Natural Sciences.

The dissertation is available online at https://trepo.tuni.fi/handle/10024/117974