BRIGHTER lasers for tomorrow's technologies

Medical applications are extremely important for European society, but the market is still fragmented and poorly connected to technology developers. One example is the minimally-invasive procedure known as photodynamic therapy or PDT. The PDT technique uses photosensitive drugs to precisely target tumours within the body — the chemotherapy-like drugs administered to the patient preferentially attach themselves to malignant tissue, causing no harm to the surrounding healthy tissue, and are only activated when illuminated by a specific colour of laser light (for example, red). Ultimately, the winner is the patient, who will benefit from better treatment with fewer side-effects and an improved quality of life.

Blue and red lasers are being developed in the BRIGHTER project for PDT applications in medicine. The blue lasers are used for fluorescence spectroscopy imaging of fluorescent markers used to locate malignant tissue. The red lasers are then used to activate the cancer drug (photosensitizer) which, like the fluorescent marker, accumulates in the tumour.

In the medical field, however, technological success is no guarantee for clinical or commercial success. Thus, to ensure the clinical success, the BRIGHTER project is addressing all areas in the development chain from device and module development to systems integration and even includes clinical testing.

In the first year of the project, improved red lasers have already been demonstrated and are ready for incorporation into a PDT delivery system. A high-brightness blue laser source has been demonstrated by the frequency-doubling of a high-power infrared laser. Frequency-doubling is an advanced technique that uses a special nonlinear optical crystal to convert the colour of the laser output. The new blue laser has been incorporated into a fluorescence imaging system for looking at malignant tissue at the Lund Laser Centre and the first clinical tests have already begun.

Projection display systems are a relatively new application of laser diodes with several challenges that still need to be overcome before such systems become portable and affordable for everyday use. A laser display requires red, green and blue lasers to be integrated into a single module. Red and blue lasers are being developed within the project for the medical market, so that the main challenges remaining are the realisation of a high-brightness green laser diode and the development of a full system prototype. The green laser diode is a particular challenge as no semiconductor material exists that can be used to directly produce green laser light. In BRIGHTER, the frequency-doubling principle, successfully demonstrated in the realisation of the blue medical laser, is now being extended to produce this all important green laser from a high-brightness infrared device.