Semiconductor lasers or laser diodes are found in a wide range of technologies, from CD players to laser pointers, laser printers and optical communications networks. Being the smallest lasers, they boast a small spot size, monochromaticity, high light density, and coherence. With continuously improving efficiency and robustness, they will continue to be mass-produced and displace legacy technologies.
Use of lasers in the medical field
High-brightness semiconductor diode laser technology can be used in a wide range of medical applications where solid-state lasers were the only solution previously. Lasers emitting high-power visible light are highly valued in medical (therapeutic) applications as this light is mostly absorbed by organic matter. As a result, most medical laser devices have so far utilised complicated, expensive and sensitive laser systems such as diode-pumped solid-state lasers. Still, these lasers are limited in their ability to emit certain wavelengths in the visible spectrum that are highly important in the treatment of certain diseases. “Lasers have a fixed place in many application areas. However, there are wavelengths for which either no systems exist, or at best only large and expensive ones. This is the case with high-brightness yellow lasers which are seen as the next step in the medical laser treatment of eye diseases,” notes Oliver Hvidt, coordinator of the EU-funded project CoDiS. However, this spectral region is relatively difficult to access, at least when high output power, power efficiency and beam quality are required.
Getting to yellow
Nonlinear optics offer invaluable ways to fill gaps in the laser spectrum: frequency doubling allow near-infrared lasers to produce visible light. CoDiS envisioned using tapered diode lasers (TDDL) to emit visible light at desired wavelengths via the doubling frequency mechanism. Researchers have successfully unveiled TDDL technology emitting at the yellow part of the spectrum (577 nm). The new 3-W yellow laser has been developed for photocoagulation ophthalmic treatments – sealing burst blood vessels at the back of the eye. Its yellow wavelength is considered ideal for this work because it permits maximum absorption in blood. “Compared to the existing photocoagulation systems operating at the green part of the spectrum, yellow light has higher absorption in haemoglobin and lower absorption in melanin. As a result, more energy is delivered to the target blood vessels, while less collateral damage is being done to the surrounding tissue,” explains Hvidt. The yellow wavelength and power level is also useful for some applications in dermatology.
Poised for big market traction
The CoDiS yellow TDDL is smaller, more robust and more energy efficient than competing technology. This enables the system to be integrated into compact, portable and more affordable laser medical devices. Indeed, the project team successfully integrated the TDDL system into a laser device and obtained positive treatment results when testing the technology on animal eyes. “Several lasers on the market today can produce a beam that is a greenish-yellow, but a true-yellow, 577-nm laser light is difficult to achieve and, if so, only at a very high cost,” concludes Hvidt. Accelerated lifetime testing proved the stable and reliable long-term performance of the yellow TDDL. All these are offering hope to get the technology to the commercial stage very soon.
CoDiS, tapered diode laser (TDDL), diode laser, yellow laser, semiconductor laser, photocoagulation, eye disease, dermatology