Pump Laser Modules Show Promise for Ophthalmologic Treatments

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Researchers at the Berlin-based Ferdinand-Braun-Institut (FBH) developed a pump laser module for ophthalmologic treatments. The module offers a cost-effective pump source for laser systems that are used to treat retinal detachments. The miniaturized module can be flexibly adjusted to provide the optimal wavelength for its intended application.

The semiconductor-based, miniaturized laser module could provide a reliable, efficient way to provide laser surgery that is targeted to the condition being treated and could reduce the costs of ophthalmologic laser surgery.

Retinal detachment can lead to visual impairment and blindness, and must be treated promptly. Laser coagulation, a well-established method that uses laser points to treat holes and fissures in the retina, is used to treat a number of eye conditions, including detached retina. Existing laser coagulation systems are expensive and limited to only a few laser wavelengths.

The module builds on miniaturized, robust laser sources previously developed by FBH scientists. These sources, which emit in the near-infrared (NIR) and provide high spectral radiance, are well suited for industrial applications.

Each laser source consists of a pump laser, the NIR light from which can be converted using a nonlinear crystal. When the NIR light is converted, the wavelength is halved through second harmonic generation (SHG). Halving the wavelength causes the laser to emit light in the visible spectral range.

Current laser coagulation systems specifically use the wavelengths of 532 and 577 nm, and the FBH researchers designed their pump laser module to target these wavelengths. Lasers emitting at 577 nm are particularly relevant for ophthalmology procedures, because the oxygen-rich blood pigment, oxyhemoglobin, absorbs light most strongly at this wavelength.
A miniaturized, robust pump laser module for ophthalmology offers high spectral radiance and industrial-grade performance. Courtesy of FBH/P. Immerz.
A miniaturized, robust pump laser module for ophthalmology offers high spectral radiance and industrial-grade performance. Courtesy of FBH/P. Immerz.
The spectrally narrowband pump sources at 1154 and 1064 nm provide high optical output powers with an excellent beam quality, which simplifies their subsequent frequency doubling into the yellow-green spectral range, according to the researchers. This process also reduced the cost and weight of the module, compared to the more complex laser sources used for laser coagulation.

To demonstrate demonstrate the suitability of the light modules as pump sources, the researchers developed prototypes of the module with separate laser beam generation (i.e., the master oscillator) and power amplification. The researchers integrated a commercial miniaturized isolator between these two components to protect the master oscillator from external feedback. According to the researchers, the feedback can be high in SHG crystals with waveguides — greater than 1% — and can significantly interfere with the master oscillator.

Despite a small footprint of only 25 × 25 mm, the prototype modules achieved optical output powers of more than 8 W in continuous-wave mode at 1064 and 1156 nm. They also realized a good beam quality of M2 < 2 and a spectral linewidth of < 5 MHz. The researchers said that the results of the demonstration are transferable to other wavelengths.

The use of miniaturized light modules as pump sources, followed by the use of highly efficient SHG phases, enabled the laser module to cover the visible range from 400 to 600 nm. In contrast, the wavelengths of previous solid-state laser systems are limited to the 532-, 561-, 577-, and 586-nm laser lines. The laser diodes and amplifiers for the laser module can be manufactured in large quantities on wafers to further reduce costs. For example, 400 active components can fit on a 3-in. wafer with a diameter of 7.6 cm. Portable, flexible systems for use in an outpatient environment are possible with the laser module.

Published: November 2022
Research & TechnologyeducationEuropeFBHFerdinand Braun InstitutLasersmedicalBiophotonicsNIRopthalmicsecond harmonic generationpump lasersemiconductor lasertreatmentBioScan

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