TeraXion Launches HPR Med-2 Series Cavity Mirrors to Enhance the Use of TFLs in Urology

Posted  by GoPhotonics


TeraXion, an indie Semiconductor Company has launched the HPR Med-2 series cavity mirrors, which are Bragg grating reflectors specifically designed to meet the requirements of medical thulium fibre lasers. Unique processes make it possible to considerably limit the heating of the gratings compared to conventional processes which results in a measurable reduction in the laser’s wavelength shift as a function of output power.

With low insertion losses, Med-2 series reflectors help produce laser cavities that are less likely to initiate the phenomenon of self-pulsing, where high-energy pulses can cause significant damage to the components of the optical chain. The product can be configured for different cavity designs, whether in reflectivity, bandwidth, or fiber type. The performance of these cavity mirrors is highly reproducible from unit to unit, helping to achieve equally-repeatable laser performance.

The unique manufacturing process and efficient thermal management of the HPR Med-2 series reflectors ensure minimal heating at the operating power required by the application. By limiting the component insertion loss and thus improving the efficiency of optical conversion, the reflectors reduce the overall costs of medical Thulium fiber lasers and ensure that each laser oscillator produces optimal power, simplifying laser system design and reducing the cost per watt.

Thulium Fibre Lasers

The TFL uses a thulium-doped silica optical fiber most often pumped using fiber laser diodes emitting around 793 nm. In addition to its doped core, the active fiber has cladding that guides the pump photons that are gradually absorbed by the Tm ions from the entry point. Due to this double clad fiber, both the laser emission and the pump are simultaneously guided.

The laser’s central wavelength, located in the emission spectrum of thulium, is determined by that of the Bragg gratings which serve as cavity mirrors. These gratings are fabricated in passive double-clad fiber compatible with active Tm-doped fiber. Urological TFL is usually designed to emit at 1940 nm. As this wavelength is closer to the water absorption peak, the laser energy is absorbed over four times shorter distance. Given the exponential character of the absorption (the Beer-Lambert law), the TFL’s radiation is absorbed approximately 16,000 times more than that from the conventional solid-state lasers over a distance of 1 mm. This results in a much more confined laser-tissue or laser-stone interaction and a marked reduction in the minimum energy required to initiate vapor microbubble formation.

Advantages of Thulium Fibre Laser

The increased confinement provided by TFL translates into a four times lower ablation threshold. The consequence is that for a given energy, the TFL makes it possible to disintegrate a significantly larger volume of stones. As a corollary, the energy required to ablate a given volume is reduced. This makes the TFL less prone to the retropulsion effect. Increased containment also means safer treatment, with less risk of inflicting collateral damage to surrounding tissues.

In the case of the TFL, the pulses generated from the direct modulation of the pump diode current provide greater flexibility and better control of the irradiation conditions over generally wider ranges. The pulses produced by the TFL present an almost rectangular profile with a peak power that varies very little over the duration of the pulse and this duration can be adjusted between 100 and 12,000 µs. The pulse repetition rate can be between 5 and 2200 Hz. As for the energy of the pulses, the TFL provides a finer control at the bottom of the adjustment range, with lower minimum energy (25 mJ). This is a valuable asset to generate the smallest possible fragments (dust) while keeping retropulsion to a minimum.

Several studies have demonstrated TFL’s effectiveness in urological treatments. The very localized absorption of the radiation causes explosive vaporization of the water trapped in the interstices, micro-fissures, and pores located on the surface of the stone, which generates pressure peaks accompanied by waves of mechanical stress propagating in the whole of the stone. These stresses weaken the stone while removing debris from the irradiation site. TFL can produce extremely small particles of less than 0.1 mm, which is real dust. The high repetition rates produce this dust at a higher rate. The major reduction in retropulsion is another determining factor in the duration of TFL treatments, as the surgeon does not need to constantly readjust the position of the fiber towards the stone.

Another advantage, the use of smaller diameter fibers results in greater flexibility with the endoscopes and the ability to treat otherwise inaccessible sites. The space freed up also enables increased irrigation and better visibility. The TFL has many other advantages compared to other solid-state lasers, including nearly 10 times lower power consumption, no high-voltage circuitry, a seven times smaller footprint, and eight times lighter weight. In an operating room, these reduced constraints greatly favor using the TFL. Add to that significantly lower maintenance costs, and this new technology becomes almost irresistible.

With all their advantages, TFLs are expected to gradually replace other solid-state lasers used in urology. The transition has already begun, and TeraXion is a part of it by offering innovative, efficient, and reliable products specifically designed for this type of laser.

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