Product Code: ILSC2007_1007

Filter and Mirror Design for a Micromanipulator used with a Medical Dual Wavelength Laser
Authors:
Wolfgang Wöllmer, University Medical Center Hamburg-Eppendorf; Hamburg Germany
Reinhardt Thyzel, A.R.C. Laser GmbH; Nürnberg Germany
Presented at ILSC 2007

One of the special properties of lasers is the emission of monochromatic radiation. Filters and mirrors have to provide high coefficients of absorption and/or reflection. Especially for eye safety filters the transient laser radiation must not exceed the MPE. Various medical laser systems on the market today include different lasers and allow a combined application with more than one wavelength.These new developments lead to new challenges for optical surfaces, as used in filters and mirrors. The present paper discusses the approach to work with a frequency doubled Nd:YAG-laser (KTP-laser) with a wavelength of 532 nm, and one (or more) diode lasers with a wavelength of 808 nm, 940 nm or 980 nm using the same optics, without changing the unit or the fiber, neither the delivery device, like a micromanipulator, used for laser microsurgery or coagulation. In order to avoid doubled eye protection filters built into the microscope to protect the surgeons eyes, a new coating of the beam steering mirror was applied to obtain high reflection coefficients for both the 532 nm-, as well as the near infrared wavelengths. A first prototype of this beam steering mirror with these coating properties provides an excellent reflection coefficient. However, in practical use the microscopic view is superimposed with a colour alteration, which is dependent on the angle of the mirror, i.e. which changes during the performed treatment. Does this irritate the surgeon? Other improvements of the new coating are also necessary: the transmission of the 532 nm laser light at the mirror is too high to be accepted. Working with laser output powers in the range of 1 to 3 W, causes irritation of the user due to the high intensity of the green laser light. On the other hand the visible illumination of the viewing field is reduced to an extent that is not sufficient for the observation of the treatment site. As a first improvement, the shape of the mirror is changed in a way, which allows the free vision of the surgical field, but still yields the reflection of a high percentage of the laser beam. However, in this design the surgeons eye protecting filter is mandatory again. Also, protection means against the infrared wavelengths have to be applied. The next step will be the modification of the mirror coating in order to improve the selective reflection of the green laser light with still an improved visibility of the treatment area. This paper presents our development work in this important field.