## 4 Discussion  
Diode lasers are characterized by their great versatility. Their bandwidths in terms of wavelength (ultraviolet 375 nm up to mid-infrared > 10 \(\upmu\)m), emission power (>1 W per emitter) and operating mode (CW or pulsed) prove to be enormously advantageous, especially in the medical field. Both their size and the possibility of connecting optical fibers directly to these laser systems predestine them for practical applications in medicine. However, these laser systems are also subject to continuous technical development to improve and expand their range of applications. This can be seen in the generation of \(\upmu\)s-pulses for the wavelength 445 nm which, hitherto, has been technically implemented only for the wavelength 810 nm in dentistry [17; 18; 19]. Regarding the lifetime of the laser diodes used, no reduction in the laser output power could be observed so far in the over-pulsing operation mode. In fact, two distinct damage mechanisms which can be responsible for the destruction of a laser diode should be taken into consideration: optical as well as electrical overloads. The optical overload describes the  
Figure 13: Depth of the thermal damage zones below the incisions. Graphs show the dependency of the different duty-cycles for pulse durations of 10 \(\upmu\)s, 100 \(\upmu\)s and 1 ms, (**left side**) as well as on different pulse durations for the corresponding duty-cycles (**right side**). Additionally, trend curves of the thermal damage zones for continuous wave operation are included in all graphs (for a better overview without error bars), which also are in the same order of magnitude as for the pulsed operation. destruction of the optical resonator induced by exceeding the resonator threshold based on high-intracavity light intensities (vaporization of the mirror surface), whereas the electrical overload describes the destruction of the p-n-junction caused by a localized overheating effect. Both phenomena can be provoked by an over-voltage or an over-current condition, especially in low-power laser diodes with an output power \(\leq\) 200 mW [23]. According to the manufacturer's information [oral communication with A.R.C. Laser GmbH], no limitations could be observed after testing the laser diodes used for approx. 10,000 h in an over-current condition of 20% above standard operation. The characterization of the used laser diodes showed only a thermal influence at high set point voltages, resulting in a saturation behaviour of the output power in CW operation mode, as well as for the over-pulsing mode, as illustrated in Figures 6 and 8. Therefore, an efficient cooling system is of importance to guarantee a long lifetime independent of the mode of operation. The wavelength 445 nm is highly absorbed in different tissue structures, primarily in hemoglobin (\(\mu_{\text{A(HbO}_{2})}\) = 440 cm\({}^{-1}\); \(\mu_{\text{A(Hb)}}\) = 1526.7 cm\({}^{-1}\)) and melanin (\(\mu_{\text{A(Skin)}}\) = 1033 cm\({}^{-1}\)) [24; 25]. The absorption in water is negligible (\(\mu_{\text{A(H2O)}}\) = 2.85 \(\times\) 10\({}^{-4}\) cm\({}^{-1}\)) [26]. This results in strong interactions between laser radiation and the blood-carrying tissue layers, which can be verified in the effect of tissue cutting (Figure 12 and Table 3). [PERSON] et al. [20] compared eight different laser wavelengths (405, 445, 514, 532, 810, 980, 1064 and 1470 nm) for surgical applications in soft tissue. They investigated cutting effects and thermal influences depending on the laser wavelengths. Finally, a new parameter, the so-called \"efficiency factor\" was defined. This factor enables researchers to make forecasts about the expected tissue interaction processes. In this work, very promising results for soft tissue cutting were achieved for 445, 514 and 532 nm. Furthermore, a bactericidal effect for 445 nm could be verified for different dental applications, e.g., cavity disinfection within the scope of restorative dentistry [27], and decontamination of implants [28], as well as in the field of endodontics [29].