## 2 Design of the Laser Scalpel  
### General Structure and Components  
To gain a better understanding of the research subject, Figure 1a illustrates the 3D model of the fully assembled device that integrates three mechanical amplifiers. Figure 1b presents the physical device, in this proof-of-concept stage, highlighting its key components:  
_Laser subsystem_: the element responsible for the collimation of the laser beam that is used for cutting, ablation, or controlled burning during surgical procedures. A laser diode source with a center wavelength of 808 nm (considered for proof-of-concept testing), with a red pilot beam is utilized. _Mobile platform_: the component that moves together with the laser subsystem to adjust the position of the laser spot on a target plane in order to compensate for any unintended hand movements made by the surgeon. It is equipped with sensing electronics that allow for monitoring movements across all six DOF. _Compliant spherical joints_: the component represented by a metal wire that transmits the motion from the mechanical amplifier to the mobile platform. _Mechanical amplifiers_: the mechanisms that transmit and amplify the movements generated by the piezoelectric actuator, thus enabling the compensation of vibrations with the level of precision that can be achieved. Figure 1: (**a**) Three-dimensional model and (**b**) physical realization of the developed proof-of-concept variant of the compensation device. Central joint: the pivot point that allows for a controlled movement of the mobile platform, thus eliminating parasitic movements. It facilitates only two rotations and a slight displacement (i.e., translation) along the optical axis and the laser terminal. P-010.20 piezo actuators: they are responsible for generating the fast and precise movements required to counteract unintended vibrations. This type of actuator provides a high resolution and a short response time, thus making it an appropriate choice for active vibration compensation. Conical end caps: they are utilized to secure and self-center the piezoelectric actuators, therefore minimizing the bending stress on the stack. Central guidance rod: it is made of an aluminum alloy; it serves to rigidly connect the central joint to the support platform, and it allows for routing signal/power wires through its interior. Support platform: the base of the system that ensures the stability of the entire structure and maintains all the components in their correct positions. It is the point from which the operator holds the system, as well as the area where the hand vibrations are measured. A discussion should be made at this point, before starting the design and analysis process, regarding the necessary number of DOF of the proposed system. Thus, depending on the application, a translation along the optical axis of the laser may or may not be required. In applications involving tissue removal, such as plastic microsurgery, the precise control of laser focusing is not essential. Vibrations along the optical axis caused by hand tremors are within acceptable limits (considering the amplitude of the tremor in this direction) and can be disregarded. However, in other applications, such as the manipulation of nerve endings or high-precision laser scanning of surfaces, focus control becomes critical, making the axial translation of the device indispensable. The current structure of the device has been designed as a platform that can be further developed for various applications. The functionality demonstration has been focused solely on rotational movements for two primary reasons. First, the intended application is surgery involving tissue removal. Second, active vibration compensation using translational piezoelectric actuators (with or without compliant mechanisms) is already a well-established technique, which is extensively documented in the specialized literature and is available in commercial products.