Plasma plume expansion dynamics in nanosecond Nd:YAG laserosteotome

Abstract

In minimal invasive laser osteotomy precise information about the ablation process can be obtained with LIBS in order to avoid carbonization, or cutting of wrong types of tissue. Therefore, the collecting fiber for LIBS needs to be optimally placed in narrow cavities in the endoscope. To determine this optimal placement, the plasma plume expansion dynamics in ablation of bone tissue by the second harmonic of a nanosecond Nd:YAG laser at 532 nm has been studied. The laserinduced plasma plume was monitored in different time delays, from one nanosecond up to one hundred microseconds. Measurements were performed using high-speed gated illumination imaging. The expansion features were studied using illumination of the overall visible emission by using a gated intensified charged coupled device (ICCD). The camera was capable of having a minimum gate width (Optical FWHM) of 3 ns and the timing resolution (minimum temporal shift of the gate) of 10 ps. The imaging data were used to generate position-time data of the luminous plasma-front. Moreover, the velocity of the plasma plume expansion was studied based on the time-resolved intensity data. By knowing the plasma plume profile over time, the optimum position (axial distance from the laser spot) of the collecting fiber and optimal time delay (to have the best signal to noise ratio) in spatial-resolved and time-resolved laser-induced breakdown spectroscopy (LIBS) can be determined. Additionally, the function of plasma plume expansion could be used to study the shock wave of the plasma plume.

Combined Nd:YAG and Er:YAG lasers for real-time closed-loop tissue-specific laser osteotomy

“…Around 80 ns after opening the Q-switch (information was provided by the manufacturing company), the Nd:YAG emits a pulse lasting 5 ns. Based on the applied energy and also the targeted material, the plasma expansion dynamics can vary [79,80]. Since the plasma generated in the current study had very low energy (4.1 mJ), it quenched quickly.…”

Differentiation of femur bone from surrounding soft tissue using laser-induced breakdown spectroscopy as a feedback system for smart laserosteotomy

“…The emitted light from the produced plasma (H) with a diameter of ca. 3 mm [35] was collected by a light collector placed at 45-degree angle in reference to the laser beam (I), passed through an optical fiber (J) and finally guided to a high-resolution Echelle spectrometer (K) that sent the spectrometer data forward to the computer (L). The spectrometer was empowered with a 16-bit ICCD with a built-in delay generator and adjustable gain.…”

Infrared laser ablation dynamics using light scattering

“…The velocity of an expanding ablation plume can be determined experimentally using high-speed photography with light scattering [40,41], interference methods such as schlieren and shadowgraphy [32,42], and spectroscopy [43,44]. Light scattering fast photography uses two pulsed lasers: the first laser irradiates the sample target to create a plume of material and the second laser is used as a strobe light to illuminate material in the expanding plume which is imaged using a high speed camera [45,46].…”