Background and Objectives Laser‐induced thermal injuries are a heavily researched topic in laser medicine and biomedicine. To explore the quantitative biological effects of laser‐induced injury repair, we propose an optical imaging‐based in vivo evaluation method and discuss the injury effect and repair characteristics of skin tissue. Study Design/Materials and Methods A supercontinumm laser (spectrum width ranged from 400 to 2400 nm) was used to irradiate live mice. The radiation doses were set as 32.85, 65.69, 98.4, and 197.08 J/cm2. Laser‐induced cutaneous thermal injuries were observed and measured after laser radiation. Optical coherence tomography (OCT) was used to image the injured spots. The optical attenuation coefficient (OAC) was computed using a Fourier‐domain algorithm. Three‐dimensional (3D) visualizations of the injured spots in the OCT images were constructed to qualitatively demonstrate the degree of the thermal injury at different times. The corresponding pathological changes of the skin injuries were observed dynamically. Results Under increasing radiation doses, the injured spots, which ranged in degree from mild to severe, appeared accordingly. The mean OAC value of normal skin was 1.15 ± 0.01 mm−1. The mean values of the OAC maps in the region of interests (ROIs) were 0.88 ± 0.05, 0.91 ± 0.02, 0.93 ± 0.04, and 0.98 ± 0.08 mm−1 at each of the four radiation levels, respectively. Additionally, the 3D OCT visualization showed a directed view of the injured spots and the healing process and was used as a qualitative evaluation method. The OCT images and pathological results showed that the damage tended to vary across all groups, but this trend tended to weaken as the radiation dose increased. Conclusion Optical imaging provides an in vivo noninvasive and real‐time evaluation method to comprehensively quantify supercontinuum laser‐induced thermal injuries and wound healing. The OACs and 3D visualizations of the OCT cubic data enable the areas of the direct injured spots to be measured and the inner structure to be viewed. The results obtained with these techniques indicate that the skin injuries are aggravated and tissue repair trends weaken as the radiation doses increase. This method would have a potential application for laser‐medicine and laser‐biological effects in the future. Lasers Surg. Med. © 2020 Wiley Periodicals LLC

Laser biological effects are a hot topic in laser medicine. In this study, to explore the quantitative biological effect of laser-induced wound healing and to provide guidance for expanding the clinical application of laser therapy, the injury effects and repair characteristics of skin tissue are studied through infrared laser irradiation of the skin of miniature pigs. Live pig skin was irradiated at multiple spots one time by using a grid-array method with a 1064 nm laser at different power outputs. The skin injury reaction was observed immediately after laser irradiation from low to high doses. The incidence of skin injury was calculated quantitatively. The healing and pathological changes after laser-induced skin injury were observed dynamically within 6 h and for 28 d after laser irradiation. With the increase of irradiation dose, laser-induced skin injuries ranging from mild to severe appeared in turn. The damage threshold of laser irradiation ED 50 is 47.4 J cm −2 with the laser; from 3 d to 28 d after irradiation, the pathological results showed that wound healing tended to be different in all groups, but this trend weakened with the increase in laser irradiation intensity. With the increased irradiation dose, skin injury appears as different types of injury plaques, ranging from mild to severe. Skin injury is worsened and the tissue repair trend is weakened with the increase in laser irradiation dose, producing a good dose-effect and time-effect relationship.

at the 3-µm transition are attractive for use as pump sources for tunable mid-IR generation using optical parametric oscillation (OPO) or optical parametric generation (OPG) laser systems [4,5], which have broad applications in spectroscopy and atmospheric detection [6]. A simplified Er 3+ energy level diagram is shown in Fig. 1. The 4 I 11/2 upper laser state is directly pumped with a 970-nm laser-diode, and the laser output at 2.79 µm from Er 3+ -doped lasers is because of a transition between the 4 I 11/2 and the 4 I 13/2 energy levels [7]. According to classical laser theory, continuous-wave (CW) operation of the Er 3+ -doped laser is impossible because the upper lasing level has a shorter lifetime than the lower one [8]. However, because of the complex energy transfer processes inherent in these systems and the splitting of the laser levels into manifolds of Stark sub-levels, efficient CW operation for the Er 3+ -doped laser at 2.79 µm was achieved [9].The Er:Y 3 Sc 2 Ga 3 O 12 (Er:YSGG) crystal was demonstrated to be an excellent laser material for a diode-pumped laser at 2.79 µm because of its lower laser threshold and higher laser efficiency compared with other Er 3+ -doped garnet crystals, such as Er:YAG and Er:GGG crystals [10]. Dinerman et al. [9] reported a CW laser output with a power of 511 mW at 2.79 µm from a laser-diode-pumped Er:YSGG crystal. Waarts et al. [11] obtained a 900-mW CW laser output at 2.8 µm using a laser-diode array to pump the Er:YSGG microlaser arrays. Jensen et al. [12] reported a free-running laser with pulse energy of 40 mJ at 20 Hz from a quasi-continuous-wave (QCW) diode end-pumped monolithic Er:YSGG crystal. Arbabzadah et al. obtained a free-running pulse energy of up to 55 mJ at 14 Hz with a QCW diode pumping the Er:YSGG crystal [13]. Recently, we obtained a CW laser output at 2.79 µm with a power of 900 mW from a laser-diode end-pumped composite YSGG/ Er:YSGG crystal [14]. However, because of the thermal Abstract The performance of a laser-diode side-pumped Er:YSGG slab at a wavelength of 2.79 µm was investigated experimentally, and the laser output mode was analyzed using the theory of a thermally induced refractive index planar waveguide. Experimentally, a maximum continuouswave output of 1.84 W with a slope efficiency of 11.2 %, and an optical-to-optical efficiency of 7.5 % at 2.79 µm was obtained with a 970-nm laser-diode dual-side-pumped Er:YSGG slab. To the best of our knowledge, the output power was the highest reported for a laser-diode-pumped Er:YSGG laser with a continuous-wave output at 2.79 µm. The numerical analysis showed that the output power was mainly limited by thermal effects in the thickness direction and the laser output transverse mode in the experiment was the fundamental mode in this direction.

Background and Objective: Lasers are widely employed in clinical applications. In vivo monitoring of real-time information about different-wavelength laser surgeries would provide important surgical feedback for surgeons or clinical therapy instruments. However, the quantitative effect of laser ablation or vaporization still needs to be further explored and investigated. Here, we investigate and quantitatively evaluate the ablation variations and morphological changes of two laser ablation models: point-and sweeping-based models. Methods: An infrared thermal imager was used to monitor the temperature variations, and curve fitting was used to build the relationship between the laser radiation duration/sweeping speed and quantitative parameters of the ablated areas. Optical coherence tomography (OCT) images were used to visualize the inner structure and evaluate the depth of the ablated craters. Optical attenuation coefficients (OACs) were computed to characterize the normal and ablated tissues.Results: The results demonstrated that there was a good linear relationship between radiation duration and temperature variation. Similarly, a linear relationship was observed between the sweeping speed and quantitative parameters of craters or scratches (width and depth). The mean OAC of normal tissues was significantly distinguished from the mean OACs of the ablated craters or scratches. Conclusion: Laser ablation was investigated based on a quantitative parameter analysis, thermal detection, and OCT imaging, and the results successfully demonstrated that there is a linear relationship between the laser parameters and quantitative parameters of the ablated tissues under the current settings. Such technology could be used to provide quantitative solutions for exploring the lasertissue biological effect and improve the performance of medical image-guided laser ablation in the future.

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