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Lasers: Fundamentals And Applications

Medical lasers for various clinical procedures including dermatology and plastic surgery, wound healings, nerve stimulation, dentistry, cancer therapy, and ophthalmic surgeries are reviewed. The fundamental principles behind the technologies are also presented. The laser spectra of UV (200-400) um, visible (400-700) nm, near-IR (700-2900) nm, and mid-IR (3-5) um having various penetration depths define invasive and noninvasive procedures. Diode lasers have been widely used in many surgical procedures including soft tissue cutting, coagulation and cancer thermal therapy. Various photosensitizers are presented in matching the laser absorption wavelengths. Finally, the principles and applications of photothermal therapy (PTT) and photodynamic therapy (PDT) are discussed in great details.

Lasers: fundamentals and applications

In this review article, the fundamental principles behind the medical laser applications will be presented, including the laser spectra of UV (200-400) um, visible (400-700) nm, near-IR (700-2900) nm, and mid-IR (3-5) um having various penetration depths which define invasive and noninvasive procedures. Diode lasers for various surgical procedures including soft tissue cutting, coagulation and cancer thermal therapy will be reviewed. Various photosensitizers are presented in matching the laser absorption wavelengths. Finally, the principles and applications of photothermal therapy (PTT) and photodynamic therapy (PDT) will be discussed in great details.

Laser-tissue (or other media) interaction, in general, could be categorized into three processes: (a) pure thermal, (b) non-thermal, and (c) combined thermal and non-thermal effects. As shown in Figure 1, laser can be reflected, absorbed, scattered or transparent to the matter. These processes are governed by not only the tissues (media) optical properties but also the laser parameters such as its wavelength, energy, intensity, pulse-width, repetition rate and the operation modes, continuous wave (CW) or pulsed mode. For example, an ablative Er:YAG laser operated at short pulse could become a thermal laser when it is operated at low power and/or long pulse; whereas a thermal laser at 1540-nm operated at long pulse could become an ablative, non-thermal laser when it is operated at very short pulse, say less than 10 picoseconds. Furthermore, laser at very short wavelength such as (154-193) nm, could ablate tissues without causing too much heat. Other short pulsed lasers can ablate matter via so-called plasma-assisted process. Various fiber structures for effective delivery of the laser energy to the treated areas are also critical in specific applications.

Lasers have been used for various medical procedures including dermatology, plastic surgery, wound healings, nerve stimulation, dentistry, ophthalmology and many other therapeutic and surgical procedures [1-17]. Combining the nanoparticles and photosensitizers, diode lasers have been also used for cancer diagnosis and therapy [18-23]. Selected medical laser systems (devices) which have been commercialized or used for research are shown in Table 1 for both photodynamic and photothermal and applications, where pulsed lasers are in energy per pulse (mJ) and CW lasers are in power (W).

PDT involves selective light (often low-power laser light or LED) absorption by the external chemical agent, or a PDT drug. As shown in Table 2, various dyes (drugs) have been developed at specific laser absorption wavelengths from visible to near-IR. The PDT drugs may be administered either intravenously or topically depending on applications. Three principal mechanisms have been proposed for the destruction of cells and tissues by PDT: localized cell damage by targeting on a specific organelle by a particular drugs, including apoptosis (localized in mitochondiria) and necrosis (localized in plasma membrane); vascular damage induced by PDT action. For example, the porphyrin-induced PDT produces a rapid onset of vascular blood flow stasis (stopping) and hemorrhage causing tumor cell death; and immunological response of PDT results a strong inflammatory reaction which contributes to tumor destruction.

In contrast to the PDT without too much heat involved, photothermal therapy (PTT) is a thermal process with heat generated by the thermal lasers. Examples of PTT for various applications in cancer therapy, cosmetic and dermatology are presented as follows.

Figure 4 shows various cosmetic lasers and their applications for invasive and non-invasive uses defined by their tissue penetration depth (d). Lasers with small depth (d 2 mm) suitable for non-invasive simulation or hair removal. Figure 4 can be compared with Figure 2 for the penetration depth. Figure 4 shows the commercial laser for hair removal (using a diode laser at 810 nm with large penetration depth about 4 mm) and hair growth device (using a red, 635 -690 nm, LED or laser with smaller penetration depth and low power for surface stimulation). Figure 5 shows a UV (308 nm) light device for the treatment of psoriasis; and a pen-type blue laser (at 405 nm) combined with a red laser (at 660 nm) for the treatment of acne.

As shown by Table 3, various lasers have been used for various ophthalmic applications including retinal photocoagulation using argon blue-green laser (488/514 nm), double-YAG green laser (at 532 nm), krypton laser (at 647 nm) and diode lasers (at 806-810 nm). Photocoagulation process was also used to seal leak blood vessels for the treatment of age-related macular degeneration (AMD).

Random fiber lasers blend together attractive features of traditional random lasers, such as low cost and simplicity of fabrication, with high-performance characteristics of conventional fiber lasers, such as good directionality and high efficiency. Low coherence of random lasers is important for speckle-free imaging applications. The random fiber laser with distributed feedback proposed in 2010 led to a quickly developing class of light sources that utilize inherent optical fiber disorder in the form of the Rayleigh scattering and distributed Raman gain. The random fiber laser is an interesting and practically important example of a photonic device based on exploitation of optical medium disorder. We provide an overview of recent advances in this field, including high-power and high-efficiency generation, spectral and statistical properties of random fiber lasers, nonlinear kinetic theory of such systems, and emerging applications in telecommunications and distributed sensing.

Feature papers represent the most advanced research with significant potential for high impact in the field. A FeaturePaper should be a substantial original Article that involves several techniques or approaches, provides an outlook forfuture research directions and describes possible research applications.

Since its discovery, the laser has found innumerable applications from astronomy to zoology. Subsequently, we have also become familiar with other sources of coherent radiation such as the free electron laser, optical parametric oscillators, and coherent interferometric emitters. The aim of this book series Coherent Sources, Quantum Fundamentals, and Applications is to explore and explain the physics and technology of widely applied sources of coherent radiation and to match them with utilitarian and cutting-edge scientific applications. Coherent sources of interest are those that offer advantages in particular emission characteristics areas, such as broad tunability, high spectral coherence, high energy, or high power. An additional area of inclusion are those coherent sources capable of high performance in the miniaturized realm. Understanding of quantum fundamentals can lead to new and better coherent sources and unimagined scientific and technological applications. Application areas of interest include the industrial, commercial, and medical sectors. Also, particular attention is given to scientific applications with a promising future such as coherent spectroscopy, astronomy, biophotonics, space communications, space interferometry, quantum entanglement, and quantum interference.

F J Duarte is a laser and quantum physicist based in the USA. His career has spanned three continents while contributing in the academic, industrial, and defense sectors. Duarte is editor/author of 15 laser optics books and sole author of three books: Tunable Laser Optics, Quantum Optics for Engineers, and Fundamentals of Quantum Entanglement. Duarte has made original contributions in the fields of coherent imaging, directed energy, high-power tunable lasers, laser metrology, liquid and solid-state organic gain media, narrow-linewidth tunable laser oscillators, organic semiconductor coherent emission, N-slit quantum interferometry, polarization rotation, quantum entanglement, and space-to-space secure interferometric communications. He is also the author of the generalized multiple-prism grating dispersion theory and pioneered the use of Dirac's quantum notation in N-slit interferometry and classical optics. His contributions have found applications in numerous fields, including astronomical instrumentation, dispersive optics, femtosecond laser microscopy, geodesics, gravitational lensing, heat transfer, laser isotope separation, laser medicine, laser pulse compression, laser spectroscopy, mathematical transforms, nonlinear optics, polarization optics, and tunable diode laser design. Duarte was elected Fellow of the Australian Institute of Physics in 1987 and Fellow of the Optical Society of America in 1993. He has received various recognitions, including the Engineering Excellence Award and the David Richardson Medal from the Optical Society (Optica).

This special issue covers a series of cutting-edge works on advanced physics and applications of optical microcavities and microlasers, ranging from the study of chaotic resonances, microcombs and soliton physics, lasers with tailored orbital angular momentum, coherent light-matter coupling and quantum condensation, optical nonreciprocity, to multiplexed biochemical sensing. In what follows, a brief introduction to each topic will be presented along with their key implications highlighted. 041b061a72


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