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Leveraging the Concept of Laser Physics in Healthcare

Abstract

Laser therapy is a type of radiation therapy in which a concentrated beam of light injures or kills the tissue. It is a cutting-edge scientific development that has been successfully applied to treating and managing a wide variety of diseases around the world with zero environmental impact. Pain and inflammation relief and tissue repair have all been examined, and their underlying mechanisms have been found and analyzed. A wide range of clinical conditions, including musculoskeletal pain, osteoarthritis, joint pain and inflammation, neuropathic pain, otitis, dermatitis, chronic, or non-healing wounds, and decubitus ulcers, can be alleviated with laser therapy, which employs light energy of varying wavelengths and power densities. Laser medicine has several therapeutic benefits. When using laser therapy techniques, all appropriate safety measures must be taken. This chapter introduces laser systems and their potential use in healthcare.

Keywords: Laser optics, laser beam, photobiomodulation, optical emission spectroscopy, X-ray

1.1 Introduction

Light amplification by stimulated emission of radiation or LASER: Albert Einstein initially proposed the concept of stimulated emission, the physical mechanism that produces lasers, in 1917 [1].

The electromagnetic radiation spectrum, which includes visible light, has a photon as its energy unit. The energy of a photon is absorbed by an electron as it orbits a nucleus, and the electron then bounces to a higher orbit. When this occurs, they say that the atom is “stimulated.”

When photons called “stimulating photons” strike electrons of atoms in an excited state, the electrons release the energy they receive in the form of photons that move in the same direction, phase, and wavelength as the stimulating photons. This process is known as “stimulated emission” as shown in Figure 1.1.

The light is amplified because of a process called stimulated emission, which requires the medium to reach a state called “population inversion” that has more excited atoms than in their resting state. To achieve this, an excitation source must be able to “pump” photons into the medium.

The medium is made up of two mirrors at either end that together forms an optical cavity where the emitted photons bounce back and forth. The light beams are magnified because the trapped reflected light causes the production of extra photons.

Eventually, a laser beam will be created when the amplified light is reflected off of one of the partially reflective mirrors.

Therefore, the laser beam is “unidirectional,” “monochromatic,” and “spatially coherent,” making it distinct from regular light. A laser’s beam may concentrate its power in a small area by maintaining its tiny profile even at large distances (collimation).

Ophthalmic lasers cover the visible light spectrum, which begins at 193 nm and extends to 10,800 nm (390–700 nm). The higher the frequency and energy of a laser’s photons, the shorter its wavelength.

The duration of an emitted laser can range from a few femtoseconds to an infinitely long time (continuous wave laser).

Electronic shutters may generate pulses as short as 1 ms. Pulsed flash bulbs can generate pulses in the microsecond range. Nanosecond pulses (Q-switching) can generate pulses in the nanosecond range, and femtosecond pulses can generate pulses in the femtosecond range (mode locking) [2].

Figure 1.1 Mechanism of stimulated emission.

1.2 Physics of Laser

At its most basic level, a light beam produced by a laser device interacts with the target tissue to have an effect (this process is technically referred to as “laser–tissue interaction”) as shown in Figure 1.2.

1.2.1 Principles of Optics

Photons are the fundamental particles that make up all forms of electromagnetic energy (quantum of light). Light particles or photons constantly move and travel through space at the speed of light (2,998×108 meters per second) in a sinusoidal wave pattern. For electromagnetic sine waves, the spectrum spans from extremely short (gamma rays) to extremely long (AM radio waves), depending on the frequency of the wave (Figure 1.3) [3].

The human eye can only detect electromagnetic radiation with a wavelength of 390 nm (violet) to 700 nm (red), hence, this is the narrow portion of the spectrum that contains visible light. Majority of medically important lasers operate at wavelengths between those of visible light and the electromagnetic spectrum’s extended infrared end.

Figure 1.2 Schematic flowchart of a laser theory.

Figure 1.3 Electromagnetic wave.

1.2.2 Laser Gadget

Any laser apparatus primarily consists of an energy source and an optical resonator (Figure 1.4).

The photons are produced when electrons are stimulated from a ground state by the energy source. This power supply may be in the form of conventional light bulbs, electricity, and other lasers. The medium of an optical resonator is sandwiched between two mirrors, one of which is fully opaque and the other is only partially opaque, at the tube’s ends (and therefore partially transmissible) [3]. It could be a solid, liquid, liquid crystal, or gas as the medium (with the distinction that liquid crystals have an atomic organization that is between that of solids and liquids). The medium in which a laser operates determines both its wavelength and the type of laser used (e.g., ruby, argon gas, CO2, Er: Yttrium Aluminum Garnet (YAG), alexandrite, diode, Potassium Titanyl-Phosphate (KTP), argon, Nd: YAG).

The electrons in a medium can be stimulated by the addition of energy. Particles inside the tube emit light of a specific wavelength when they settle back to their starting place. To continue the spread of light, a “chain reaction” occurs when an electron in an excited state interacts with another photon of the correct energy, causing the electron to emit another photon of the same wavelength without absorbing it. One can generate a “laser beam” by using a partially transmitting mirror to direct a subset of photons moving in a parallel direction out of an optical resonator [3].

1.2.3 Laser Beam

Several characteristics of the resulting beam of light set it apart from the light produced by a regular incandescent flashlight or lamp. Polychromic, incoherent, and not collimated best describe incandescent illumination [3].

Figure 1.4 Laser components.

Figure 1.5 Electron excitement.

In contrast, the light emitted by a laser is uniform in wavelength, coherent, and collimated (Figure 1.5).

1.2.3.1 Monochromatic

The photons making up a laser beam have all the same wavelength, making the beam monochromatic. In contrast, a flashlight can produce light at a wide range of wavelengths.

1.2.3.2 Coherent

A laser beam contains photons that are coherent because the waves are in phase with one another in both space and time.

1.2.3.3 Collimated

All the photons in the laser beam are aligned in the same direction, making the beam collimated. This means a laser beam can travel far without deforming significantly.

Because of this, the laser beam’s energy density is raised. As a result of the process being so poorly efficient (just about 0.01% of the input energy is converted to laser output), the total amount of energy produced by a laser is quite small. Collimation, on the other hand, concentrates the beam’s energy in a tiny space.

The ability of a laser to convert one form of energy (e.g., electricity or light) into a coherent, collimated beam of photons with a high energy output is what makes it such a powerful tool [3].

1.3 Laser Classification

According to their maximum output power or energy and wavelength, lasers can be divided into four separate groups. As a result, Class I lasers are the safest and least powerful type. Commonplace lasers include those found in things like grocery store scanners and other bar code reading devices. The visible spectrum is where Class II lasers shine (400–700 nm). Some laser pointers and medical lasers belong here. Prolonged exposure to the laser in the eye can cause damage [4–6].

Lasers utilized for therapeutic purposes are classified as Class III. To further categorize these lasers, Class IIIB lasers can be either continuously operating pulsed or continuous visible light or range from visible to infrared. Lasers in the Class IIIR variety are constantly emitting light within the visible spectrum but are weaker than Class IIIB lasers. The highest powerful lasers fall into the Class IV category and are commonly used in surgical procedures. They can cause severe burns or blindness [7, 8].

1.4 The Workings of a Laser Therapy

Researchers in the field are currently debating the mechanism of action related to photobiomodulation. It is envisaged that the targets and cell types being controlled would have different mechanisms of action. Photobiomodulation, or low-level laser therapy, is a painless, non-invasive treatment alternative that stimulates natural biological processes that promote...