Derived from the terms "excited" and "dimers," these types of lasers use reactive gases, such as chlorine and fluorine, mixed with inert gases such as argon, krypton or xenon. When electrically stimulated, a pseudo molecule (dimer) is produced. When lased, the dimer produces light in the ultraviolet range.

A laser is a device that controls the way that energized atoms release photons. "Laser" is an acronym for light amplification by stimulated emission of radiation, which describes very succinctly how a laser works.

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The concept of vergence is crucial to understanding why lenses refract light and how to determine the focal length. Vergence is the angle at which light rays converge or diverge as they pass through a lens. Converging light has a positive vergence, and diverging light has a negative vergence. Vergence is determined by the curvature of the lens surfaces and the refractive index of the material.[4]

Myopia, or nearsightedness, occurs when the eye axial length is longer than normal, or the cornea is overly curved, causing light rays to focus in front of the retina rather than directly on it. The focal length of the refracting cornea and crystalline lens in the myopic eye is shorter than the ideal focal length; distant objects appear blurred, while near objects are seen more clearly.[12][9] Myopia can be corrected using concave lenses with a minus power focal length, which increases the focal length of the resulting compound lens comprising the refractive correction, cornea, and crystalline lens. The compound lens system shifts the focus of light onto the retina and improves distance vision.

Hyperopia, or farsightedness, occurs when the eye axial length is shorter than normal, or the cornea is less curved, causing light rays to focus behind the retina instead of directly on it. The focal length of the hyperopic eye is longer than the ideal focal length, making near objects appear blurred while distant objects may be seen more clearly.[13] Hyperopia can be corrected using convex lenses with a plus power focal length, which decreases the focal length of the compound lens system comprising the refractive correction, cornea, and crystalline lens. The compound lens system shifts the focus of light onto the retina and improves distance and near vision.[13]

Astigmatism is a refractive error in which refraction varies in the different meridians of the eye. The light rays passing through the eye cannot converge at a single focal point but form focal lines. If the cornea or lens has an oval surface or unequal refractive power, there will be different focal distances in different meridians, light rays will be focused at multiple points, and vision will be blurred or distorted. Depending on which focal distance coincides with the position of the retina, images focused by the astigmatic eye may appear smeared or have a shadow in a particular orientation.[11]

The photon emitted has a very specific wavelength (color) that depends on the state of the electron's energy when the photon is released. Two identical atoms with electrons in identical states will release photons with identical wavelengths.

Refractive surgery aims to correct refractive errors, such as myopia, hyperopia, and astigmatism, by modifying the curvature of the cornea or replacing the lens. Refractive surgeries like laser-assisted in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) aim to optimize the ability of the cornea to focus light onto the retina.

Presbyopia is an age-related condition that typically begins around 40 years of age when the natural crystalline lens loses flexibility. Flexing of the crystalline lens increases the curvature of its surface, decreasing the focal length of the lens and allowing the convergence of divergent light. Since near objects form more divergent light than distant objects, the impaired ability to change shape and accommodate affects near vision. As the lens gradually loses its ability to accommodate, the effective focal length of the eye increases, leading to increasing difficulty in near-vision tasks.[14][15] Presbyopia is typically managed using single-vision reading, bifocal, trifocal, or progressive addition lenses, which add plus focal power to the compound lens system to improve near vision.[14]

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in which f  = focal length of the refracting surface, n = index of refraction of the lens, d = distance between the two refracting surfaces R1 and R2 (the thickness of the lens), R1 = radius of curvature of the refracting surface facing the initial medium, and R2 = radius of curvature of the refracting surface facing the final medium. R values will be positive for concave lenses and negative for convex lenses.

Light adjustable IOLs allow for a change in the focal length of the IOL after it has been implanted. This breakthrough technology uses light to polymerize macromolecules in the IOL and carefully adjust its spherical and astigmatic power. Light is used to manipulate the curvature of the anterior surface of the IOL and achieve ideal focal lengths.[17]

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When the radii of curvature of the front and back surface and the refractive index of the material of a lens are known, the formula for calculating the focal length of the lens is derived from the lens maker formula given by,

Helium and helium-neon, HeNe, are the most common gas lasers. They have a primary output of visible red light. CO2 lasers emit energy in the far-infrared, and are used for cutting hard materials.

During LASIK, a flap is created on the cornea, and a laser is used to reshape the underlying corneal tissue. The selective removal of corneal tissue modifies the corneal curvature, altering its refractive power and adjusting the focal length. During PRK, the corneal outer layer is removed before reshaping the cornea using an excimer laser. Both procedures aim to achieve the focal length necessary to correct the underlying refractive error.[22]

Once the lasing medium is pumped, it contains a collection of atoms with some electrons sitting in excited levels. The excited electrons have energies greater than the more relaxed electrons. Just as the electron absorbed some amount of energy to reach this excited level, it can also release this energy. The electron can simply relax, and in turn rid itself of some energy. This emitted energy comes in the form of photons (light energy).

The focal length of a lens can be measured via various methods as dictated by the precision required and the lens type. The most commonly used method of measuring focal length in clinical practice is lensometry, a procedure performed using a lensmeter, focimeter, or vertometer. Lensmeters project a parallel beam of light onto a lens and measure the position of the focal point. The lensometer works by projecting a parallel beam of light onto the lens and then measuring the position of the focal point. Lensometry may be used to measure the focal length of spectacle lenses, rigid gas permeable or polymethyl methacrylate (PMMA) contact lenses, and intraocular lenses.[6]

Accommodating IOLs mimic the natural ability of the eye to change shape or accommodate and adjust its focal point to view objects at different distances. The flexible optics of accommodating IOLs permit changes in curvature and provide a range of clear vision from far to near. Patients with accommodating IOLs can experience a more natural and continuous transition as they shift their gaze between objects at different distances, similar to the function of a healthy, natural lens.[21]

Focaldistance vsfocallength

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Schematic: Convex Lens. Convex, positive, or converging lenses bring parallel light rays together to converge at a specific point on the other side of the lens. The point at which these rays converge is known as the focal point, and the distance from (more...)

Consider the illustration from the previous section. Although more modern views of the atom do not depict discrete orbits for the electrons, it can be useful to think of these orbits as the different energy levels of the atom.

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Effective interprofessional communication is fundamental to achieving successful patient outcomes. The healthcare team must establish clear communication channels to facilitate the exchange of information, treatment plans, and progress updates. Regular meetings and shared electronic health records promote seamless coordination and foster a patient-centered approach to care. For instance, when addressing refractive errors or eye diseases, ophthalmologists, optometrists, and opticians collaborate closely to ensure accurate prescription, proper fitting of glasses or contact lenses, possible surgical intervention, and timely follow-up.[32][33][34]

Although there are many types of lasers, all have certain essential features. In a laser, the lasing medium is “pumped” to get the atoms into an excited state. Typically, very intense flashes of light or electrical discharges pump the lasing medium and create a large collection of excited-state atoms (atoms with higher-energy electrons). It is necessary to have a large collection of atoms in the excited state for the laser to work efficiently.

The lens maker formula can be further modified to accommodate a "thick" lens to account for the distance light rays must travel through the lens itself. This modification gives a more accurate calculation of the focal length.[8] The thick lens equation for a lens in air is given by,

Focallength

Converging or convex lenses are thicker at their center and thinner at their edges. Convex lenses bring parallel light rays together to converge at a specific point on the other side of the lens and create an image in front of the lens. The point where the light rays converge is the focal point; the distance from the lens to the focal point is the focal length of the lens.[5] (See Image. Schematic: Convex Lens.) Light rays passing through a convex lens bend or refract toward the center of the lens. The curvature of the lens surface determines the degree of bending or refraction. As a result, these rays converge to a focal point located at a specific distance from the lens. The focal length of the lens determines the degree of convergence. The closer an object is to the lens, the farther away the image is projected. (See Image. Photograph: Convex Lens.)

Laser pointers work through the principles of light amplification and stimulated emission. Inside a laser diode, which is designed to produce a concentrated beam, a process called light amplification occurs. This process involves exciting atoms or molecules, causing them to release photons, which are particles of light. This release of photons is known as stimulated emission, and it creates a synchronized and coherent beam of laser light.

If this photon (possessing a certain energy and phase) should encounter another atom that has an electron in the same excited state, stimulated emission can occur. The first photon can stimulate or induce atomic emission such that the subsequent emitted photon (from the second atom) vibrates with the same frequency and direction as the incoming photon.

A ruby laser (depicted earlier) is a solid-state laser and emits at a wavelength of 694 nm. Other lasing mediums can be selected based on the desired emission wavelength (see table below), power needed and pulse duration.

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Once an electron moves to a higher-energy orbit, it eventually wants to return to the ground state. When it does, it releases its energy as a photon — a particle of light.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

The distance between an x-ray source and an image receptor affects the focal length and determines the magnification and resolution of the resulting image. When the x-ray source is closer to the image receptor, the focal length is shorter, resulting in increased image magnification. Conversely, a longer focal length leads to reduced magnification. The size of the focal spot, the area on the x-ray tube from where x-rays are emitted, is another important consideration related to focal length in radiography. A smaller focal spot size allows for improved spatial resolution and finer detail in the radiographic image. However, a smaller focal spot size typically corresponds to a longer focal length, which can result in decreased magnification. Choosing the appropriate focal length and focal spot size allows radiologists to achieve the desired level of image magnification and resolution for accurate diagnosis.[29][30]

But what is a laser? What makes a laser beam different from the beam of a flashlight? Specifically, what makes a laser light different from other kinds of light? How are lasers classified?

Focal length calculations are important when managing common eye conditions such as cataracts and evaluating patients for refractive surgical therapy.

Several equations are used in optics, optometry, and ophthalmology to calculate the focal length and power of lenses needed to correct refractive errors, such as myopia, hyperopia, and astigmatism.[7]

"Star Wars," "Star Trek," "Battlestar Galactica" — laser technology plays a pivotal role in science fiction movies and books. It's no doubt thanks to these sorts of stories that we now associate lasers with futuristic warfare and sleek spaceships.

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­But lasers play a pivotal role in our everyday lives, too. The fact is, they show up in an amazing range of products and technologies. You'll find them in everything from CD players to dental drills to high-speed metal cutting mac­hines to measuring systems. Tattoo removal, hair replacement, eye surgery — they all use lasers.

The photon that any atom releases has a certain wavelength that is dependent on the energy difference between the excited state and the ground state.

Laser light is monochromatic, meaning it contains only one specific color or wavelength. It is also coherent, with all the photons moving in sync with each other. This coherence gives laser light its focused nature, allowing it to travel over long distances without significant divergence.

From the intricate mechanisms of the human eye to the design of advanced imaging systems, understanding focal length holds paramount importance. The following sections will explore the nuances of focal length, its mathematical underpinnings, its manifestations in optical aberrations, and its crucial implications for medical applications.[1]

Dye lasers use complex organic dyes, such as rhodamine 6G, in liquid solution or suspension as lasing media. They are tunable over a broad range of wavelengths.

The thin lens equation is a simplified version of the formula for the focal length of a refracting surface, specifically designed for thin lenses. The thin lens equation assumes that the thickness of the lens is negligible compared to the radii of curvature of the lens surfaces.

Focal length is the distance between the lens and the focal point, where the light rays converge or diverge. It is a critical parameter that determines the image quality and magnification of optical systems, including the human eye.[3]

Human eyesfocallength

Other lasers, such as diode lasers, are very weak and are used in today’s pocket laser pointers. These lasers typically emit a red beam of light that has a wavelength between 630 nm and 680 nm.

When two thin lenses are placed a certain distance apart, the focal distance of this "compound lens system" can be calculated by,

Multifocal and accommodating IOLs are designed to improve vision at various distances, reducing patient dependence on corrective eyewear. Selecting the appropriate focal length for these IOLs is crucial to optimize visual acuity and minimize side effects, such as halos or reduced contrast sensitivity. Careful patient selection and a thorough preoperative assessment ensure successful outcomes with these specialized IOLs.[18][19]

FOV tofocallength

Photograph: Convex Lens. A photograph of a convex or converging lens bringing parallel light rays together to converge at a specific point on the other side of the lens. Fir0002, CC BY 3.0, via Wikipedia.

in which f  = focal length of the refracting surface, n = index of refraction of the lens, R1 = radius of curvature of the refracting surface facing the initial medium, and R2 = radius of curvature of the refracting surface facing the final medium. R values will be positive for concave lenses and negative for convex lenses.

Focallength formula

Solid-state lasers have lasing material distributed in a solid matrix (such as the ruby or neodymium:yttrium-aluminum garnet "Yag" lasers). The neodymium-Yag laser emits infrared light at 1,064 nanometers (nm). A nanometer is 1x10-9 meters.

Focallength camera

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Sometimes called diode lasers, these are not solid-state lasers. These electronic devices are generally very small and use low power. They may be built into larger arrays, such as the writing source in some laser printers or CD players.

Schematic: Concave Lens. Concave lenses, also known as diverging or negative lenses, cause parallel light rays to diverge as they pass through the lens. Diverging lenses have a virtual focal point from which the divergent rays appear to originate when (more...)

Focal length plays a significant role in optical aberrations within the eye. Optical aberrations are deviations from ideal optical performance that can impact the quality and clarity of vision. Several factors, including the shape and size of the eye, the curvature of the cornea and lens, and the presence of refractive errors, can contribute to optical aberrations.[9]

Atoms are constantly in motion. They continuously vibrate, move and rotate. Even the atoms that make up the chairs that we sit in are moving around. Solids are actually in motion! Atoms can be in different states of excitation. In other words, they can have different energies. If we apply a lot of energy to an atom, it can leave what is called the ground-state energy level and go to an excited level. The level of excitation depends on the amount of energy that is applied to the atom via heat, light, or electricity.

In other words, if we apply some heat to an atom, we might expect that some of the electrons in the lower-energy orbitals would transition to higher-energy orbitals farther away from the nucleus.This is a highly simplified view of things, but it actually reflects the core idea of how atoms work in terms of lasers.

Some lasers are very powerful, such as the CO2 laser, which can cut through steel. The CO2 laser is so dangerous is because it emits laser light in the infrared and microwave region of the spectrum. Infrared radiation is heat, and this laser basically melts through whatever it is focused upon.

in which f = the focal length of the combined lenses, f1 = the focal length of the first lens, f2 = the focal length of the second lens, and d = the distance between the two lenses.

Photons, with a very specific wavelength and phase, reflect off the mirrors to travel back and forth through the lasing medium. In the process, they stimulate other electrons to make the downward energy jump and can cause the emission of more photons of the same wavelength and phase.

You see atoms releasing energy as photons all the time. For example, when the heating element in a toaster turns bright red, the red color is caused by atoms, excited by heat, releasing red photons. When you see a picture on a TV screen, what you are seeing is phosphor atoms, excited by high-speed electrons, emitting different colors of light.

Lasers are utilized in industry and research to do many things, including using intense laser light to excite other molecules to observe what happens to them.

Endoscopy is a widely used medical procedure that permits the visual examination of many internal anatomical structures. An endoscope is a rigid or flexible tube with a camera attached at one end. The focal length of the endoscopic camera lens determines the distance over which objects in the field of view remain in sharp focus. A shorter focal length results in a shallower depth of field; objects beyond this depth appear blurred. A longer focal length provides a greater depth of field, and a larger range of distances can be captured in sharp focus. The focal length of the endoscopic lens is adjustable; the chosen focal length is dictated by the procedure being performed and the anatomy being examined. Some endoscopes have a "near-focus" mode and a "traditional" mode to vary the size and clarity of the visual field. For example, during gastrointestinal endoscopy, a shorter focal length may be preferred to examine mucosal details closely. In contrast, during bronchoscopy, a longer focal length may be more suitable for visualizing deeper structures of the pulmonary tree.[26][27]

Anything that produces light — fluorescent lights, gas lanterns, incandescent bulbs — does it through the action of electrons changing orbits and releasing photons.

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in which f = the combined focal length of the adjacent lenses, f1 = the focal length of the first lens, and f2 = the focal length of the second lens.

Multifocal IOLs are designed with multiple optical zones, similar to multifocal eyeglass lenses. These zones allow the eye to focus on objects at varying distances, such as near, intermediate, and far. Multifocal IOLs can reduce dependence on eyeglasses for particular visual tasks such as reading, using digital devices, and engaging in distance activities.[20]

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This simple atom consists of a nucleus (containing the protons and neutrons) and an electron cloud. It's helpful to think of the electrons in this cloud circling the nucleus in many different orbits.

Matthew Weschler holds an MS degree in Physical Organic Chemistry from Florida State University. His thesis topic was picosecond laser spectroscopy, and he studied how molecules react picoseconds after being bombarded by laser light.

Lens With Spherical Aberration. The diagram demonstrates spherical aberration, which occurs when light rays passing through different parts of a spherical lens converge at varying focal points, resulting in blurred and distorted images. This aberration (more...)

What is a CMOS sensor? A CMOS sensor is an electronic chip that converts photons to electrons for digital processing. The chip is based on complementary metal ...

Focal length is a critical parameter in high-resolution imaging of microscopic specimens. Microscopes utilize objective lenses with different focal lengths to focus light and magnify the subject. Researchers and clinicians adjust this magnification to achieve the proper depth of focus for various applications, including histopathology and cytology.[28]

One method of determining the focal length of a thin lens in air is the thin lens equation, which relates the focal length of a lens to the distance between the lens and the object. Focal length is always represented in meters. Lens powers are represented in diopters. The thin lens equation is given by,

A ruby laser consists of a flash tube (like you would have on a camera), a ruby rod and two mirrors (one half-silvered). The ruby rod is the lasing medium, and the flash tube pumps it.

Industrial machine vision is the most effective way to realize smart and automated manufacturing. It has been regarded as the Machine Eyes of modern industry.

A cascade effect occurs, and soon we have propagated many, many photons of the same wavelength and phase. The mirror at one end of the laser is "half-silvered," meaning it reflects some light and lets some light through. The light that makes it through is the laser light.

If the thick lens is in a medium other than air, the value of (n -1) can be replaced with [(nl - nm)/nm], in which nl = index of refraction of the lens and nm = index of refraction of the medium.

WORKING DISTANCE- distance between the objective lens and the slide. FIELD OF VIEW- area you can see through the microscope.

Focal length is relevant in minimally invasive surgical procedures, such as traditional or robotic-assisted laparoscopy. Laparoscopic camera systems use lenses with adjustable focal lengths to visualize the surgical field. Surgeons can manipulate the focal length to enhance depth perception and magnification, aiding in the precise manipulation of instruments and improving visualization during procedures.[31]

In general, the atoms are excited to a level that is two or three levels above the ground state. This increases the degree of population inversion. The population inversion is the number of atoms in the excited state versus the number in ground state.

Diverging or concave lenses have a thinner center and thicker edges. These lenses cause parallel light rays to spread out or diverge as they pass through the lens. Diverging lenses have a virtual focal point from which the divergent rays appear to originate when projected backward, creating an image behind the lens.[4] (See Image. Schematic: Concave Lens.) Light rays that pass through a diverging lens spread out, and when projected backward, they appear to converge at a virtual focal point behind the lens. The focal length of a diverging lens is deemed negative due to this virtual focal point.[4] (See Image. Photograph: Concave Lens.)

There are many different types of lasers. The laser medium can be a solid, gas, liquid or semiconductor. Lasers are commonly designated by the type of lasing material employed.

The concept of focal length is a fundamental pillar in optics, helping elucidate the behavior of light rays and their interactions with optical elements. Focal length is applied in the crafting of lenses in telescopes, cameras, and corrective eyewear for individuals with refractive errors. Focal length governs the convergence or divergence of light rays, dictating the precise point where they either converge to form an image or diverge from an origin.[1][2]

The interprofessional collaboration between ophthalmologists, optometrists, ophthalmic technicians, opticians, nurses, pharmacists, and other health professionals ensures that patients receive optimal management, appropriate interventions, and a high standard of safety and quality throughout their eye care journey.

To make these three properties occur takes something called stimulated emission. This does not occur in your ordinary flashlight — in a flashlight, all of the atoms release their photons randomly. In stimulated emission, photon emission is organized.

The extent of corneal tissue removal during refractive surgery directly affects the resulting focal length. In myopia correction, corneal tissue is removed centrally to flatten the cornea, increase its focal length, and allow light rays to converge on the retina. In hyperopia correction, corneal tissue is removed peripherally to steepen the cornea, reduce its focal length, and focus light rays on the retina. Astigmatism correction alters the corneal shape to eliminate irregularities and adjust the focal length in different meridians.[23] Precisely calculating the desired focal length is essential to achieving the intended refractive correction. Failure to accurately determine the appropriate focal length can result in undercorrection, overcorrection, or optical aberrations, leading to suboptimal visual outcomes.[24][25]

Photograph: Concave Lens. A photograph of a concave or diverging lens causing parallel light rays to diverge as they pass through the lens. Diverging lenses have a virtual focal point from which the divergent rays appear to originate when projected (more...)

In this article, you'll learn all about the different types of lasers, their different wavelengths and the uses to which we put them (like laser pointers). But first, let's start with the fundament­als of laser technology by explaining the basics of an atom.

Lasers are classified into four broad areas depending on the potential for causing biological damage. When you see a laser, it should be labeled with one of these four class designations:

The intraocular lens (IOL) power determines its focal length. The IOL power is calculated using the length of the eye determined by ultrasound and the focal length of the cornea determined by keratometry. Inserting an IOL will create a compound lens system comprising the IOL and the cornea; the exact position of the IOL within the eye is another critical factor. These values, along with necessary adjustment factors, are used by cataract surgeons to provide accurate refractive outcomes following cataract surgery.[16]

Spherical aberrations occur when light rays passing through the periphery of a refracting surface focus on a different point than rays passing through the center of the same refracting surface. A lens with a shorter focal length has a steeper curvature, resulting in greater refraction of light rays passing through its periphery and a greater deviation in focal points. Therefore, a lens with a shorter focal length exhibits more spherical aberration than one with a longer focal length. Aspheric lenses can be used to correct spherical aberrations. Aspheric lenses are designed with a nonuniform surface curvature that counters the unequal bending of light rays at the periphery of a spherical lens. This design helps achieve a single focal point, reducing spherical aberration and improving image clarity.[10] (See Image. Lens with Spherical Aberration.)

When a lens is placed in a medium other than air, which has a refractive index of approximately 1.0, the lens maker formula is modified slightly. This modification is given by,

There are only about 100 different kinds of atoms in the entire universe. Everything we see is made up of these 100 atoms in an unlimited number of combinations. How these atoms are arranged and bonded together determines whether the atoms make up a cup of water, a piece of metal, or the fizz that comes out of your soda can.

It's important to note that laser pointers also emit unconverted infrared laser light, which is invisible to the human eye. Manufacturers include filters to block most of this invisible light, but it is essential to handle laser pointers responsibly and avoid pointing them at reflective surfaces or anyone's eyes.