Objectives allow microscopes to provide magnified, real images and are, perhaps, the most complex component in a microscope system because of their multi-element design. Objectives are available with magnifications ranging from 2X – 200X. They are classified into two main categories: the traditional refractive type and reflective. Each category is further divided into types: finite conjugate and infinite conjugate (infinity corrected). In order to choose the correct objective, it is important to know the benefits of one category and type from another.

The term YAG laser is usually used for solid-state lasers based on neodymium-doped YAG (Nd:YAG, more precisely Nd3+:YAG), YAG is the acronym for yttrium aluminum garnet (Y3Al5O12), a synthetic crystal material which became popular in the form of laser crystals in the 1960s.

Microscope and objectives are complex optical systems with many uses. They are no longer used solely for biological setups (e.g. looking at cheek cells in an introductory biology class); rather, they can be used to study the emission wavelength of a flourophore, to analyze a 5μm defect on a machined part, to oversee the ablation of material off a base, and within a host of other applications in the optics, imaging, and photonics industries. Understanding the importance of each constituent part of a microscope and their specifications enables any user to choose the best system and achieve the best results.

By selectively targeting these chromophores the energy of the laser heats them to a point where they are vaporized. In the case of ink, melanin, and hemoglobin this causes the pigment to break up into particles which are small enough for the body’s own immune system to remove

With darkfield illumination, direct rays of light are not sent into the objective but instead strike the object at an oblique angle. It is important to keep in mind that these rays still illuminate the object in the object plane. The resultant darkfield illumination image produces high-contrast between the transparent object and the light source. When used in a microscopy setup, darkfield illumination produces a light source that forms an inverted cone of light blocking the central rays of light but still allowing the oblique rays to light the object. Figure 3 illustrates a sample darkfield illumination setup where the hollow cone of light is the numerical aperture of the objective. By comparison, no rays are blocked in a brightfield illumination setup. The design of darkfield illumination forces the light to illuminate the object under inspection, but not to enter the optical system, making it better for a transparent object.

When microscopes were first invented, eyepieces played a major role in their design since they were the only means to actually see the object under inspection. Today, analog or digital cameras are used to project an image of the object onto a monitor or a screen. Microscope eyepieces generally consist of a field lens and an eye lens, though multiple designs exist that each creates a larger field of view (FOV) than a single element design. For a simple guide on selecting the right design, view Choosing the Correct Eyepiece.

Illumination within a microscope is just as important as selecting the proper eyepiece or objective. It is crucial to choose the correct illumination in order to obtain the most conclusive results. Before deciding on the type of illumination setup to work with, consider the application setup, object under inspection, and desired results.

YAG is a host medium with favorable properties, particularly for high-power lasers and Q-switched lasers emitting at 1064 nm.

A fluorophore (or fluorescent dye) is used to mark proteins, tissues, and cells for examination or study. Fluorophores can absorb light of one wavelength and emit (fluoresce) light of another wavelength. In a typical fluorescence microscopy setup three filters are used: an excitation filter, an emission filter and a dichroic filter. Each fluorophore has a specific absorption or excitation wavelength band, the excitation filter will transmit only that specific range of wavelengths. The fluorophore, once excited, will emit a different range of wavelengths. The emission filter transmits only the emission wavelengths. A dichroic filter that is specifically designed to reflect the emission wavelengths and transmit the excitation wavelengths is used to separate the excitation and emission channels. Figure 13 illustrates a typical fluorescence imaging setup. For additional information on fluorescence microscopy, view Fluorophores and Optical Filters for Fluorescence Microscopy.

The most common type is the actively Q-switched solid-state bulk laser. Solid-state gain media have a good energy storage capability, and bulk lasers allow for large mode areas (thus for higher pulse energies and peak powers) and shorter laser resonators (e.g. compared with fiber lasers). The laser resonator contains an active Q-switch – an optical modulator, which in most cases is an acousto-optic modulator.

Plan, also known as planar, semi-plan, semi-planar, or microplan, objectives correct for field curvature. Field curvature is a type of aberration present when the off-axis image cannot be brought to focus in a flat image plane, resulting in a blurred image as it deviates from the optical axis. Figure 10 illustrates field flatness measured radially from the center in achromatic, semi-plan, and plan objective designs. Achromatic objectives have a flat field in the center 65% of the image. Plan objectives correct best overall and display better than 90% of the field flat and in focus. Semi-plan objectives are intermediate to the other two types with 80% of the field appearing flat.

1 ms (millisecond) = 10−3 s 1 μs (microsecond) = 10−6 s 1 ns (nanosecond) = 10−9 s 1 ps (picosecond) = 10−12 s 1 fs (femtosecond) = 10−15 s 1 as (attosecond) = 10−18 s

Most microscope objective specifications are listed on the body of the objective itself: the objective design/standard, magnification, numerical aperture, working distance, lens to image distance, and cover slip thickness correction. Figure 7 shows how to read microscope objective specifications. Since the specifications are located directly on the body of the objective, it is easy to know exactly what one has, a very important fact when incorporating multiple objectives into an application. Any remaining specifications, such as focal length, FOV, and design wavelength, can easily be calculated or found in the specifications provided by the vendor or manufacturer.

If the objective follows a simple microscope standard (such as DIN or JIS) then it is listed on the body to show what required specifications must be present within the system. Most compound microscopes employ the Deutsche Industrie Norm, or DIN, standard. The DIN standard has a 160mm distance from the objective flange to the eyepiece flange (Figure 8). The other available standard is the Japanese Industrial Standard, or JIS. The JIS standard has a 170mm distance from objective flange to eyepiece flange (Figure 9). Paying attention to these two distances is necessary when choosing the proper objective and eyepiece in order to make sure that the image projected from the former is properly imaged through the latter. Though the image distances are different for DIN and JIS, there is no difference in optical performance; they are equal in quality. Similarly, each standard utilizes the same RMS mounting thread of 0.7965" x 36TPI.

Q-switched lasers offer the only non-invasive, effective method for removing tattoos without scarring, plus treat other cosmetic issues such as fine lines, enlarged pores, pigmented lesions, vascular lesions, and toenail fungus. Because they cause minimal side effects and deliver reliable results, Q-switched lasers are the future of the aesthetics industry.

When the laser energy is absorbed by water, the water in the tissue is completely vaporized. This causes the skin treated to shrink and shrivel stimulating the production of the new younger-looking firmer skin.

Two common uses of lasers are to (1) heat material onto a base or (2) to ablate material off of a base. Laser ablation systems require microscope components because of the precision beam manipulation (i.e. focusing, bending, scattering reduction, etc) required. A laser ablation setup typically contains custom optics, rather than off-the-shelf components, with the laser precisely designed into the system (Figure 14). The laser is oriented in an epi-illumination design to utilize the microscope objective's ability to focus light at the object plane, and to produce extremely small spot sizes with minimal aberrations. Also, an eyepiece allows the user to see where the laser is located and to make sure everything is working properly. Filters are necessary to block the laser from causing damage to the user's eye. Laser ablation setups are used in medical and biological applications because they offer higher precision than conventional surgical methods.

How manytypes of laser

Knowledge Center/ Application Notes/ Microscopy Application Notes/ Understanding Microscopes and Objectives

Optical pumping uses light to create the necessary population inversion for a laser. Usually, high-pressure xenon or krypton lamps are used to excite solid or liquid laser systems. The active material in the laser absorbs the light from the pump lamp, promoting the population from the ground state to the higher energy state. The material used in the laser can be continuously exposed to the pumping light which creates a continuous wave laser (CW). A pulsed laser can be created by using flashes of pumping light.

A laser oscillator usually comprises an optical resonator (laser resonator, laser cavity) in which light can circulate (e.g. between two mirrors), and within this resonator a gain medium (e.g. a laser crystal), which serves to amplify the light. Without the gain medium, the circulating light would become weaker and weaker in each resonator round trip, because it experiences some losses, e.g. upon reflection at mirrors.

Types of laserppt

Figure 1: Setup of a simple optically pumped laser. The laser resonator is made of a highly reflecting curved mirror and a partially transmissive flat mirror, the output coupler, which extracts some of the circulating laser light as the useful output. The gain medium is a laser crystal, which is side-pumped, e.g.

Field of view or FOV is the area of the object that is imaged by a microscope system. The size of the FOV is determined by the objective magnification. When using an eyepiece-objective system, the FOV from the objective is magnified by the eyepiece for viewing. In a camera-objective system, that FOV is relayed onto a camera sensor. The sensor on a camera is rectangular and therefore can only image a portion of the full circular FOV from the objective. In contrast, the retina in your eye can image a circular area and captures the full FOV. This is why the FOV produced by a camera-microscope system is typically slightly smaller than that of an eyepiece-microscope system. Equations 3 and 4 can be used to calculate the FOV in the aforementioned systems. In Equations 3 and 4, $ \small{H_{\small{\text{Camera Sensor}}}} $ is the sensor size of the camera and $ \small{H_{\small{\text{Eyepiece Field Stop}}}} $ is the field stop of the eyepiece.

The gain medium (also called lasing medium) consists of a group of atoms, molecules, or ions in solid, liquid or gaseous form, which acts as an amplifier for light waves. For amplification, the medium has to achieve population inversion, which means in a state in which the number of atoms in the upper energy level is greater than the number of atoms in the lower energy level. The output coupler serves as the energy source which provides for obtaining such a state of population inversion between a pair of energy levels of the atomic system. When the active medium is placed inside an optical resonator, the system acts as an oscillator.

The Numerical Aperture (NA) of an objective is a function of the focal length and the entrance pupil diameter. Large NA objectives sometimes require the use of immersion oils between the object under inspection and the front of the objective. This is because the highest NA that can be achieved within air is an NA of 1 (corresponding to 90° angle of light). To get a larger angle and increase the amount of light entering the objective (Equation 2), it is necessary to use immersion oil (index of refraction typically = 1.5) to change the refractive index between the object and the objective. High NA objectives in conjunction with immersion oil are a simple alternative to changing objectives, a move that may be costly.

The most commonly used category of objectives is refractive. In a refractive design light passing through the system is refracted, or bent, by the optical elements. Each optical element is typically anti-reflection coated to reduce back reflections and improve overall light throughput. Refractive objectives are often used in machine vision applications that require resolution of extremely fine details. There are multiple refractive objective designs each utilizing different optical configurations. The designs can range from two elements in basic achromatic objectives (an achromatic lens and a meniscus lens) to fifteen elements in plan-apochromatic objectives (Figure 5). Plan-apochromatic objectives are the most complex, high-end objective design with chromatic and flat field correction done within the objective itself.

In general shorter laser wavelengths of laser light energy are absorbed most readily in pigmented tissue such as melanin and hemoglobin whereas higher wavelengths are principally absorbed by water and hydroxyapatite.

In order to understand how the components of a microscope can be integrated with various optical, imaging, and photonics products, consider the following optical microscopy applications: fluorescence microscopy and laser ablation. Each utilizes its own unique setup in order to work with components from a microscope.

Types of laserPDF

Longer wavelength lasers are increasingly being used for the removal of fine lines and wrinkles (skin resurfacing). Generally, at longer wavelengths, laser energy penetrates deeper into the skin. However, beyond a certain wavelength, the energy of the laser is instead absorbed by water in the skin. When this point has reached the water in the first live cell in the laser’s path will absorb the energy. This makes lasers using mediums such as Erbium ideal for skin resurfacing.

In an infinite conjugate, or infinity corrected, optical design, light from a source placed at infinity is focused down to a small spot. In an objective, the spot is the object under inspection and infinity points toward the eyepiece, or sensor if using a camera (Figure 12). This type of modern design utilizes an additional tube lens between the object and eyepiece in order to produce an image. Though this design is much more complicated than its finite conjugate counterpart, it allows for the introduction of optical components such as filters, polarizers, and beamsplitters into the optical path. As a result, additional image analysis and extrapolation can be performed in complex systems. For example, adding a filter between the objective and the tube lens allows one to view specific wavelengths of light or to block unwanted wavelengths that would otherwise interfere with the setup. Fluorescence microscopy applications utilize this type of design. Another benefit of using an infinite conjugate design is the ability to vary magnification according to specific application needs. Since the objective magnification is the ratio of the tube lens focal length $ ( \small{f_{\small{\text{Tube Lens}}}} ) $ to the objective focal length $ (\small{f_{\small{\text{Objective}}}} ) $ (Equation 5), increasing or decreasing the tube lens focal length changes the objective magnification. Typically, the tube lens is an achromatic lens with a focal length of 200mm, but other focal lengths can be substituted as well, thereby customizing a microscope system's total magnification. If an objective is infinite conjugate, there will be an infinity symbol located on the body of the objective.

DIN and JIS have historically been used when considering a classic compound microscope. Some microscope manufacturers prefer to list the tube lens length by the optical properties instead of the mechanical. For a DIN standard objective, this changes the tube lens length to 150mm because the eyepiece is imaging the intermediate image plane (Figure 8). Lastly, there is a dimension typically listed for objectives to allow the user to consistently know what length it is: the parfocal distance (PD). The parfocal distance is the distance from the flange of the objective to the object under inspection. For DIN objectives this distance is a standard 45mm and for JIS is it 36mm (Figures 8 and 9).

Types of laserwith example

Many microscopes utilize backlight illumination compared to traditional direct light illumination because the latter usually over-saturates the object under inspection. A specific type of backlight illumination used in microscopy applications is Koehler illumination. In Koehler illumination, incident light from an illumination source, such as a light bulb, floods the object under inspection with light from behind (Figure 2). It employs two convex lenses: the collector lens and the condenser lens. It is designed to provide bright and even illumination on the object plane and on the image plane where the image produced from the objective is then reimaged through the eyepiece. This is important because it ensures the user is not imaging the filament of the light bulb. Since backlight illumination floods the object with light from behind, it is also referred to as brightfield illumination.

A third type of illumination used in microscopy is epi-Illumination. Epi-illumination produces light above the objective. As a result, the objective and epi-illumination source substitute for a Koehler illumination setup. Using the objective for a large section of the illumination makes epi-illumination very compact – a major benefit of this design. Figure 4 illustrates an epi-illumination setup that is used frequently in fluorescence applications. For more information on fluorescence microscopy, view Fluorophores and Optical Filters for Fluorescence Microscopy.

However, the gain medium can amplify the circulating light, thus compensating the losses if the gain is high enough. The gain medium requires some external supply of energy – it needs to be “pumped”, e.g. by injecting light (optical pumping) or an electric current (electrical pumping → semiconductor lasers). The principle of laser amplification is stimulated emission.

When viewing fluid materials such as bacteria, cell cultures, blood, etc, it is necessary to use a coverslip in order to protect the object under inspection and microscope components from contamination. A coverslip, or glass microscope slide, changes the way light refracts from the object into the objective. As a result, the objective needs to make proper optical corrections to produce the best quality image. This is why objectives denote a range of coverslip thicknesses for which they are optimized. Typically, this is listed after the infinity symbol (which denotes that an objective is an infinite conjugate, or infinity corrected design) and ranges from zero (no coverslip correction) to 0.17mm.

Types oflasers for skin

Electrical pumping is a much more complicated process than optical pumping. Usually used for gas and semiconducting lasers, electrical pumping uses electrical current to excite and promote the ground state population. In a simple gas laser that contains only one species (A), current passes through the gas medium and creates electrons that collide with the gas molecules to produce excited state molecules.

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In a finite conjugate optical design, light from a source (not at infinity) is focused down to a spot (Figure 11). In the case of a microscope, the image of the object under inspection is magnified and projected onto the eyepiece, or sensor if using a camera. The particular distance through the system is characterized by either the DIN or JIS standard; all finite conjugate microscopes are either one of these two standards. These types of objectives account for the majority of basic microscopes. Finite conjugate designs are used in applications where cost and ease of design are major concerns.

The basic components of any laser include a gain medium in an optical cavity, reflecting mirrors at either end, and laser pumping energy in the form or either photon or electrical current.

Types of laserin Physics

Reflective objectives utilize a reflective, or mirror-based design. They are often overlooked in comparison to their refractive counterparts, though they can correct for many issues present in the latter. Reflective objectives consist of a primary and secondary mirror system (Figure 6) to magnify and relay the image of the object under inspection. Edmund Optics® utilizes the popular Schwarzschild design, though other designs are available. Since light is reflected by metallic surfaces and not refracted by glass surfaces, reflective objectives do not suffer from the same aberrations as refractive objectives and, thus, do not need the additional designs to compensate for these aberrations. Reflective objectives can produce higher light efficiency as well as better resolving power for fine detail imaging because the system is primarily dependent upon the mirror coating instead of upon the glass substrate being used. Another benefit of reflective objectives is the possibility of working deeper into either the ultra-violet (UV) or infrared (IR) spectral regions due to the use of mirrors compared to conventional refractive optics.

Q-switching, or quality switching, of a laser, is a mechanism used to control the light output by concentrating all the energy into intense bursts or series of pulses by modulating the intracavity losses, the so-called Q-factor of the laser resonator. The technique is mainly applied for the generation of nanosecond pulses of high energy and peak power with solid-state bulk lasers. Laser devices that incorporate Q-switching are able to achieve selective photo thermolysis due to their high energy and short-pulse duration. This can be applied in the setting of removal of the tattoo pigment to arrive at the desired clinical results without much damage to the surrounding tissues and with relatively faster and uncomplicated healing time.

What are the 3types oflasers

Thousands of kinds of laser are known, but most of them are used only for specialized research. If you’re interested to find out more about different types of lasers and its applications follow this link.

Types of laser lightand their uses

The quality of an objective and eyepiece determine how well the system performs. In addition to choosing the magnification and complexity of the design, understanding correct quality correction is extremely important when deciding on the type of objective to use. Quality correction (i.e. achromatic, apochromatic, plan, semi-plan) is denoted on the objective itself to allow the user to easily see the design of the objective in question. There are typically two levels of chromatic aberration correction: achromatic and apochromatic. Achromatic objectives are among the simplest and least expensive of objectives. They are designed to correct for chromatic aberration in the red and blue wavelengths, in addition to being corrected for spherical aberration in a green wavelength. Limited correction for chromatic aberration and lack of a flat FOV reduce objective performance. Apochromatic objectives, by contrast, provide higher precision and are chromatically corrected for red, blue, and yellow. They also provide spherical aberration correction for a broad spectral range and generally have a long working distance given the extremely high numerical apertures (NA) that this optical design offers. Apochromatic objectives are ideal for white light applications, whereas achromatic objectives are best suited for monochromatic. Both objective designs, however, suffer significantly from distortion and field curvature, which worsen as objective magnification increases. Therefore, it is always important to focus on the complete system performance, rather than just objective performance alone.

Solid-state lasers based on ion-doped crystals or glasses (doped insulator lasers), pumped with discharge lamps or laser diodes, generating high output powers, or lower powers with very high beam quality, spectral purity and/or stability (e.g. for measurement purposes), or ultrashort pulses with picosecond or femtosecond durations.

Fluorite objectives further correct for aberrations using advanced glass types containing fluorspar or other synthetic substitutes. Just like achromatic objectives, fluorite objectives are designed to correct for chromatic aberrations for red and blue wavelengths. However, fluorite objectives are designed to correct for spherical aberration at two or three wavelengths instead of just green, typically have a higher NA, and feature a better resolving power and higher degree of contrast.

Eyepieces and objectives both have magnification that each contribute to the overall system magnification. Magnification is usually denoted by an X next to a numeric value. Most objectives contain a colored band around the entire circumference of the body that indicates their magnification (Figure 7). For example, a yellow band denotes a 10X magnification.

A microscope is an optical device used to image an object onto the human eye or a video device. The earliest microscopes, consisting of two elements, simply produced a larger image of an object under inspection than what the human eye could observe. The design has evolved over the microscope's history to now incorporate multiple lenses, filters, polarizers, beamsplitters, sensors, illumination sources, and a host of other components. To understand these complex optical devices, consider a microscope's components, key concepts and specifications, and applications.

Brightfield illumination requires a change in opacity throughout the object. Without this change, the illumination creates a dark blur around the object. The end result is an image of relative contrast between parts of the object and the light source. In most cases, unless the object is extremely transparent, the resulting image allows the user to see each part of the object with some clarity or resolution. In cases where an object's transparency makes it difficult to distinguish features using brightfield illumination, darkfield illumination can be used.

An optical cavity, resonating cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback on the laser light. They are also used in optical parametric oscillators and some interferometers. Light confined in the cavity reflects multiple times producing standing waves for certain resonance frequencies. The standing wave patterns produced are called modes; longitudinal modes differ only in frequency while transverse modes differ for different frequencies and have different intensity patterns across the cross-section of the beam.

A compound microscope is one that contains multiple lens elements. It works similar to a simple magnifier which utilizes a single lens to magnify a small object in order for the human eye to discern its details. With a simple magnifier, the object is placed within the focal length of the single lens. This produces a magnified, virtual image. With a microscope, a relay lens system replaces the single lens; an objective and an eyepiece work in tandem to project the image of the object onto the eye, or a sensor – depending upon the application. There are two parts to a microscope that increase the overall system magnification: the objective and the eyepiece. The objective, located closest to the object, relays a real image of the object to the eyepiece. This part of the microscope is needed to produce the base magnification. The eyepiece, located closest to the eye or sensor, projects and magnifies this real image and yields a virtual image of the object. Eyepieces typically produce an additional 10X magnification, but this can vary from 1X – 30X. Figure 1 illustrates the components of a compound microscope. Additionally, Equation 1 demonstrates how to calculate the overall system magnification. In Equation 1, m is magnification.

Laser pumping is the act of energy transfer from an external source into the gain medium of a laser. The energy is absorbed in the medium, producing excited states in its atoms. When the number of particles in one excited state exceeds the number of particles in the ground state or a less-excited state, population inversion is achieved. In this condition, the mechanism of stimulated emission can take place and the medium can act as a laser or an optical amplifier. The pump power must be higher than the lasing threshold of the laser.

Medical practitioners take advantage of the fact that different wavelengths of laser energy are absorbed differently in human tissue. This is because certain targets (chromophores) in the skin can absorb specific wavelengths of laser energy without any damage to the surrounding tissue. These include water, melanin (the pigment that gives your skin and hair its color), hemoglobin (the compound that makes blood red), as well as hydroxyapatite (which is found in teeth). In addition, the inks in tattoos respond in a similar way to chromophores with different colors of ink, absorbing different wavelengths of light energy.

Because of this thermal effect on chromophores lasers are increasingly used for hair removal (melanin), tattoo removal (inks) and for the treatment of birthmarks such as Port Wine Stains (hemoglobin).