Láser en Odontología

 

Hay tres categorías de lasers usados en odontología:

1. Lasers para tejidos blandos: Estos lasers incluyen el Nd: Lasers de YAG, de argón, de diodo y de CO2. Cada uno tiene diversas fuerzas y debilidades, pero todos pueden realizar numerosos procedimientos en los tejidos blandos tales como: gingivectomía, gingivoplastía, desbridamiento del surco, frenectomías, y hemostasia. Una característica única de los lasers comparados con otras modalidades es su capacidad de matar bacterias y de prevenir su nuevo crecimiento por hasta tres meses. Además, debido a la manera en que los lasers interactúan con los tejidos blandos, hay menos edema y dolor postoperatorio.

2. Lasers para tejidos duros: Los lasers en este grupo son ER: YAG y Er: YAGYSGG. Estos lasers se pueden utilizar para la preparación de la cavidad (remover el esmalte, la dentina y la caries, pero no la amalgama), a menudo sin anestesia. Son también excelentes para el retiro del hueso. Estos lasers se pueden utilizar para algunos procedimientos quirúrgicos pero debido a que no tienen la capacidad de inducir hemostasia, son más limitados que los lasers para tejidos blandos.

3. Lasers de nivel bajo: Ésta es la tercera categoría de lasers, que a diferncia de los dos lasers anteriores, no tienen ninguna capacidad de cortar tejidos blandos, sólo afectan los tejidos a nivel celular. Hay dos gamas de longitud de onda que se utilizan; el HeNe (630-650 nm) y el diodo (790-850nm). Los lasers de HeNe son excelentes para las heridas superficiales pero tienen penetración muy limitada. Los lasers de diodo son buenos para las heridas superficiales, pero penetran los 2-3cm , por lo tanto, son más eficaces para las áreas profundas dentro de los huesos, de los músculos y de las articulaciones. Esta longitud de onda tiene mayor aplicación en odontología.

Mecanismo de acción:

Los experimentos basados en pruebas de laboratorio en una variedad de tipos células in vitro han demostrado respuestas primarias y secundarias producidas cuando estas células son irradiadas con fotones. Las respuestas incluyen lo siguiente:


Respuestas primarias:

* Los fotones son absorbidos por los citocromos.

* Las moléculas de oxígeno ( radicales libres) se generan, afectando la síntesis del ATP ( aumentando así la energía disponible a las células)

* Se produce óxido nítrico.

* Se produce el aumento reversible en la permeabilidad de membrana celular al calcio y a otros iones, provocando cambios en la actividad de la célula, por ejemplo respuestas secundarias. Respuestas secundarias:

* Síntesis de DNA y RNA.

* Proliferación celular.

* Liberación del factor de crecimiento

* Síntesis del colágeno por los fibroblastos.

* Cambios en la conducción nerviosa, el lanzamiento del neurotransmisores, etc. Efectos clínicos del tratamiento Los efectos de los lasers en los tejidos blandos se refieren comúnmente como bioestimulación, e incluyen lo siguiente:

* Estimula la producción de ATP (éste es la fuente de combustible y de energía para las células)

* Síntesis incrementada del colágeno en los fibroblastos.

* Formación creciente de tubos capilares por el lanzamiento de los factores de crecimiento

* Actividad creciente de leucocitos.

* Transformación de fibroblastos a miofibroblastos.

* Estímulo de osteoblastos.

* Estímulo de odontoblastos.

* Flujo linfático incrementado que conduce a una reducción del edema.

* Reducción de la respuesta inmune (reducción de la liberación de histamina, bradikininas, de la sustancia P y de acetilcolina)

* Reducción de la despolarización de las fibras aferentes C (las fibras que llevan dolor pulpar)

* Estimula la regeneración del nervio.

* Estímulo de la producción de þ-endorfinas.

Donde aplicarse:

Con cualquier herida, el laser se debe aplicar en el sitio de la herida. En los dientes, el laser se debe aplicar al área del dolor pero también se debe aplicar en el ápice. El momento ideal para tratar cualquier lesión con LLLT es cuando ocurre la lesión. La terapia con laser reduce la respuesta inflamatoria mientras que permite la producción de los factores esenciales del crecimiento. Sin embargo, las ventajas serán mayores si el laser se aplica poco después de ocurrida la lesión.

Dolor agudo y dolor crónico:

* En el dolor agudo, el tratamiento se aplica con más frecuencia que en el dolor crónico.

* En el dolor agudo, la dosificación puede ser mucho más alta que en condiciones crónicas.

* Las condiciones agudas se tratan a menudo 3 a 4 veces por semana.

* Las condiciones crónicas se tratan a menudo dos veces semanalmente para las primeras dos semanas y luego una vez por semana.

* En condiciones crónicas el paciente puede incluso experimentar un aumento leve del dolor el día después del primer tratamiento y pueden experimentar un malestar. Esto es causada en gran parte por el aumento en flujo y la circulación de la linfa que ?vacia los productos inflamatorios en la circulación general?

Usos dentales clínicos:

1. Post Quirúrgico

Efectos del uso d el laser:

* Reducción del dolor post operatorio y de la necesidad de administrar analgésicos.

* Reducción del sangrado en la primera media-hora seguido por un incremento de la circulación lo cual da por resultado una curación más rápida.

* Reducción del edema postoperatorio.

* Mejor formación del hueso.

* Menor probabilidad de obtener un alvéolo seco.

2. Endodoncia

Efectos de usar el laser:

* Reducción del dolor y de la inflamación postoperatorio y necesidad reducida de analgesia postoperatoria.

* Diagnosis de pulpitis irreversible: Aplicar el laser en el ápice del diente. Si el paciente siente dolor, el laser se retira y es apagado. Entonces se reaplica; si el dolor severo aparece inmediatamente, entonces se trata de una pulpitis irreversible. Si no hay dolor cuando se aplica el laser, se continúa para eliminar la sensibilidad.

* Tratamiento de la hipersensibilidad dentinaria.

* Reducción de la hiperemia de la pulpa.

3. Lesiones de los tejidos blandos

Efectos de usar el laser:

* Reducción del dolor

* Prevención

* Curación más rápida

* Índice disminuido de recidiva Procedimientos y dosificación:

* Lesión herpética, úlceras provocadas por prótesis: con contacto muy ligero o apenas alejado. Puede ser repetido una vez o dos veces más cualquier otro día. Si una lesión se puede detectar en la etapa inicial, la aplicación es suficiente para prevenir la aparición de la lesión. El laser también reduce la posibilidad de recidiva en el área tratada.

* Queilitis angular: se debe encontrar la causa de la lesión para prevenir la repetición

* Contusión después de la inyección: En el sitio de la contusión

4. Implantes:

Efectos de usar el laser:

* Reducción del dolor después de la cirugía

* Una integración más rápida

5. Alveolo seco

Efectos de usar el laser:

* Alivio del dolor

* Curación más rápida

6. Sinusitis

Efectos de usar el laser:

* El laser puede ayudar a drenar el seno y a reducir el dolor de la sinusitis.

7. Procedimientos restaurativos

Efectos de usar el laser:

* Analgesia para preparaciones pequeñas del diente y para las cementaciones de la corona que reducen el uso del anestésico local. Disminución en estos casos de la sensibilidad postoperatoria.

* Eliminación más rápida de la anestesia

* Producción de dentina secundaria en situaciones de restauraciones profundas

8. Síndrome del Túnel Carpal

El laser ha probado un alternativa conservadora al tratamiento de esta dolencia, lo cuál está llegando a ser mucho más común en odontología. El laser se aplica entre los procesos espinosos de C5 y T1 y entonces en la muñeca. El dentista debe realizar la consulta con un médico o un fisioterapeuta. Generalmente se realizan de 10 a 30 sesiones. Se han publicado índices de éxito del 70-80% con el uso del laser. Ésta es un índice de éxito casi igual que el que se obtiene con cirugía pero a diferencia de la cirugía , no hay ningún seguimiento posible a excepción de más cirugía.

9. Lesiones del nervio

Efectos de los tratamientos con laser:

* Recuperación de la sensibilidad después del daño traumático o de la ruptura de un nervio

* Tratamiento de la neuralgia del trigémino

10. Dolor facial

Efectos de los tratamientos con laser:

* Relajación de los espasmos del músculo

* Tratamiento de los puntos gatillo en los músculos

* Reducción de la inflamación dentro de las articulaciones

* Reducción de los síntomas de la osteoartritis

* Tratamiento del dolor crónico de la ATM

* Tratamiento de las lesiones neurológicas asociadas a dolor facial

11. Acupuntura

El laser se puede utilizar con mucho éxito en puntos de acupuntura y los efectos en la curación y en el alivio del dolor pueden ser muy beneficiosos.

Jesús Ramirez
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Un futuro más brillante para Europa con la tecnología de diodo láser

 Los diodos láser son láseres semiconductores de bombeo eléctrico que tienen un uso muy extendido en aplicaciones industriales como las impresoras láser, los lectores de códigos de barras y los escáneres. En los últimos años, diversos avances han mejorado el rendimiento energético de estos láseres y los han hecho más compactos y robustos, lo cual ha facilitado la fabricación en serie de productos dotados de esta tecnología.

Sin embargo, el uso de estos láseres en muchos campos como la sanidad, las comunicaciones y el entretenimiento se ha topado a menudo con la dificultad de lograr un rendimiento satisfactorio por lo que concierne a equilibrar la potencia y la calidad del haz. Actualmente hay un grupo de científicos e ingenieros europeos que están cooperando para desarrollar la próxima generación de tecnología de diodo láser a través del proyecto WWW.BRIGHTER.EU («World Wide Welfare: High-Brightness Semiconductor Lasers for Generic Use»), financiado con fondos comunitarios. Este proyecto recibió de la UE una financiación de 9,7 millones de euros.

Los socios de este proyecto, que parten de los positivos resultados obtenidos por el proyecto WWW.BRIGHT.EU, que finalizó en 2006, desarrollarán el aspecto del gran brillo de la tecnología de diodo láser. Este gran brillo se refiere a la capacidad de un diodo láser de gran potencia de proporcionar un haz de gran calidad.

Concretamente, en este proyecto se proponen crear fuentes de luz de gran brillo y bajo coste en una amplia gama de colores (es decir, longitudes de onda), así como lograr una mayor luminosidad con fibras ópticas de menor diámetro. Según el consorcio, estos avances dejarán atrás las fuentes de láser costosas y difíciles de manejar e impulsarán nuevas aplicaciones.

Seguidamente, el proyecto se propone demostrar las aplicaciones de esta tecnología, inexistentes hasta ahora en el mercado, tales como fuentes de láser que permitan obtener imágenes médicas para el diagnóstico del cáncer y administrar tratamientos más certeros, amplificadores ópticos para redes de telecomunicaciones y fuentes compactas para realizar proyecciones.

La tecnología láser encierra un gran negocio. Según la plataforma tecnológica europea Photonics21, en 2005 el mercado mundial de la fotónica ascendió a más de 225.000 millones de euros, y se espera que este mercado se triplique en los próximos diez años. A base de combinar sus conocimientos sobre tecnología de diodos láser con tecnologías ópticas originales, los socios de proyecto BRIGHTER confían en explotar este mercado de miles de millones de euros con la creación de láseres más pequeños, brillantes, eficientes y económicos.

«La tecnología de diodos láser tiene ante sí mercados enormes», aseguró el Dr. Michel Krakowski, de Alcatel-Thales III-V Lab, coordinador del proyecto. «Hay montones de aplicaciones que hoy en día resultan imposibles sin contar con láseres de diodo de gran potencia, sea por su coste, limitación de colores o transportabilidad», añadió. «La meta de este proyecto es crear láseres nuevos que ofrezcan más potencia y brillo. Se trata de nuestra capacidad de reconcentrar el haz.»

«En el seno del proyecto hay una colaboración muy estrecha entre los grupos encargados de las movilizaciones y los socios que fabrican la extensa variedad de diodos láser de gran brillo necesarios para las aplicaciones futuras», señaló el Dr. Slawomir Sujecki de la Universidad de Nottingham, que está a cargo de las actividades de diseño y simulación de láseres en WWW.BRIGHTER.EU. «Esta colaboración viene motivada por una sólida creencia en el carácter crucial del software de diseño y modelización predictiva de diodos láser para poder comprender las limitaciones de la tecnología actual y desarrollar nuevas estructuras que ofrezcan un brillo superior.»

El proyecto, además de crear tecnología nueva, es parte integral del Espacio Europeo de Investigación. Según el profesor Eric Larkins de la Universidad de Nottingham, que también está en el consorcio, este proyecto sirve de ayuda para la comunidad científica, al intensificar la cooperación entre la industria y el mundo académico. Esto, según dijo, redunda en un mayor número de oportunidades de promoción profesional. «También estamos creando módulos formativos sobre tecnologías de vanguardia, los cuales están disponibles en formato de tutorial en el sitio web del proyecto para estudiantes e investigadores ajenos al consorcio», explicó el profesor Larkins.

Jesús Ramirez
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Diodo láser ultra compacto iBeam smart

Diodo láser compacto más avanzado del mercado. Con sus prestaciones innovadoras el iBeam smart permite a los usuarios aumentar la productividad y fiabilidad en sus aplicaciones, al mismo tiempo que optimiza el peso y dimensiones de sus sistemas.

El iBeam smart representa la primera solución en una caja en módulos de diodo láser
compactos. Mide sólo 100 mm x 40 mm x 40 mm y es capaz de mejorar la casi totalidad de aplicaciones de diodos láser existentes. Esto ha sido posible gracias a una alta integración de electrónica basada en microprocesador en combinación con un sobresaliente diseño de óptica mecánica.

El controlador láser integrado permite al iBeam smart no sólo ser una solución altamente compacta sino también potente, por ejemplo, proporciona 150 mW en operación monomodo a 660 nm.
Incluso, con este nuevo láser pueden llevarse a cabo procedimientos de modulación analógica rápida y compleja, y por supuesto la característica TOP de Toptica el Feedback Induced Noise Eraser (FINE), incluida como una función estándar en el iBeam smart.

Especificaciones principales del iBeam smart:
- Los más altos niveles de potencia alcanzados con diodos láser compactos: 120 mW a 405 nm, 50 mW a 445 nm, 30 mW a 488 nm, 100 mW a 640 nm, 150 mW a 642 nm y 150 mW a 660 nm.
- Verdadera solución en una caja (100 x 40 x 40 mm) con un controlador láser integrado.
- Sólido contra retroalimentación óptica vía FINE.
- Diámetro de haz de aproximadamente 1,1 mm 1/e2.
- Excelente calidad de haz y el ruido más bajo de la industria (menos del 0,2%,
10 MHz).

Algunas de las aplicaciones del iBeam smart: microlitografía, exploración de retina, angiografía por fluorescencia, microscopia confocal, citometría de flujo.

Jesús Ramirez
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Sección: 2

Diode Stacks

A diode stack (also called diode laser stack, multi-bar module, or two-dimensional laser array) contains a number of diode bars, which are arranged in the form of a stack. The most common arrangement is that of a vertical stack as shown in Figure 1. Effectively this is a two-dimensional array of edge emitters. Such a stack can be fabricated by cleaving linear diode laser arrays (diode bars) from a wafer, attaching them to thin heat sinks, and stacking these assemblies so as to obtain a periodic array of diode bars and heat sinks. There are also horizontal diode stacks (see below), and two-dimensional stacks.

For the highest beam quality, the diode bars should be as close to each other as possible. On the other hand, efficient cooling requires some minimum thickness of the heat sinks which need to be mounted between the bars. Due to that minimum spacing, the beam quality of the combined output of a diode stack in the vertical direction (and subsequently its brightness) is much lower than that of a single diode bar. There are, however, several techniques for significantly mitigating this problem, e.g. by spatial interleaving of the outputs of different diode stacks, by polarization coupling, or by wavelength multiplexing. Various types of high-power beam shapers and related devices have been developed for such purposes.

Depending on the application, a diode stack may be used with or without attached optics. A common option is the use of fast axis collimation lenses, which are directly attached to the bars (see Figure 2). Further optics can be used for collimation also in the slow axis (horizontal) direction, or even for coupling the output into a multimode fiber.




Diode stacks can provide extremely high output powers of hundreds or thousands of watts, as used for pumping of high-power solid-state lasers, or used directly e.g. for material processing. There are also fiber-coupled diode stacks, delivering e.g. several kilowatts from a multimode fiber with a core diameter of 600 μm. Some applications such as welding of metals or plastics, where a high beam quality is not required, can directly utilize the output of such a laser system, which can have a very high wall-plug efficiency. This is also attractive for other direct laser diode applications such as hardening, alloying, and cladding of metallic surfaces. If laser radiation with much higher brightness is required, the laser radiation may be used for pumping a high-power fiber laser based on a double-clad fiber. Such a device can serve as a brightness converter, delivering a somewhat reduced output power but with much higher beam quality.

There are also horizontal stacks, where the diode bars are arranged side-by-side, leading to a long linear array of emitters. Such an arrangement is more easily cooled, and may thus also allow for a higher output power per emitter. The emission pattern of a horizontal stack is suitable for, e.g., pumping of rod lasers, whereas it is probably less convenient when an approximately circular output beam is required. The number of diode bars in a horizontal stack (and thus the total output power) is more limited than in a vertical stack.

The cooling of such diode stacks is somewhat challenging for continuous-wave operation, but less so for quasi-continuous-wave operation with pulses of e.g. a few hundred microseconds duration and a pulse repetition rate of some tens of hertz. The latter mode of operation makes it possible to obtain very high peak powers, which can be used e.g. for pumping Q-switched high-power solid-state lasers.

Jesús Ramirez
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Sección: 2

Diode Stacks

A diode stack (also called diode laser stack, multi-bar module, or two-dimensional laser array) contains a number of diode bars, which are arranged in the form of a stack. The most common arrangement is that of a vertical stack as shown in Figure 1. Effectively this is a two-dimensional array of edge emitters. Such a stack can be fabricated by cleaving linear diode laser arrays (diode bars) from a wafer, attaching them to thin heat sinks, and stacking these assemblies so as to obtain a periodic array of diode bars and heat sinks. There are also horizontal diode stacks (see below), and two-dimensional stacks.

For the highest beam quality, the diode bars should be as close to each other as possible. On the other hand, efficient cooling requires some minimum thickness of the heat sinks which need to be mounted between the bars. Due to that minimum spacing, the beam quality of the combined output of a diode stack in the vertical direction (and subsequently its brightness) is much lower than that of a single diode bar. There are, however, several techniques for significantly mitigating this problem, e.g. by spatial interleaving of the outputs of different diode stacks, by polarization coupling, or by wavelength multiplexing. Various types of high-power beam shapers and related devices have been developed for such purposes.

Depending on the application, a diode stack may be used with or without attached optics. A common option is the use of fast axis collimation lenses, which are directly attached to the bars (see Figure 2). Further optics can be used for collimation also in the slow axis (horizontal) direction, or even for coupling the output into a multimode fiber.




Diode stacks can provide extremely high output powers of hundreds or thousands of watts, as used for pumping of high-power solid-state lasers, or used directly e.g. for material processing. There are also fiber-coupled diode stacks, delivering e.g. several kilowatts from a multimode fiber with a core diameter of 600 μm. Some applications such as welding of metals or plastics, where a high beam quality is not required, can directly utilize the output of such a laser system, which can have a very high wall-plug efficiency. This is also attractive for other direct laser diode applications such as hardening, alloying, and cladding of metallic surfaces. If laser radiation with much higher brightness is required, the laser radiation may be used for pumping a high-power fiber laser based on a double-clad fiber. Such a device can serve as a brightness converter, delivering a somewhat reduced output power but with much higher beam quality.

There are also horizontal stacks, where the diode bars are arranged side-by-side, leading to a long linear array of emitters. Such an arrangement is more easily cooled, and may thus also allow for a higher output power per emitter. The emission pattern of a horizontal stack is suitable for, e.g., pumping of rod lasers, whereas it is probably less convenient when an approximately circular output beam is required. The number of diode bars in a horizontal stack (and thus the total output power) is more limited than in a vertical stack.

The cooling of such diode stacks is somewhat challenging for continuous-wave operation, but less so for quasi-continuous-wave operation with pulses of e.g. a few hundred microseconds duration and a pulse repetition rate of some tens of hertz. The latter mode of operation makes it possible to obtain very high peak powers, which can be used e.g. for pumping Q-switched high-power solid-state lasers.

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Laser Cooling

Laser cooling is usually not meant to be the cooling of lasers, but rather the use of dissipative light forces for reducing the random motion and thus the temperature of small particles, typically atoms or ions. Depending on the mechanism used, the temperature achieved can be in the regime of millikelvins, microkelvins, or even nanokelvins. A totally different kind of laser cooling, where macroscopic samples are cooled, is treated in a separate article on optical refrigeration.



Methods of Laser Cooling

A simple scheme for laser cooling is Doppler cooling, where light forces are exerted by absorption and subsequent spontaneous emission of photons and the rate of these processes depends on the velocity of an atom or ion due to the Doppler shift. For example, a beam of atoms in a vacuum chamber can be stopped and cooled with a counterpropagating single-frequency laser beam, the optical frequency of which is first chosen to be somewhat higher than the atomic resonance, so that only the fastest atoms can absorb photons. Subsequently, the laser frequency is reduced so that slower and slower atoms participate in the interaction, and finally all atoms have a greatly reduced speed (at least in one dimension). This corresponds to a lower temperature, assuming that thermal equilibrium can be re-established.

Doppler cooling can also be used in an optical molasses for damping the atomic motion in one to three spatial dimensions.

The method of Doppler cooling is limited in terms of the reachable temperature (→ Doppler limit). There are other methods, most notably Sisyphus cooling, which allow one to get substantially below the Doppler limit, down to the much lower recoil limit associated with the recoil momentum related to the absorption or emission of a single photon. Even the recoil limit is not the final one: specifically the method of velocity-selective coherent population trapping allows sub-recoil temperatures in the nanokelvin regime.

Another technique is evaporative cooling, where the capturing potential in an atom or ion trap is gradually reduced so that the fastest particles can escape, and the average energy of the remaining particles is reduced. Subsequent collisions can re-establish a thermal equilibrium, corresponding to a reduced temperature.


Applications


Some examples of applications of laser cooling are:

high-resolution spectroscopic measurements (e.g. for frequency standards in optical clocks) by the elimination of Doppler broadening studying the behavior of ultracold gases, which can exhibit interesting phenomena such as Bose–Einstein condensation (BEC), for example ultraprecise measurement of gravitational fields (used e.g. for gravitational physics or for oil field exploration), based on the Doppler shift of free-falling cooled atoms, on Bloch oscillations lithography with cold atomic beams to form very accurately controlled structures.

In 1997, the Nobel Prize in Physics was awarded to Steven Chu, Claude Cohen-Tannoudji and William D. Phillips, for the development of methods to cool and trap atoms with laser light. Important early contributions to this field were also brought by Theodor W. Hänsch [1], Nobel Prize winner in 2005 (for other achievements).

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Laser Microscopy

Laser microscopy (or laser scanning microscopy) is a class of techniques for generating microscopic images of some sample by raster scanning it with a diffraction-limited laser beam. Scanning may be achieved by moving either the laser beam or the sample. Typically, the laser beam excites fluorescence in its focus, and the intensity of that fluorescence light is recorded for each point in the sample (→ fluorescence microscopy). From these data, images can be produced on a computer, and of course they can be stored in electronic form. Numerical methods can be applied to process the images, e.g. to enhance the contrast.

A frequently used imaging technique is based on a confocal geometry, where the light from the focus in the sample is imaged (e.g. with a microscope objective) onto a pinhole, behind which the optical power is detected. This geometry suppresses the influence of light coming from other regions in the sample, e.g. from before or after the focus, because such light can not efficiently pass through the pinhole. In effect, mainly the depth resolution is improved. The confocal principle is emphasized in the term confocal laser scanning microscopy, and discussed in more detail in the article on fluorescence microscopy.

Instead of fluorescence, one may exploit acoustic effects of pulsed laser beams; the resulting method is called optoacoustic or photoacoustic microscopy.

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High-power Lasers

Lasers with high output powers are required for a number of applications, e.g. for

material processing (welding, cutting, drilling, soldering, marking, surface modification)
large-scale laser displays (→ RGB sources)
remote sensing (e.g. with LIDAR)
medical applications (e.g. surgery)
military applications (e.g. anti-missile weapons)
fundamental science (e.g. particle acceleration)
laser-induced nuclear fusion (e.g. in the NIF project)
There is no commonly accepted definition of the property "high power"; in the context of laser material processing, it usually means multiple kilowatts or at least a few hundred watts, whereas for laser displays some tens of watts many already be considered high. In some areas, this label is assigned simply for generating a significantly higher output power than other lasers based on the same technology; for example, some "high-powered" laser pointers emit a few hundred milliwatts, whereas ordinary laser pointers are limited to a few milliwatts.

Technical Challenges
The generation of high optical powers in lasers involves a number of technical challenges:

One requires one or several powerful pump sources. While lamp pumping was originally the only viable approach for most solid-state lasers, pumping with high-power laser diodes (diode bars or diode stacks) has become more and more widespread. Diode-pumped lasers now offer the highest output powers in continuous-wave operation. For very high pulse energies (e.g. tens of joules), lamp pumping is still more practical.
At least for long-term continuous-wave operation, a high wall-plug efficiency is an important economic factor. Unfortunately, various technical challenges (e.g. thermal effects, see below) tend to make it more difficult at very high power levels to achieve a good efficiency.
Even in a fairly efficient gain medium, a substantial fraction of the pump power is converted into heat, which can have a number of detrimental side effects. In the worst case, thermally induced stress leads to fracture of the laser crystal. High-power solid-state lasers also exhibit strong thermal lensing, making it substantially more difficult to achieve a high beam quality. In lasers with polarized output, depolarization loss often compromises the efficiency. Efficient heat removal and thermal management are therefore important issues, and additional measures (e.g. in the context of resonator design) are often required for coping with various kinds of thermal effects.
Particularly in Q-switched lasers, very high optical intensities can occur, which may lead to optical damage e.g. via laser-induced breakdown. Even if the optical intensities remain well below the damage threshold of all optical elements, tiny dust particles can provoke damage phenomena. It can therefore be essential to keep the laser setup very clean, e.g. by operating it in a sealed case which may be opened only in a clean room.
Various types of nonlinear effects can also become relevant, particularly in high-power fiber lasers. Examples are stimulated Raman scattering, Brillouin scattering and four-wave mixing.
Laser resonators with large effective mode areas tend to be sensitive to misalignment and vibrations of optical components. It can therefore be more challenging to achieve robust maintenance-free operation and a good beam pointing stability.
Types of High-power Lasers
There are several different types of high-power lasers:

High-power diode bars and diode stacks have already been mentioned above as possible pump sources for solid-state lasers. They allow the generation of kilowatts of output power, but with a poor beam quality. For some applications, where beam quality is not essential, the direct use of high-power laser diodes (direct-diode applications) e.g. for laser welding, cladding, brazing and heat treatment, is an interesting option, offering a comparatively simple, compact, cost-effective and energy-efficient solution.
There are various types of lamp-pumped or diode-pumped solid-state bulk lasers. Rod lasers can be optimized for several kilowatts of output power, but diffraction-limited beam quality is possible only up to a few hundred watts (with significant efforts). Slab lasers can be developed for tens of kilowatts or more with relatively high beam quality. Thin-disk lasers easily generate hundreds of watts with diffraction-limited beam quality and have the potential to reach that even at power levels well above 10 kW. The power efficiency is usually fairly good.
High-power fiber lasers and amplifiers can generate up to a few kilowatts with close to diffraction-limited beams and high power efficiency. With relaxed beam quality requirements, even significantly higher powers are possible. Strictly, such fiber devices are often not lasers, but master oscillator power amplifier (MOPA) configurations.
Some gas lasers, e.g. CO2 lasers and excimer lasers, are also suitable for hundreds or thousands of watts of output power. They typically operate in different other regions than solid-state lasers, e.g. in the mid-infrared or ultraviolet region.
There are chemical lasers with multi-kilowatt or even megawatt output powers, explored e.g. in the context of anti-missile weapons.
A perhaps not very practical, but theoretically very interesting high-power laser concept is that of the radiation-balanced laser. Here, the heat generation in the gain medium is essentially eliminated by optical refrigeration.

An aspect of great importance for further laser development is that of power scaling, based on certain power-scalable laser architectures. Even for not power-scalable laser types, it can be very helpful to understand the scaling properties of various parts or techniques.

Jesús Ramirez
C.I:18564428
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Laser Pointers

A laser pointer is a small (usually battery-powered) laser device designed for pointing at objects by illuminating them with a collimated visible laser beam. Most laser pointers, particularly the cheap ones, contain a small GaInP/AlGaInP laser diode operating somewhere in the red spectral region, a collimating lens, a simple electronic diode driver, and a battery compartment for e.g. three coin cells. Some significantly more expensive pointers, as shown in Figure 1, emit green or even blue or yellow light and normally contain a small diode-pumped solid-state laser with a nonlinear crystal for frequency doubling. Green laser pointers are usually based on a miniature Nd:YVO4 laser with a KTP crystal for intracavity frequency doubling. Here, Nd:YVO4 is beneficial for a low threshold pump power, and KTP works in a relatively wide temperature range, thus not requiring means for temperature stabilization.



Laser pointers should not be confused with lamps containing light-emitting diodes (LEDs), which emit a much more diffuse beam (with much lower spatial coherence, similar to that of an incandescent lamp) and can also emit light with different colors, or white light.

Applications
A typical use of a hand-held laser pointer is to point at some screen or chart during a presentation, e.g. a conference talk. This is convenient because it can be done from a large distance and requires only a small hand-held device. However, the visibility of the generated spot on the screen is often poor (particularly for red laser pointers with relatively long emission wavelength), and a fast-moving light spot can have a somewhat nervous appearance. Therefore, some people prefer an old-fashioned telescopic pointing device for presentations.

Laser pointers can be useful for, e.g., aligning some machinery, or for certain optical distance measurements.

Brightness and Color
The apparent brightness of the illuminated spot depends strongly on the wavelength of the emitted light. Most devices operate in the red spectral region, where the sensitivity of the eye rapidly decreases with increasing wavelength. Devices with 650-nm output appear about twice as bright as those emitting the same power at 670 nm, and 635-nm devices still about two times brighter. However, the shorter-wavelength laser pointers are typically more expensive. This is particularly true for green lasers, which are significantly brighter than their red counterparts, but are still expensive. They involve a diode-pumped solid-state laser and a frequency doubler. Due to the typically poor conversion efficiency of the frequency doubler at low power levels, hundreds of milliwatts of infrared (typically 1064-nm) light are required for generating a few milliwatts in the green, and the batteries will accordingly not last very long, unless they are comparatively heavy.

Range of a Laser Pointer
Lay persons often ask what is the range of a laser pointer is, and responding to this interest some producers specify some more or less questionable numbers.

If the question is meant to be how far the light of a laser pointer can propagate, the correct answer is that there is no limit, provided that the light is not absorbed or scattered away in the atmosphere. However, the beam area will eventually become larger due to the beam divergence, so that the intensity e.g. on a screen will be reduced even if the overall power remains constant. Accordingly, an airplane pilot looking down into such a beam from an altitude of 10 km will not be disturbed by the remaining small intensity.

The range of a laser pointer may also be understood as the maximum distance from which the spot on the screen can be seen. That kind of range is normally not limited by the beam divergence but by the overall optical power (apart from the wavelength and level of ambient light), since the issue is not the comparatively minor divergence on the way from the laser pointer to the screen, but rather the huge divergence of the scattered light on the way back. Therefore, someone standing next to the illuminated screen would easily see the spot when it is already hardly perceivable from the position of the laser pointer.

Safety Hazards
There have been extensive debates on laser safety issues associated with laser pointers. Typical output powers are a few milliwatts – normally below 5 mW in order to comply with safety class 3R, and sometimes below 1 mW for class 2. Direct staring into a 1-mW beam can be irritating for the eye: it can cause temporary flash blindness. However, nobody would normally do that long enough to cause serious eye damage. Nevertheless, great care should be taken, e.g. when children are playing with laser pointers, if laser pointers are at all considered to be suitable as toys. Significant hazards could arise e.g. if somebody walking down stairs or a car driver is irritated by a laser beam.

There are some reports saying that cheap green laser pointers are sold which do not have a filter to eliminate the infrared light, and therefore can emit hundreds of milliwatts in the infrared spectral region. This is obviously a terrible safety hazard; an eye directly hit by such a beam could be destroyed within a fraction of a second.

Jesús Ramirez
C.I:18564428
Sección: 2

Distance Measurements with Lasers

Lasers can be used in various ways to measure distances or displacements without physical contact. In fact they allow for the most sensitive and precise length measurements, for extremely fast recordings (sometimes with a bandwidth of many megahertz), and for the largest measurement ranges, even though these qualities are usually not combined by a single technique. Depending on the specific demands, very different technical approaches can be appropriate. They find a wide range of applications, for example in architecture, inspection of fabrication halls, criminal scene investigation (CSI), and in the military.

Techniques for Distance Measurements

Some of the most important techniques used for laser distance meters are as follows:

Triangulation is a geometric method, useful for distances in the range of ∼ 1 mm to many kilometers.
Time-of-flight measurements (or pulse measurements) are based on measuring the time of flight of a laser pulse from the measurement device to some target and back again. Such methods are typically used for large distances such as hundreds of meters or many kilometers. Using advanced techniques, it is possible to measure the distance between Earth and the Moon with an accuracy of a few centimeters. Typical accuracies of simple devices for short distances are a few millimeters or centimeters.
The phase shift method uses an intensity-modulated laser beam. Compared with interferometric techniques, its accuracy is lower, but it allows unambiguous measurements over larger distances and is more suitable for targets with diffuse reflection.
Note that the phase shift technique is sometimes also called a time-of-flight technique, as the phase shift is proportional to the time of flight, but the term is more suitable for methods as described above where the time of flight of a light pulse is measured.
For small distances, one sometimes uses ultrasonic time-of-flight methods, and the device may contain a laser pointer just for getting the right direction, but not for the distance measurement itself.
Frequency modulation methods involve frequency-modulated laser beams, for example with a repetitive linear frequency ramp. The distance to be measured can be translated into a frequency offset, which may be measured via a beat note of the sent-out and received beam.
Interferometers allow for distance measurements with an accuracy which is far better than the wavelength of the light used.


Laser Radar

A laser radar is a device which uses one of the distance measurement techniques as described above, and scans the direction of the distance measurement in two dimensions. This allows the acquisition of an image, or more precisely a depth profile of some object, as required e.g. in robotics. For acquiring such depth profiles at a higher rate, there are sensor chips similar to CCDs (charge-coupled devices) with internal electronics to detect phase shifts, so that the distance for each pixel can be measured simultaneously. This allows for rapid three-dimensional imaging with very compact devices.

Compared with ultrasonic or radio and microwave frequency devices (radar), the main advantage of laser distance measurement techniques is that laser light has a much smaller wavelength, allowing one to send out a much more concentrated probe beam and thus to achieve a higher transverse spatial resolution. Another advantage that an optical bandpass filter makes it possible to very effectively remove noise influences at other optical frequencies.

Jesús Ramirez
C.I:18564428
Sección: 2

EL LECTOR DE DISCOS COMPACTOS

Una de las muchas aplicaciones de los diodos láser es la de lectura de información digital de soportes de datos tipo CD-ROM o la reproducción de discos compactos musicales. El principio de operación de uno y otro es idéntico.

Esquema del funcionamiento del CD-ROM
Un haz láser es guiado mediante lentes hasta la superficie del CD. A efectos prácticos, se puede suponer dicha superficie formada por zonas reflectantes y zonas absorbentes de luz. Al incidir el haz láser en una zona reflectante, la luz será guiada hasta un detector de luz: el sistema ha detectado un uno digital. Si el haz no es reflejado, al detector no le llega ninguna luz: el sistema ha detectado un cero digital.
Un conjunto de unos y ceros es una información digital, que puede ser convertida en información analógica en un convertidor digital-analógico. Pero esa es otra historia que debe de ser contada en otra ocasión.

Jesús Ramirez
C.I:18564428
Sección: 2