A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below)

A maser is a device that produces coherent electromagnetic waves through amplification by stimulated emission. Historically, “maser” derives from the original, upper-case acronym MASER, which stands for "Microwave Amplification by Stimulated Emission of Radiation". The lower-case usage arose from technological development having rendered the original denotation imprecise, because contemporary masers emit EM waves (microwave and radio frequencies) across a broader band of the electromagnetic spectrum; thus, the physicist Charles H. Townes’s suggested usage of “molecular” replacing “microwave”, for contemporary linguistic accuracy.^[1] In 1957, when the optical coherent oscillator was first developed, it was denominated optical maser, but usually called laser (Light Amplification by Stimulated Emission of Radiation), the acronym Gordon Gould established in 1957.

History[link]

The theoretical principles describing the operation of a maser was described by Nikolay Basov and Alexander Prokhorov from Lebedev Institute of Physics at an All-Union Conference on Radio-Spectroscopy held by USSR Academy of Sciences in May 1952.

The results were subsequently published in October 1954. A precursor of the maser was the first show boosted hydrogen device built and tested by physicists Theodor V. Ionescu and Vasile Mihu in 1946. Independently, Charles H. Townes, J. P. Gordon, and H. J. Zeiger built the first ammonia maser at Columbia University in 1953. The device used stimulated emission in a stream of energized ammonia molecules to produce amplification of microwaves at a frequency of 24 gigahertz.

Townes later worked with Arthur L. Schawlow to describe the principle of the optical maser, or laser, which Theodore H. Maiman first demonstrated in 1960. For their research in this field Townes, Basov, and Prokhorov were awarded the Nobel Prize in Physics in 1964.

Technology[link]

The maser is based on the principle of stimulated emission proposed by Albert Einstein in 1917. When atoms have been induced into an excited energy state, they can amplify radiation at the proper frequency. By putting such an amplifying medium in a resonant cavity, feedback is created that can produce coherent radiation.

Some common types of masers[link]

• Atomic beam masers
  • Ammonia maser
  • Free electron maser
  • Hydrogen maser
• Gas masers
  • Rubidium maser
• Solid state masers
  • Ruby maser
  • Whispering-gallery modes iron-sapphire maser

The dual noble gas of a masing medium which is nonpolar.^[2]

Uses[link]

Masers serve as high precision frequency references. These "atomic frequency standards" are one of the many forms of atomic clocks. They are also used as electronic amplifiers in radio telescopes. Masers are being developed as directed-energy weapons.

Hydrogen maser[link]

A hydrogen maser.

Today, the most important type of maser is the hydrogen maser which is currently used as an atomic frequency standard. Together with other types of atomic clocks, they constitute the "Temps Atomique International" or TAI. This is the international time scale, which is coordinated by the Bureau International des Poids et Mesures, or BIPM.

It was Norman Ramsey and his colleagues who first realized this device. Today's masers are identical to the original design. The maser oscillation relies on stimulated emission between two hyperfine levels of atomic hydrogen. Here is a brief description of how it works:

• First, a beam of atomic hydrogen is produced. This is done by submitting the gas at low pressure to an RF discharge (see the picture on this page).

• The next step is "state selection"—in order to get some stimulated emission, it is necessary to create a population inversion of the atoms. This is done in a way that is very similar to the famous Stern-Gerlach experiment. After passing through an aperture and a magnetic field, many of the atoms in the beam are left in the upper energy level of the lasing transition. From this state, the atoms can decay to the lower state and emit some microwave radiation.

• A high quality factor microwave cavity confines the microwaves and reinjects them repeatedly into the atom beam. The stimulated emission amplifies the microwaves on each pass through the beam. This combination of amplification and feedback is what defines all oscillators. The resonant frequency of the microwave cavity is exactly tuned to the hyperfine structure of hydrogen: 1420 405 751.768 Hz.

• A small fraction of the signal in the microwave cavity is coupled into a coaxial cable and then sent to a coherent receiver.

• The microwave signal coming out of the maser is very weak (a few pW). The frequency of the signal is fixed and extremely stable. The coherent receiver is used to amplify the signal and change the frequency. This is done using a series of phase-locked loops and a high performance quartz oscillator.

Astrophysical masers[link]

Maser-like stimulated emission also occurs in nature in interstellar space, and is frequently called superradiant emission to distinguish it from laboratory masers. Such emission is observed from molecules such as water (H₂O), hydroxyl radicals (OH), methanol (CH₃OH), formaldehyde (CH₂O), and silicon monoxide (SiO). Water molecules in star-forming regions can undergo a population inversion and emit radiation at 22 GHz, creating the brightest spectral line in the radio universe. Some water masers also emit radiation from a vibrational mode at 96 GHz.

Extremely powerful masers, associated with active galactic nuclei, are known as megamasers and are up to a million times more powerful than stellar masers.

Terminology[link]

The meaning of the term maser has changed slightly since its introduction. Initially the acronym was universally given as "microwave amplification by stimulated emission of radiation," which described devices which emitted in the microwave region of the electromagnetic spectrum.

The principle and concept of stimulated emission has since been extended to more devices and frequencies. Thus the original acronym is sometimes modified, as suggested by Charles H. Townes,^[1] to "molecular amplification by stimulated emission of radiation." Some have asserted that Townes's efforts to extend the acronym in this way were primarily motivated by the desire to increase the importance of his invention, and his reputation in the scientific community.^[3]

When the laser was developed, Townes and Schawlow and their colleagues at Bell Labs pushed the use of the term optical maser, but this was largely abandoned in favor of laser, coined by their rival Gordon Gould.^[4] In modern usage, devices that emit in the X-ray through infrared portions of the spectrum are typically called lasers, and devices that emit in the microwave region and below are commonly called masers, regardless of whether they emit microwaves or other frequencies.

Gould originally proposed distinct names for devices that emit in each portion of the spectrum, including grasers (gamma ray lasers), xasers (x-ray lasers), uvasers (ultraviolet lasers), lasers (visible lasers), irasers (infrared lasers), masers (microwave masers), and rasers (RF masers). Most of these terms never caught on, however, and all have now become (apart from in science fiction) obsolete except for maser and laser.

In the early 1960's JPL developed a Maser to provide ultra low noise amplification of S band signals received from deep space probes. This Maser used refrigerated Hydrogen to chill the amplifier to four degrees Kelvin. Amplification was achieved by exciting a ruby comb with a 12gHz Klystron. In the early days it took days to chill [and remove impurities from] the Hydrogen lines. Refrigeration was two stage with a large Linde unit on the ground and a crosshead compressor within the antenna; final injection was at 3000psi through a six thou inch [micrometer adjustable] entry to the chamber. The whole system noise temperature looking at cold sky [2.7K] was 17 degrees K. This gave such a low noise figure that the Mariner 64 Spacecraft could send pictures of Mars back to Earth even though the spacecraft transmitter was only 15 Watts and the signal received was -169 dbm

See also[link]

• Masers in science fiction
• Spaser
• List of laser types

References[link]

Further reading[link]

• J.R. Singer, Masers, John Whiley and Sons Inc., 1959.
• J. Vanier, C. Audoin, The Quantum Physics of Atomic Frequency Standards, Adam Hilger, Bristol, 1989.
• Cartoon Megas XLR 2005

External links[link]

• arXiv.org search for "maser"
• Noble gas Maser
• "The Hydrogen Maser Clock Project". Harvard-Smithsonian Center for Astrophysics. Archived from the original on 2006-10-10. http://web.archive.org/web/20061010151459/http://www.cfa.harvard.edu/hmc/. 
• Bright Idea: The First Lasers
• Invention of the Maser and Laser, American Physical Society
• Shawlow and Townes Invent the Laser, Bell Labs

This biographical article needs additional citations for verification. Please help by adding reliable sources. Contentious material about living persons that is unsourced or poorly sourced must be removed immediately, especially if potentially libelous or harmful. (June 2008)

Carole Samaha (Arabic: كارول سماحة‎) is a Lebanese musician and actress. She has released five studio albums. Samaha has a masters degree in acting and directing, which she earned in 1999.^[3] In 2004 she won the Arab Music Award for best female newcomer.^[4] She has also won multiple Murex d'Or awards and was nominated for Best Arabia Act in the 2008 MTV Europe Music Awards.

Biography[link]

Early life[link]

Samaha was born in Lebanon 1972 to Antoine Samaha of Kenshara and Nouhad Hawi. She grew up with her parents and two brothers, having only one dream since childhood, being on stage.

She started her career as an actress in the theater as well as television

Musicals era[link]

After introducing herself to Mansour Rahbani, one of the biggest Lebanese and Arab composers, she experienced a turning point in her career as she shifted from drama to musical theatre and found success.

Discography[link]

2011 Al- Shahroura

Videography[link]

Awards[link]

• "Revelation of the year" (actress and singer) Murex d'Or in 2000.^[5]
• "Best female newcomer" Arab Music Award (2003) - This was the first year for which Arab Music Awards were awarded and the ceremony was held in Dubai in May 2004.^[4]
• "Best Polyvalent talent" (actress and singer) Murex d'Or in 2003.^[5]
• "Best Female Romantic Song" ("Tala3 Fiyyi") Murex d'Or in 2003.^[5]
• "Best album of the year" (Adwa' Al Shohra) ART Music Award in 2006. The ceremony was held in Cairo.^{[citation needed]}
• "Best Lebanese Female Singer" Murex d'Or in 2007.^[5]
• "Best Lebanese Song" ("Ya Rab", with Marwan Khoury) Murex d'Or in 2007.^[5]
• nominated for "Best Arab Act" in the MTV Europe Music Awards 2008 (along with Mohamed Hamaki, Karl Wolf, Abri and others).
• "Best album of the year" (Hdoudi Sama, 2009) Murex d'Or in June 2010.
• Samahe was honored for best music video – "Khalik Behalik" – at the 2011 Murex d'Or ceremony.^[6]

References[link]

1. ^ "This section is dedicted to Carole's super fans who are interested in learning even the smallest details about her.". carolesamaha.com. http://carolesamaha.com/#/biography. Retrieved 5 June 2011.  - From the website's main page, click on "Enter," then on "Biography," then on "Close and personal" at the bottom.
2. ^ "The Journey of a Multi Dimensional Artist !". carolesamaha.com. carolesamaha.com. http://carolesamaha.com/#/biography. Retrieved 13 September 2010. "Originally from Khonchara - Lebanon, [...]"  - From the website's main page you have to click on Enter, then on Biography.
3. ^ "The Journey of a Multi Dimensional Artist !". carolesamaha.com. http://carolesamaha.com/#/biography. Retrieved 5 June 2011. 
4. ^ ^{a b} "Fiascos affect Arab music awards". BBC News Online. 17 May 2004. http://news.bbc.co.uk/2/hi/entertainment/3720631.stm. Retrieved 15 December 2010. 
5. ^ ^{a b c d e} Murex d'Or website - click on "Official Website", then on "Menu" and then on "Results", and then slide the slider to the desired year.
6. ^ "Arab stars receive top honors at Murex d’Or Awards". Daily Star (Jounieh). 25 June 2011. http://www.dailystar.com.lb/Culture/Music/2011/Jun-25/Arab-stars-receive-top-honors-at-Murex-dOr-Awards.ashx#axzz1QhXmj2fu. Retrieved 30 June 2011. "Also honored for best music video was Carole Samahe for 'Khalik Behalik.'" 

External links[link]

• Official Website
• Official Facebook Page

This biographical article needs additional citations for verification. Please help by adding reliable sources. Contentious material about living persons that is unsourced or poorly sourced must be removed immediately, especially if potentially libelous or harmful. (December 2008)

Mahmoud Saad محمود سعد is an Egyptian football player. Currently, he is the assistant coach of Zamalek.^[1] He was previously the manager of Zamalek, and of the Egyptian National Olympic Team in the 1992 Summer Olympics.

Titles as a Manager for Zamalek[link]

1 Egyptian League Title for Zamalek
2 Egyptian Cup Titles for Zamalek
1 Egyptian Super Cup Title for Zamalek
4 African Champions League Titles For Zamalek
2 Afro-Asian Cup Titles For Zamalek
2 African Super Cup Titles For Zamalek

Titles as a player for Zamalek[link]

1 Egyptian League Titles for Zamalek
3 Egyptian Cup Titles for Zamalek

References[link]

This biographical article related to Egyptian football is a stub. You can help Wikipedia by expanding it. v t e

Delwar Hossain is a first class and List A cricketer from Bangladesh. He made his debut for Rajshahi Division in 2006/07 and played 1 first class and 2 list A one day games in that season. He scored an unbeaten 51 on his first class debut against Barisal Division and got figures of 3-46 in the one day clash against Dhaka Division.

This biographical article related to Bangladeshi cricket is a stub. You can help Wikipedia by expanding it. v t e