Argon Ion Laser

Posted: October 17th, 2013

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Argon Ion Laser

            Ion laser

An ion laser falls in the category of gas lasers that utilize gas that has been ionized as the lasting medium. Similar to other gas lasers, the ion laser adorns a characteristic sealed cavity that houses the laser medium and mirrors making up the Fabry–Pérot resonator. However, they are dissimilar to HeNe lasers, in that the characteristic energy levels that make up the laser actions are derived from the ions. These devices require considerable quantities of energy for the excitation of the ionic transitions required by the ion lasers. The required current is therefore much intense. In the process, only the small ion lasers are water-cooled.

The operation of a small air-cooled ion laser could lead to the production of about 130mW of light. This is when it is operated at a tube current of 10A @ 105V. This results in the production of power that is in the range 1 kW and the consequent of a considerable amount of energy in the form of heat that must be dissipated to prevent damage of the equipment (Argon-ion Laser, 77).

The Argon-Ion laser one of the laser systems that are widely used in the technological applications because of its dependability. The device was originally invented by William Bridges in the year 1964. The operation of the device leads to the production of a continuous wave beam ranging in the tens of watts. This renders it potent enough to be applied in the areas of industry and for research purposes (Bennett, 80).

The argon ion laser is a predecessor to previously invented lasers. However, it has surpassed these in terms of application and relevance in the industry. Just as its name implies, the device utilizes high purity argon gas as the medium for laser production. The use of a multiple line argon ion laser can lead to the production of close to eighteen discrete laser wavelengths that come in the ranges of ultraviolet (275.4nm) to the visible green (528.7nm) in the color spectrum. Optimal power is often generated at the 488nm and 514.5nm lines.

These ion lasers are commercially produced and come in a variety of configurations because of the wide range of its applications. The argon ion laser has a primal advantage in that it can be easily configured to produce single laser a line or the simultaneous production of multiple laser lines. These lasers are also preferred because of their ability to be fitted with polarizing optics resulting in the production of polarized laser beams. Another advantage is the ability to manufacture them for the production of optical power levels that come in a wide range of power levels. Commercially produced lasers are commonly available with power levels ranging from a couple of miliwatts to excesses of twenty watts.

These enable them to have wide and varying applications that include Raman Spectroscopy, Microscopy, Flow Cytometry, Holography, Entertainment, Forensics, Ophthalmic Surgery and sources for optical pumping. These lasers are highly applied in the realm of scientific research and scholarly applications. Although there have been significant advances in terms of laser technology since the inception of the argon ion laser,  these additional laser light sources are yet to surpass the use of the argon ion laser because of its inherent reliability and predictability laser light source. The design of the argon ion laser is primarily based on three distinctive parts, namely: the plasma tube, resonator assembly, and the power supply.

The Plasma Tube

The plasma tube lies at the heart of the argon ion laser and an essential component of the device. The essential component that makes up the plasma tube is the bore. The construction of the plasma tube is in a way that it is not distorted or destroyed by the high temperatures produced during the operation of the device. The tube is also designed to withstand the high temperatures while still maintaining a vacuum. The preferred material in the design of the plasma tube is predominantly BeO. This is mainly because the material is characterized by a low vapor pressure.

This makes it easy to produce with a high chemical purity essential for the design of the plasma tube. When the plasma is sealed in the correct manner, the utilization of BeO enables the argon gas pressure that is contained in the tube to maintain its standardized one torr level for a considerable amount of time usually in terms of years. This renders the device effective and efficient to use for many hours without compromising its reliability and accuracy.

BeO is also highly used in the design of the argon ion laser due to its property of being an excellent thermal conductor.

This makes it an effective conductor of the intense heat generated during the operation of the device. The BeO conducts this intense heat to the external parts of the bore where it is dissipated using forced air-cooling. Other cooling means includes the use of flowing water trapped inside water jackets. The first cooling method is primarily preferred when using low to medium power argon lasers whereas the later technique is mainly employed when using high power argon lasers.

The Resonator Assembly

Another important part of the argon ion laser is the resonator assembly. This part enables the bore to function as an optical resonant cavity. This is made possible through the design of the mirrors that are placed at the ends of the bore. The mirrors are made in such a way that they face the perpendicular length of the bore. However, one of the mirrors is designed in such a manner that it acts as a high reflective mirror while the adjacent one is designed to be partially reflective. The angle of the mirrors are then finely tuned in the attempt of align them in the best possible manner.

Previous argon ion laser designs involved the design of the two ends of the plasma tube by fitting them with Brewster Windows. This enabled the optical energy contained inside the bore to come out of the two ends of the plasma tube efficiently. The plasma tubes in these lasers were installed inside a bulky resonator assembly. The mirrors were then fixed in a rigid manner and angled against the adjustable end plates. Once this fete was achieved, the mirrors were then properly aligned and maintained in this manner by the bulky nature of the of the resonator assembly (Chen, 45).

These are in sharp contrast to the technology of the nineties whereby the rigid resonator has been shed off and the mirrors are now freely adjustable to attain optimal alignment. The argon ion lasers of today have undergone considerable change with the shedding of the bulky resonator as indicated above and the incorporation of the sealed mirror technology. The modern lasers are now designed with mirrors that are bonded in a permanent manner. This is done in a vacuum tight approach.

The specially constructed mounts are then placed directly at the ends of the plasma. When the mirrors have been mounted in such a manner, they abolish the need for the Brewster windows. The highly essential optically resonant cavity is then attained by minimizing the bulkiness, size and weight of the resonant tube. These modern lasers are not only less bulky, and weightless, they also come up with the advantage of having lengthier alignment stability that lasts for a considerable longer time. This design is also less susceptible to undergoing misalignment during transportation.

The Power Supply

Another essential component of the argon ion laser tube is the power supply. This laser is electrically powered and hence it is rendered obsolete with the malfunctioning or lack of the power supply. The laser is made to operate through the supply of energy to facilitate the plasma discharge within the bore. The power supply is specifically designed so that it supplies an initial trigger pulse of between six kilovolts to eight kilovolts for the discharge of the plasma discharge. However, one this has been achieved, the maintenance of the discharge requires a significantly smaller amount of voltage (Carlson, 56).

Small and medium sized lasers are constructed with power supplies that deliver close to 12 amps of DC current. This is in conjunction with 140VDC. Larger argon ion lasers deliver currents in the levels of 45 amps of DC current at up to 600VDC. Earlier models of the argon ion lasers contained very large, bulky and inefficient designs. Significant developments in technology have realized considerable changes in the argon ion laser through the enhancement of the electrical and electronic components. This has led to underlying enhancements of the power supplies for the lasers (Craig, Norman, and Ira, 475).

The modern argon ion lasers are designed in such a manner that they are now smaller, lighter, efficient, reliable, highly accurate and much lighter. The modern state of the art lasers come with high efficiencies with some operating at up to ninety-three percent efficiency. These designs come with power factor corrections and are able to operate under varying AC line voltage. This is usually in the rage of 95VAC to 265VAC. The basic design of the argon ion laser as in indicated below.

Uses and Specifications

The argon ion lasers are highly preferred to other lasers. This is mainly because of their high power potential and established emission lines. The device is used for lithographic purposes, for pumping other lasers including the dye lasers and in the field of microscopy. These lasers come with characteristic brilliant colors compounded by multiple line operation capability. This makes them preferred in the entertainment industry. These designs are also applied in most f the light scattering studies. This includes studies like Raman and Brillouin, in addition to many of the international research laboratories. These lasers are also utilized in forensic laboratories and during ophthalmic surgeries (Hitz, 102).

The argon ion lasers are designed with a characteristic gain system in comparison to their helium neon laser counterparts. These designs are able to produce beams that vary in array in continuous wave output. The lasers are further predictable and reliable and thus preferred in for use in most of the research laboratories.

The argon ion lasers do not lack their own shortcomings. The high temperatures necessary for the maintenance of the plasma state require that the vacuum tune be designed with expressly designed reinforced resources. The lasers are also comparatively inefficient irrespective of the high power output. This is mainly because of the excess energy that is produced in terms of heat. These devices have operating efficiencies to the tune of 0.1 %. This therefore requires the need of highly effective cooling systems to be installed to prevent damage to the instrument. The components also require the application of a relatively high direct current to the tune of tens of amperes operating and hundreds of volts. This also creates the need of large external power sources (Dunn, & Ross 250).

The argon ion laser also comes with a gain profile that is primarily Doppler broadened. This is mainly because of the inherent high temperatures and pressures resulting from its operation. The device has a gain profile linewidth of significant GHz. This results in the possibility of having different cavity modes. On the other hand, the incorporation of an etalon may realize the operation of single mode with a laser frequency linewidth that lies in the range of tens of MHz. The realization of this single mode selection is advantageous for the application during the need of extreme spectral purity (Kovač, Janez, and Anton, 45).

Emission lines and Single-Line Operation

The ability of the pumping mechanism to excite the argon ions to varying possible excited states, there is the ability for the creation of random multiple population conversions. These come with many transitions that have common lower levels. This characteristic of having a common lower level tends to refrain from preventing the population inversion. This is primarily because the decay rate of the lower level is often high. With this regard, the argon ion laser has the ability to produce gain and laser action at varying wavelengths simultaneously and in proportion to the energy difference that lies between the higher and lower levels. The occurring laser lines vary form the ultra violet to the near infrared. However, the mostly preferred wavelengths that are used in practice are the green 514 nm and blue 488 nm. Although the device is able to produce all the transitions simultaneously, most of the output occurs at these two wavelengths. In reality, the argon laser ion operates in multiple line operation with all the laser lines being emitted at the same time. A prism can therefore be placed in the cavity to enable the gain for one of the transition wavelength. This is referred to as single line operation (Paschotta, 58).

Works Cited

“Argon-ion Laser.” A-to-z Guide to Thermodynamics, Heat and Mass Transfer, and Fluids Engineering. (2006). Print.

Bennett, W.R J. “Collision Processes in the Argon Ion Laser.” Pp 61-85 of Physics of Electronic and Atomic Collisions. Branscomb, Lewis M. (ed.). Boulder, Colo., Univ. of Colorado, 1968. (1968). Print.

Carlson, Randolph L. “A Parametric Study of the Pulsed Argon Ion Laser.” (1968). Print.

Chen, C C. A Quantitative Theory of Noble Gas Ion Laser Discharge: Argon Ion Laser. Santa Monica, Calif: Rand, 1975. Print.

Craig, Norman C, and Ira W. Levin. “Calibrating Raman Spectrometers with Plasma Lines from the Argon Ion Laser.” Applied Spectroscopy. 33.5 (1979): 475-476. Print.

Dunn, M.H, and J.N Ross. “The Argon Ion Laser.” Progress in Quantum Electronics. 4 (1976): 233-269. Print.

Hitz, Breck. “Solid-state Lasers Are Gunning for Argon-Ion’s Place the Venerable Air-Cooled Argon-Ion Laser Appears to Be the Next Target on Solid-State Technology’s Hit List.” Photonics Spectra. 37.9 (2003): 54. Print.

Kovač, Janez, and Anton Zalar. “Surface Composition Changes in Gan Induced by Argon Ion Bombardment.” Book of Abstracts. (2001). Print.

Paschotta, Rüdiger. Field Guide to Lasers. Bellingham, Wash: SPIE Press, 2008. Print.