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78-461: Q-switching was first proposed in 1958 by Gordon Gould , and independently discovered and demonstrated in 1961 or 1962 by R.W. Hellwarth and F.J. McClung at Hughes Research Laboratories using electrically switched Kerr cell shutters in a ruby laser . Optical nonlinearities such as Q-switching were fully explained by Nicolaas Bloembergen , who won the Nobel prize in 1981 for this work. Q-switching

156-433: A settlement deal. Other laser manufacturers and users quickly agreed to settle their cases and take out licenses from Patlex on Patlex's terms. The thirty year patent war that it took for Gould to win the rights to his inventions became known as one of the most important patent battles in history. In the end, Gould was issued forty-eight patents, with the optical pumping, collisional pumping, and applications patents being

234-769: A Nd:YAG laser) with a resonator length of e.g. 10 cm can produce light pulses of several tens of nanoseconds duration. Even when the average power is well below 1 W, the peak power can be many kilowatts. Large-scale laser systems can produce Q-switched pulses with energies of many joules and peak powers in the gigawatt region. On the other hand, passively Q-switched microchip lasers (with very short resonators) have generated pulses with durations far below one nanosecond and pulse repetition rates from hundreds of hertz to several megahertz (MHz) Q-switched lasers are often used in applications which demand high laser intensities in nanosecond pulses, such as metal cutting or pulsed holography . Nonlinear optics often takes advantage of

312-408: A better transverse mode . A frosted flow tube or diffuse reflector, while leading to lowered transfer efficiency, helps increase this effect, improving the gain . Laser host materials are chosen to have a low absorption; only the dopant absorbs. Therefore, any light at frequencies not absorbed by the doping will go back into the lamp and reheat the plasma, shortening lamp life. Flashlamps were

390-399: A circular path. This helps eliminate the standing wave generated by most Fabry–Pérot resonators, leading to a better use of the gain medium's energy. Microwaves or radiofrequency EM radiation can be used to excite gas lasers. A solar-pumped laser uses solar radiation as a pump source. Electric glow discharge is common in gas lasers . For example, in the helium–neon laser

468-451: A gas discharge (as in helium–neon lasers ), optical amplifiers , Q-switching , optical heterodyne detection , the use of Brewster's angle windows for polarization control, and applications including manufacturing, triggering chemical reactions , measuring distance, communications , and lidar . Schawlow and Townes had already applied for a patent on the laser, in July 1958. Their patent

546-546: A good quantity of molecules remain in the upper state, a population inversion is created, which often extends for quite a distance downstream. Continuous wave outputs as high as 100 kilowatts have been obtained from dynamic carbon dioxide lasers. Similar methods of supersonic expansion are used to adiabatically cool carbon monoxide lasers, which are then pumped either through chemical reaction, electrical, or radio frequency pumping. The adiabatic cooling replaces bulky and costly cryogenic cooling with liquid nitrogen, increasing

624-593: A laser to be constructed, given that Gould's team at TRG was unable to do so. Gould was able to obtain patents on the laser in several other countries, however, and he continued fighting for U.S. patents on specific laser technologies for many years afterward. In 1967, Gould left TRG and joined the Polytechnic Institute of Brooklyn, now New York University Tandon School of Engineering , as a professor. While there, he proposed many new laser applications, and arranged government funding for laser research at

702-641: A member of the Sigma Chi fraternity, and a master's degree at Yale University , specializing in optics and spectroscopy . Between March 1944 and January 1945 he worked on the Manhattan Project but was dismissed due to his activities as a member of the Communist Political Association . In 1949 Gould went to Columbia University to work on a doctorate in optical and microwave spectroscopy . His doctoral supervisor

780-419: A narrow, coherent , intense beam. Since the sides of the cavity did not need to be reflective, the gain medium could easily be optically pumped to achieve the necessary population inversion . Gould also considered pumping of the medium by atomic-level collisions, and anticipated many of the potential uses of such a device. Gould recorded his analysis and suggested applications in a laboratory notebook under

858-420: A near-perfect beam "switch" to couple the beam out of the cavity. The modulator that dumps the beam may be the same modulator that Q-switches the cavity, or a second (possibly identical) modulator. A dumped cavity is more complicated to align than simple Q-switching, and may need a control loop to choose the best time at which to dump the beam from the cavity. In regenerative amplification, an optical amplifier

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936-420: A normal flashlamp, which provides a shorter flash discharge. Rarely, a "coaxial" design is used for dye lasers, which consists of a normal flashlamp surrounded by an annular shaped dye cell. This provides better transfer efficiency, eliminating the need for a reflector, but diffraction losses cause a lower gain. The output spectrum of a flashlamp is primarily a product of its current density . After determining

1014-413: A patent on his innovation, and agreed to act as a witness. By 1957, many scientists including Townes were looking for a way to achieve maser-like amplification of visible light . In November of that year, Gould realized that one could make an appropriate optical resonator by using two mirrors in the form of a Fabry–Pérot interferometer . Unlike previously considered designs, this approach would produce

1092-546: A private research company, TRG (Technical Research Group). He convinced his new employer to support his research, and they obtained funding for the project from the Advanced Research Projects Agency , ironically with support from Charles Townes. Unfortunately for Gould, the government declared the project classified , which meant that a security clearance was required to work on it. Because of his former participation in communist activities, Gould

1170-446: A rod and a flashlamp in a cavity made of a diffuse reflecting material , such as spectralon or powdered barium sulfate . These cavities are often circular or oblong, as focusing the light is not a primary objective. This doesn't couple the light as well into the lasing medium, since the light makes many reflections before reaching the rod, but often requires less maintenance than metalized reflectors. The increased number of reflections

1248-429: A rod located at one focus of a mirrored cavity, consisting of an elliptical cross-section perpendicular to the rod's axis. The flashlamp is a tube located at the other focus of the ellipse. Often the mirror's coating is chosen to reflect wavelengths that are shorter than the lasing output while absorbing or transmitting wavelengths that are the same or longer, to minimize thermal lensing . In other cases an absorber for

1326-474: A small flash is initiated just milliseconds before the main flash, to preheat the gas for a faster rise time . Dye lasers sometimes use "axial pumping," which consists of a hollow, annular shaped flashlamp, with the outer envelope mirrored to reflect suitable light back to the center. The dye cell is placed in the middle, providing a more even distribution of pumping light, and more efficient transfer of energy. The hollow flashlamp also has lower inductance than

1404-440: A suitable type can be used to pump another laser. The pump laser's narrow spectrum allows it to be closely matched to the absorption lines of the lasing media, giving it much more efficient energy transfer than the broadband emission of flashlamps. Diode lasers pump solid state lasers and liquid dye lasers . A ring laser design is often used, especially in dye lasers. The ring laser uses three or more mirrors to reflect light in

1482-448: Is achieved by putting some type of variable attenuator inside the laser's optical resonator . When the attenuator is functioning, light which leaves the gain medium does not return, and lasing cannot begin. This attenuation inside the cavity corresponds to a decrease in the Q factor or quality factor of the optical resonator . A high Q factor corresponds to low resonator losses per roundtrip, and vice versa. The variable attenuator

1560-406: Is an externally controlled variable attenuator. This may be a mechanical device such as a shutter, chopper wheel, or spinning mirror/prism placed inside the cavity, or (more commonly) it may be some form of modulator such as an acousto–optic device, a magneto-optic effect device or an electro-optic device – a Pockels cell or Kerr cell . The reduction of losses (increase of Q)

1638-490: Is because the spectral lines in the near-IR range better match the absorption lines of neodymium, giving krypton better transfer efficiency even though its overall power output is lower. This is especially effective with Nd:YAG, which has a narrow absorption profile. Pumped with krypton, these lasers can achieve up to twice the output power obtainable from xenon. Spectral line emission is usually chosen when pumping Nd:YAG with krypton, but since all of xenon's spectral lines miss

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1716-460: Is commonly called a "Q-switch", when used for this purpose. Initially the laser medium is pumped while the Q-switch is set to prevent feedback of light into the gain medium (producing an optical resonator with low Q). This produces a population inversion , but laser operation cannot yet occur since there is no feedback from the resonator. Since the rate of stimulated emission is dependent on

1794-406: Is compensated for by the diffuse medium's higher reflectivity: 99% compared to 97% for a gold mirror. This approach is more compatible with unpolished rods or multiple lamps. Parasitic modes occur when reflections are generated in directions other than along the length of the rod, which can use up energy that would otherwise be available to the beam. This can be a particular problem if the barrel of

1872-456: Is in the cooling. Arc lamps need to be cooled with water, ensuring that the water washes beyond the glass, and across the electrode connectors as well. This requires the use of deionized water with a resistivity of at least 200 kilohms, to keep from shorting out the circuit and corroding the electrodes through electrolysis . Water is typically channeled through a flow tube at a rate of 4 to 10 liters per minute. Arc lamps come in nearly all of

1950-400: Is often in the form of a crystal rod containing a metallic impurity or a glass tube containing a liquid dye, in a condition known as "side-pumping." To use the lamp's energy most efficiently, the lamps and lasing medium are contained in a reflective cavity that will redirect most of the lamp's energy into the rod or dye cell. In the most common configuration, the gain medium is in the form of

2028-407: Is placed inside a Q-switched cavity. Pulses of light from another laser (the "master oscillator") are injected into the cavity by lowering the Q to allow the pulse to enter and then increasing the Q to confine the pulse to the cavity where it can be amplified by repeated passes through the gain medium. The pulse is then allowed to leave the cavity via another Q switch. A typical Q-switched laser (e.g.

2106-410: Is re-emitted at suitable wavelengths. The flow tube also serves to protect the rod in the event of a violent lamp failure. Smaller ellipses create fewer reflections, (a condition called "close-coupling"), giving higher intensity in the center of the rod. For a single flashlamp, if the lamp and rod are equal diameter, an ellipse that is twice as wide as it is high is usually the most efficient at imaging

2184-432: 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 for a period of time 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

2262-468: Is triggered by an external event, typically an electrical signal. The pulse repetition rate can therefore be externally controlled. Modulators generally allow a faster transition from low to high Q, and provide better control. An additional advantage of modulators is that the rejected light may be coupled out of the cavity and can be used for something else. Alternatively, when the modulator is in its low-Q state, an externally generated beam can be coupled into

2340-438: The noble gas types, including xenon , krypton , argon , neon , and helium , which all emit spectral lines that are very specific to the gas. The output spectrum of an arc lamp is mostly dependent on the gas type, being narrow band spectral lines very similar to a flashlamp operated at low current densities. The output is highest in the near infrared, and are usually used to pump infrared lasers such as Nd:YAG. A laser of

2418-427: The supersonic flow of gases, such as carbon dioxide , to excite the molecules past threshold. The gas is pressurized and then heated to as high as 1400 kelvins . The gas is then allowed to expand rapidly through specially shaped nozzles to a very low pressure. This expansion occurs at supersonic velocities, sometimes as high as mach 4 . The hot gas has many molecules in the upper excited states, while many more are in

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2496-419: The "explosion energy" for the pulse duration, (the amount of energy that will destroy it in one to ten flashes), and choosing a safe energy level for operation, the balance of voltage and capacitance can be adjusted to center the output anywhere from the near infrared to the far ultraviolet. Low current densities result from the use of very high voltage and low current. This produces broadened spectral lines with

2574-767: The Office seemed determined to prevent Gould from obtaining any more patents, and to rescind the two that had been granted. Things finally began to change in 1985. After years of legal process, the Federal Court in Washington, D.C. ordered the Patent Office to issue Gould's patent on collisionally pumped laser amplifiers. The Patent Office appealed, but was ultimately forced to issue U.S. patent 4,704,583 , and to abandon its attempts to rescind Gould's previously issued patents. The Brewster's angle window patent

2652-488: The absorption bands of Nd:YAG, when pumping with xenon the continuum emission is used. Arc lamps are used for pumping rods that can support continuous operation, and can be made any size and power. Typical arc lamps operate at a voltage high enough to maintain the certain current level for which the lamp was designed to operate. This is often in the range of 10 to 50 amps. Due to their very high pressures, arc lamps require specially designed circuitry for start up, or "striking"

2730-480: The amount of light entering the medium, the amount of energy stored in the gain medium increases as the medium is pumped. Due to losses from spontaneous emission and other processes, after a certain time the stored energy will reach some maximum level; the medium is said to be gain saturated . At this point, the Q-switch device is quickly changed from low to high Q, allowing feedback and the process of optical amplification by stimulated emission to begin. Because of

2808-474: The arc length of the lamp, but across the electrode portion of the glass as well. Water-cooled flashlamps are usually manufactured with the glass shrunken around the electrode to allow direct cooling of the tungsten . If the electrode is allowed to heat much more than the glass thermal expansion can crack the seal. Lamp lifetime depends primarily on the energy regime used for the particular lamp. Low energies give rise to sputter , which can remove material from

2886-402: The arc. Striking usually occurs in three phases. In the triggering phase, an extremely high voltage pulse from the "series triggering" transformer creates a spark streamer between the electrodes, but the impedance is too high for the main voltage to take over. A "boost voltage" phase is then initiated, where a voltage that is higher than the voltage drop between the electrodes is driven through

2964-404: The barrel of the rod is rough ground (frosted), or grooved, internal reflections can be dispersed. Pumping with a single lamp tends to focus most of the energy on one side, worsening the beam profile. It is common for rods to have a frosted barrel, to diffuse the light, providing a more even distribution of light throughout the rod. This allows more energy absorption throughout the gain medium for

3042-420: The battle for the U.S. patent on the laser itself, primarily on the grounds that his notebook did not explicitly say that the sidewalls of the laser medium were to be transparent, even though he planned to optically pump the gain medium through them, and considered loss of light through the sidewalls by diffraction . Questions were also raised about whether Gould's notebook provided sufficient information to allow

3120-708: The body's lymphatic system . Full removal can take between six and twenty treatments depending on the amount and colour of ink, spaced at least a month apart, using different wavelengths for different coloured inks. Nd:YAG lasers are currently the most favoured lasers due to their high peak powers, high repetition rates and relatively low costs. In 2013 a picosecond laser was introduced based on clinical research which appears to show better clearance with difficult-to-remove colours such as green and light blue. Q-switched lasers can also be used to remove dark spots and fix other skin pigmentation issues. Gordon Gould Richard Gordon Gould (July 17, 1920 – September 16, 2005)

3198-475: The business. Gould was able to buy back his patent rights for a thousand dollars, plus a small fraction of any future profits. In 1973, Gould left the Polytechnic Institute of Brooklyn to help found Optelecom , a company in Gaithersburg, Maryland that makes fiberoptic communications equipment. He later left his successful company in 1985. Shortly after starting Optelecom, Gould and his lawyers changed

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3276-475: The carbon monoxide laser's efficiency. Lasers of this type have been able to produce outputs as high as a gigawatt, with efficiencies as high as 60%. Charge-displacement self-channeling can give rise to high energy concentration along a column created and maintained by the ponderomotive expulsion of electrons. The channel will also columnate shorter wavelength secondary radiation and ultimately extremely short wavelength lasing. Chemical reaction

3354-512: The cathode and redeposit it on the glass, creating a darkened, mirrored appearance. The life expectancy at low energies can be quite unpredictable. High energies cause wall ablation , which not only gives the glass a cloudy appearance, but also weakens it structurally and releases oxygen , affecting pressure, but at these energy levels the life expectancy can be calculated with a fair amount of accuracy. Pulse duration can also affect lifetime. Very long pulses can strip large amounts of material from

3432-432: The cathode, depositing it on the walls. With very short pulse durations, care must be taken to ensure that the arc is centered in the lamp, far away from the glass, preventing serious wall ablation. External triggering is not usually recommended for short pulses. Simmer voltage triggering is usually used for extremely fast discharges, as are used in dye lasers, and often combine this with a "pre-pulse technique", where as

3510-488: The cavity end mirrors are 100% reflective, so that no output beam is produced when the Q is high. Instead, the Q-switch is used to "dump" the beam out of the cavity after a time delay. The cavity Q goes from low to high to start the laser buildup, and then goes from high to low to "dump" the beam from the cavity all at once. This produces a shorter output pulse than regular Q-switching. Electro-optic modulators are normally used for this, since they can easily be made to function as

3588-401: The cavity through the modulator. This can be used to "seed" the cavity with a beam that has desired characteristics (such as transverse mode or wavelength). When the Q is raised, lasing builds up from the initial seed, producing a Q-switched pulse that has characteristics inherited from the seed. In this case, the Q-switch is a saturable absorber , a material whose transmission increases when

3666-407: The company Patlex, to hold the patent rights and handle licensing and enforcement. The legal battles continued, as the laser industry sought to not only prevent the Patent Office from issuing Gould's remaining patents, but also to have the already-issued ones revoked. Gould and his company were forced to fight both in court, and in Patent Office review proceedings. According to Gould and his lawyers,

3744-615: The earliest energy source for lasers. They are used for high pulsed energies in both solid-state and dye lasers. They produce a broad spectrum of light, causing most of the energy to be wasted as heat in the gain medium. Flashlamps also tend to have a short lifetime. The first laser consisted of a helical flashlamp surrounding a ruby rod. Quartz flashlamps are the most common type used in lasers, and, at low energies or high repetition rates, can operate at temperatures as high as 900 °C. Higher average powers or repetition rates require water cooling. The water usually has to wash across not only

3822-458: The electrons from the discharge collide with the helium atoms, exciting them. The excited helium atoms then collide with neon atoms, transferring energy. This allows an inverse population of neon atoms to build up. Electric current is typically used to pump laser diodes and semiconductor crystal lasers (for example germanium ) Electron beams pump free electron lasers and some excimer lasers . Gas dynamic lasers are constructed using

3900-516: The ends of the pump cavity to reduce loss. Variations on this design use more complex mirrors composed of overlapping elliptical shapes, to allow multiple flashlamps to pump a single rod. This allows greater power, but are less efficient because not all of the light is correctly imaged into the rod, leading to increased thermal losses. These losses can be minimized by using a close-coupled cavity. This approach may allow more symmetric pumping, increasing beam quality, however. Another configuration uses

3978-507: The focus of their patent battle. Having lost many court cases on the laser itself, and running out of appeal options, they realized that many of the difficulties could be avoided by focusing instead on the optical amplifier , an essential component of any laser. The new strategy worked, and in 1977 Gould was awarded U.S. patent 4,053,845 , covering optically pumped laser amplifiers. The laser industry, by then grown to annual sales of around $ 400 million, rebelled at paying royalties to license

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4056-404: The heading "Some rough calculations on the feasibility of a LASER: Light Amplification by Stimulated Emission of Radiation"—the first recorded use of this acronym. Gould's notebook was the first written prescription for making a viable laser and, realizing what he had in hand, he took it to a neighborhood store to have his work notarized. Arthur Schawlow and Charles Townes independently discovered

4134-569: The high peak powers of these lasers, offering applications such as 3D optical data storage and 3D microfabrication . However, Q-switched lasers can also be used for measurement purposes, such as for distance measurements ( range finding ) by measuring the time it takes for the pulse to get to some target and the reflected light to get back to the sender. It can be also used in chemical dynamic study, e.g. temperature jump relaxation study. Q-switched lasers are also used to remove tattoos by shattering ink pigments into particles that are cleared by

4212-547: The importance of the Fabry–Pérot cavity—about three months later—and called the resulting proposed device an "optical maser". Gould's name for the device was first introduced to the public in a conference presentation in 1959, and was adopted despite resistance from Schawlow and his colleagues. Eager to achieve a patent on his invention, and believing incorrectly that he needed to build a working laser to do this, Gould left Columbia without completing his doctoral degree and joined

4290-412: The institute. Gould's first laser patent was awarded in 1968, covering an obscure application—generating X-rays using a laser. The technology was of little value, but the patent contained all the disclosures of his original 1959 application, which had previously been secret. This allowed the patent office greater leeway to reject patent applications that conflicted with Gould's pending patents. Meanwhile,

4368-434: The intensity of light exceeds some threshold. The material may be an ion-doped crystal like Cr:YAG , which is used for Q-switching of Nd:YAG lasers , a bleachable dye, or a passive semiconductor device. Initially, the loss of the absorber is high, but still low enough to permit some lasing once a large amount of energy is stored in the gain medium. As the laser power increases, it saturates the absorber, i.e., rapidly reduces

4446-433: The lamp, until the gas is heated to a plasma state. When impedance becomes low enough, the "current control" phase takes over, where the main voltage begins to drive the current to a stable level. Arc lamp pumping takes place in a cavity similar to a flashlamp pumped laser, with a rod and one or more lamps in a reflector cavity. The exact shape of the cavity is often dependent on how many lamps are used. The main difference

4524-411: The large amount of energy already stored in the gain medium, the intensity of light in the laser resonator builds up very quickly; this also causes the energy stored in the medium to be depleted almost as quickly. The net result is a short pulse of light output from the laser, known as a giant pulse , which may have a very high peak intensity. There are two main types of Q-switching: Here, the Q-switch

4602-593: The laser and related technologies. He also fought with laser manufacturers in court battles to enforce the patents he subsequently did obtain. Born in New York City, Gould was the oldest of three sons. His father was the founding editor of Scholastic Magazine Publications in New York City. He grew up in Scarsdale, a small suburb of New York, and attended Scarsdale High School . He earned a Bachelor of Science degree in physics at Union College , where he became

4680-627: The laser was disputed over decades, Gould was elected to the National Inventors Hall of Fame in 1991. Gould died of natural causes on September 16, 2005. At the time of his death, Gould's role in the actual invention continued to be disputed in scientific circles. Apart from the dispute, Gould had realized his hope to "be around" when the Brewster's angle window patent expired in May 2005. Laser pumping Laser pumping

4758-434: The laser's pump power and the amount of saturable absorber in the cavity. Direct control of the repetition rate can be achieved by using a pulsed pump source as well as passive Q-switching. Jitter can be reduced by not reducing the Q by as much, so that a small amount of light can still circulate in the cavity. This provides a "seed" of light that can aid in the buildup of the next Q-switched pulse. With cavity dumping ,

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4836-576: The light into the rod. The rod and the lamp are relatively long to minimize the effect of losses at the end faces and to provide a sufficient length of gain medium. Longer flashlamps are also more efficient at transferring electrical energy into light, due to higher impedance . However, if the rod is too long in relation to its diameter a condition called "prelasing" can occur, depleting the rod's energy before it can properly build up. Rod ends are often antireflection coated or cut at Brewster's angle to minimize this effect. Flat mirrors are also often used at

4914-423: The longer wavelengths is used. Often, the lamp is surrounded by a cylindrical jacket called a flow tube. This flow tube is usually made of a glass that will absorb unsuitable wavelengths, such as ultraviolet, or provide a path for cooling water which absorbs infrared. Often, the jacket is given a dielectric coating that reflects unsuitable wavelengths of light back into the lamp. This light is absorbed and some of it

4992-414: The lower states. The rapid expansion causes adiabatic cooling , which reduces the temperature to as low as 300 K. This reduction in temperature causes the molecules in the upper and lower states to relax their equilibrium to a value that is more appropriate for the lower temperature. However, the molecules in the lower states relax very quickly, while the upper state molecules take much longer to relax. Since

5070-415: The medium can act as a laser or an optical amplifier . The pump power must be higher than the lasing threshold of the laser. The pump energy is usually provided in the form of light or electric current , but more exotic sources have been used, such as chemical or nuclear reactions . A laser pumped with an arc lamp or a flashlamp is usually pumped through the lateral wall of the lasing medium, which

5148-433: The most important. Between them, these technologies covered most lasers used at the time. For example, the first operating laser, a ruby laser , was optically pumped; the helium–neon laser is pumped by gas discharge . The delay—and the subsequent spread of lasers into many areas of technology—meant that the patents were much more valuable than if Gould had won initially. Even though Gould had signed away eighty percent of

5226-408: The output centered in the near-IR, and is best for pumping infrared lasers such as Nd:YAG and erbium:YAG . Higher current densities broaden the spectral lines to the point where they begin to blend together, and continuum emission is produced. Longer wavelengths reach saturation levels at lower current densities than shorter wavelengths, so as current is increased the output center will shift toward

5304-423: The patent hearings, court cases, and appeals on the most significant patent applications continued, with many other inventors attempting to claim precedence for various laser technologies. The question of just how to assign credit for inventing the laser remains unresolved by historians. By 1970, TRG had been bought by Control Data Corporation , which had little interest in lasers and was disposing of that part of

5382-419: The proceeds in order to finance his court costs, he made several million dollars. "I thought that he legitimately had a right to the notion to making a laser amplifier", said William R. Bennett , who was a member of the team that built the first laser that could fire continuously. "He was able to collect royalties from other people making lasers, including me." Even though his role in the actual invention of

5460-454: The resonator loss, so that the power can increase even faster. Ideally, this brings the absorber into a state with low losses to allow efficient extraction of the stored energy by the laser pulse. After the pulse, the absorber recovers to its high-loss state before the gain recovers, so that the next pulse is delayed until the energy in the gain medium is fully replenished. The pulse repetition rate can only indirectly be controlled, e.g. by varying

5538-467: The rod is polished. Cylindrical laser rods support whispering gallery modes due to total internal reflection between the rod and the cooling water, which reflect continuously around the circumference of the rod. Light pipe modes can reflect down the length of the rod in a zig-zag path. If the rod has an antireflection coating, or is immersed in a fluid that matches its refractive index , it can dramatically reduce these parasitic reflections. Likewise, if

5616-713: The technology they had been using for years, and fought in court to avoid paying. The industry outcry caused the patent office to stall on releasing Gould's other pending patents, leading to more appeals and amendments to the pending patents. Despite this, Gould was issued U.S. patent 4,161,436 in 1979, covering a variety of laser applications including heating and vaporizing materials, welding , drilling, cutting, measuring distance, communication systems, television, laser photocopiers and other photochemical applications, and laser fusion . The industry responded with lawsuits seeking to avoid paying to license this patent as well. Also in 1979, Gould and his financial backers founded

5694-408: The visual spectrum, which is better for pumping visible light lasers, such as ruby . At this point, the gas becomes nearly an ideal " greybody radiator ." Even higher current densities will produce blackbody radiation , centering the output in the ultraviolet. Xenon is used extensively because of its good efficiency, although krypton is often used for pumping neodymium doped laser rods. This

5772-416: Was Nobel laureate Polykarp Kusch , who guided Gould to develop expertise in the then-new technique of optical pumping . In 1956, Gould proposed using optical pumping to excite a maser , and discussed this idea with the maser's inventor Charles Townes , who was also a professor at Columbia and later won the 1964 Nobel prize for his work on the maser and the laser. Townes gave Gould advice on how to obtain

5850-507: Was an American physicist who is sometimes credited with the invention of the laser and the optical amplifier . (Credit for the invention of the laser is disputed, since Charles Townes and Arthur Schawlow were the first to publish the theory and Theodore Maiman was the first to build a working laser). Gould is best known for his thirty-year fight with the United States Patent and Trademark Office to obtain patents for

5928-572: Was granted on March 22, 1960. Gould and TRG launched a legal challenge based on his 1957 notebook as evidence that Gould had invented the laser prior to Schawlow and Townes's patent application. (At the time, the United States used a first to invent system for patents.) While this challenge was being fought in the Patent Office and the courts, further applications were filed on specific laser technologies by Bell Labs , Hughes Research Laboratories , Westinghouse , and others. Gould ultimately lost

6006-427: Was later issued as U.S. patent 4,746,201 . The end of the Patent Office action freed Gould's enforcement lawsuits to proceed. Finally, in 1987, Patlex won its first decisive enforcement victory, against Control Laser corporation, a manufacturer of lasers. Rather than be bankrupted by the damages and the lack of a license to the technology, the board of Control Laser turned ownership of the company over to Patlex in

6084-654: Was unable to obtain a clearance. He continued to work at TRG, but was unable to contribute directly to the project to realize his ideas. Due to technical difficulties and perhaps Gould's inability to participate, TRG was beaten in the race to build the first working laser by Theodore Maiman at Hughes Research Laboratories . During this time, Gould and TRG began applying for patents on the technologies Gould had developed. The first pair of applications, filed together in April 1959, covered lasers based on Fabry–Pérot optical resonators, as well as optical pumping, pumping by collisions in

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