ALKALI-VAPOR LASER WITH TRANSVERSE PUMPING

Alkali-vapor laser and related methods of lasing are described herein. In some embodiments, a diode-pumped gas-vapor laser is provided that can be scaled to high power. For example, in one embodiment, a triply-transverse configuration of a diode-pumped-alkali-laser (DPAL) is disclosed in which alkali-buffer gain medium is flowed through an laser chamber (for example, configured as an optical resonator or amplifier) whose optical axis is nominally transverse to the flow direction, and whose pump array radiation is propagated into the alkali-buffer gain medium in a direction nominally transverse to both the direction of gain medium flow and the direction of the optical axis.

DETAILED DESCRIPTION OF THE INVENTION

While diode-pumped alkali lasers (DPALs) in the end pumped configuration as described earlier with references toFIGS. 1-3are known, there are a number of limitations in scaling the output power of a DPAL utilizing the end-pumped configuration, especially while retaining high beam quality.

First, the relatively small separation of the DPAL pump and output wavelengths (Cs: 43 nm; Rb: 15 nm; K: 4 nm) makes it extremely difficult to fabricate low-loss dichroic resonator end mirrors, through which to transmit pump radiation into the DPAL, and which serves as a relatively high reflectivity laser resonator mirror at the laser output wavelength.

Second, all of the diode pump radiation is concentrated into a relatively small end-area of the optical resonator. Additionally, the in-coupled pump radiation must propagate relatively long distances along the optical resonator axis, possibly using reflective containment cell walls. Taken together then, the end-pump configuration requires the use of a diode pump source with extraordinarily high brightness.

Third, as one increases the diameter of a capillary end-pumped DPAL or the waveguide height in a waveguide end-pumped DPAL to scale the emitted output power, transverse thermal gradient values scale with the characteristic dimension. At some point, the thermal gradients become large enough to cause unacceptable thermal focusing of the output beam. Also, as mentioned above, the end area aspect ratio becomes too large.

Accordingly, several embodiments of the present invention overcome one or more of the limitations of the end-pumped DPAL, enabling the increase of diode-pumped gas-vapor laser (such DPAL) output power by one or more orders of magnitude higher than practically realizable with the end-pump type DPAL, while preserving high beam quality at the same time. For example, in some embodiments, the DPAL output power is scaled to at least 1 kW and up to many tens of kilowatts and beyond while preserving high beam quality.

According to some embodiments, a DPAL architectural configuration is provided that comprises: 1) a laser chamber (e.g., to be configured as an oscillator or amplifier) having a volume therein and with a defined optical axis; 2) an alkali-buffer vapor-gas medium flowing in a direction nominally transverse to the optical axis; and 3) one or more diode pump arrays whose radiation is directed into the flowing vapor-gas medium in a direction that is simultaneously nominally transverse to the optical axis and to the direction of the flowing laser medium.

According to some embodiments, gas-vapor (such as an alkali vapor), diode pumped lasers, and related methods of lasing, are provided including one or more of the following features: 1) the gas-vapor medium flows through a volume of a laser chamber (e.g., forming an optical resonator or an amplifier); 2) the direction of flow of the gas-vapor medium is transverse to an optical axis of the resonator; 3) the cavity is side-pumped by the one or more diode arrays or a laser pump source; 4) the direction of radiation from one or more diode arrays is transverse to the one or both of the direction of gas-vapor flow and the optical axis of the chamber.

An object of some embodiments is to provide a diode pumped gas-vapor (such as an alkali vapor) configuration that produces output powers of at least 1 kilowatt (kW) and up to 5 kW, up to 10 kW, up to 100 kW, up to 1 MW, up to 5 MW with high beam quality. In some embodiments, high beam quality is defined in terms of M2values, where an M2value is a well understood metric in the art for beam quality and is often referred to as a beam quality factor, where an M2value of 1 is ideal. By way of example, see Siegman et al., “Output Beam Propagation and Beam Quality from a Multimode Stable-Cavity Laser”, IEEE Journal of Quantum Electronics, Vol. 29, No. 4, April 1993, which is incorporated herein by reference, for a description of M2values. In some embodiments, high beam quality is defined as having an M2value of less than 5. In other embodiments, the M2value is less than 3 and in some embodiments, the M2value is less than 2.

Another object of some embodiments is to provide a diode pumped gas-vapor (such as a alkali vapor) configuration that greatly reduces the demand brightness of diode pump arrays compared to that demanded in an end-pumped DPAL of comparable output power.

Another object of some embodiments is to provide a diode pumped gas-vapor (such as an alkali vapor) configuration that avoids the need to fabricate optical resonator end mirrors with simultaneously high reflectivity at the output wavelength and high transmission at the pump wavelength.

Other objects and advantages of several embodiments will become apparent to the reader and it is intended that these objects and advantages are within the scope of at least some embodiments of the present invention.

Referring first toFIG. 4, a simplified view is shown of one embodiment of a diode pumped gas-vapor laser in a triply-transverse configuration in which a direction of gas-vapor medium flow104is transverse to a laser resonator axis (generically referred to as an optical axis or laser axis102), both of which are transverse to the direction of diode pump radiation106entering a cavity formed within a chamber110(also referred to as a laser head or cell) through which the gas-vapor medium flows.

The chamber110forming the cavity or volume therein is a solid structure having walls or windows, some of which are at least partially transmissive to the wavelengths of interest. In one form, an optical window at each end of the chamber is transparent to the laser wavelength allowing laser emission to enter and exit the chamber along a laser resonator axis. When used as an oscillator, mirrors (not shown inFIG. 4, one or more of which is partially transmitting) are located outside of the chamber110at each end to form the resonator. Alternatively, in some embodiments, a mirror is formed on a surface of the chamber. In the illustrated embodiment, a diode pump array is located proximate to a side of the chamber110and provides pump radiation in a side-pumping configuration. The gas-vapor medium is flowed through the chamber110, for example, via inlets and outlets (not shown inFIG. 4), such as by using manifolds that may include flow conditioning devices, such as screens or honeycomb structures to evenly distribute the flow of the medium about the length L of the chamber110. By flowing the medium, waste heat deposited in the medium is convected out of the chamber. A pump (not shown inFIG. 4) is used to cause the medium to flow. In some embodiments, the gas-vapor medium is flowed through a heat exchanger (not shown inFIG. 4) after exiting the chamber. It is noted that whileFIG. 4is shown in schematic form, one or ordinary skill in the art understands the physical components needed to affect the illustrated arrangement.

In a variant of this configuration (single-sided pumping), a mirror may be placed facing the pump array, on the opposite side of the optical axis, serving the purpose of reflecting the pump radiation not absorbed on the first pass back through the flowing gain medium for a second pass. An example of such an embodiment is illustrated inFIG. 10. In this variant, the additional mirror also tends to render more uniform the laser gain profile in the plane perpendicular to the optical axis. Such mirror may be formed on an interior surface of the cavity opposite the pump array or may be external to the cavity and on the opposite side of the cavity.

FIG. 5shows another embodiment of the laser ofFIG. 4in which pump light or pump radiation106is directed into the chamber110on opposite sides, again facilitating a more uniform distribution of gain in the laser medium than is achievable in the scheme shown inFIG. 4. For example, diode arrays are placed on opposite sides of the chamber110from one-another. In the illustrated configurations ofFIGS. 4 and 5, the vapor-gas laser medium is flowed through the laser chamber110(e.g., configured as an optical resonator or an amplifier) in a direction nominally transverse to the laser axis102of the chamber110. Waste heat generated in the pump excited gain medium is convected out of the chamber, resulting in an approximated linear thermal gradient in the flow direction whose magnitude scales inversely with the flow velocity. The magnitude of the thermal gradient can therefore be reduced by increasing the flow velocity.

Referring next toFIG. 6, a perspective view is shown of a laser device600in accordance with several embodiments. The laser device600includes a chamber110having end windows602, pump windows604, a flow entrance606, a flow exit608, An entrance coupler610(which may also be referred to as a diffuser), an exit coupler612(which may also be referred to as an infuser), diode arrays614and616(which may be generically referred to as pump sources), conduit sections618,620and622, a heat exchanger624and a pump626, which in operation provides a laser emission628(also referred to as a laser output) along the laser axis102.

In the illustrated implementation, the chamber110takes the form of a solid structure, preferably made of a metallic material and includes the pump windows604that are at least partially transmissive to pump radiation or pump light from one or more pump sources (e.g., the diode arrays614and616). The end windows602of the chamber110are at least partially transmissive to a laser emission resulting from operation of the laser device600. In one form, the end windows602are at opposite ends of the long dimension or length L of the chamber110and are aligned along the laser axis102. The laser chamber110also includes a volume (seeFIGS. 7 and 8, for example) and the flow entrance606and the flow exit608that couple to the entrance coupler610and the exit coupler612. The chamber110also includes the pump windows604on opposite surfaces of the side of the chamber110that are at least partially transmissive to the pump radiation provided by the diode arrays614,616. Thus, the configuration of the chamber110, pump windows604and the diode arrays614is such that a pump source, e.g., the diode arrays614,616will side pump the chamber110. The diode arrays may include bars of semiconductor laser diodes. It is understood that the pump source may alternatively comprise pump sources other that laser diodes, such as a laser pump source, for example, a titanium sapphire laser.

The gas vapor gain medium flow104flows into the volume of the chamber via the entrance coupler610and the flow entrance606, through the volume, and exits the volume via the flow exit608and the exit coupler612. The gain medium flow is coupled via the conduit section618to the heat exchanger624to remove heat110. The medium flow then flows via the conduit section620to the pump626, which then pumps the medium flow back to the entrance coupler610via the conduit section622. Thus, during operation, the gas-vapor medium is flowed through the chamber110, heat is removed and then it is circulated back to the chamber110. It is noted that in several embodiments, the entrance coupler610functions to transition the flowing gain medium from the cross sectional area, dimension and/or shape of the conduit section622to the cross sectional area, dimension and/or shape of the flow entrance606of the chamber110. In some embodiments, the entrance coupler slows and spreads the flow to that desired through the volume of the chamber110. In some embodiments, the entrance coupler610functions to or includes features to condition the flow of the gas-vapor medium to distribute the gas-vapor medium substantially uniformly along the length L of the chamber as it flows therethrough. Likewise, the exit coupler612functions to transition the flowing gain medium from the cross sectional area, dimension and/or shape of the flow exit608of the chamber110to the cross sectional area, dimension and/or shape of the conduit section618. In some embodiments, the exit coupler slows and spreads the flow to that desired through the volume of the chamber110. While the gas-medium vapor is flowed through the chamber110, the diode arrays604and616provide optical pump radiation or pump light into the volume through coupling optics (not shown inFIG. 6, seeFIG. 8) and the pump windows604.

Referring next toFIG. 7, a top cutaway view is shown of one embodiment of the laser device ofFIG. 6additionally illustrating a volume706within the chamber110and mirrors702and704outside of the laser windows602. When implemented as a resonator or oscillator, the laser device600includes the mirrors702and704. In one form, each of mirrors702and704are slightly curved, the concave surface thereof facing the respective end window602. Mirror704is designed to reflect substantially at least the entire wavelength of interest back into the volume706. The mirror702is configured to partially reflect at least the entire wavelength of interest back into the volume706via the respective end window602, and partially transmit at least the entire wavelength of interest therethrough for output to other components of a laser system. It is understood that the mirrors702and704may be implemented with the laser device600as illustrated inFIG. 6(but have been omitted for clarity). A laser device600does not require the mirrors702and704. When configured in a laser system without the mirrors, the laser device is in an amplifier configuration (seeFIG. 13, for example). The physical components of the laser device600may be held in fixed relationship with each other using one or more frame or support structures and other mechanically coupling devices.

Referring next toFIG. 8, a side cutaway view of one embodiment of the laser chamber110is shown and which further illustrates pump coupling optics802. Diode array604is positioned above the top pump window604and the diode array616is positioned below the bottom pump window604. The pump light or pump radiation from the diode arrays614and616is focused toward and through the pump windows604by the pump coupling optics802. The pump coupling optics802may include one or more optical elements. The end windows602, the mirrors702and704, and the laser emission628are also illustrated in the view ofFIG. 8.

In the illustrated embodiments ofFIGS. 4-8, the pump light or radiation106from the diode pump arrays (from either one array as shown inFIG. 4, or two diode arrays as show inFIGS. 5-8) is directed generally into the flowing gas-vapor gain medium in a direction nominally transverse to the flow direction104and nominally transverse to the optical axis102of the chamber. This side-pumping orientation of the pump flux (es) to the optical axis102means that the pump radiation does not have to pass through an end mirror (such as mirrors702,704) of the laser device. Thus, the end mirror reflection and transmission characteristics at the laser output wavelength can be set without regard to transmission and loss at the pump wavelength. This configuration also greatly relieves the demand brightness on the diode pump array (relative to a known end-pumped type DPAL), since the pump radiation may freely propagate through the gas-vapor gain medium without the need for reflective containment cell walls. When used as an amplifier, seeFIG. 13, for example, it is understood that the laser chamber containing the gain medium is part of a train of optical elements including mirrors, lenses, gain mediums (one of which is a laser chamber used to amplify a laser emission directed therethrough), etc.

As described above, in accordance with many embodiments, the gain medium is a flowing gas-vapor mixture that is flowed through the laser chamber110. In preferred embodiments, the gas-vapor medium comprises a mixture of at least one buffer gas and an alkali atomic vapor. In some embodiments, the alkali atomic vapor is selected from among, but not limited to, cesium (Cs), rubidium (Rb), potassium (K), sodium (Na), and lithium (Li). Furthermore, by way of example, in some embodiments, the at least one buffer gas comprises one or more the rare gases: xenon, argon, krypton, neon, helium and their isotopes; hydrogen and deuterium; and the small hydrocarbon molecular gases: propane, ethane, and methane and their deuterated analogues and all other isotopes. In these embodiments, the chamber provides an optical cavity resonant at a wavelength substantially matching the wavelength λ1of the D1transition of an alkali vapor. Additionally, the alkali atomic vapor has a second D2transition at wavelength λ2, where the at least one buffer gas has the dual purpose of collisionally broadening the D2transition and collisionally transferring excitation energy from the upper level of the D2transition to the upper level of the D1transition at a rate larger than the radiative decay rate of either of these levels.FIG. 9illustrates the basic energy level scheme of the DPAL class of lasers. In many embodiments, only the three lowest lying electronic levels of the alkali atom are utilized, the2S1/2ground electronic level and the first two2P electronic levels,2P1/2and2P3/2to form a pure three level laser. InFIG. 9, n stands for the principal quantum number for the ground configuration of each alkali atom (Cs: n=6; Rb: n=5; K: n=4; Na: n=3; Li: n=2). In the DPAL laser, the alkali atom gain medium is excited (pumped) at a wavelength matching the wavelength of the2S1/2-2P3/2electric-dipole-allowed transition (conventionally called the D2transition). After kinetic relaxation of pump excitation to the excited2P1/2electronic level, laser emission takes place on the2P1/2-2S1/2transition (conventionally called the D1transition). The energy splitting of the2P electronic level, divided by the energy of the2P3/2level, is defined as the quantum energy defect, and is a measure of the minimum waste energy required to produce an excited2P1/2upper laser level excitation in a DPAL device.

It is understood that in other embodiments, other gas-vapor combinations may be used in accordance with the principles of several embodiments of the invention.

It is noted that in embodiments using an alkali-buffer medium, the pump lasers are configured to emit at a wavelength substantially matching the wavelength λ2of the D2transition, and with an emission spectral width of at least 0.01 nm (FWHM, full wave at half maximum) for optically pumping the gain medium at the wavelength λ2of the D2transition, including optical pumping in the Lorentzian spectral wings of the D2transition, generating laser emission output at wavelength λ1.

Characteristic Parameters of a Triply-Transverse DPAL

Table 1 provides a summary of typical device parameters of a triply-transverse diode pumped gas-vapor laser comprising an alkali-buffer medium, also referred to as a DPAL, in accordance with one embodiment of the present invention. By triply transverse, in this embodiment, all three of the directions of gain medium flow, the laser axis and the direction of pump radiation are substantially transverse with respect to one another. In this embodiment, the alkali atomic vapor comprises potassium.

In this embodiment, the demand pump array flux is a few kW/cm2compared with a pump array demand pump flux of many tens of kW/cm2for the conventional “end-pumped” configuration. In comparison, the demand pump array flux in a conventional end-pumped DPAL is typically greater than 20 to 30 kW/cm2. Thus, in accordance with some embodiments in which the diode arrays614,616side pump the chamber, demand pump array flux is less than 5 kW/cm2, while in other embodiments, the demand pump array flux is less than 3 kW/cm2. It is understood that variance of other parameters can result in different values. Moreover the output area of this embodiment (e.g., the area of the end window at one end of the chamber) is 100 cm2compared to a power-scaling-limited end-pumped DPAL of perhaps a few cm2, giving rise to a correspondingly higher output power from the triply-transverse DPAL.

Several embodiments also provide the ability to operate at higher power and/or with a larger aperture area at the laser window602. For example, according to applicants knowledge, non-flowing, end-pumped DPALs have only been demonstrated to operate at about 20 watts with an aperture area of about 1 mm2. In contrast, a flowing gas-vapor DPAL that is side pumped as in some embodiments described herein can operate at a power of greater than 1 kW and up to 5 kW. In other embodiments, the output power is greater than 1 kW and up to 10 kW, up to 100 kW, up to 1 MW, or up to 5 MW depending on various parameters and configuration. This power will eventually be limited by parasitic issues. Similarly, such flowing medium DPALs can be implemented where the aperture area of the laser emission at the laser window602is greater than 0.1 cm2and up to 1 cm2. In alternative embodiments, the aperture area of the laser emission at the laser window602is greater than 0.1 cm2and up to 10 cm2, up to 100 cm2or up to 500 cm2depending on various parameters and configuration.

Accordingly, described herein are diode pumped gas-vapor lasers that are capable of being scaled to high power. Applicants believe that one of ordinary skill in the art would be skeptical that scaling a conventional gas-vapor laser, such as a DPAL, to high power would work. Additionally, applicants believe that due to the absorption lengths involved, one of ordinary skill in the art understands end-pumping to be practical as demonstrated in the art (for example, as described in U.S. Pat. No. 6,643,311, U.S. Pat. No. 7,061,958 and U.S. Pat. No. 7,061,960), but would be skeptical that the side-pumping of a gas-vapor laser, such as a DPAL, would be effective. This follows from the fact that generally it is necessary to have a diode pump absorption length of several centimeters in order to ensure efficient absorption. A conventional cell designed for end pumping does not have a sufficient transverse length to efficiently absorb a transverse (side pumping configuration) diode pump.

Referring next toFIG. 10, one embodiment of the laser device ofFIGS. 6-8is illustrated in which the chamber110is pumped by a pump source on one side of the chamber (i.e., a single side pumping configuration). That is, pump light is provided by diode array616and directed into the volume702via the pump coupling optics802and the pump window604. A mirror1002is located at an opposite side of and external to the chamber110. The mirror1002reflects pump radiation not absorbed on a first pass through the volume702back to the volume702through the flowing gain medium for a second pass. In this embodiment, the mirror1002also tends to render more uniform the laser gain profile in the plane perpendicular to the optical axis102. In an alternative embodiment, the mirror1002may be formed on an interior surface of the chamber opposite the pump array, for example, the mirror be formed on an inner surface of the chamber at the location of the top pump window604.

Referring next toFIG. 11, an embodiment of the laser device ofFIG. 7is illustrated in accordance with several embodiments. In this embodiment, the entrance coupler610includes a flow conditioner1102located at the flow entrance606. In preferred embodiments, the flow conditioner1102is used to ensure substantially uniform flow and distribution of the flowing gas-vapor medium along the length L and height of the chamber, or at least that portion of the length and height of the volume where the laser emission and the pump radiation intersect. The flow conditioner may be any known device to accomplish these functions and may include a screen, honeycomb structure, or vane structure, for example. The flow conditioner1102may also serve to provide a substantially uniform flow rate along the length and height of the chamber110.

It is noted that although many of the illustrated embodiments describe generally rectangular prism or cuboid shaped laser chambers, other geometries may be used without departing from the scope of the invention. For example, rectangular parallelepiped, prism shaped, circular or oval cylinder shaped chambers may be employed in some embodiments.

Referring next toFIG. 12, a side end view is show of one embodiment of the laser device ofFIGS. 6-8illustrating the laser window602and one embodiment of the pump coupling optics1202. In this embodiment, the pump coupling optics each comprise two optical elements. Additionally, it is noted that in some embodiments, when referring to the aperture size achievable in some embodiments, the aperture size refers to the output area of the output laser beam (or laser emission) exiting a surface (e.g., the laser window602) of the chamber. It is generally understood that the area (or envelope) of the output laser beam will fit within the area of the laser window602. In preferred embodiments, the laser window602is designed such that the output area of the laser beam fills most of the area of the laser window602.

Referring next toFIG. 13, an embodiment of the laser device ofFIGS. 6-8configured as a laser amplifier is shown. In this embodiment, mirrors are not provided. Instead, a master oscillator1302provides a laser emission that is directed along the laser axis102through the chamber110. The laser chamber outputs an amplified output1304or laser emission which is directed to other components of the system. For example, in some embodiments, the laser output is directed through multiple stages of similar laser chambers configured as laser amplifiers. It is noted that in some embodiments, the master oscillator may comprise a laser chamber such as described herein including the mirrors702and704and configured as a resonator or oscillator.

The following are some variations to the embodiments described thus far. In some embodiments, the gas-vapor laser chamber is side pumped, but the gas-vapor medium is static and does not flow through the laser chamber. One example of such a configuration is illustrated inFIG. 14. In this embodiment, a laser device1400includes a laser chamber1410having a volume formed therein and statically containing a gas-vapor gain medium as described herein. Similar to flowing embodiments, the laser device1400also includes one or more diode arrays614,616or other pump sources, pump windows, laser windows602, and when configured as a resonator, mirrors702and704. However, in contrast to the flowing embodiments described herein, there are no flow entrance or flow exit. The sides of the laser chamber1410are enclosed. Preferably, heat removal features are included to conduct away heat generated within the chamber1410. For example, as illustrated, convective heat sinks1402and1404are positioned against the exterior surfaces of the laser chamber1410. Alternatively, other conventional heat removing means could be used to remove heat from the chamber1410, such as cold plates, micro channel coolers, etc.

In other embodiments, the gas-vapor laser flows, but in a direction not transverse to the laser axis, e.g., it flows about the laser axis102.FIG. 15illustrates such an embodiment. That is,FIG. 15illustrates a laser device1500including a laser chamber1501having a volume1502formed therein. A flow entrance1506is located at a bottom surface of one end of the chamber1501, while a flow exit1508is located at a top surface of an opposite end of the chamber1501. It is noted that the location of the flow entrance1506and the flow exit1508is for illustrative purposes; thus, one or both of the flow entrance1506and the flow exit1508may be implemented on different surfaces. An entrance coupler1510is coupled to the flow entrance1506and directs the flowing gas-vapor gain medium1504into the chamber1501, which flows substantially along the laser axis102while within the chamber1501. The flowing gas-vapor gain medium1504then exits the chamber via the flow exit1508and the exit coupler1512. Although not illustrated, it is understood that the flow may be circulated through a heat exchanger and pumped back into the entrance coupler1510. As other embodiments described herein, the diode arrays614and616pump optical pump radiation into the chamber1501via the pump coupling optics802and pump windows602. When configured as a resonator, the mirrors702and704are employed. In this embodiment, the end walls of the chamber1501are oriented at an angle in order to provide a smooth flow transition as the flowing gas-vapor gain medium1504is introduced into and exits the volume1502. Accordingly, in one embodiment, the chamber1501has a rectangular parallelepiped shape. One of ordinary skill in the art can easily vary the illustrated structure and arrangement without departing from the scope of several embodiments of the invention.

In other embodiments, the direction of diode side-pumping is not transverse to the direction of flow, e.g., the direction of diode side-pumping is along the same axis as the direction of medium flow. This results in the thermal gradients in the gain medium being parallel to the optical axis, reducing transverse optical aberrations.FIG. 16illustrates such an embodiment. That is,FIG. 16illustrates a laser device1600including a laser chamber1601having a volume1602formed therein. A flow entrance1606is located along a bottom edge of side of a length of the chamber1601, while a flow exit1608is located along a bottom edge of an opposite side of the length of the chamber1601. An entrance coupler1610is coupled to the flow entrance1606and directs the flowing gas-vapor gain medium1604into the chamber1601, which flows substantially transverse to the laser axis102while within the chamber1601. The flowing gas-vapor gain medium1604then exits the chamber via the flow exit1608and the exit coupler1612. Although not illustrated, it is understood that the flow may be circulated through a heat exchanger and pumped back into the entrance coupler1610. In this embodiment, the diode arrays614and616provide pump radiation along the same axis as the flow of the gas-vapor gain medium. That is, the diode arrays614and616are located to direct pump radiation through pump windows604formed in the side walls of the length of the chamber1501. As other embodiments described herein, the diode arrays614and616pump optical pump radiation into the chamber1501via the pump coupling optics1202and the pump windows602. When configured as a resonator, the mirrors (not illustrated in this view) are employed. In this embodiment, the side walls of the chamber1501along its length that contain the pump windows604are oriented at an angle in order to provide a smooth flow transition as the flowing gas-vapor gain medium1604is introduced into and exits the volume1602. Accordingly, in one embodiment, the chamber1501has a prism shape. One of ordinary skill in the art can easily vary the illustrated structure and arrangement without departing from the scope of several embodiments of the invention.

It is noted that in some embodiments, the gas-vapor gain medium is flowed through the volume of the laser chamber at an angle offset from transverse (i.e., perpendicular) to one or both of the laser axis102and the pump direction. That is, one or more of the entrance coupler, the flow entrance, shape of the chamber walls, the flow exit and the exit coupler may be configured to direct the flowing gain medium through the volume at an angle other than substantially transverse to one or both of the laser axis and the pump axis. Such an angle may be any angle between 1 and 89 degrees depending on the implementation. However, in preferred form, the gain medium is flowed through the volume at an angle that is substantially transverse to one or both of the laser axis and the pump axis. For example, in some embodiments, such an angle may be within 5 degrees of being exactly transverse.

In some embodiments, a gas-vapor laser is defined in terms of its output and/or performance characteristics, rather than in terms of its physical configuration. For example, in one embodiment, a gas-vapor (such as an alkali-buffer medium) laser is provided that is capable of high power operation of described herein can operate at a power of greater than 1 kW and up to 5 kW with high beam quality. In other embodiments, the output power is greater than 1 kW and up to 10 kW, up to 100 kW, up to 1 MW, or up to 5 MW with high beam quality depending on various parameters and configuration. This power will eventually be limited by parasitic issues. In some embodiments, high beam quality is defined in terms of M2values (a value of beam quality factor), which are a well understood metric in the art for beam quality, where an M2value of 1 is ideal. For example, in some embodiments, high beam quality is defined as having an M2value of less than 5. In other embodiments, the M2value is less than 3 and in some embodiments, the M2value is less than 2. In another embodiment, a gas-vapor (such as an alkali-buffer medium) laser is provided that is capable of operating such that an output aperture area of the laser emission exiting the chamber at a surface is greater than 0.1 cm2and up to 1 cm2with high beam quality, the surface being the portion or window of the laser chamber through which a laser emission exits the chamber or cell. In alternative embodiments, the aperture area of the laser emission at the laser window602is greater than 0.1 cm2and up to 10 cm2, up to 100 cm2or up to 500 cm2with high beam quality depending on various parameters and configuration. In a further embodiment, a gas-vapor laser is provided that is capable of operating with high beam quality in which the laser diode pump flux is less than 20 kW/cm2, and preferably, less than 10 kW/cm2, less than 5 kW/cm2, or less than 3 kW/cm2. Performance characteristics such as described herein are understood to be the result of the interaction of at least the physical configuration and dimensions of the laser device, optical design of the system (including coupling optics and mirrors), temperature of the system, the gain medium used, flow characteristics, pump source characteristics, etc.

Reference throughout this specification to “one embodiment,” “an embodiment,”, “several embodiments”, or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment or embodiments is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” “in several embodiments”, and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment or embodiments.