All-optical laser-driven light source with electrodeless ignition

Abstract

The electrodeless laser driven light source includes a laser source generating a CW sustain light and a pump laser generating a pump. An optical beam combiner combines the CW sustain light and the pump such that the CW sustain light and the pump propagate collinearly. The Q-switched laser crystal generates pulsed light in response to the pump. The gas-filled valve is configured such that the pulsed light ignites a pulsed plasma in a breakdown region of the gas valve and the sustain light sustains a CW plasma in a CW plasma region of the gas valve, thereby emitting high brightness light from the gas valve, and the gas-filled valve is disposed between an output of the pump laser and a pump input of the Q-switched laser crystal such that the CW plasma absorbs the pump light and extinguishes the pulsed light generated by the Q-switched laser crystal.

Description

[Technical field]

[0001]

[0001] The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described in the present application.

[0002] [preface]

[0002] For example, laser-driven light sources that provide high brightness over a spectral range from the extreme ultraviolet to the visible and infrared regions of the spectrum are available with high reliability and long life. Various examples of such high brightness light sources are manufactured by Energetiq, a Hamamatsu Company located in Wilmington, MA. Summary of the Invention

[0003]

[0003] There is an increasing demand for high brightness light sources for applications in a variety of fields, including biology, chemistry, climate, and physics, including, for example, semiconductor metrology, sensor calibration and testing, creating shaped light, surface metrology, spectroscopy, and other optical measurement applications. Thus, there is a need for advances in high brightness light sources that can improve, for example, the size, cost, complexity, reliability, stability, and efficiency of these important types of broadband light sources.

[0004]

[0004] In the following detailed description, the present teachings according to preferred exemplary embodiments, together with further advantages thereof, will be described in more detail in conjunction with the accompanying drawings. Those skilled in the art will appreciate that the drawings described below are for illustrative purposes only. The drawings are not necessarily to scale, with the emphasis generally being on illustrating the principles of the present teachings. The drawings are not intended to limit the scope of the applicant's teachings. [Brief description of the drawings]

[0005] [Figure 1] 1 is a schematic diagram of an embodiment of a laser-driven light source including electrodeless ignition in accordance with the present teachings. [Figure 2A]1 is an image of a gas-filled bulb of an electrodeless laser-driven light source in accordance with the present teachings, showing emission due to pulsed laser excitation only. [Figure 2B] 13 is an image of a gas-filled bulb of an electrodeless laser-driven light source in accordance with the present teachings, showing emission due to CW laser excitation only. [Diagram 3] 1A-1D illustrate method steps for igniting a plasma in an electrodeless all-optical laser-driven light source in accordance with the present teachings. [Figure 4A] 1A-1C show an embodiment of a Q-switched crystal of the present teachings that includes a gain region and a saturable gain / loss region. [Figure 4B] FIG. 1 illustrates a passively Q-switched laser rod suitable for an electrodeless laser driven light source in accordance with the present teachings. [Diagram 5] 1 is a graph of pump laser pulse energy and pump current threshold to generate a laser pulse sufficient to cause gas breakdown as a function of pulse length for a quasi-CW pump pulse suitable for an electrodeless laser driven light source in accordance with the present teachings. [Figure 6] FIG. 1 illustrates a gas-filled valve system having a focusing lens assembly suitable for use in an electrodeless laser-driven light source in accordance with the present teachings. [Figure 7] FIG. 1 illustrates an electrodeless laser-driven light source in accordance with the present teachings, where the pump light is collinear with the CW laser light, the pulsed laser light is projected onto the gas-filled valve in one plane, and the CW laser light is projected onto the gas-filled valve in a second plane. [Figure 8] FIG. 13 illustrates an embodiment of an electrodeless laser-driven light source in accordance with the present teachings, in which CW laser light and pump light are combined by a fiber coupler, and the pump light, CW laser light, and pulsed light are projected along the same plane onto a gas-filled bulb. [Figure 9] 1 is a detailed diagram of an excitation region of an embodiment of an electrodeless laser driven light source having collinear laser excitation in accordance with the present teachings. [Figure 10] FIG. 1 illustrates an embodiment of a packaged electrodeless laser driven light source with collinear laser excitation in accordance with the present teachings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] Description of Various Embodiments

[0017] The present teachings will be described in more detail below with reference to exemplary embodiments shown in the accompanying drawings. Although the present teachings will be described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be understood by those skilled in the art. Those skilled in the art who have access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, within the scope of the disclosure described herein.

[0007]

[0018] References herein to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present teachings. The appearances of the phrase "one embodiment" in various places in the specification do not necessarily all refer to the same embodiment.

[0008]

[0019] It should be understood that the individual steps of the methods of the present teachings can be performed in any order and / or simultaneously so long as the present teachings remain operable. Further, it should be understood that the apparatus and methods of the present teachings can include any number or all of the described embodiments so long as the present teachings remain operable.

[0009]

[0020] Laser-driven light sources use a CW laser to directly heat a gas plasma to the high temperatures required to generate broadband optical light. High-intensity laser-driven light sources have important advantages over light sources that use high-voltage electrodes to maintain the plasma. Laser-driven sources rely on an optical discharge plasma as opposed to an electric discharge plasma used in, for example, arc lamp devices. In electric discharge lamps, the electrode material can evaporate and change the characteristics of the discharge over the life of the lamp. This shortens the lamp's life. Electrode-based systems also cause thermal, mechanical, and electrical stresses in the light source. Known laser-driven light sources do not rely on electrodes to maintain the plasma, but still use electrodes for plasma ignition.

[0010]

[0021] Known light sources that rely on electrodes can have significant limitations. For example, electrode-based light sources can have limitations on the size of the lamp head and limitations on how the bulb can be mounted. Electrode-based light sources must be designed to avoid parasitic arcs, and the lamp head must be constructed with sufficient volume for the electrodes and ignition circuit. Electrode-based light sources have constraints on the cold fill pressure of the bulb, for example, because the glass-to-metal seal of the electrodes can limit the maximum fill pressure. Also, the bulb size can be larger in electrode-based light sources, which can affect the bulb fill pressure. Electrode-based light sources are also limited in the bulb shapes that can be accommodated, for example, because electrode-based light sources require electrodes to be positioned, fixed, and connected. These design constraints can result in noise in the light source.

[0011]

[0022] Thus, providing a laser-driven light source with electrodeless ignition can lead to high reliability, high performance, reduced cost, and reduced complexity, among other advantages. Ignition of a plasma by optical illumination requires careful design and control of the light source and associated light delivery mechanism used to ignite the plasma. One feature of the present teachings is to provide a laser-driven light source with electrodeless ignition. In such a light source, the plasma is ignited by optical illumination, and not by electrical energy provided by electrodes as in known laser-driven high brightness light sources.

[0012]

[0023] There are many features and advantages of electrodeless laser-driven light sources. Electrodeless light sources can be implemented using smaller bulbs with higher maximum fill pressures than prior art light sources. In particular, for a given laser output modality, higher fill pressures can result in higher brightness. Electrodeless light sources are free of contamination from electrode materials. In addition, there are fewer geometric limitations on the lamp shape. In general, smaller lamp heads can be used for the same characteristics. Also, the lack of high voltage active electrical components to be powered reduces the need for associated power supplies, control electronics, and electrical connections, greatly reducing the number of parts required. However, some embodiments of electrodeless laser-driven light sources can be implemented in existing lamp packages of laser-driven light sources that do not have electrode ignition. This is at least in part because electrodeless devices are generally less complex and smaller than electrode-based laser-driven light sources. For example, electrodeless laser-driven light sources are described in U.S. Patent Application Serial No. 17 / 328,433, entitled "Lase-Driven Light Source with Electrodeless Ignition," which is assigned to the present assignee and is incorporated herein by reference.

[0013]

[0024] One feature of the present teachings is the ability to provide an electrodeless laser-driven light source without the need for electronically controlling a separate ignition light pulse. Rather, the light ignition pulse is generated all-optically within the light source component. Such an approach has several advantages over electrodeless laser-driven light sources in which the pulse source is electrically controlled. For example, smaller bulbs can be used. Also, the number of electronic connections to the light source package can be reduced. Also, no specialized power supplies or laser drive electronics are required to form an electronically driven and controlled pulse source.

[0014]

[0025] FIG. 1 is a schematic diagram of an embodiment of a laser-driven light source 100 including electrodeless ignition according to the present teachings. A pump laser 102 provides optical pump light 104 to a gas cell 106. The pump light passes through the cell and exits as transmitted pump light 108 that is provided to a Q-switched crystal 110. The transmitted pump light 108 exiting the gas cell 106 has sufficient energy for the Q-switched crystal 110 to generate pulsed optical light 112 that returns to the gas cell 106. The energy of the pulsed optical light 112 is provided to a plasma breakdown region of the gas cell 106 to ignite a plasma. In some embodiments, the gas cell 106 is a gas-filled bulb. In some embodiments, the gas cell 106 is a gas chamber that includes at least one window that is transparent to the wavelengths of the pump light 104, the pulsed optical light 112, the CW light 114, and the high-brightness CW plasma light 118.

[0015]

[0026] The CW laser 114 generates a CW laser light 116. The CW laser light 116 is delivered to the gas cell 108 as a sustain light to the plasma breakdown region of the gas cell 108. The area illuminated by the pulsed laser light 112 in the gas cell 106 may be referred to as a pulsed illumination area, and has a well-defined location and shape based on the optical projection elements (not shown) used to direct the pulsed light 112 from the Q-switched crystal 110 and the CW laser light 116 to the cell 106. These projection elements include various focusing and / or directing elements in various different embodiments. The energy of the optical pulsed light 112 delivered to the plasma breakdown region of the cell 106 ignites the plasma. The area illuminated by the CW sustain light may be referred to as a CW sustain illumination area, and has a well-defined location and shape based on the projection elements (not shown) used to direct the optical light from the CW laser 114. These projection elements include various focusing and / or directing elements in various different embodiments. Energy from the CW laser light 114 delivered to the plasma breakdown region sustains the plasma. The plasma breakdown region generates a high intensity CW plasma light 118.

[0016]

[0027] The pulsed optical light 112 has a high peak power required to ignite a plasma in the gas cell 106. However, to generate the sustaining CW plasma light 118, the pulsed optical light 112 must not exceed a certain energy / power threshold, which can occur when an optical pulse is present in the plasma after a predefined delay after the plasma light 118 reaches a predefined threshold. If the pulsed optical light 112 is delivered to the gas cell 106 with too much energy, the plasma can be extinguished. To prevent the pulsed optical light 112 from extinguishing the plasma, a mechanism is needed to extinguish the pulsed optical light 112 after the sustaining CW plasma light is generated. This can be implemented in the all-optical laser-driven light source 100 by taking advantage of the reduction in pump laser light in the gas cell 106 that occurs upon ignition of the plasma. When the plasma is ignited, the pump light that passes through the cell and exits as the transmitted pump light 108 delivered to the Q-switched crystal 110 has a much lower power than the pump light 104 from the pump laser 102. Also, the pump light that passes through the cell 106 and exits as the transmitted pump light 108 when the plasma is ignited has a much lower output than the pump light that passes through the cell 106 and exits as the transmitted pump light 108 when the plasma is not ignited. This extinguished transmitted pump light 108 extinguishes the pulsed laser light 112. By extinguishing the pulsed light 112 before the next pulse extinguishes the CW plasma, the plasma light can be sustained by applying only the CW sustain light 116 from the CW laser 114.

[0017]

[0028] Because the pulsed light 112 is stopped once the CW plasma is ignited, no sensors and / or electronic shutters and / or other electronic shutoffs are needed to actively extinguish the pulsed light 112 after breakdown. If the plasma is extinguished for some unexpected reason, it will automatically start trying to pulse again since the plasma is not there to absorb the pump light. In other words, the plasma is automatically reignited. This results in a simple, compact, and very reliable electrodeless light source. No active monitoring is needed to control the pulsed light.

[0018]

[0029] One feature of the all-optical electrodeless light source embodiments of the present teachings is that the positions of the pulsed illumination region and the CW sustain illumination region can be adjusted to produce the desired performance of the plasma light. The relative positions of the pulsed illumination region and the CW sustain illumination region affect the energy / power threshold that the CW sustained plasma exceeds. In some embodiments, the two regions are separate and do not overlap. In some embodiments, the two regions overlap slightly.

[0019]

[0030] FIG. 2A is an image 200 of a gas-filled bulb of an embodiment of an electrodeless laser-driven light source according to the present teachings, showing light emission due to pulsed laser excitation only. Both images 202, 204 are shown from the side, but are angled to show the three-dimensional arrangement of the pulsed illumination area and the location of the CW laser focus. The extent and location of the pulsed illumination area are visible in these images 202, 204. Note that the location of the pulsed breakdown depends on the pulse energy. With increasing energy, the breakdown location moves toward the pulsed laser. The three-dimensional alignment of the pulsed laser breakdown plasma with respect to the pulsed light and with respect to the CW laser focus allows the method to be performed with lower CW laser power and / or lower pulse energy.

[0020]

[0031] FIG. 2B is an image 250 of the gas-filled valve shown in FIG. 2A showing light emission due to CW laser excitation only. Both images 252, 254 are shown from the side, but at an angle to show the three-dimensional arrangement of the pulsed illumination area and the location of the CW laser focus. The extent and location of the pulsed illumination area are visible in these images 252, 254. The outlines 256, 258 of the pulsed illumination area of ​​images 202, 204 of FIG. 2A are also shown. In this embodiment, the relative positions and shapes of the pulsed illumination area and the CW sustained illumination area are such that the two areas are distinct and do not overlap. The more tightly focused the light, the smaller the pulsed illumination area and the higher the density of the pulsed energy delivered to the plasma by the illumination.

[0021]

[0032] The images in Figures 2A and 2B were collected during an experiment to determine the operating parameters of the pulses that result in plasma ignition. Below, some details of the experimental conditions are described. For example, with a pulse rate of 2 kHz and a pulse duration of 1 ns, stable plasma ignition can be achieved over the energy range of 135 to 225 microjoules in a bulb filled with xenon gas. The pulsed light had a wavelength of 1064 nm. For this particular example of the experimental setup, the threshold energy for the breakdown light to achieve a stable CW plasma was 135 microjoules. Furthermore, at 210 microjoules, the plasma can be ignited and eventually stabilized, but there may be ignition and extinction of the CW plasma prior to stable operation. It is also possible to achieve ignition above 225 microjoules. The relative positions of the pulsed and CW light illuminations are important. Ignition can be improved or "turned off" by adjusting the alignment of the bulb and the CW laser along the optical axis of the pulsed laser. In this experiment, after ignition of the CW plasma, the CW laser power could be reduced to 8-10 watts and still maintain the CW laser power. A reliable transition from pulsed to CW occurred at any value of CW laser power above 15.5 watts. There was no upper limit to the CW laser power. As will be appreciated by those skilled in the art, beam quality affects the energy delivered to the gas for a given laser power.

[0022]

[0033] One feature of the all-optical electrodeless laser-driven light source of the present teachings is that the pulsed laser light can be extinguished by an absorption process in a gas cell, rather than relying on external electronic feedback. FIG. 3 illustrates steps of a method for igniting a plasma in an electrodeless all-optical laser-driven light source according to the present teachings. In a first step 302, electromagnetic energy is provided to a gas in a valve using a continuous wave CW laser light (e.g., light 116 from laser 104 to gas cell 106 in FIG. 1). In a second step 304, laser pump radiation is provided to a Q-switched crystal (e.g., light 108 from laser 112 to crystal 116 in FIG. 1). The laser pump radiation causes the Q-switched crystal to generate pulsed light having a specific pulse duration and pulse repetition rate depending on the power of the laser pump radiation input to the crystal. In a third step 306, the generated pulsed light is provided to a gas (e.g., light 112 to cell 106 in FIG. 1). In some embodiments, the gas is included in a pressurized valve. In some embodiments, the gas is xenon gas. The supplied pulsed laser light causes breakdown in a region of the gas, i.e., the breakdown region. In a fourth step 308, a sufficient density of ions and electrons are generated in the breakdown region to absorb the supplied CW laser light and seed a CW plasma. In a fifth step 310, the electromagnetic energy provided by the CW laser light generates a CW plasma that emits high brightness light in the plasma region. In a sixth step 312, the generation of the CW plasma causes the pulsed light generated by the Q-switched crystal to extinguish. In some embodiments, the extinction is due to absorption of the pump light through the gas containing the ignited plasma before it hits the Q-switched crystal. In a seventh step, after the extinction of the pulsed laser light, the high brightness light is maintained by using the CW laser light to maintain the plasma in a bulb or other container. Note that in some embodiments, the CW continuous light is nominally a continuous light source generated by a pulsed laser operating at a high pulse repetition rate. In some configurations, the laser that maintains the CW plasma may be the same laser that excites the nonlinear crystal.

[0023]

[0034] Various embodiments of the laser-driven high brightness source with electrodeless ignition of the present teachings use different parameters of the light delivered to the gas. For example, the repetition rate of the Q-switched laser pulses can be controlled. The pulse energy of the pulsed light delivered to the gas can be controlled. The duration of the Q-switched laser pulses can also be controlled. In addition, the power of the CW laser light is also controlled. In some embodiments, the pulse repetition rate of the pulsed laser light is between 1 kHz and 20 kHz.

[0024]

[0035] Experimental and / or theoretical evaluations have determined that, for example, a Q-switched laser crystal can provide a good quality CW plasma when the Q-switched laser crystal is configured such that the pulse repetition rate of the pulsed laser light is 1 kHz or less. A continuous wave plasma can be generated when the Q-switched laser crystal is configured such that the pulse energy of the pulsed laser light is in the range of 50 microjoules to 500 microjoules.

[0025]

[0036] Continuous wave plasmas are generated at various pulse energies, pulse durations, and CW output conditions depending on the particular configuration. For example, continuous wave plasmas are generated when the Q-switched laser crystal is configured such that the pulse energy of the pulsed laser light ranges from 500 microjoules to 5 millijoules. In addition, continuous wave plasmas can be generated when the Q-switched laser crystal is configured such that the pulse duration of the pulsed laser light ranges from 0.1 ns to 10 ns. Continuous wave plasmas can also be generated when the CW laser source is configured such that the power of the CW sustaining light ranges from 5W to 50W. Continuous wave plasmas can also be generated when the CW laser source is configured such that the power of the CW sustaining light ranges from 5W to 1500W. The above ranges are merely examples of operating ranges and are not intended to limit the present teachings.

[0026]

[0037] One feature of the present teachings is that different known Q-switch crystals can be used. The wavelength of the pulsed light must be appropriate to cause breakdown of the gas species of the valve. FIG. 4A shows an embodiment of a Q-switch crystal 400 of the present teachings, including a gain region 402 and a saturable gain / loss region 404. As will be appreciated by those skilled in the art, different host materials and dopants can be used to provide suitable gain region 402 and saturable absorber region 404. For example, crystal 400 can have a host material that can be a glass host, an yttrium aluminum garnet host, or a spinel host. For example, crystal 400 can have a dopant in one or both of the gain region 402 and the saturable absorber region 404 that can be an ytterbium dopant, a chromium dopant, a cobalt dopant, or a vanadium dopant. The Q-switch crystal can also include a narrow band filter that can be used, for example, to reflect at least a portion of the plasma light and / or to block wavelengths in the xenon spectrum. The coating may be, for example, a protective coating, a reflective coating, and / or an anti-reflective coating.

[0027]

[0038] FIG. 4B shows a passively Q-switched laser rod 450 suitable for an electrodeless laser driven light source according to the present teachings. The yttrium aluminum garnet-based (YAG-based) passively Q-switched laser rod 450 has a curved surface 452. The saturable absorber region 454 is a chromium dopant in a yttrium aluminum garnet host. The gain region 456 is an ytterbium dopant in a yttrium aluminum garnet host. The dopant and host contribute to setting the wavelength of the pulsed light and the rise and fall times of the pulse. The length 458 (L2) of the saturable absorber region, the length 460 (L1) of the gain region, and the width 462 (W) of the crystal are selected to provide desired output pulse parameters including, for example, pulse repetition rate, pulse duration, and pulse energy.

[0028]

[0039] Q-switched crystals are a proven technology. For example, Q-switched crystals are used in known passively Q-switched microchip lasers. As one particular example, a microchip laser using a crystal with a saturable absorber region length of 458 (L2) = 1.36 mm, a gain region length of 460 (L1) = 3 mm, and a crystal width of 462 (W) = 3 mm, delivered 1.6 ns pulses with an energy of 74 microjoules at a repetition rate of 14 kHz, and was realized from a pump power of 10 W with a pump laser of wavelength 970 nm. With increasing pump power, the average output power and the generated pulse repetition rate can be increased to 1 W and 13.6 kHz, respectively, for a pump power of 9.3 W. The maximum output power can be reached without noticeable thermal rollover. An average pulse width of 1.58 ± 0.04 ns can also be realized. In practice, pulse energies of 73.8 ± 0.7 μJ and peak power values ​​of 46.0 ± 0.8 kW, respectively, could be realized. One feature of the present teachings is that electrodeless ignition can be achieved using pulsed light parameters achievable by such a highly available, compact and reliable light source of light pulses delivered by Q-switched crystals 400, 450 excited by optical pump light.

[0029]

[0040] The pump efficiency and pulse power depend on various characteristics of the crystals 400, 450, including the gain crystal 402, 456, doping element (e.g., YB or Nd), doping percentage, and diameter and length. For the saturable absorber crystals 404, 452, it is the doping element (e.g., Cr or V), doping percentage, percent of initial absorption, diameter and / or length. In some embodiments, reflective and / or transmissive coatings for the pump wavelength and the pulsed light wavelength are provided at one or more ends of the crystals 400, 450. For example, a Yb:YAG-Cr:YAG combined crystal can include a coating at the Yb:YAG end that is highly transmissive for 940 nm and highly reflective for 1030 nm. The crystal can also have a coating at the Cr:YAG end that is only partially reflective at 1030 nm (i.e., the output coupler). While many Q-switched lasers have a pump configuration with a saturable absorber and output coupler at the end opposite the incoming pump laser, pulsed Q-switched crystals for electrodeless ignition can have an output coupler at the pump input end rather than the saturable absorber end.

[0030]

[0041] Some embodiments of the crystal 400, 450 may have undoped ends around the Yb:YAG or Cr:YAG, which may be referred to as non-absorbing mirrors. Such a configuration avoids thermal overload and facet breakage. In the gain region 402, 456, Nd:YAG gain medium is common and relatively low cost. Nd:YAG gain regions 402, 456 are pumped at 808 nm and emit at 1064 nm. Yb:YAG gain regions 402, 456 are less common and more expensive. This material is pumped at wavelengths of 940 nm or 970 nm and emits at 1030 nm. Such Yb:YAG crystals are most commonly coated to accommodate 940 nm pumping. Crystals coated for 940 nm may not work well at 970 nm (e.g., 940 nm coatings transmit only 60% at 970 nm). In addition, 940 nm wavelength light is generally easier to separate from 1030 nm than 970 nm light. It is also possible to pump Yb-doped glass at 975 nm. This pump wavelength is the same as that used in known laser-driven light sources.

[0031]

[0042] Some important features of the design of the Q-switched crystal to generate pulsed light for electrodeless ignition according to the present teachings include, for example, the choice of laser wavelength, the order of placement of the coatings, gain section, saturable absorber section, and the direction of the pump pulse input and output. Other important features include coupling / separation of the pump beam and plasma beam, and addressing the need to protect the CW laser from the pulses generated by the Q-switched crystal. Referring again to FIG. 1, different embodiments of the light source 100 can have different configurations for the location of the pump laser 102, Q-switched crystal 116, and CW laser 114, which affect these design choices. In addition, due to the high pulse energy, the mounting of the crystal 116 and associated thermal management are important considerations.

[0032]

[0043] FIG. 5 is a graph 500 of the pump laser pulse energy and pump current threshold to generate a laser pulse sufficient to cause gas breakdown as a function of the pulse length of the quasi-CW (QCW) pump pulse used in an embodiment of an electrodeless laser driven light source according to the present teachings. That is, the pulse length is the width of the repetitive pulse (e.g., the width of the pulse of a square wave signal) used to generate the quasi-CW pump light signal. The graph 500 represents measurements on a bulb containing xenon gas. The graph 500 shows exemplary operating points and indicates that operation can occur over a range of pulse durations. The threshold is above a pulse length of 500 microseconds. It should be noted that various embodiments of the light source of the present teachings can be operated with different parameters than those shown in this exemplary data. Some example operating parameters for pulse ignition and transition handoff for a 22 atmosphere cryogenic bulb filled with xenon gas are as follows: (1) CW transfer handoff can be achieved with CW laser power as low as 14 W at a wavelength of 980 nm, (2) CW transfer handoff can be achieved with CW laser light central wavelength as low as 972 nm, (3) near instantaneous CW transfer handoff can be achieved with CW laser light central wavelength as low as 975 nm, and 4) CW transfer handoff can be achieved with CW laser power as high as 50 W. When the laser spectral content at 980 nm is zero, the transfer handoff can take from a few seconds to a minute or two. When the CW laser power is 20 W, the fluctuating central wavelength is 1-2 nm off the 980 nm central wavelength for a smooth transfer handoff. With a 30 atmosphere cold-fill bulb, it is possible to achieve a CW transfer handoff with 30 W from a CW laser and a central wavelength of 976 nm. In general, ignition is stronger with a high pressure bulb than with a low pressure bulb. For example, a valve at a pressure above 30 atm will generally have a stronger ignition than a valve at a pressure of about 22 atm.

[0033]

[0044] FIG. 6 illustrates a gas-filled valve system 600 having focusing lens assemblies 604, 606 suitable for use in an electrodeless laser-driven light source according to the present teachings. A plasma region 608 is shown. The focusing lens assemblies 604, 606 are arranged in planes oriented 90 degrees from each other. One assembly 604 directs pulsed light to the plasma region 608 of the bulb 602, and the other assembly 606 directs CW sustain light to the plasma region 608 of the bulb 602. As described herein, the shapes of the pulsed illumination and the CW sustain illumination of the plasma region 608 may be the same or different. The positions of the pulsed illumination and the CW sustain illumination of the plasma region 608 may be overlapping or separate. In some embodiments, the bulb 602 is filled with xenon gas. In some embodiments, the bulb 602 is formed in a spherical shape. Also, in some embodiments, the pressure of the gas-filled bulb 602 may be between 20 atm and 50 atm. Returning to FIG. 5, there is shown a graph of pump laser pulse energy and pump current threshold to generate a laser pulse sufficient to cause gas breakdown as a function of pulse length for a passively Q-switched laser crystal suitable for an electrodeless laser driven light source in accordance with the present teachings.

[0034]

[0045] FIG. 7 illustrates an electrodeless laser driven light source 700 in which pump light 702 is collinear with CW laser light 704, pulsed laser light 706 is projected onto a gas filled valve (not shown) in one plane, and CW laser light 704 is projected onto the gas filled valve in a second plane, in accordance with the present teachings. Pump laser 708 generates pump light 702. In some embodiments, pump light 702 is a continuous light having a particular average power. CW laser 710 generates CW light 704. CW laser 710 may be a fiber laser, and light 704 is delivered via optical fiber 712 into free space using collimation package 714. Pump light 702 has a wavelength λp, CW light 704 has a wavelength λCW, and pulsed laser light 706 has a wavelength λpulse. A dichroic mirror 716 is used to combine the output light from CW laser 710 and pump laser 708 into collinear propagation. An optional directing element 718 can be used to direct the light from the collimation package 714 to a dichroic mirror 716. In some embodiments, the mirror 716 is a long-pass transmissive component with high transmission below about 900 nm and high reflectivity above about 900 nm. An optional directing mirror 720 can be used to project the co-linearly propagating pump light 702 and CW laser light 704 to a focusing element 724 and a plasma sustaining region 722. A second focusing element 726 focuses the pulsed light 706 from a Q-switched crystal 728 to a breakdown region 730. The focusing element 726 also collimates and / or refocuses the pump light through a gas 732 to the Q-switched crystal 728. The figure shows how the plasma sustaining region 722 and the plasma breakdown region 730 overlap in this perspective view. However, the angles of incidence and / or planes of incidence and beam shapes of the CW light 704 and the pulsed light 706 can be adjusted so that regions 730, 722 do not overlap or only partially overlap in the three-dimensional region of the gas. A high intensity light 734 emerges from the CW plasma sustained by the CW sustain light 704.

[0035]

[0046] 8 illustrates an embodiment of an electrodeless laser driven light source 800 in which CW laser light 802 and pump light 804 are combined at a fiber coupler 820 and pump light 804, CW laser light 802, and pulsed light 806 are projected along the same plane into a gas filled bulb 810 in accordance with the present teachings. Pump laser 812 has an optical fiber output 814. In some embodiments, pump laser 812 is a fiber laser. In some embodiments, pump laser 812 is a fiber coupled diode or other solid state laser. CW laser 816 has an optical fiber output 818. In some embodiments, CW laser 816 is a fiber laser. In some embodiments, CW laser 816 is a fiber coupled diode or other solid state laser. In some embodiments, CW laser 816 is a pulsed laser with a sufficiently high pulse repetition rate to have a quasi-continuous output light.

[0036]

[0047] The light from the fibers 814, 818 at the output of the pump laser 812 and the CW laser 816 are combined in a fiber beam combiner 820. In some embodiments, the fiber beam combiner 822 is a fused fiber combiner. The fiber output 822 of the fiber beam combiner 820 provides the combined CW laser light 802 and pump light 804, and the combined light is collimated in a collimator 824. In some embodiments, the collimator 824 collimates light from a fiber core of 100 microns or less, nominally at a wavelength of 980 nm, to form a collimated beam of 8-10 mm or less. In some embodiments, the collimator 824 collimates light from a fiber core of 100 microns or less, nominally at a wavelength of 808 nm, to form a collimated beam of 2-3 mm or less. In some embodiments, the collimator 824 is a graded index (GRIN) lens. An optional filter 826 can be used to prevent the pulsed light 806 from entering either or both of the pump laser 812 or the CW laser 816 .

[0037]

[0048] Optional directing elements 828, such as mirrors and focusing elements 830, are used to direct and / or focus the CW light 802 and the pump light into the gas-filled valve 810. Focusing element 832 is used to direct and / or collimate the pump light 804 that has passed through the gas-filled valve 810, i.e., the transmitted pump light 834, into a Q-switched crystal 836. The transmitted pump light 806 generates pulsed light 806 in the Q-switched crystal 836. Collimating element 832 projects the pulsed light 806 into the gas-filled valve 810.

[0038]

[0049] A breakdown region is formed in the gas-filled bulb 810 where the energy of the pulsed light 806 causes breakdown of the gas. A sufficient density of ions and electrons from the breakdown region of the bulb 810 absorbs the bulb's CW light 802 and seeds a CW plasma. The CW plasma emits high intensity light 838 that is sustained by the CW light 802. When plasma is generated in the bulb, the power of the transmitted pump light 806 decreases, thereby extinguishing the generation of the pulsed light 806 from the Q-switch crystal 836.

[0039]

[0050] One feature of the present teachings is the ability to support collinear propagation of pump, CW, and pulsed light beams all together, with focal positions for multiple wavelengths of these beams arranged to overlap in a plane. FIG. 9 is a detailed view of the excitation region of an embodiment of an electrodeless laser driven light source 900 with collinear laser excitation in accordance with the present teachings. Pump beam 902 and CW light beam 904 are incident on lens 906. In some embodiments, the pump beam 902 has a wavelength of 808 nm. In some embodiments, the CW laser light beam 904 has a wavelength of 980 nm. In some embodiments, lens 906 is an aspheric lens. In some embodiments, lens 906 is a nominal 0.5 inch aperture, f=10 mm (wavelength dependent), NA=0.55 lens. Lens 904 focuses the incoming CW light wavelength light beam to a focal plane 908, B. A plasma sustaining region 910 is also located at this plane 908. A second lens 912 is positioned at a distance from the surface 908,B equal to the focal length of the lens 912 at the wavelength of the pulsed light 914. In some embodiments, the wavelength of the pulsed light 914 is 1064 nm. Thus, even if the same lens element model is used for the lenses 906, 912, the position of the first lens 906 from the surface 908,B is different from the position of the second lens 912 from the surface 908,B because the focal lengths of the lenses 906, 912 change with wavelength. In some embodiments, the width of the CW light beam 904 is larger than the width of the pump beam 902, which is larger than the width of the pulsed light beam 914. Thus, the focused spot size of the CW light beam 904 is smaller than the spot size of the pump beam 902, which is smaller than the spot size of the pulsed light beam 914 at the focal plane 908,B. In some embodiments, the width of the CW light beam 904 is nominally 9 mm, the width of the pump beam 902 is nominally 3 mm, and the width of the pulsed light beam 914 is nominally 1 mm. In various embodiments, the spot size and / or beam width of the pulsed light beam 914 is adjusted based on the desired energy density required at the plasma breakdown region.

[0040]

[0051] One feature of the all-optical electrodeless laser-driven light source of the present teachings is that it can be configured to fit into a single optical package. FIG. 10 shows an embodiment of a packaged electrodeless laser-driven light source 1000 with collinear laser pumping in accordance with the present teachings. A high pressure electrodeless xenon gas filled bulb 1002 is disposed in a package 1004. A focusing lens 1006 is used to focus the pump light generated by the pump laser diode 1008 and the CW light generated by the laser diodes 1010, 1012. The light from the laser diodes 1008, 1010, 1012 is collimated by collimating optics 1014, 1016, 1018. The pump light is directed by mirror 1020 and the CW light is coupled and collinear into the pump beam path by dichroic elements 1022, 1024. A filter 1026 transmits the pump light and the CW light but blocks the pulsed light. A focusing lens 1028 focuses the pulse generated by the Q-switch crystal 1030 onto the breakdown region of the xenon gas filled bulb 1002. The Q-switch crystal includes a Yb:YAG rod section and a Cr:YAG or V:YAG saturable absorber section 1034. A highly reflective coating 1036 is applied to the end of the crystal 1030.

[0041] [Equivalent]

[0052] While applicants' teachings have been described in conjunction with various embodiments, it is not intended that applicants' teachings be limited to such embodiments. On the contrary, applicants' teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those skilled in the art, which can be made without departing from the spirit and scope of the present teachings.

Claims

1. a) a sustain laser source generating continuous wave (CW) sustain light at its output; b) a pump laser generating pump light at its output; c) an optical beam combiner having a first input optically coupled to the output of the sustain laser source and a second input optically coupled to the output of the pump laser, the optical beam combiner combining the CW sustain light and the pump light at an output such that the CW sustain light and the pump light propagate collinearly; d) a Q-switched laser crystal having a pump input optically coupled to the output of the pump laser, the Q-switched laser crystal configured to generate pulsed light at its output in response to the pump light; e) a gas-filled bulb optically coupled to the output of the sustain laser and optically coupled to the output of the Q-switched laser crystal, wherein the pulsed light ignites a pulsed plasma in a breakdown region of the gas bulb and the sustain light sustains a CW plasma in a CW plasma region of the gas bulb, thereby emitting high intensity light from the gas bulb; and Equipped with an electrodeless laser driven light source, the gas filled valve being disposed between the output of the pump laser and the pump input of the Q-switched laser crystal, such that the CW plasma absorbs the pump light, thereby quenching the pulsed light generated by the Q-switched laser crystal.

2. The electrodeless laser driven light source of claim 1 , wherein the sustain laser source and the pump laser comprise the same laser.

3. 10. The electrodeless laser driven light source of claim 1, wherein the sustain laser source and the pump laser are configured in a single laser housing.

4. The electrodeless laser driven light source of claim 1 , wherein the optical coupler comprises a dichroic beam splitter.

5. The electrodeless laser driven light source of claim 1 , wherein the optical coupler comprises a fiber coupler.

6. 2. The electrodeless laser driven light source according to claim 1, wherein the Q-switched laser crystal is configured so that the pulse repetition rate of the pulsed laser light is in the range of 1 kHz to 20 kHz.

7. 2. The electrodeless laser driven light source according to claim 1, wherein the Q-switched laser crystal is configured so that the pulse repetition rate of the pulsed laser light is in the range of 1 kHz or less.

8. 2. The electrodeless laser driven light source according to claim 1, wherein the Q-switched laser crystal is configured so that the pulse energy of the pulsed laser light is in the range of 350 μJ to 50 mJ.

9. 2. The electrodeless laser driven light source of claim 1, wherein the Q-switched laser crystal is configured such that the pulse duration of the pulsed laser light is in the range of 0.1 ns to 10 ns.

10. 2. The electrodeless laser driven light source of claim 1, wherein the laser source is configured so that the output power of the CW sustain light is in the range of 5W to 50W.

11. 2. The electrodeless laser driven light source of claim 1, wherein the laser source is configured so that the output power of the CW sustain light is in the range of 5W to 1500W.

12. 2. The electrodeless laser driven light source of claim 1, wherein the Q-switched laser crystal comprises a gain section and a saturable absorber section.

13. 10. The electrodeless laser driven light source of claim 1, wherein the Q-switched laser crystal comprises at least one of a glass host, a yttrium aluminum garnet host, and a spinel host.

14. 10. The electrodeless laser driven light source of claim 1, wherein the Q-switched laser crystal includes at least one of a chromium dopant, a cobalt dopant, and a vanadium dopant.

15. 2. The electrodeless laser driven light source of claim 1, wherein the Q-switched laser crystal comprises a narrow band filter.

16. The electrodeless laser driven light source of claim 15 , wherein the narrow band filter reflects at least a portion of the plasma light.

17. 16. The electrodeless laser driven light source of claim 15, wherein the narrow band filter blocks wavelengths in the xenon spectrum.

18. The electrodeless laser driven light source of claim 1 , wherein the gas filled bulb contains xenon gas.

19. The electrodeless laser driven light source of claim 1 , wherein the gas filled bulb contains a noble gas.

20. The electrodeless laser driven light source of claim 1 , wherein the gas-filled bulb is spherically shaped.

21. 2. The electrodeless laser driven light source of claim 1, wherein the pressure in the gas-filled valve is in the range of 20 atm to 50 atm.

22. a) providing electromagnetic energy to a gas in a gas-filled valve using a continuous CW laser light; b) generating laser pulses by providing laser pump radiation to a Q-switched laser crystal; c) delivering the laser pulse to the gas in the gas-filled valve to generate a pulsed plasma in a breakdown region of the gas; d) generating a CW plasma using the supplied electromagnetic energy and the pulsed plasma in an ionized gas, the CW plasma emitting high intensity light in a CW plasma region; e) passing the laser pump radiation provided to the Q-switched laser crystal through the CW plasma region, whereby the CW plasma absorbs the pump light, thereby quenching the pulsed light generated by the Q-switched laser crystal; 23. A method for igniting an electrodeless laser driven light source, comprising:

23. 23. The method of igniting an electrodeless laser driven light source of claim 22, wherein the steps of providing electromagnetic energy to a gas in a gas-filled bulb and providing laser pump radiation to a Q-switched laser crystal include using the same laser to provide the electromagnetic energy and the pump radiation.

24. 23. The method of igniting an electrodeless laser driven light source of claim 22, wherein the breakdown region and the CW plasma region overlap.

25. 23. The method of igniting an electrodeless laser driven light source of claim 22, wherein the breakdown region and the CW plasma region do not overlap.

26. 23. The method of igniting an electrodeless laser driven light source of claim 22, wherein the pulse repetition rate of the laser pulses is in the range of 1 kHz or less.

27. 23. The method of igniting an electrodeless laser driven light source of claim 22, wherein the pulse repetition rate of the laser pulses is in the range of 1 kHz to 20 kHz.

28. 23. The method of igniting an electrodeless laser driven light source of claim 22, wherein the pulse energy of the laser pulse is in the range of 350 μJoules to 50 mJoules.

29. 23. The method of igniting an electrodeless laser driven light source of claim 22, wherein the laser pulse has a pulse duration in the range of 0.1 ns to 10 ns.

30. 23. The method of igniting an electrodeless laser driven light source of claim 22, wherein the output power of the continuous CW laser light is in the range of 5W to 1500W.

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