All-optical laser-driven light source with electrodeless ignition
The electrodeless laser-driven light source addresses the limitations of electrode-based systems by optically igniting plasma, resulting in smaller, more reliable, and efficient high-brightness light sources.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- HAMAMATSU PHOTONICS KK
- Filing Date
- 2026-03-25
- Publication Date
- 2026-07-07
Smart Images
Figure 2026113519000001_ABST
Abstract
Description
Technical Field
[0001]
[0001] The headings of the sections used in this specification are for purposes of organization only and are not to be construed as limiting the subject matter described in this application.
[0002] [Preface]
[0002] For example, a laser-driven light source that provides high brightness over a spectral range from the extreme ultraviolet region to the visible and infrared regions of the spectrum is available with high reliability and long life. Various examples of such high-brightness light sources are manufactured by Energetiq, a Hamamatsu Company, in Wilmington, MA.
Summary of the Invention
[0003]
[0003] In various fields including biology, chemistry, climate, and physics, there is a growing demand for high-brightness light sources for applications such as semiconductor metrology, sensor calibration and testing, creation of shaped light, surface metrology, spectroscopy, and other optical measurement applications. Therefore, there is a need for progress in high-brightness light sources that can improve 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 will be described in more detail, together with the accompanying drawings and their further advantages. Those skilled in the art will understand that the drawings described below are for illustrative purposes only. The drawings are not necessarily to scale and generally emphasize showing 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] It is a schematic diagram of an embodiment of a laser-driven light source including electrodeless ignition according to the present teachings. [Figure 2A]This is an image of a gas-filled valve of an electrodeless laser-driven light source according to this instruction, showing emission due to pulsed laser excitation alone. [Figure 2B] This is an image of a gas-filled valve of an electrodeless laser-driven light source according to this instruction, showing emission solely due to CW laser excitation. [Figure 3] This figure shows the steps for igniting the plasma of an electrodeless, all-optical laser-driven light source according to this instruction. [Figure 4A] This figure shows an embodiment of the Q-switch crystal described herein, including the gain region and the saturable gain / loss region. [Figure 4B] This figure shows a passive Q-switched laser rod suitable for an electrodeless laser-driven light source according to this instruction. [Figure 5] This graph shows the pulse energy of a pump laser and the pump current threshold, as a function of pulse length, for generating a laser pulse sufficient to cause gas dielectric breakdown, suitable for a quasi-CW pump pulse suitable for an electrodeless laser-driven light source according to this instruction. [Figure 6] This figure shows a gas-filled valve system with a focusing lens assembly suitable for use in the electrodeless laser-driven light source described in this instruction. [Figure 7] This figure shows an electrodeless laser-driven light source according to this instruction, in which 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] This figure shows an embodiment of an electrodeless laser-driven light source according to this instruction, in which CW laser light and pump light are coupled in a fiber coupler, and the pump light, CW laser light, and pulsed light are projected onto a gas-filled valve along the same plane. [Figure 9] This is a detailed diagram of the excitation region of an electrodeless laser-driven light source embodiment having colinear laser excitation, as taught in this document. [Figure 10] This figure shows an embodiment of a packaged electrodeless laser-driven light source having colinear laser excitation, according to this instruction. [Modes for carrying out the invention]
[0006] [Description of various embodiments]
[0017] The teachings described below will be explained in more detail with reference to the exemplary embodiments shown in the accompanying drawings. While the teachings will be explained in conjunction with various embodiments and examples, they are not intended to be limited to such embodiments. Rather, as will be understood by those skilled in the art, the teachings encompass a variety of alternative forms, modifications, and equivalents. Those skilled in the art who can utilize 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] Any reference to “an embodiment” or “an embodiment” in this specification means that certain features, structures, or characteristics described in relation to an embodiment are included in at least one embodiment of this teaching. The phrase “an embodiment” appearing in various parts of this specification does not necessarily refer to the same embodiment.
[0008]
[0019] It should be understood that the individual steps of the method in this teaching can be performed in any order and / or simultaneously, as long as this teaching is practicable. Furthermore, it should be understood that the apparatus and method in this teaching can include any number or all of the embodiments described, as long as this teaching is practicable.
[0009]
[0020] Laser-driven light sources use CW lasers to directly heat a gas plasma to the high temperatures necessary to generate broadband optical light. High-brightness laser-driven light sources have significant advantages over light sources that use high-voltage electrodes to maintain the plasma. Laser-driven sources rely on photodischarge plasma, as opposed to the electric discharge plasma used in, for example, arc lamp devices. In electric discharge lamps, electrode materials can evaporate, altering the discharge characteristics over the lamp's lifespan. This shortens the lamp's life. Also, electrode-based systems introduce thermal, mechanical, and electrical stresses to 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 electrode-based light sources can have significant limitations. For example, electrode-based light sources may have limitations on lamp head size and the method by which bulbs can be mounted. Electrode-based light sources must be designed to avoid parasitic arcs, and the lamp head must be configured with sufficient volume for the electrodes and ignition circuit. Electrode-based light sources have constraints on the low-temperature filling pressure of the bulb, for example, because the glass-metal seal of the electrodes may limit the maximum filling pressure. Also, electrode-based light sources may have larger bulb sizes, which can affect the bulb filling pressure. Electrode-based light sources also have limitations on the shapes of bulbs they can adapt to, for example, because electrode-based light sources require the electrodes to be positioned, fixed, and connected. These design constraints can introduce noise into the light source.
[0011]
[0022] Therefore, providing a laser-driven light source with electrodeless ignition can lead to higher reliability, higher performance, cost reduction, and reduced complexity, in addition to other advantages. Ignition of plasma by optical illumination requires careful design and control of the light source and associated light supply mechanism used to ignite the plasma. One feature of this teaching is the provision of 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-intensity light sources.
[0012]
[0023] Electrodeless laser-driven light sources have many features and advantages. Electrodeless light sources can be implemented using smaller bulbs with higher maximum filling pressures than conventional light sources. In particular, for certain laser output modes, higher filling pressures can result in higher brightness. Electrodeless light sources are free from contamination from electrode materials. In addition, there are fewer geometric constraints on the lamp shape. Generally, smaller lamp heads can be used for the same characteristics. Furthermore, the absence of high-voltage active electrical components to supply power reduces the need for associated power supplies, control electronics, and electrical connections, significantly reducing the number of required components. However, some embodiments of electrodeless laser-driven light sources can be implemented in existing lamp packages of laser-driven light sources without electrode ignition. This is because, at least in part, electrodeless devices are generally less complex and smaller than electrode-based laser-driven light sources. For example, an electrodeless laser-driven light source is described in U.S. Patent Application No. 17 / 328,433, entitled "Lase-Driven Light Source with Electrodeless Ignition," which has been assigned to the assignee and is incorporated herein by reference.
[0013]
[0024] One feature of this teaching is that it provides an electrodeless laser-driven light source without the need to electronically control a separate ignition light pulse. Rather, the light ignition pulse is generated all optically within the light source component. This approach has several advantages over electrodeless laser-driven light sources where the pulse source is electrically controlled. For example, a smaller bulb can be used. Also, the number of electronic connections to the light source package can be reduced. Furthermore, special power supplies or laser driving electronics are not required to form an electronically driven and controlled pulse source.
[0014]
[0025] Figure 1 is a schematic diagram of an embodiment of the laser-driven light source 100 including electrodeless ignition according to this teaching. The pump laser 102 supplies optical pump light 104 to the gas cell 106. The pump light passes through the cell and exits as transmitted pump light 108 supplied to the Q-switched crystal 110. The transmitted pump light 108 exiting the gas cell 106 has sufficient energy to cause the Q-switched crystal 110 to generate optical pulsed light 112 returning to the gas cell 106. The energy of the optical pulsed light 112 is supplied to the plasma dielectric breakdown region of the gas cell 106, igniting the plasma. In some embodiments, the gas cell 106 is a gas-filled valve. In some embodiments, the gas cell 106 is a gas chamber including at least one window that allows the wavelengths of the pump light 104, optical pulsed light 112, CW light 114, and high-brightness CW plasma light 118 to pass through.
[0015]
[0026] The CW laser 114 generates CW laser light 116. The CW laser light 116 is supplied to the gas cell 108 as maintenance light to the plasma breakdown region of the gas cell 108. The region illuminated by the pulsed laser light 112 in the gas cell 106 may be called the pulsed illumination region and has a distinct position and shape based on the optical projection elements (not shown) used to direct the pulsed light 112 from the Q-switch crystal 110 and the CW laser light 116 towards the cell 106. These projection elements include various focusing elements and / or orientation elements in various different embodiments. The energy of the optical pulsed light 112 supplied to the plasma breakdown region of the cell 106 ignites the plasma. The region illuminated by the CW maintenance light may be called the CW maintenance illumination region and has a distinct position 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 elements and / or orientation elements in various different embodiments. The energy of the CW laser light 114 supplied to the plasma breakdown region maintains the plasma. The plasma breakdown region generates high-intensity CW plasma light 118.
[0016]
[0027] The optical pulsed light 112 has a high peak output necessary for igniting the plasma in the gas cell 106. However, in order to generate the sustained CW plasma light 118, the optical pulsed light 112 must not exceed a certain energy / output threshold, and can occur when the optical pulse is present in the plasma after a predetermined delay after the plasma light 118 reaches a predetermined threshold. If the energy of the optical pulsed light 112 supplied to the gas cell 106 is too high, the plasma may extinguish. To prevent the optical pulsed light 112 from extinguishing the plasma, a mechanism for extinguishing the pulsed light 112 after the generation of the sustained CW plasma light is required. This can be implemented in the all-optical laser drive light source 100 by utilizing the decrease in the pump laser light of the gas cell 106 that occurs during plasma ignition. When the plasma is ignited, the pump light that passes through the cell and exits as the transmitted pump light 108 supplied to the Q-switch crystal 110 has a much lower output compared to the pump light 104 exiting 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 compared to 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 maintained by applying only the CW maintenance light 116 from the CW laser 114.
[0017]
[0028] Since the pulsed light 112 is stopped when the CW plasma is ignited, a sensor and / or an electronic shutter and / or other electronic shut-off for actively extinguishing the pulsed light 112 after breakdown is not required. If the plasma extinguishes for some unexpected reason, the plasma is not present to absorb the pump light, so an attempt at pulsed ignition is automatically started again. In other words, the plasma is automatically reignited. This results in a simple, small, and very reliable electrodeless light source without the need for active monitoring to control the pulsed light.
[0018]
[0029] One feature of the all-optical electrodeless light source embodiments described herein is that the positions of the pulsed illumination region and the CW sustained illumination region can be adjusted to produce desired performance of the plasma light. The relative positions of the pulsed illumination region and the CW sustained 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 slightly overlap.
[0019]
[0030] Figure 2A is an image 200 of a gas-filled valve in an embodiment of the electrodeless laser-driven light source according to this teaching, showing emission due to pulsed laser excitation alone. Both images 202 and 204 are shown from the side, but their angles are shifted to show the three-dimensional arrangement of the pulsed illumination region and the focal point of the CW laser. The extent and location of the pulsed illumination region are visible in these images 202 and 204. Note that the location of pulsed dielectric breakdown is determined by the pulse energy. As the energy increases, the dielectric breakdown location moves toward the pulsed laser. Three-dimensional alignment of the pulsed laser dielectric breakdown plasma with respect to the pulsed light and the focal point of the CW laser allows the method to be performed with lower CW laser power and / or lower pulse energy.
[0020]
[0031] Figure 2B is an image 250 of the gas-filled valve shown in Figure 2A, showing emission due to CW laser excitation alone. Both images 252 and 254 are shown from the side, but their angles are shifted to show the three-dimensional arrangement of the pulsed illumination region and the focal point of the CW laser. The extent and position of the pulsed illumination region are visible in these images 252 and 254. The contours 256 and 258 of the pulsed illumination region in images 202 and 204 of Figure 2A are also shown. In this embodiment, the relative position and shape of the pulsed illumination region and the CW sustained illumination region are such that the two regions are separate and do not overlap. The more densely the light is focused, the smaller the pulsed illumination region becomes, and the higher the density of pulsed energy supplied to the plasma by the illumination.
[0021]
[0032] The images in Figures 2A and 2B were collected during experiments to determine the operating parameters of the pulses that produce plasma ignition. Some details of the experimental conditions are described below. For example, with a pulse repetition rate of 2 kHz and a pulse duration of 1 ns, stable plasma ignition can be achieved in a xenon-filled valve over an energy range of 135–225 microjoules. The pulsed light had a wavelength of 1064 nm. For a specific example of this experimental configuration, the threshold energy for dielectric breakdown light to achieve a stable CW plasma was 135 microjoules. Furthermore, at 210 microjoules, the plasma can be ignited and eventually stabilized, although ignition and extinction of the CW plasma may occur before stable operation. Ignition can also be achieved at 225 microjoules and above. The relative positions of the pulsed light illumination and the CW light illumination are important. Ignition can be improved or "stopped" by adjusting the alignment of the valve and the CW laser along the optical axis of the pulsed laser. In this experiment, after ignition of the CW plasma, the CW laser output was reduced to 8-10 watts, and it was still possible to maintain the CW laser output. A reliable transition from pulsed to CW occurred at any CW laser output value above 15.5 watts. There was no upper limit to the CW laser output. As will be understood by those skilled in the art, beam quality affects the energy supplied to the gas for a given laser output.
[0022]
[0033] One feature of the all-optical electrodeless laser-driven light source described in this teaching is that the pulsed laser light can be extinguished by an absorption process in the gas cell, rather than relying on external electronic feedback. Figure 3 shows the steps of the method for igniting the plasma of the electrodeless all-optical laser-driven light source described in this teaching. In the first step 302, electromagnetic energy is supplied to the gas in the valve using continuous wave CW laser light (e.g., light 116 from laser 104 to gas cell 106 in Figure 1). In the second step 304, laser pump radiation is supplied to a Q-switched crystal (e.g., light 108 from laser 112 to crystal 116 in Figure 1). The laser pump radiation generates pulsed light in the Q-switched crystal having a specific pulse duration and pulse repetition rate depending on the output of the laser pump radiation input to the crystal. In the third step 306, the generated pulsed light is supplied to the gas (e.g., light 112 supplied to cell 106 in Figure 1). In some embodiments, the gas is contained in a pressurized valve. In some embodiments, the gas is xenon gas. The supplied pulsed laser light causes dielectric breakdown in the gas region, i.e., the dielectric breakdown region. In the fourth step 308, a sufficient density of ions and electrons is generated in the dielectric breakdown region, absorbing the supplied CW laser light and seeding a CW plasma. In the fifth step 310, the electromagnetic energy supplied by the CW laser light generates a CW plasma that emits high-intensity light in the plasma region. In the sixth step 312, the generation of the CW plasma extinguishes the pulsed light generated by the Q-switched crystal. In some embodiments, the extinguishment is due to the absorption of the pump light passing through the gas containing the ignition plasma before it hits the Q-switched crystal. In the seventh step, after the extinguishment of the pulsed laser light, the high-intensity light is maintained by using the CW laser light to maintain the plasma in a valve or other container. Note that in some embodiments, the CW continuous light is nominally a continuous light source generated by pulsed laser operation at a high pulse repetition rate. In some configurations, the laser maintaining the CW plasma may be the same laser that excites the nonlinear crystal.
[0023]
[0034] Various embodiments of the laser-driven high-intensity source with electrodeless ignition described herein utilize different parameters of the light supplied to the gas. For example, the repetition rate of the Q-switched laser pulse can be controlled. The pulse energy of the pulsed light supplied to the gas can be controlled. The duration of the Q-switched laser pulse can also be controlled. In addition, the output power of the CW laser light is also controlled. In some embodiments, the pulse repetition rate of the pulsed laser light is 1 kHz to 20 kHz.
[0024]
[0035] Experimental and / or theoretical evaluations have determined that, for example, a high-quality CW plasma can be supplied 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 plasma can be generated under various pulse energies, pulse durations, and CW output conditions depending on the specific configuration. For example, continuous wave plasma can be generated when the Q-switched laser crystal is configured such that the pulse energy of the pulsed laser beam is in the range of 500 microjoules to 5 millijoules. In addition, continuous wave plasma can be generated when the Q-switched laser crystal is configured such that the pulse duration of the pulsed laser beam is in the range of 0.1 ns to 10 ns. Continuous wave plasma can also be generated when the CW laser source is configured such that the output of the CW-sustained light is in the range of 5 W to 50 W. Continuous wave plasma can also be generated when the CW laser source is configured such that the output of the CW-sustained light is in the range of 5 W to 1500 W. The above ranges are merely examples of the operating range and are not intended to limit this teaching.
[0026]
[0037] One feature of this teaching is that different known Q-switch crystals can be used. The wavelength of the pulsed light must be appropriate for causing dielectric breakdown of the gas species in the valve. Figure 4A shows an embodiment of the Q-switch crystal 400 of this teaching, including a gain region 402 and a saturation gain / loss region 404. As will be understood by those skilled in the art, different host materials and dopants can be used to provide appropriate gain regions 402 and saturation absorber regions 404. For example, crystal 400 may have a host material that may be a glass host, a yttrium aluminum garnet host, or a spinel host. For example, crystal 400 may have dopants in one or both of the gain region 402 and the saturation absorber region 404, which may be a ytterbium dopant, a chromium dopant, a cobalt dopant, or a vanadium dopant. The Q-switch crystal may also include a narrowband filter that can be used, for example, to reflect at least a portion of the plasma light and / or to block wavelengths of the xenon spectrum. This coating may be, for example, a protective coating, a reflective coating, and / or an anti-reflective coating.
[0027]
[0038] Figure 4B shows a passive Q-switched laser rod 450 suitable for an electrodeless laser-driven light source according to this teaching. The yttrium aluminum garnet-based (YAG-based) passive Q-switched laser rod 450 has a curved surface 452. The saturating absorber region 454 is a chromium dopant of the yttrium aluminum garnet host. The gain region 456 is a ytterbium dopant of the yttrium aluminum garnet host. The dopants and host contribute to setting the wavelength of the pulsed light as well as the rise and fall times of the pulse. The length 458 (L2) of the saturating absorber region, the length 460 (L1) of the gain region, and the crystal width 462 (W) 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 passive Q-switched microchip lasers. As one specific example, a microchip laser using a crystal with a saturation 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 was realized from a 10 W pump output with a 970 nm wavelength pump laser, supplying 1.6 ns pulses with an energy of 74 microjoules at a repetition rate of 14 kHz. With increasing pump output, the average output power and generated pulse repetition rate can be increased to 1 W and 13.6 kHz, respectively, for a pump output of 9.3 W. Maximum output power can be reached without noticeable thermal rollover. An average pulse width of 1.58 ± 0.04 ns can also be achieved. In practice, pulse energies of 73.8 ± 0.7 μJ and peak output values of 46.0 ± 0.8 kW were achieved, respectively. One feature of this instruction is that electrodeless ignition can be achieved using pulsed optical parameters that can be realized by such a highly available, compact, and reliable light source, supplied by the Q-switched crystals 400 and 450 excited by optical pump light.
[0029]
[0040] Pump efficiency and pulse output are determined by various properties of crystals 400, 450, including gain crystals 402, 456, doping element (e.g., YB or Nd), doping percentage, and diameter and length. For saturated absorber crystals 404, 452, these are doping element (e.g., Cr or V), doping percentage, initial absorption percentage, diameter, and / or length. In some embodiments, reflective and / or transmitting coatings for the pump wavelength and pulse light wavelength are provided on one or more ends of crystals 400, 450. For example, a Yb:YAG-Cr:YAG bonded crystal may include a coating on the Yb:YAG end that is highly transmittant at 940 nm and highly reflective at 1030 nm. Alternatively, the crystal may have a coating on the Cr:YAG end that is only partially reflective at 1030 nm (i.e., an output coupler). Many Q-switched lasers have a pump configuration with a saturable absorber and output coupler at the end opposite to the incident pump laser. However, pulsed Q-switched crystals for electrodeless ignition can have the output coupler at the pump input end instead of the saturable absorber end.
[0030]
[0041] Some embodiments of crystals 400 and 450 may have undoped edges around the Yb:YAG or Cr:YAG, which can be called unabsorbent mirrors. Such configurations avoid thermal overload and facet damage. In gain regions 402 and 456, the gain medium of Nd:YAG is common and relatively inexpensive. The gain regions of Nd:YAG 402 and 456 are excited at 808 nm and emit at 1064 nm. The gain regions of Yb:YAG 402 and 456 are less common and more expensive. This material is excited at wavelengths of 940 nm or 970 nm and emits at 1030 nm. Such Yb:YAG crystals are most commonly coated to adapt to 940 nm excitation. Crystals coated for 940 nm will not function well at 970 nm (for example, a 940 nm coating will only transmit 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 excite Yb-doped glass at 975 nm. This pump wavelength is the same as those used in known laser-driven light sources.
[0031]
[0042] Some key features of the design of the Q-switched crystal for generating pulsed light for electrodeless ignition according to this teaching include, for example, the selection of the laser wavelength, the coating, the order of arrangement of the gain portion and the saturable absorber portion, and the direction of the pump pulse input and output. Other key features include the coupling / separation of the pump beam and the plasma beam, and addressing the need to protect the CW laser from pulses generated by the Q-switched crystal. Referring again to Figure 1, different embodiments of the light source 100 can have different configurations regarding the positions of the pump laser 102, the Q-switched crystal 116, and the 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] Figure 5 is graph 500 of the pulse energy and pump current threshold of the pump laser that generates a laser pulse sufficient to cause gas dielectric breakdown, as a function of the pulse length of the quasi-CW (QCW) pump pulse used in the electrodeless laser-driven light source embodiment of this teaching. That is, the pulse length is the width of the repeating pulses used to generate the quasi-CW pump optical signal (e.g., the pulse width of the square wave signal). Graph 500 represents measurements for a valve containing xenon gas. Graph 500 shows an exemplary operating point and indicates that operation can occur over a range of pulse durations. The threshold exceeds a pulse length of 500 microseconds. Note that various embodiments of the light source of this teaching may operate with parameters different from those shown in this exemplary data. Some examples of operating parameters for pulse ignition and transition handoff of a 22-atm cryogenic valve filled with xenon gas are as follows: (1) CW transition handoff can be achieved with a low CW laser output of 14W at a wavelength of 980nm, (2) CW transition handoff can be achieved with a low CW laser light center wavelength of 972nm, (3) a nearly instantaneous CW transition handoff can be achieved with a low CW laser light center wavelength of 975nm, and 4) CW transition handoff can be achieved with a high CW laser output of 50 watts. When the content of the laser spectrum at 980nm becomes zero, the transition handoff may take several seconds to one or two minutes. When the CW laser output is 20 watts, the fluctuating center wavelength deviates by 1-2 nm from the 980nm center wavelength of a smooth transition handoff. Using a 30-atmosphere low-temperature filling valve, it is possible to achieve CW transition handoff with 30 watts from a CW laser and a center wavelength of 976nm. Generally, ignition is stronger when using a high-pressure valve than a low-pressure valve. For example, a valve with a pressure of over 30 atm generally has a stronger ignition than a valve with a pressure of around 22 atm.
[0033]
[0044] Figure 6 shows a gas-filled valve system 600 having focusing lens assemblies 604, 606 suitable for use in an electrodeless laser-driven light source according to this teaching. A plasma region 608 is shown. The focusing lens assemblies 604, 606 are configured in planes facing each other at 90 degrees. One assembly 604 directs pulsed light to the plasma region 608 of the valve 602, and the other assembly 606 directs CW-sustaining light to the plasma region 608 of the valve 602. As described herein, the shapes of the pulsed illumination and CW-sustaining illumination of the plasma region 608 may be the same or different. The positions of the pulsed illumination and CW-sustaining illumination of the plasma region 608 may overlap or be separate. In some embodiments, the valve 602 is filled with xenon gas. In some embodiments, the valve 602 is formed in a spherical shape. Also, in some embodiments, the pressure of the gas-filled valve 602 may be between 20 atm and 50 atm. Returning to Figure 5, the graph shows the pulse energy and pump current threshold of a pump laser that generates a laser pulse sufficient to cause gas dielectric breakdown, as a function of pulse length for a passive Q-switched laser crystal suitable for an electrodeless laser-driven light source according to this teaching.
[0034]
[0045] Figure 7 shows an electrodeless laser-driven light source 700 according to this teaching, in which the pump light 702 is collinear with the CW laser light 704, the pulsed laser light 706 is projected onto a gas-filled valve (not shown) in one plane, and the CW laser light 704 is projected onto the gas-filled valve in a second plane. The pump laser 708 generates the pump light 702. In some embodiments, the pump light 702 is continuous light with a specific average power. The CW laser 710 generates the CW light 704. The CW laser 710 may be a fiber laser, and the light 704 is supplied into free space via an optical fiber 712 using a collimation package 714. The pump light 702 has a wavelength λp, the CW light 704 has a wavelength λCW, and the pulsed laser light 706 has a wavelength λ pulse. A dichroic mirror 716 is used to couple the output light from the CW laser 710 and the pump laser 708 to propagate collinearly. An optional orientation element 718 can be used to direct light from the collimation package 714 to the dichroic mirror 716. In some embodiments, the mirror 716 is a long-path transmitting component with high transmittance of less than about 900 nm and high reflectance of more than about 900 nm. An optional orientation mirror 720 can be used to project the colinearly propagating pump light 702 and CW laser light 704 onto the focusing element 724 and the plasma maintenance region 722. The second focusing element 726 focuses pulsed light 706 from the Q-switched crystal 728 into the breakdown region 730. The focusing element 726 also collimates and / or refocuses the pump light passing through the gas 732 to the Q-switched crystal 728. The figure shows how the plasma maintenance region 722 and the plasma breakdown region 730 overlap in this perspective view. However, the incident angle and / or incident plane and beam shape of the CW light 704 and pulsed light 706 can be adjusted so that regions 730 and 722 do not overlap, or only partially overlap, in the three-dimensional region of the gas. The high-brightness light 734 emanates from the CW plasma maintained by the CW-maintaining light 704.
[0035]
[0046] Figure 8 shows an embodiment of an electrodeless laser-driven light source 800 according to this teaching, in which a CW laser beam 802 and a pump beam 804 are coupled in a fiber coupler 820, and the pump beam 804, the CW laser beam 802, and the pulsed beam 806 are projected onto a gas-filled valve 810 along the same plane. The pump laser 812 has an optical fiber output 814. In some embodiments, the pump laser 812 is a fiber laser. In some embodiments, the pump laser 812 is a fiber-coupled diode or other solid-state laser. The CW laser 816 has an optical fiber output 818. In some embodiments, the CW laser 816 is a fiber laser. In some embodiments, the CW laser 816 is a fiber-coupled diode or other solid-state laser. In some embodiments, the CW laser 816 is a pulsed laser with a sufficiently high pulse repetition rate to have quasi-continuous output light.
[0036]
[0047] The light from fibers 814 and 818 at the outputs of the pump laser 812 and the CW laser 816 is coupled in a fiber beam coupler 820. In some embodiments, the fiber beam coupler 822 is a fused fiber coupler. The fiber output 822 of the fiber beam coupler 820 provides the coupled CW laser light 802 and the pump light 804, and the coupled light is collimated in a collimator 824. In some embodiments, the collimator 824 collimates light with a nominal wavelength of 980 nm from a fiber core of 100 microns or less to form a collimated beam of 8 to 10 mm or less. In some embodiments, the collimator 824 collimates light with a nominal wavelength of 808 nm from a fiber core of 100 microns or less to form a collimated beam of 2 to 3 mm or less. In some embodiments, the collimator 824 is a distributed refractive index (GRIN) lens. An optional filter 826 can be used to prevent pulsed light 806 from entering either or both of the pump laser 812 or the CW laser 816.
[0037]
[0048] Optional orientation elements 828, such as mirrors and focusing elements 830, are used to direct and / or focus the CW light 802 and pump light towards the gas-filled valve 810. Focusing elements 832 are used to direct and / or collimate the pump light 804, i.e., transmitted pump light 834, that has passed through the gas-filled valve 810, towards the Q-switched crystal 836. The transmitted pump light 806 generates pulsed light 806 in the Q-switched crystal 836. The collimating element 832 projects the pulsed light 806 onto the gas-filled valve 810.
[0038]
[0049] A dielectric breakdown region is formed in the gas-filled valve 810, where the energy of the pulsed light 806 causes dielectric breakdown of the gas. A sufficient density of ions and electrons from the dielectric breakdown region of valve 810 absorbs the CW light 802 of the valve, seeding a CW plasma. The CW plasma emits high-intensity light 838 maintained by the CW light 802. When plasma is generated in the valve, the output of the transmitted pump light 806 decreases. This eliminates the generation of pulsed light 806 from the Q-switched crystal 836.
[0039]
[0050] One feature of this teaching is that it can support the colinear propagation of the pump light beam, the CW light beam, and the pulsed light beam, and can have multiple wavelength focal positions for these beams arranged to overlap in a plane. Figure 9 is a detail view of the excitation region of an embodiment of an electrodeless laser-driven light source 900 having colinear laser excitation according to this teaching. The pump beam 902 and the CW light beam 904 are incident on lens 906. In some embodiments, the wavelength of the pump beam 902 is 808 nm. In some embodiments, the wavelength of the CW laser light beam 904 is 980 nm. In some embodiments, lens 906 is an aspherical lens. In some embodiments, lens 906 is a lens nominally with a 0.5-inch aperture, f=10 mm (wavelength-dependent), and NA=0.55. Lens 904 focuses the incident CW light beam to the focal plane 908, B. The plasma maintenance region 910 is also located on this plane 908. The second lens 912 is positioned at a distance from plane 908, B equal to the focal length of lens 912 at the wavelength of pulsed light 914. In some embodiments, the wavelength of pulsed light 914 is 1064 nm. Therefore, even if the same lens element model is used for lenses 906, 912, the focal lengths of lenses 906, 912 vary with wavelength, so the position of the first lens 906 from plane 908, B is different from the position of the second lens 912 from plane 908, B. In some embodiments, the width of the CW light beam 904 is greater than the width of the pump beam 902, and the width of the pump beam 902 is greater than the width of the pulsed light beam 914. Therefore, the focused spot size of the CW light beam 904 is smaller than the spot size of the pump beam 902, and the spot size of the pump beam 902 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 are adjusted based on the desired energy density required in the plasma dielectric breakdown region.
[0040]
[0051] One feature of the all-optical electrodeless laser-driven light source described in this teaching is that it can be configured to fit into a single optical package. Figure 10 shows an embodiment of a packaged electrodeless laser-driven light source 1000 having colinear laser excitation according to this teaching. A high-pressure electrodeless xenon gas-filled valve 1002 is located in 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 and 1012. The light from the laser diodes 1008, 1010 and 1012 is collimated by collimating optics 1014, 1016 and 1018. The pump light is directed by a mirror 1020, and the CW light is coupled to the pump beam path and made colinear by dichroic elements 1022 and 1024. A filter 1026 transmits the pump light and CW light but blocks the pulsed light. The focusing lens 1028 focuses the pulses generated by the Q-switch crystal 1030 to the dielectric breakdown region of the xenon gas-filled valve 1002. The Q-switch crystal includes a Yb:YAG rod portion and a Cr:YAG or V:YAG saturated absorber portion 1034. A high-reflection coating 1036 is applied to the ends of the crystal 1030.
[0041] [Equal amounts]
[0052] While the applicant's teachings have been described with various embodiments, the applicant's teachings are not intended to be limited to such embodiments. Rather, the applicant's teachings encompass a variety of alternative forms, modifications, and equivalents that will be understood by those skilled in the art, and these can be done without departing from the spirit and scope of these teachings. This specification contains the following provisions: [Clause 1] a) A sustained laser source that generates continuous wave (CW) sustained light at output, b) A pump laser that generates pump light as output, c) An optical beam coupler 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, wherein the CW sustain light and the pump light are coupled at the output so that the CW sustain light and the pump light propagate along the same line, d) A Q-switched laser crystal having a pump input optically coupled to the output of the pump laser, configured to generate pulsed light at its output in response to the pump light, e) A gas-filled valve optically coupled to the output of the sustaining laser and optically coupled to the output of the Q-switched laser crystal, wherein the pulsed light ignites a pulsed plasma in the dielectric breakdown region of the gas valve, and the sustaining light maintains a CW plasma in the CW plasma region of the gas valve, thereby causing the gas valve to emit high-intensity light. Equipped with, An electrodeless laser-driven light source wherein the gas-filled valve is positioned between the output of the pump laser and the pump input of the Q-switched laser crystal, and the CW plasma absorbs the pump light, thereby eliminating the pulsed light generated by the Q-switched laser crystal. [Clause 2] The electrodeless laser-driven light source according to Clause 1, wherein the maintenance laser source and the pump laser include the same laser. [Clause 3] The electrodeless laser driving light source according to Clause 1, wherein the maintenance laser source and the pump laser are configured in a single laser housing. [Clause 4] The electrodeless laser-driven light source according to Clause 1, wherein the optical coupler comprises a dichroic beam splitter. [Clause 5] The electrodeless laser-driven light source according to Clause 1, wherein the optical coupler comprises a fiber coupler. [Clause 6] The electrodeless laser driving light source according to Clause 1, wherein the Q-switched laser crystal is configured such that the pulse repetition rate of the pulsed laser light is in the range of 1 kHz to 20 kHz. [Clause 7] The electrodeless laser driving light source according to Clause 1, wherein the Q-switched laser crystal is configured such that the pulse repetition rate of the pulsed laser light is in the range of 1 kHz or less. [Clause 8] The electrodeless laser-driven light source according to Clause 1, wherein the Q-switched laser crystal is configured such that the pulse energy of the pulsed laser light is in the range of 350 μjoules to 50 mjoules. [Clause 9] The electrodeless laser-driven light source according to Clause 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. [Clause 10] The electrodeless laser-driven light source according to Clause 1, wherein the laser source is configured such that the output of the CW-maintaining light is in the range of 5W to 50W. [Clause 11] The electrodeless laser-driven light source according to Clause 1, wherein the laser source is configured such that the output of the CW-maintained light is in the range of 5W to 1500W. [Article 12] The electrodeless laser-driven light source according to Clause 1, wherein the Q-switched laser crystal includes a gain portion and a saturable absorber portion. [Clause 13] The electrodeless laser-driven light source according to Clause 1, wherein the Q-switched laser crystal comprises at least one of a glass host, a yttrium aluminum garnet host, and a spinel host. [Clause 14] The electrodeless laser-driven light source according to Clause 1, wherein the Q-switched laser crystal comprises at least one of a chromium dopant, a cobalt dopant, and a vanadium dopant. [Article 15] The electrodeless laser driving light source according to Clause 1, wherein the Q-switched laser crystal comprises a narrowband filter. [Clause 16] The electrodeless laser-driven light source according to Clause 15, wherein the narrowband filter reflects at least a portion of the plasma light. [Article 17] The electrodeless laser-driven light source according to Clause 15, wherein the narrowband filter blocks wavelengths of the xenon spectrum. [Clause 18] The electrodeless laser-driven light source according to Clause 1, wherein the gas-filled valve contains xenon gas. [Article 19] The electrodeless laser-driven light source according to Clause 1, wherein the gas-filled valve contains a rare gas. [Clause 20] The electrodeless laser-driven light source according to Clause 1, wherein the gas-filled valve is formed in a spherical shape. [Article 21] The electrodeless laser-driven light source according to Clause 1, wherein the pressure of the gas-filled valve is in the range of 20 atm to 50 atm. [Article 22] a) A step of supplying electromagnetic energy to the gas in a gas-filled valve using continuous CW laser light, b) A step of generating laser pulses by supplying laser pump radiation to a Q-switched laser crystal, c) The step of supplying the laser pulse to the gas in the gas-filled valve to generate pulsed plasma in the dielectric breakdown region of the gas, d) A step of generating a CW plasma that emits high-brightness light in the CW plasma region using the electromagnetic energy supplied to the ionized gas and the pulsed plasma, e) The step of passing the laser pump radiation supplied to the Q-switched laser crystal through the CW plasma region so that the CW plasma absorbs the pump light and thereby eliminates the pulsed light generated by the Q-switched laser crystal. A method for igniting an electrodeless laser-driven light source, including [the specified method]. [Article 23] A method for igniting an electrodeless laser-driven light source according to Clause 22, wherein the step of supplying electromagnetic energy to a gas in a gas-filled valve and the step of supplying laser pump radiation to a Q-switched laser crystal include the step of supplying the electromagnetic energy and the pump radiation using the same laser. [Article 24] A method for igniting an electrodeless laser-driven light source as described in Clause 22, wherein the dielectric breakdown region and the CW plasma region overlap. [Article 25] A method for igniting an electrodeless laser-driven light source as described in Clause 22, wherein the dielectric breakdown region and the CW plasma region do not overlap. [Article 26] A method for igniting an electrodeless laser-driven light source as described in Clause 22, wherein the pulse repetition rate of the laser pulse is in the range of 1 kHz or less. [Article 27] A method for igniting an electrodeless laser-driven light source as described in Clause 22, wherein the pulse repetition rate of the laser pulse is in the range of 1 kHz to 20 kHz. [Article 28] A method for igniting an electrodeless laser-driven light source according to Clause 22, wherein the pulse energy of the laser pulse is in the range of 350 μjoules to 50 mjoules. [Article 29] A method for igniting an electrodeless laser-driven light source as described in Clause 22, wherein the pulse duration of the laser pulse is in the range of 0.1 ns to 10 ns. [Clause 30] A method for igniting an electrodeless laser-driven light source according to claim 22, wherein the output of the continuous CW laser light is in the range of 5W to 1500W.
Claims
1. a) A continuous-wave (CW) laser source that generates a CW light beam, b) A pump laser that generates a pump light beam at output, c) A light beam coupler positioned to receive the CW light beam at one input and the pump light beam at the other input, wherein the CW light beam and the pump light beam are coupled at the output to form a combined CW and pump light beam, d) A Q-switched laser crystal arranged in the optical path of the pump light beam, which generates a Q-switched pulsed light beam as an output in response to the pump light beam, e) A gas-filling valve, wherein the gas-filling valve is positioned in the path of the CW light beam and the Q-switched pulsed light beam, so that the Q-switched pulsed light beam ignites a pulsed plasma in the dielectric breakdown region of the gas valve, the CW light beam maintains the CW plasma in the gas valve, the CW plasma emits light from the gas valve, and the CW plasma absorbs the pump light beam, thereby extinguishing the Q-switched pulsed light beam generated by the Q-switched laser crystal. An electrodeless laser-driven light source equipped with the above features.
2. The electrodeless laser driving light source according to claim 1, wherein the CW laser source and the pump laser include the same laser.
3. The electrodeless laser driving light source according to claim 1, wherein the CW laser source and the pump laser are configured in a single laser housing.
4. The electrodeless laser-driven light source according to claim 1, wherein the optical beam coupler comprises a dichroic beam splitter.
5. The electrodeless laser-driven light source according to claim 1, wherein the optical beam coupler comprises a fiber coupler.
6. The electrodeless laser driving light source according to claim 1, wherein the Q-switched laser crystal is configured such that the pulse repetition rate of the Q-switched pulsed light beam is in the range of 1 kHz to 20 kHz.
7. The electrodeless laser driving light source according to claim 1, wherein the Q-switched laser crystal is configured such that the pulse repetition rate of the Q-switched pulsed light beam is in the range of 1 kHz or less.
8. The electrodeless laser driving light source according to claim 1, wherein the Q-switched laser crystal is configured such that the pulse energy of the Q-switched pulsed light beam is in the range of 350 μjoules to 50 mjoules.
9. The electrodeless laser-driven light source according to claim 1, wherein the Q-switched laser crystal is configured such that the pulse duration of the Q-switched pulsed light beam is in the range of 0.1 ns to 10 ns.
10. The electrodeless laser driving light source according to claim 1, wherein the CW laser source is configured such that the output of the CW light beam is in the range of 5W to 50W.
11. The electrodeless laser driving light source according to claim 1, wherein the CW laser source is configured such that the output of the CW light beam is in the range of 5W to 1500W.
12. The electrodeless laser driving light source according to claim 1, wherein the Q-switched laser crystal includes a gain portion and a saturable absorber portion.
13. The electrodeless laser-driven light source according to 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. The electrodeless laser-driven light source according to claim 1, wherein the Q-switched laser crystal comprises at least one of a chromium dopant, a cobalt dopant, and a vanadium dopant.
15. The electrodeless laser driving light source according to claim 1, wherein the Q-switched laser crystal comprises a narrowband filter.
16. The electrodeless laser-driven light source according to claim 15, wherein the narrowband filter reflects at least a portion of the light emitted from the CW plasma.
17. The electrodeless laser-driven light source according to claim 15, wherein the narrowband filter blocks wavelengths of the xenon spectrum.
18. The electrodeless laser-driven light source according to claim 1, wherein the gas-filled valve contains xenon gas.
19. The electrodeless laser-driven light source according to claim 1, wherein the gas-filled valve contains a rare gas.
20. The electrodeless laser-driven light source according to claim 1, wherein the gas-filled valve is formed in a spherical shape.
21. The electrodeless laser-driven light source according to claim 1, wherein the pressure of the gas-filled valve is in the range of 20 atm to 50 atm.