Device for Providing Optical Radiation

Abstract

The apparatus for providing optical radiation (9) comprises a first seed source (1) for providing a first seed radiation (11), a second seed source (2) for providing a second seed radiation (12), a coupler (3) connected to the first seed source (1) and the second seed source (2) for coupling the first seed radiation (11) and the second seed radiation (12), and at least one amplifier (4) for amplifying the first seed radiation (11) and the second seed radiation (12).

Description

[Technical field]

[0001] The present invention relates to an apparatus for providing optical radiation. The present invention is particularly suited to continuous wave and pulsed lasers, including semiconductor diode lasers and fiber lasers, and marking, cutting, scribing and welding using such lasers. The present invention is also suited to lasers used to process highly reflective materials such as copper and diamond, and sintering metal powders using lasers, commonly referred to as additive manufacturing or 3D printing. [Background technology]

[0002] Industrial lasers, such as fiber lasers and disk lasers, have important applications in marking, cutting, scribing, welding, sintering metal powders using lasers in a process commonly referred to as additive manufacturing or 3D printing, and other material production processes. Lasers are used in a variety of industries, including consumer electronics, medical devices, automotive, and aerospace. Lasers can be pulsed or continuous wave. Typical achievable pulse lengths range from a few picoseconds to a few nanoseconds, microseconds, and milliseconds. The pulse repetition rate is electronically controlled and can span a wide range.

[0003] As power levels and intensities increase, so do the problems associated with nonlinear effects, such as spectral noise, temporal noise, speckle, nonlinear wavelength conversion of optical radiation, and self-Q-switching, which are undesirable in industrial processing systems where process repeatability is required.

[0004] For example, wavelength conversion can introduce errors into the optical focusing system, reducing the optical power reaching the material, and self-Q-switching can destroy the optical amplifiers and optical fibers in the laser system.

[0005] The local population inversion in the fiber amplifier increases considerably before the pulse reaches the output of the amplifier. As the pulse propagates, it depletes the population inversion and the intensity increases. The amplification process also contributes to significant reshaping and re-sharpening of the pulse. This is very important in defining the pulse duration and peak power, and therefore the various nonlinear manifestations such as Stimulated Raman Scattering (SRS) and Stimulated Brillouin Scattering (SBS). Above a certain energy level, all pulses are reshaped (re-sharpened) and the pulse duration decreases. This is due to the pulse gaining enough energy to start saturating the amplifier. In this situation, the energy is mainly extracted at the onset of the pulse, which is known to cause pulse deformation and distortion. Depending on the fiber design and pulse shape, the peak power increases nonlinearly with pulse energy and always exceeds the SRS threshold, which is typically around 5kW to 10kW.

[0006] Another important effect limiting the output power of pulsed fiber lasers is the formation of giant pulses. These can unfortunately damage optical elements in the system. This effect is highly dependent on the peak power and spectral characteristics of the laser and is believed to be caused by stimulated Brillouin scattering (SBS). When the nonlinear threshold is reached, the forward pulse is reflected. Giant pulses are observed and they can unfortunately damage amplifiers (and other devices) in the pulsed laser system. Unfortunately, the nature of this effect is stochastic and as such is highly unpredictable. A momentary change in the spectral characteristics, such as narrowing the linewidth of the seed laser (such as a laser diode), may cause an SBS event, leading to the formation of giant pulses and subsequent catastrophic damage.

[0007] US Patent No. 7,936,796 discloses a master oscillator power amplifier using a multi-longitudinal mode Fabry-Perot semiconductor laser whose output is amplified by an optical fiber amplifier. A reflector such as a fiber Bragg grating is inserted between the semiconductor laser and the amplifier. The reflector narrows the bandwidth of the laser radiation emitted from the optical fiber amplifier, reducing the effects of stimulated Brillouin scattering, such as the formation of backward random pulses and giant pulses. This result was surprising, since a narrower bandwidth would normally be expected to worsen the effects of stimulated Brillouin scattering. However, as the required peak and average powers continue to increase, stimulated Brillouin scattering and other nonlinear effects are once again becoming a problem. Summary of the Invention [Problem to be solved by the invention]

[0008] What is needed is an apparatus for providing optical radiation that avoids or reduces the problems identified above. [Means for solving the problem]

[0009] According to a non-limiting embodiment of the present invention, a first seed source providing a first seeding radiation; a second seed source providing a second seeding radiation; a coupler connected to the first seed source and the second seed source for coupling the first seed radiation and the second seed radiation; at least one amplifier for amplifying the first seed radiation and the second seed radiation; An apparatus for providing optical radiation is provided, comprising:

[0010] The apparatus may comprise a controller for controlling the first seed source, the second seed source and the amplifier, increasing a frequency and amplitude of the random optical pulses if the peak power of the second seeding radiation is reduced.

[0011] The apparatus may include a controller for controlling the first seed source, the second seed source, and the amplifier, wherein optical radiation emitted by the apparatus has a higher peak power, a higher average power, and / or a higher pulse energy than when the apparatus does not include the second seed source.

[0012] The apparatus may include a controller for controlling the first seed source, the second seed source, and the amplifier, such that the optical radiation emitted by the apparatus can achieve a higher peak power before exceeding a damage threshold of the apparatus than if the apparatus did not include the second seed source.

[0013] Surprisingly, the first seed source, the second seed source, and the amplifier are controllable to increase the frequency and amplitude of the random optical pulses as the peak power of the second seeding radiation is decreased. Such random optical pulses are believed to be indicative of the presence of stimulated Brillouin scattering, which can cause catastrophic damage to the device. The reduction in the presence of the random optical pulses and associated stimulated Brillouin scattering when the peak power of the second seeding radiation is increased enables the device to more reliably provide higher peak powers.

[0014] Also, surprisingly, it is possible to control the first seed source, the second seed source, and the amplifier such that the optical pulses emitted from the optical amplifier have higher peak power and higher average power than a similar device that does not include a second seed source. Limitations on achievable peak power arise from the generation of random and giant optical pulses believed to be induced by stimulated Brillouin scattering.

[0015] The first seeding radiation may be characterized by a first wavelength. The second seeding radiation may be characterized by a second wavelength. The first wavelength may be the same as the second wavelength.

[0016] The coupler is preferably a polarisation combiner.The apparatus may be configured such that the first seeding radiation and the second seeding radiation are orthogonally polarised.

[0017] The apparatus may include a depolarising element between the coupler and the amplifier.

[0018] The first seed source may be a Fabry-Perot semiconductor laser.The second seed source may be a Fabry-Perot semiconductor laser.

[0019] The first seed source may be a superluminescent diode. The second seed source may be a superluminescent diode.

[0020] The apparatus may include a first reflector that reflects a portion of the first seeding radiation towards the first seed source. The apparatus may include a second reflector that reflects a portion of the second seeding radiation towards the second seed source.

[0021] The first seed source and the first reflector may be separated by a first distance. The second seed source and the second reflector may be separated by a second distance. The first distance may be the same as the second distance, which allows pulses from the first and second seed sources to overlay if the first and second seed sources are pulsed synchronously. Alternatively, the first distance may be different from the second distance, which allows pulses from the first and second seed sources to be out of phase with each other or decoupled from each other.

[0022] The first and second reflectors may have the same spectral characteristics or may have different spectral characteristics.

[0023] The spectral characteristics of the first and second reflectors and the first and second distances may be selected to optimize the peak power and pulse energy of the optical radiation.

[0024] The first reflector and the second reflector may be optical fiber Bragg gratings.

[0025] The controller may emit a first control signal to drive the first seed source and a second control signal to drive the second seed source. The first control signal may be different from the second control signal. Driving the first seed source and the second seed source with different control signals helps ensure that the gain dynamics of the first seed source and the second seed source are different from each other, which can reduce the risk of Stimulated Brillouin Scattering occurring.

[0026] The apparatus may comprise a first optical isolator between the first seed source and the amplifier for isolating the first seed source from backward traveling optical radiation.

[0027] The apparatus may include a second optical isolator between the second seed source and the amplifier for isolating the second seed source from backward traveling optical radiation.

[0028] The apparatus may include a third optical isolator between the coupler and the amplifier for isolating both the first seed source and the second seed source from backward optical radiation.

[0029] The apparatus may include at least one preamplifier and a fourth optical isolator, the fourth optical isolator being located between the preamplifier and the amplifier. The apparatus may include a visible laser diode and a coupler, the coupler combining optical radiation emitted from the visible laser diode and the preamplifier and passing the combined optical radiation to the amplifier. The coupler may be incorporated into the fourth optical isolator.

[0030] The apparatus may further comprise a beam delivery cable and output optics, the beam delivery cable comprising an optical fiber for transmitting the optical radiation emitted from the amplifier. The optical fiber may be a hollow core fiber. The output optics may comprise an optical isolator.

[0031] The present invention also provides providing a first seeding radiation by a first seed source; providing a second seeding radiation by a second seed source; coupling the first seed radiation and the second seed radiation with a coupler; amplifying the first seed radiation and the second seed radiation with at least one amplifier; The present invention provides a method for providing optical radiation, comprising:

[0032] The method of the present invention may include the steps necessary to use any of the above-described aspects of the apparatus of the present invention. [Brief description of the drawings]

[0033] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 shows an apparatus for providing optical radiation according to the present invention. [Diagram 2] FIG. 2 shows an example of a forward pulse in the prior art. [Diagram 3] FIG. 3 shows a prior art pulse that includes an additional spike. [Figure 4] FIG. 4 shows an example of a giant pulse in the prior art. [Diagram 5] FIG. 5 shows a pulse emitted from a device of the present invention. [Figure 6] FIG. 6 shows a cross section of a polarization-maintaining hollow fiber. [Figure 7] FIG. 7 shows a cross section of a polarization-maintaining hollow fiber. [Figure 8] FIG. 8 shows an apparatus for providing optical radiation in accordance with the present invention, including a thermocouple for monitoring proper operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] FIG. 1 shows the present invention. a first seed source 1 providing a first seeding radiation 11; a second seed source 2 providing a second seeding radiation 12; a coupler 3 connected to the first seed source 1 and the second seed source 2 for coupling the first seed radiation 11 and the second seed radiation 12; at least one amplifier 4 for amplifying the first seeding radiation 11 and the second seeding radiation 12; 1 shows an apparatus for providing optical radiation 9, comprising:

[0035] The apparatus may comprise a first seed source 1 , a second seed source 2 and a controller 5 for controlling the amplifier 4 .

[0036] The controller 5 may control the first seed source 1, the second seed source 2, and the amplifier 4 so that the peak power 35 of the first seeding radiation 11 is greater than a peak power threshold 36 that would result in stimulated Brillouin scattering of sufficient intensity to damage the device in the absence of the second seeding radiation 12 from the second seed source 2, thereby enabling the peak power 37 of the optical radiation 9 emitted by the device to be increased.

[0037] The controller 5 may control the first seed source 1, the second seed source 2, and the amplifier 4 so that the peak power 37 of the optical radiation 9 is greater than the damage threshold 38 in the absence of the second seeding radiation 12 by the second seed source 2.

[0038] As shown in Figure 1, the controller 5 may be configured so that the first seed source 1 and the second seed source 2 emit optical pulses. Alternatively, or in addition, as shown in Figure 1, the controller 5 may be configured so that the first seed source 1 and the second seed source 2 emit continuous wave optical radiation.

[0039] As explained in US Pat. No. 7,936,796, FIG. 2 shows the optical power 201 of a forward pulse traveling from the first seed source 1 through the amplifier 4. The output power 201 was measured at the output of the amplifier 4. FIG. 2 also shows the output power 202 of a backward pulse traveling to the first seed source 1 during normal operation. The measurement was performed with an apparatus similar to that shown in FIG. 1, but with only the first seed source laser 1 present. The optical powers 201 and 202 are plotted on different scales because the output power 201 has a much higher power than the optical power 202. The output power 202 includes a first reflection 203 and a second reflection 204 due to different splices in the apparatus. The pulse shape shown in FIG. 2 is typical of most pulses generated in an apparatus such as that shown in FIG. 1.

[0040] FIG. 3 shows two examples of backward pulses 211, 212 propagating towards the primary seed source 1. The pulses 211 and 212 contain the same optical powers 203 and 204 as before, but also contain additional spikes 213 and 214. These additional spikes 213 and 214 occur infrequently and are random in both occurrence and intensity. The frequency of occurrence can be changed by changing the operating conditions of the primary seed source 1 (such as temperature, drive current and pulse shape). At a pulse repetition frequency of 25 kHz, the additional spikes have been observed at frequencies between approximately 1 in a period of 48 hours or more and 30,000 times in 5 minutes. In addition, the frequency of occurrence can be changed by using different primary seed sources 1, either from different or the same manufacturer. The additional spikes 213, 214 have been observed in the backward direction, but no evidence is observable in the forward pulse shape 201. It is believed that the spikes 213 and 214 are evidence of stimulated Brillouin scattering (SBS). Spikes 213 and 214 are random in nature, are generally undesirable, and are referred to elsewhere in this specification as random pulses.

[0041] Figure 4 shows an example of a giant pulse 221 superimposed on a normal looking pulse 201 generated in the forward direction. The associated pulse 222 measured by the back reflection detector has a complex shape and is several times larger than the pulse 202 shown in Figure 2. In fact, the optical powers 203 and 204 are not visible at this scale. The pulse 222 has a spike 223, a trailing edge 224, and a dip 225. These data were obtained by setting up the device so that the backward spikes 213 and 214 occurred around 100 Hz. At this repetition frequency, the giant pulse 221 and associated pulse 222 were observed to occur once every 5 minutes. In other words, the giant pulse 221 occurs much less frequently than the backward pulses 213 and 214 and occurs randomly.

[0042] The dip 225 is also believed to be evidence of SBS. The backward pulse 222 has enough energy to excite the forward pulse via SBS. This creates a forward giant pulse 221, which extracts energy from the backward pulse 222, creating the dip 225. All of these pulses are further amplified by the active gain medium in amplifier 4.

[0043] 4, the amplitude 226 of the giant pulse 221 shown is approximately twice the amplitude 227 of the pulse 201 (without the superimposed giant pulse 221). The amplitude 226 varies randomly and can be several times the amplitude 227 of the pulse 201. It is believed that the amplitude of the giant pulse 221 is sufficient to exceed the optical damage threshold of the fiber in the amplifier 4, which, together with the additional energy released by the acoustic waves associated with the SBS propagation, probably caused the random and unpredictable catastrophic damage described above. However, this explanation is merely theoretical, and any attempt herein to explain possible damage mechanisms is not intended to limit the scope of the invention.

[0044] Referring again to FIG. 1, the first seed source 1, the second seed source 2 and the amplifier 4 are controllable so that the frequency and amplitude of the random optical pulses 213, 214 increase as the peak power 10 of the second seeding radiation 12 decreases.

[0045] The first seed source 1, the second seed source 2, and the amplifier 4 are controllable so that the optical pulses 41 emitted from the optical amplifier 4 shown in Figure 5 have higher peak power 42, higher average power 43, and higher pulse energy 44 than a similar device that does not include the second seed source 2. In both cases, limitations on the achievable peak power arise from the generation of random and giant optical pulses, believed to be induced by stimulated Brillouin scattering.

[0046] This result is surprising because it was thought that a device with a first seed source 1 but no second seed source 2 (as described in US Pat. No. 7,936,796) would operate at a peak power that could not be increased further due to nonlinear optical effects. Nonlinear effects that limit the achievable peak power, pulse energy, and average power include spectral noise, temporal noise, speckle, nonlinear wavelength conversion of the optical radiation, stimulated Brillouin scattering, stimulated Raman scattering, and self-Q-switching. It is therefore surprising that by introducing a second seed source 2, combining the first seed radiation 11 and the second seed radiation 12 in a coupler 3, and amplifying the first seed radiation 11 and the second seed radiation 12 in an amplifier 4, the peak power and / or the pulse energy can be increased.

[0047] The first seeding radiation 11 may be characterized by a first wavelength 13. The second seeding radiation 12 may be characterized by a second wavelength 14. The first wavelength 13 may be identical to the second wavelength 14.

[0048] The coupler 3 is preferably a polarisation combiner. The apparatus may be arranged such that the first seeding radiation 11 and the second seeding radiation 12 are orthogonally polarised at respective inputs 15, 16 of the polarisation combiner.

[0049] The apparatus may include a depolarizer 17 between coupler 3 and amplifier 4. Depolarizer 17 may be a Riot depolarizer. The Riot depolarizer may comprise two lengths of polarization-maintaining optical fiber spliced ​​together, one twice the length of the other. When a single seed source is used, the depolarizer scrambles the polarization of the seeding radiation before it enters amplifier 4, allowing the peak power of the optical radiation to be increased before nonlinear effects such as stimulated Brillouin scattering become problematic.

[0050] The first seed source 1 may be a Fabry-Perot semiconductor laser. The second seed source 2 may be a Fabry-Perot semiconductor laser.

[0051] The first seed source 1 may be a superluminescent diode. The second seed source 2 may be a superluminescent diode.

[0052] The apparatus may comprise a first reflector 17 for reflecting a portion of the first seeding radiation 11 towards the first seed source 1. The apparatus may comprise a second reflector 18 for reflecting a portion of the second seeding radiation 12 towards the second seed source 2.

[0053] The first seed source 1 and the first reflector 17 may be separated by a first distance 6. The second seed source 2 and the second reflector 18 may be separated by a second distance 7. The first distance 6 may be the same as the second distance 7. This allows the pulses from the first seed source 1 and the second seed source 2 to be overlaid if the first seed source 1 and the second seed source 2 are pulsed synchronously. Alternatively, the first distance 6 may be different from the second distance 7. This allows the pulses from the first seed source 1 and the second seed source 2 to be out of phase with each other or to be decoupled from each other. Dephasing and interleaving of the pulses can also be achieved by adjusting the first and second control signals 48 and 49 by the controller 5.

[0054] The first and second reflectors 17, 18 may have the same or different spectral characteristics, including center wavelength, bandwidth, reflectivity, and chirp.

[0055] The spectral characteristics of the first and second reflectors 17, 18 and the first and second distances 6, 7 may be selected to optimize the peak power and pulse energy of the optical radiation. The peak power when the first seed source 1 and the second seed source 2 are pulsed may be greater than the peak power when only one of the first seed source 1 and the second seed source 2 is pulsed, with the limitations of the peak power being the random pulse 223, 244 and the giant pulse 221. The peak power can be increased by at least a factor of two, and preferably by a factor of five or more.

[0056] The first reflector 17 and the second reflector 18 may be optical fiber Bragg gratings.

[0057] The controller 5 may emit a first control signal 48 to drive the first seed source 1 and a second control signal 49 to drive the second seed source 2. The first control signal 48 may be the same as the second control signal 49, or may be different. Driving the first seed source 1 and the second seed source 2 with different control signals helps to ensure that the gain dynamics of the first seed source 1 and the second seed source 2 are different from each other. This is useful, for example, when pulsing a Fabry-Perot semiconductor laser having multiple longitudinal modes. Semiconductor lasers sometimes emit laser light in a single longitudinal mode during a pulse, which may cause stimulated Brillouin scattering events such as random pulses or giant pulses described with reference to Figures 2 to 5. Driving the semiconductor lasers with different control signals can reduce the probability that the first seed source 1 and the second seed source 2 emit light in a single longitudinal mode simultaneously within a pulse. The first drive signal 48 and the second drive signal 49 can be made different from each other using passive elements or by adjusting the circuit arrangement to ensure that the capacitance or inductance is different for the two seed sources.

[0058] The apparatus may comprise a first optical isolator 8 between the first seed source 1 and the amplifier 4 for isolating the first seed source 1 from backward optical radiation 9 propagating from the amplifier 4 towards the first seed source 1.

[0059] The apparatus may include a second optical isolator 52 between the second seed source 2 and the amplifier 4 for isolating the second seed source 4 from backward optical radiation 9 propagating from the amplifier 4 towards the second seed source 2.

[0060] The apparatus may comprise a third optical isolator 53 between the coupler 3 and the amplifier 4 for isolating both the first and second seed sources 1 , 2 from backward optical radiation 9 .

[0061] The apparatus may include at least one preamplifier 21, and a fourth optical isolator 22. The fourth optical isolator 22 is located between the preamplifier 21 and the amplifier 4. The apparatus may include a visible light laser diode 24 and a coupler 25 that combines the visible light radiation 26 emitted by the visible light laser diode 24 and the optical radiation 27 emitted by the preamplifier 21 prior to amplification by the amplifier 4. The coupler 25 may be integrated into the optical isolator 22. The coupler 25 is preferably a wavelength division multiplexer. The wavelength division multiplexer may be a fused fiber coupler.

[0062] The apparatus may further comprise a beam transmission cable 31 and output optics 32, the beam transmission cable 31 comprising an optical fiber 33 for transmitting the optical radiation emitted from the amplifier 4. The output optics 32 may comprise a fifth optical isolator 34.

[0063] The optical fiber 33 may be single mode or multimode. The optical fiber 33 may be a solid core fiber, a microstructured fiber, or a hollow core fiber. The hollow core fiber may be a kagome fiber, a photonic crystal fiber, or an anti-resonant fiber. Such hollow core fibers are advantageous because they allow optical radiation to be transmitted over significantly longer distances without incurring nonlinear optical effects. The optical fiber 33 may be a polarization maintaining fiber.

[0064] Examples of anti-resonant fibers are shown in Figures 6 and 7. Anti-resonant fibers 160 and 170 comprise a capillary 161 and a number of anti-resonant tubes 163 along the inner surface 162 of the capillary 161. Advantageously, the anti-resonant fibers 160 and 170 are polarization-maintaining fibers with the anti-resonant tubes 163 providing a two-fold symmetrical element in the cross section of the fiber. This is achieved by incorporating first and second anti-resonant tubes 164 and 171, as shown in Figure 16, where the first anti-resonant tube 164 is larger and / or of a different shape compared to the second anti-resonant tube 163. Alternatively or additionally, the first anti-resonant tube may be a nested tube 171, as shown in Figure 17. The nested tube 171 may be made of an absorbing or scattering material to create a loss of one polarization of light propagating along the fiber 170 compared to the other polarization. The use of polarization-maintaining fibers is advantageous in material processing applications such as marking, cutting, and welding because material processing performance often depends on the polarization of the incident optical radiation. The ability to deliver polarized optical radiation to a workpiece and fine-tune the polarization by rotating optical fiber and / or polarizing optics such as half-wave plates is highly advantageous in applications where material processing depends on the polarization of the optical radiation.

[0065] 8 shows an example of an apparatus for providing optical radiation 9, where the first and second seed sources are semiconductor laser diodes. The controller 5 controls the first and second seed sources 1, 2 via a laser diode driver 81. The laser diode driver 81 is preferably a high speed laser diode driver.

[0066] The preamplifier 21 is controlled via an electronic pump diode driver 82 which controls the current driven by at least one pump diode 83. The pump diode 83 is preferably a multiple transverse mode semiconductor laser diode. The pump diode 83 may be an integral part of the preamplifier 21 and is not shown in FIG.

[0067] Amplifier 4 is controlled via an electronic pump diode driver 82 which controls the current conducted by a number of pump diodes 83. The outputs of pump diodes 83 are combined by pump combiner 84, which is preferably a multimode to multimode optical fiber pump combiner. Pump diodes 83 are preferably a multi-transverse mode semiconductor laser diode module comprising a number of multi-transverse mode semiconductor laser diodes. Pump diodes 83 and pump combiner 84 may be integral parts of amplifier 4 and are not shown in FIG.

[0068] The output optics 32 includes a first temperature sensor 85 whose output is fed back to the controller 5. The temperature sensor 85 is used to ensure that adequate optical isolation is provided by the fifth optical isolator 34. The temperature sensor 85 may be a thermocouple or a thermistor.

[0069] A second temperature sensor 86 is provided to monitor the temperature of a heat sink (not shown) to which the pump diode 83 is connected. The output of the second temperature sensor 86 is connected to the controller 5. The controller 5 may use the known temperature dependence in the power of the pump diode 83 to adjust the current flowing into the pump diode 83 to ensure that the output radiation 9 is stable over ambient temperature and time. Alternatively, or in addition, the controller 5 may use measurement data obtained in calibrating the device.

[0070] The beam delivery cable 31 includes a sturdy hose 87 that restrains bending to prevent sharp bends in the optical fiber 33. If the bend radius of the optical fiber 31 is too small, the optical radiation 9 will escape from the core of the optical fiber 31, resulting in thermal damage to the optical fiber 31.

[0071] The optical fiber 31 may be a single mode optical fiber. Alternatively, the optical fiber 31 may be a multimode optical fiber, in which case an optional mode adapter 88 may be provided to ensure that the optical modes guided by the optical fiber 31 are properly excited to provide the desired optical power spatial distribution at the output radiation 9. For example, if the desired output radiation 9 has a top-hat shaped distribution, it is desirable that the optical modes guided by the optical fiber 31 are evenly excited. The mode adapter 88 may be an optical fiber mode scrambler comprising at least one bend for scrambling the optical modes guided by the internal optical fiber.

[0072] Additional features not shown include a laser diode driver for controlling a visible light laser diode 24, and a fan for cooling the device.

[0073] It will be understood that the embodiments of the invention described above with reference to the accompanying drawings are by way of example only and that modifications and additional components may be provided to improve performance.

[0074] Each component shown in the drawings is not limited to its use in the drawings and may be used in other drawings and in all aspects of the invention. The invention extends to the separate components described and / or illustrated above, either alone or in any combination. [Configuration 1] a first seed source providing a first seeding radiation; a second seed source providing a second seeding radiation; a coupler connected to the first seed source and the second seed source for coupling the first seed radiation and the second seed radiation; at least one amplifier for amplifying the first seed radiation and the second seed radiation; 1. An apparatus for providing optical radiation comprising: [Configuration 2] The apparatus of configuration 1, further comprising a controller for controlling the first seed source, the second seed source, and the amplifier, and for increasing a frequency and amplitude of random optical pulses if the peak power of the second seeding radiation decreases. [Configuration 3] 3. The apparatus of configuration 1 or 2, comprising a controller for controlling the first seed source, the second seed source, and the amplifier, and configured such that the emitted optical radiation has higher peak power, higher average power, and / or higher pulse energy than if the apparatus did not include the second seed source. [Configuration 4] 2. The apparatus of configuration 1 or 1, comprising a controller for controlling the first seed source, the second seed source, and the amplifier, wherein the emitted optical radiation can achieve a higher peak power before exceeding a damage threshold of the apparatus than if the apparatus did not include the second seed source. [Configuration 5] 5. The apparatus of any one of configurations 1 to 4, wherein the first seeding radiation is characterized by a first wavelength and the second seeding radiation is characterized by a second wavelength, the first wavelength being the same as the second wavelength. [Configuration 6] 6. The apparatus of any one of configurations 1 to 5, wherein the coupler is a polarization combiner and the first seeding radiation and the second seeding radiation are orthogonally polarized. [Configuration 7] 7. The apparatus of any one of configurations 1 to 6, comprising a depolarizing element between the coupler and the amplifier. [Configuration 8] The apparatus of any one of configurations 1 to 7, wherein the first seed source is a Fabry-Perot semiconductor laser and the second seed source is a Fabry-Perot semiconductor laser. [Configuration 9] The apparatus of any one of configurations 1 to 7, wherein the first seed source is a superluminescent diode and the second seed source is a superluminescent diode. [Configuration 10] 10. The apparatus of any one of configurations 1-9, comprising a first reflector that reflects a portion of the first seeding radiation towards the first seed source. [Configuration 11] 11. The apparatus of configuration 10, comprising a second reflector that reflects a portion of the second seeding radiation towards the second seed source. [Configuration 12] 12. The apparatus of configuration 11, wherein the first seed source and the first reflector are separated by a first distance, the second seed source and the second reflector are separated by a second distance, and the first distance and the second distance are equal. [Configuration 13] 12. The apparatus of configuration 11, wherein the first seed source and the first reflector are separated by a first distance, and the second seed source and the second reflector are separated by a second distance, the first distance being different from the second distance. [Configuration 14] 14. The apparatus of any one of configurations 11 to 13, wherein the first reflector and the second reflector have the same spectral characteristics. [Configuration 15] 14. The apparatus of any one of configurations 11 to 13, wherein the first reflector and the second reflector have different spectral characteristics. [Configuration 16] 16. The apparatus of any one of configurations 14 to 15, wherein the spectral characteristics of the first reflector and the second reflector, and the first distance and the second distance are selected to optimize peak power and pulse energy of the optical radiation. [Configuration 17] 17. The apparatus of any one of configurations 11 to 16, wherein the first reflector and the second reflector are optical fiber Bragg gratings. [Configuration 18] 18. The apparatus of any one of configurations 1 to 17, wherein the controller emits a first control signal to drive the first seed source and a second control signal to drive the second seed source, the first control signal being different from the second control signal. [Configuration 19] 19. The apparatus of any one of configurations 1 to 18, comprising a first optical isolator between the first seed source and the amplifier for isolating the first seed source from backward traveling optical radiation. [Configuration 20] 20. The apparatus of any one of configurations 1 to 19, comprising a second optical isolator between the second seed source and the amplifier for isolating the second seed source from backward traveling optical radiation. [Configuration 21] 21. The apparatus of any one of configurations 1 to 20, comprising a third optical isolator positioned between the coupler and the amplifier for isolating both the first seed source and the second seed source from backward optical radiation. [Configuration 22] 22. The apparatus of any one of configurations 1 to 21, comprising at least one preamplifier and a fourth optical isolator, the fourth optical isolator being located between the preamplifier and the amplifier. [Configuration 23] 23. The apparatus of configuration 22, comprising a visible light laser diode and a coupler, the coupler combining optical radiation emitted from the visible light laser diode and the preamplifier and passing the combined optical radiation to the amplifier. [Configuration 24] 24. The apparatus of claim 23, wherein the coupler is incorporated into the fourth optical isolator. [Configuration 25] 25. The apparatus of any one of configurations 1 to 24, comprising a beam transmission cable and an output optical element, the beam transmission cable comprising an optical fiber for transmitting the optical radiation emitted from the amplifier. [Configuration 26] 26. The apparatus of claim 25, wherein the optical fiber is a hollow core fiber. [Configuration 27] 27. The apparatus of any one of configurations 25-26, wherein the output optics comprises an optical isolator. [Configuration 28] providing a first seeding radiation by a first seed source; providing a second seeding radiation by a second seed source; coupling the first seed radiation and the second seed radiation with a coupler; amplifying the first seed radiation and the second seed radiation with at least one amplifier; 23. A method for providing optical radiation comprising: [Configuration 29] 29. The method of configuration 28, comprising the first seed source, the second seed source, and the amplifier, wherein the first seed source, the second seed source, and the amplifier increase a frequency and amplitude of random optical pulses as the peak power of the second seeding radiation decreases. [Configuration 30] 29. The method of claim 28, further comprising a controller for controlling the first seed source, the second seed source, and the amplifier, wherein the first seed source, the second seed source, and the amplifier cause the optical radiation emitted by the amplifier to have a higher peak power, a higher average power, and / or a higher pulse energy than in a case where the step of providing the second seeding radiation is not included. [Configuration 31] 29. The method of claim 28, further comprising a controller for controlling the first seed source, the second seed source, and the amplifier, wherein the first seed source, the second seed source, and the amplifier are capable of achieving a higher peak power before the optical radiation emitted by the amplifier exceeds a damage threshold than in a case not including the step of providing the second seeding radiation. [Configuration 32] 32. The method of any one of configurations 28 to 31, wherein the first seeding radiation is characterized by a first wavelength and the second seeding radiation is characterized by a second wavelength, and the first wavelength is the same as the second wavelength. [Configuration 33] 33. The method of any one of configurations 28 to 32, wherein the coupler is a polarization combiner and the first seeding radiation and the second seeding radiation are of orthogonal polarizations. [Configuration 34] 34. The method of configuration 33, comprising the step of providing a depolarizing element between the coupler and the amplifier. [Configuration 35] 35. The method of any one of configurations 28 to 34, wherein the first seed source is a Fabry-Perot semiconductor laser and the second seed source is a Fabry-Perot semiconductor laser. [Configuration 36] 35. The method of any one of configurations 28 to 34, wherein the first seed source is a superluminescent diode and the second seed source is a superluminescent diode. [Configuration 37] 37. The method of any one of configurations 28-36, comprising providing a first reflector to reflect a portion of the first seeding radiation back to the first seed source. [Configuration 38] 38. The method of embodiment 37, comprising providing a second reflector to reflect a portion of the second seeding radiation towards the second seed source. [Configuration 39] 39. The method of configuration 38, wherein the first seed source and the first reflector are separated by a first distance, the second seed source and the second reflector are separated by a second distance, and the first distance and the second distance are equal. [Configuration 40] 39. The method of configuration 38, wherein the first seed source and the first reflector are separated by a first distance, and the second seed source and the second reflector are separated by a second distance, the first distance being different from the second distance. [Configuration 41] 41. The method of any one of configurations 38 to 40, wherein the first reflector and the second reflector have the same spectral characteristics. [Configuration 42] 41. The method of any one of configurations 38 to 40, wherein the first reflector and the second reflector have different spectral characteristics. [Configuration 43] The method of configuration 41 or 42, wherein the spectral characteristics of the first reflector and the second reflector, and the first distance and the second distance are selected to optimize peak power and pulse energy of the optical radiation. [Configuration 44] 44. The method of any one of configurations 38 to 43, wherein the first reflector and the second reflector are optical fiber Bragg gratings. [Configuration 45] 45. The method of any one of configurations 28 to 44, comprising providing a controller to emit a first control signal to drive the first seed source and a second control signal to drive the second seed source, the first control signal being different from the second control signal. [Configuration 46] 46. ​​The method of any one of configurations 28 to 45, comprising providing a first optical isolator between the first seed source and the amplifier to isolate the first seed source from backward traveling optical radiation. [Configuration 47] 47. The method of any one of configurations 28 to 46, comprising providing a second optical isolator between the second seed source and the amplifier to isolate the second seed source from backward traveling optical radiation. [Configuration 48] 48. The method of any one of configurations 28 to 47, comprising providing a third optical isolator positioned between the coupler and the amplifier to isolate the first seed source and the second seed source from backward optical radiation. [Configuration 49] 49. The method of embodiment 48 comprising providing at least one preamplifier and a fourth optical isolator, the fourth optical isolator being located between the preamplifier and the amplifier. [Configuration 50] 50. The method of embodiment 49, comprising providing a visible light laser diode and a coupler, the coupler combining optical radiation emitted from the visible light laser diode and the preamplifier and passing the combined optical radiation to the amplifier. [Configuration 51] 51. The method of claim 50, wherein the coupler is incorporated into the fourth optical isolator. [Configuration 52] 52. The method of any one of configurations 28 to 51, comprising providing a beam transmission cable and an output optical element, the beam transmission cable comprising an optical fiber for transmitting the optical radiation emitted from the amplifier. [Configuration 53] 53. The method of claim 52, wherein the optical fiber is a hollow core fiber. [Configuration 54] 53. The method of claim 51 or 52, wherein the output optical element comprises an optical isolator.

Claims

1. An apparatus for providing optical radiation, the apparatus comprising: a first seed source providing a first seeding radiation; a second seed source providing a second seeding radiation; a first coupler connected to the first seed source and the second seed source for coupling the first seed radiation and the second seed radiation; at least one amplifier for amplifying the first seed radiation and the second seed radiation; a controller that controls the first seed source, the second seed source, and the amplifier; Equipped with the first seeding radiation is characterized by a first wavelength and the second seeding radiation is characterized by a second wavelength, the first wavelength being the same as the second wavelength; the controller is operable to control the first seed source, the second seed source, and the amplifier to amplify the first seeding radiation and the second seeding radiation by the amplifier to prevent a peak power of the second seeding radiation from decreasing to a level that would cause the apparatus to exceed a damage threshold of the apparatus, such that the apparatus provides optical radiation having a greater peak power than in the absence of the second seed source. Device.

2. The apparatus of claim 1 , wherein the first coupler is a polarization combiner, and the first seeding radiation and the second seeding radiation are of orthogonal polarizations.

3. 3. The apparatus of claim 1, further comprising a depolarizing element between the first coupler and the amplifier.

4. The apparatus of claim 1 , wherein the first seed source is a Fabry-Perot semiconductor laser and the second seed source is a Fabry-Perot semiconductor laser.

5. The apparatus of claim 1 , wherein the first seed source is a superluminescent diode and the second seed source is a superluminescent diode.

6. 6. The apparatus of claim 1 , comprising a first reflector configured to reflect a portion of the first seeding radiation towards the first seed source.

7. 7. The apparatus of claim 6, further comprising a second reflector that reflects a portion of the second seeding radiation to the second seed source, the first seed source and the first reflector being separated by a first distance and the second seed source and the second reflector being separated by a second distance, the first distance being different from the second distance.

8. 8. The apparatus of claim 1, wherein the controller emits a first control signal to drive the first seed source and a second control signal to drive the second seed source, the first control signal being different from the second control signal.

9. 9. The apparatus of claim 1, comprising at least one preamplifier, an optical isolator, a visible light laser diode, and a second coupler, the optical isolator being located between the preamplifier and the amplifier, and the second coupler combining optical radiation emitted from the visible light laser diode and the preamplifier and passing the combined optical radiation to the amplifier.

10. 10. The apparatus of claim 1, further comprising a beam delivery cable and an output optical element, the beam delivery cable comprising an optical fiber for transmitting the optical radiation emitted from the amplifier, the optical fiber being a hollow core fiber.

11. A method for providing optical radiation by an apparatus, comprising the steps of: providing a first seeding radiation by a first seed source; providing a second seeding radiation by a second seed source; coupling the first seeding radiation and the second seeding radiation with a first coupler; amplifying the first seed radiation and the second seed radiation with at least one amplifier; Including, a controller that controls the first seed source, the second seed source, and the amplifier; the first seeding radiation is characterized by a first wavelength and the second seeding radiation is characterized by a second wavelength, the first wavelength being the same as the second wavelength; using the controller to control the first seed source, the second seed source, and the amplifier to amplify the first seeding radiation and the second seeding radiation with the amplifier to prevent a peak power of the second seeding radiation from decreasing to a level that causes the apparatus to exceed a damage threshold of the apparatus, whereby the apparatus is operable to provide optical radiation having a greater peak power than in the absence of the second seed source. method.

12. The method of claim 11 , wherein the first coupler is a polarization combiner, and the first seeding radiation and the second seeding radiation are of orthogonal polarizations.

13. The method of claim 12 including providing a depolarizing element between the first coupler and the amplifier.

14. 14. The method of claim 11, comprising providing a first reflector to reflect a portion of the first seeding radiation towards the first seed source.

15. 15. The method of any one of claims 11 to 14, comprising the step of providing a beam delivery cable and an output optics, the beam delivery cable comprising an optical fiber for transmitting the optical radiation emitted from the amplifier, the optical fiber being a hollow core fiber.

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