Light source

Abstract

To provide a light source which is able to deliver broadband or supercontinuum light at a relatively high power level.SOLUTION: A light source includes a pulse generator (11) for providing a first sequence (13) of light pulses, the first sequence (13) of light pulses including a first number of light pulses within a predetermined time period, a manipulator (15) configured to generate a second sequence (17) of light pulses from the first sequence (13) of light pulses, the second sequence (17) of light pulses having a second number of light pulses within the predetermined time period, the second number being different from the first number, and a nonlinear optical element (19) arranged to receive the second sequence (17) of light pulses.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a light source, for example a broadband light source or a supercontinuum light source. [Background technology]

[0002] A broadband light source generally refers to a light source that emits light having a wide wavelength bandwidth, for example, 50 nm or more. Broadband light sources can include, for example, incandescent or fluorescent lamps, and typically provide a wide spectrum ranging from 400 to 1700 nm. However, for such sources, the intensity is limited by the quality of the filament used or the efficiency of the gas excitation. Furthermore, because the light is not spatially coherent, coupling the light into a fiber can be difficult, resulting in a low-power, low-brightness light source of moderate quality. One or more of the aforementioned limitations may not be optimal for many applications.

[0003] Supercontinuum generation can provide improvements over one or more of the above limitations. Supercontinuum generation relates to the formation of a broad, typically continuous spectrum, by the propagation of high power light, typically a pulse, through a nonlinear element such as a nonlinear fiber. The term supercontinuum does not cover a specific phenomenon, but rather may include at least some of a number of nonlinear effects, such as self-phase modulation, Raman scattering, phase matching, and soliton generation, that result in significant broadening of the optical pulse. The spectrum achieved by supercontinuum generation in a nonlinear optical fiber typically covers a broader spectrum, e.g., in some instances, a spectrum having wavelengths in the range of 400-2400 nm for incandescent or fluorescent lamps, and can provide one or more of higher intensity, single-mode beam characteristics, excellent pointing stability, and brightness of a laser.

[0004] A common form of broadband or supercontinuum source includes an ultrashort pulse optical pump source operating at a pump wavelength in the infrared region of the spectrum and highly nonlinear microstructured optics with specially designed dispersion characteristics.

[0005] Light sources, especially those capable of providing broadband supercontinuum light, are ideal sources for many applications, such as biomedical imaging, component characterization, manufacturing control, and materials processing. Broadband light or supercontinuum sources also have applications in the fields of spectroscopy, optical coherence tomography (OCT), metrology, scientific measurement, bioimaging, semiconductor inspection, and the like.

[0006] In some applications, such as materials processing, it may also be desirable to have a broadband or supercontinuum light source capable of providing broadband or supercontinuum light at high power. Summary of the Invention [Problem to be solved by the invention]

[0007] It is therefore an object of the present invention to provide a light source capable of providing broadband or supercontinuum light at relatively high power levels. It is also an object of the present invention to provide a light source which is able to avoid or at least reduce light-induced degradation of nonlinear optical elements used for broadband or supercontinuum generation. [Means for solving the problem]

[0008] This object is achieved by a light source having the features of claim 1. Preferred embodiments of the light source according to the invention are disclosed in the dependent claims. According to the invention, the light source includes a pulse generator for providing a first sequence of light pulses, the first sequence of light pulses having a first number of light pulses within a predetermined time period. The light source also includes a manipulator configured to generate a second sequence of light pulses from the first sequence of light pulses, the second sequence of light pulses having a second number of light pulses within a predetermined time period, the second number of light pulses being different from the first number of light pulses. The light source also includes a nonlinear optical element arranged to receive the second sequence of light pulses.

[0009] The nonlinear optical element may be particularly configured to generate broadband or supercontinuum optical pulses from the pulses of the second sequence of optical pulses. The light source may include a broadband light source or a supercontinuum light source.

[0010] The manipulator can be an optical device, particularly a fully fiber-based optical device, that varies the number of light pulses present in a first sequence of light pulses within a given time period. In particular, the manipulator can increase the number of pulses to be greater than the number present in the first sequence of light pulses, thereby generating a second sequence of light pulses having an increased number of pulses within a given time period.

[0011] The degradation of a nonlinear optical element in response to a pulse that produces a broadband spectrum while propagating through the nonlinear optical element is usually a continuous process. A pulse with a high peak power or energy transmitted through the nonlinear optical element causes higher degradation than a pulse with a low peak power. The degradation rate may be nonlinear, and thus a high peak power may cause severe damage or degradation to the nonlinear optical element.

[0012] The output power of a supercontinuum source can be increased by increasing the power of the pulses fed to the nonlinear optical element to generate the supercontinuum. However, increased power, especially increased peak power of the pulses, accelerates material degradation in the nonlinear optical element. Increasing the power of the pulses therefore shortens the lifetime of the nonlinear material and therefore the lifetime of the light source. Thus, there is often a limit as to how powerful a supercontinuum can be generated without significantly reducing the fiber and therefore the laser lifetime.

[0013] It is therefore a problem to provide a supercontinuum laser that provides high power without sacrificing the lifetime of the nonlinear optical element and thus the lifetime of the laser. The present invention provides a solution whereby the optical power delivered to the nonlinear optical element as optical pulses is distributed over an increased number of pulses, thereby increasing the total optical power accepted by the nonlinear optical element while keeping the pulse peak power below a predetermined maximum level. This level may be defined, for example, from the onset of accelerated fiber degradation in response to the pulses.

[0014] In particular, increasing the number of pulses per given period in the second sequence of optical pulses allows for a higher total optical power to be input to the nonlinear optical element during that period while maintaining the peak power of the pulses accepted by the nonlinear optical element at or below a given maximum level. This allows for a high power supercontinuum output of light from the nonlinear optical element without promoting degradation of the material of the nonlinear optical element. Furthermore, the resulting supercontinuum light can have a high spectral power density and / or a high spectral energy density.

[0015] An advantage of at least some embodiments of the present invention and the distribution of pulse power over multiple pulses is that an increased accumulated power can be delivered to the nonlinear optical element within a given period of time without the need to expose the nonlinear optical element to short high intensity pulses with extreme peak powers, thereby preventing accelerated degradation of the material of the nonlinear element. The increased accumulated power can be provided by multiple pulses occurring in short succession in a pulse train. Each pulse of such a pulse train can have a peak power that is too low to damage the nonlinear optical element, but high enough to generate a supercontinuum when propagating through the nonlinear element. The supercontinuum spectrum can be detected by a detector with an integration time long enough so that the individual spectra generated from the individual pulses of the pulse train cannot be resolved. The detected supercontinuum spectrum can have high power and / or high spectral power density over a large wavelength range, which can extend, for example, over the complete visible range.

[0016] As a result, the second sequence of optical pulses has a greater number of pulses per given time than the first sequence of optical pulses, thereby enabling the power of the light output from the nonlinear optical element to be increased without accelerating degradation of the nonlinear optical element.

[0017] In some embodiments, the energy or peak power of the selected pulses can be controlled. For example, the peak power or energy of the pulses supplied to the nonlinear optical element can be controlled to a level below a predetermined threshold level, i.e., below a predetermined maximum level. The maximum level can be selected such that damage or degradation of the nonlinear optical element does not occur or is reduced to an acceptable level. In other words, the predetermined maximum level is set such that for peak powers and energies below this level, degradation of the nonlinear optical element is kept low enough to ensure a long life of the nonlinear optical element and thus the light source. Thus, having more pulses with peak powers below the predetermined maximum level per predetermined time period in the second sequence of light pulses helps to increase the life of the nonlinear optical element and avoid damage to the nonlinear optical element, while allowing a high power output and / or a high spectral energy density to be obtained.

[0018] The peak power or energy of the selected pulse may be controlled so as to be "clamped" so as not to exceed a threshold that may correspond to a predetermined maximum level. The peak power or pulse energy may vary, for example, so that the number of pulses per unit time varies (to some extent, such variations are natural when pulses are amplified; the fewer the number of pulses per unit time, the more energy per pulse and therefore the higher the peak power), but is not allowed to vary beyond a threshold. Also, the peak power or energy of the pulses may be controlled to remain substantially the same as the number of pulses per unit time varies. For example, since supercontinuum generation is responsive to peak power, it may be advantageous to keep the peak power the same and fix it below a threshold selected to reduce damage to nonlinear elements, where not controlling or fixing the peak power or energy would make it undesirably large.

[0019] The manipulator may be configured to generate, from a first sequence of light pulses having a first repetition rate, a second sequence of light pulses having a second repetition rate higher than the first repetition rate. The manipulator may, for example, be configured to double the repetition rate of the pulses in the second sequence of light pulses relative to the repetition rate of the pulses in the first sequence of light pulses.

[0020] The manipulator may be configured to generate two or more pulses or a burst of pulses having a time delay between the pulses from a single pulse of the first sequence of optical pulses. Thus, the manipulator may generate multiple pulses from a single pulse of the first sequence of optical pulses. The multiple optical pulses may have a very short time delay between successive pulses. Such a sequence of pulses may result in high power generation when sent through a nonlinear element.

[0021] The output light can provide high power broadband or supercontinuum pulses having high spectral power density over a large wavelength range, e.g., spanning the visible range, while providing a broadband or supercontinuum output with less degradation of nonlinear optical elements.

[0022] In some embodiments the inter-pulse temporal spacing between pulses in a burst may be less than 200 picoseconds, such as less than 100 picoseconds, such as 10 picoseconds. The inter-pulse temporal spacing may be greater than 1.5 times the width of a pulse in a burst, such as 5 times the width of a pulse in a burst, such as 10 times the width of a pulse in a burst, such as 20-25 times the width of a pulse in a burst.

[0023] The manipulator may include a pulse splitter configured to split each pulse of the first sequence of light pulses into a given number N of pulses, thereby generating N subsequences of light pulses including the first subsequence of light pulses and N-1 further subsequences of light pulses, and the manipulator may be configured to individually delay each of the N-1 subsequences of light pulses relative to the first subsequence of light pulses. The number N may be a natural number. N may be 2 or greater.

[0024] The manipulator may include a pulse combiner configured to combine the first subsequence of light pulses and the N-1 individually delayed subsequences of light pulses, thereby generating a second sequence of light pulses. Thus, the second sequence of light pulses may be generated by a combination or superposition of the N subsequences of light pulses after the N-1 subsequences of light pulses are delayed with respect to the first subsequence of light pulses.

[0025] The manipulator may include N optical paths of different optical lengths, and the pulse splitter is configured to provide each of the N subsequences of optical pulses to one of the N optical paths, such that each of the N subsequences of optical pulses travels along one of the optical paths. Due to the different optical lengths of the paths, each of the N-1 subsequences is individually delayed with respect to a first subsequence of optical pulses that may be provided to the shortest optical path.

[0026] The optical paths may be formed by optical fibers, each of which may have a length that induces a predetermined time delay in pulses traveling through the respective fiber. The pulse generator may include an optical pump source, such as a pulsed laser. The pulses output from the pump source may be nanosecond, picosecond, or femtosecond pulses. The central wavelength of the pulses may be infrared, such as at least about 1064 nm. In some embodiments, the central wavelength of the pulses ranges from 1020 nm to 1080 nm. In some embodiments, the central wavelength is at a wavelength of 1550 nm ± 40 nm. In some embodiments, the central wavelength ranges from 1850 nm to 2050 nm.

[0027] The pulse generator may include at least one amplifier, which may serve to amplify the optical pulses emitted by the optical pump source. The pulse generator may include a pulse picker. For example, an acousto-optical modulator or an electro-optical modulator may be used as the pulse picker. The pulse selector may be configured to selectively select pulses, thereby reducing the repetition rate of an initial sequence of optical pulses emitted by an optical pump source of the pulse generator. The pulse picker may be advantageous for generating a first sequence of optical pulses from the initial sequence of optical pulses. Reducing the repetition rate of the first sequence of optical pulses may ensure a sufficient or desired time interval between different pulse bursts in a second sequence of optical pulses generated based on the first sequence of optical pulses.

[0028] At least one amplifier may be disposed before the nonlinear optical element to amplify the pulses of the second sequence of optical pulses, and thus the pulses of the second sequence of optical pulses provided to the nonlinear optical element may be amplified pulses.

[0029] In some embodiments, the amplifier is configured to amplify the pulses of the second sequence of pulses such that the peak power of the pulses delivered to the nonlinear element remains below a predetermined power threshold level. The level can be set to avoid or reduce damage to the nonlinear optical element. In combination with an increase in the number of pulses in the second sequence, this amplification provides an increase in the total accumulated optical power accepted by the nonlinear optical element, thereby increasing the power of the generated supercontinuum, while avoiding pulses with peak powers exceeding a predetermined power threshold level. This allows for a high-power supercontinuum light source with a sustained lifetime to be realized. Furthermore, the high-power supercontinuum light can have a high spectral power density over a large wavelength range, which can, for example, span the complete visible range.

[0030] As mentioned above, in some embodiments, the peak power or energy of the pulses can be controlled to remain substantially the same and / or not exceed a selected threshold. Control is desirable when the number of pulses per unit time can vary, such as in the present invention. For example, the present invention may include one or more amplifiers. The amplifiers are typically optically pumped, such as by laser diodes, to provide energy to transfer to the optical signal to amplify the signal. Very often, reducing the number of pulses amplified per unit time tends to increase the energy or peak power per pulse, since the amount of energy of the optical pump power delivered over the time interval is distributed among fewer amplified pulses.

[0031] Thus, one way to control the optical energy or peak power of a pulse, whether to compensate for variations due to the amplifier itself or to respond to other considerations, is to control the amplification process, such as, for example, controlling the pump laser or laser that excites the amplifier. For example, the optical pump power can be reduced when fewer pulses are amplified to compensate for the typical increase in amplified pulse energy or peak power. In some embodiments, a variable optical attenuator or modulator, such as an AOM (acousto-optical modulator) or an EOM (electro-optical modulator), may be used to control the peak power or energy of the pulse. Control of the AOM or EOM can be performed in conjunction with control of the amplification.

[0032] In some embodiments, the light source includes a detector for detecting, in particular sampling, at least some of the light pulses of the second sequence of light pulses before they are input to the nonlinear optical element.

[0033] At least one parameter of the second sequence of light pulses can be controlled based on a signal obtained from the detector. For example, the peak power of the pulses in the second sequence can be controlled based on the detector signal. Thus, the light source can be configured to sample the pulses, for example with the detector. The pulses delivered to the nonlinear element can be sampled before their delivery, and the control can be responsive to the sampled pulse energy or the peak power of the pulses or a burst of pulses (for example, if the detector is not responsive to individual pulses). It is also possible to control the peak power or energy of the pulses in response to a look-up table, or in response to a formula or algorithm, or in response to a selected operation of the light source. Such control can be combined with the aforementioned feedback control using the detector, or can be performed independently of it.

[0034] With respect to the operation of the light source, the pulses can be controlled in response to the operation of the manipulator or modulator, such as in response to a pulse picking a selected pulse. Depending on the application, any pulse of the light source may be sampled and / or controlled, such as, for example, a pulse from an emitting source, an initial sequence of pulses, a first or second sequence of pulses, etc. The light source may include a controller (not shown) in suitable communication with one or more of the aforementioned elements or components to provide the desired control.

[0035] In some embodiments, the light source includes a broadband light source or a supercontinuum light source that generates broadband or supercontinuum light. The light source may include a controller that controls the operation of at least one controllable element of the light source based on a signal obtained from the detection of the first sequence of light pulses or a portion of the second sequence of light pulses. The controllable element may be one of a pulse generator, an amplifier between the manipulator and the nonlinear optical element, an amplifier of the pulse generator, a pulse picker between an optical pump source of the pulse generator and the manipulator. The present invention also relates to a light source kit, comprising a light source according to the present invention, wherein the manipulator is a first manipulator arranged in a first module removable from the light source, the light source kit further comprising at least a second manipulator configured to generate a third sequence of light pulses from the first sequence of light pulses, the second manipulator arranged in a second module configured to replace the first module after removal of the first module from the light source.

[0036] The present invention also relates to an apparatus for illuminating a material sample, in particular for optical analysis of the material sample, which comprises a light source according to the present invention and a holder for the material sample, the holder being configured to hold the material, and in use of the light source the material sample is illuminated with broadband light or supercontinuum light emitted from a nonlinear optical element of the light source.

[0037] The invention also relates to a spectroscopic system and / or device for performing spectroscopy on a sample, the system and / or device comprising a light source according to the invention for illuminating the sample with broadband or supercontinuum light and at least one detector for detecting light from the sample. The integration time of the detector preferably exceeds the duration of the pulse and / or burst of pulses. The integration time of the detector can exceed a predefined time period. Thus, the detector does not "see" the structure of the pulse or burst, but detects the multiple supercontinuum pulses of the burst as one pulse. Thus, the light power provided by the burst as a whole is detectable such that the detector effectively records a single spectrum from the supercontinuum generated by each pulse in the burst as a spectrum from a single high power supercontinuum. This is particularly advantageous for the detection of low power signals. The integration time preferably does not include more than one burst. And the at least one detector is preferably activated synchronously with the light source such that the detector is activated when receiving a burst of pulses.

[0038] In some embodiments, the integration time can include more than one burst, i.e., it can be longer than the time between two bursts, or it can be longer than the duration of a pulse, or it can be shorter than the duration of a burst of pulses.

[0039] The spectroscopy system may be used, for example, to analyze dense or thick materials. Often such materials have very strong absorption, and only a very weak signal is transmitted through the material unless a high power light source is used to illuminate the material. The spectroscopy system utilizing the disclosed light source can analyze dense materials without the need to operate the light source in a mode where laser degradation is accelerated.

[0040] In at least some embodiments, the generated supercontinuum light may include at least 0.5 W, 1 W, 2 W, 5 W, 10 W of total power in the visible wavelength range of about 350-850 nm.

[0041] In at least some embodiments, supercontinuum light can be provided having a high power spectral density, e.g., 1 mW / nm, 2 mW / nm, 5 mW / nm, 10 mW / nm, or 20 mW / nm, measured over at least a 10 nm range within the "visible range," particularly between 350 and 850 nm.

[0042] In at least some embodiments, the supercontinuum light source can provide a power spectral density of greater than 10 mW / nm, such as a power spectral density of greater than 20 mW / nm, such as a power spectral density of greater than 25 mW / nm, such as a power spectral density of greater than 50 mW / nm, measured over a range of at least 10 nm within a portion of the supercontinuum spectrum extending from at least 1200 nm to at least 1300 nm.

[0043] The present invention also relates to an apparatus for irradiating a material sample, in particular for material processing, which comprises a light source according to the present invention and a holder for a material sample, which holder is configured to hold the material such that, when the light source is in use, the material sample is irradiated with broadband light or supercontinuum light emitted from a nonlinear optical element of the light source.

[0044] The invention also relates to a system for the optical analysis of an object and / or for the optical measurement of at least one parameter of an object. In some embodiments, a system for optical analysis and / or measurement includes: A light source according to one of several embodiments arranged to illuminate an object; a detector for detecting light received from the illuminated object; and an analyzer configured to analyze the detected light and derive therefrom at least one parameter of the object.

[0045] Broadband light sources, such as supercontinuum sources, which provide a spectrally broad continuous light source, are useful in many systems for optical analysis and measurement, such as systems configured for optical coherence tomography (OCT), white light interferometry, spectroscopy, optical frequency metrology, fluorescence microscopy, fluorescence lifetime spectrometry (FLIM), hyperspectral imaging, flow cytometry, coherent anti-Stokes Raman scattering (CARS) microscopy, and two-photon fluorescence microscopy.

[0046] In some embodiments, the system is a reflectance mode measurement system configured to measure light reflected from the analysis object, such as a white light interferometry based system such as optical coherence tomography (OCT). Advantageously, the system is based on time domain, frequency domain or swept source OCT.

[0047] For example, in applications where the light probes sub-surface regions of an object being analyzed, such as OCT analysis of a patient's skin or eye, higher power allows deeper portions of the object to be probed in the same duration or allows for faster analysis.

[0048] In one embodiment, the system for optical analysis is configured for in vivo, ex vivo and / or in vitro measurements of human or animal body parts. The system can be applied to different ophthalmic analyses and treatments, such as diagnosing age-related macular degeneration (AMD), diabetic retinopathy, or glaucoma. In some embodiments, the system is used in diagnosis related to treatment for refractive eye correction, such as laser eye surgery (LASIK) for correcting refractive eye conditions. In some embodiments, the system is used to measure the border of Bowman's layer inside the human eye.

[0049] In some embodiments, the system is used for characterization and / or sorting and / or quality inspection of products. The higher power of the broadband light source allows for a larger inspection volume defined from a larger inspection area and / or depth and / or faster optical analysis of the product.

[0050] In one embodiment, the measurement system is used for analysis and quality inspection of semiconductor materials, such as nitride-containing materials. The present invention also relates to a method for optically measuring at least one parameter of an object to be measured, in some embodiments the method comprises: Providing a measurement system according to one embodiment; illuminating the object to be analyzed with at least a portion of a broadband spectrum generated by a light source of the measurement system; detecting light from the object with a detector; and analyzing the detected light to derive at least one parameter of the object.

[0051] In some embodiments, the illuminating and detecting steps are performed simultaneously, for example when the system is configured for OCT measurements or absorption spectroscopy, where the optical response of the object to received light is instantaneous.

[0052] In some embodiments, the detecting step is performed after the illuminating step, for example if the system is configured for fluorescence measurements and the fluorescence response of the object to the received light is slightly delayed.

[0053] The invention also relates to a spectroscopic system and / or device for performing spectroscopy on a sample, comprising a light source according to the invention for illuminating the sample with broadband or supercontinuum light and at least one detector for detecting light from said sample. The integration time of the detector preferably exceeds the duration of the pulse and / or burst of pulses. Thus, the detector does not "see" the structure of the pulse or burst. However, the burst is detectable as a whole. This is particularly advantageous for the detection of low power signals. The integration time preferably does not include more than one burst. In some embodiments, the integration time can include multiple bursts, i.e. it can be longer than the time between bursts. The integration time may be longer than the duration of the pulse, but shorter than the duration of the burst of pulses.

[0054] Spectroscopic systems can be used, for example, to analyze dense or thick materials. Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0055] [Figure 1] FIG. 2 is a diagram illustrating a first example of a light source according to an embodiment. [Diagram 2] FIG. 4 is a diagram illustrating a second example of a light source according to an embodiment. [Diagram 3] 3 shows diagrammatically a sequence of light pulses occurring in operation of the light source of FIG. 2; [Figure 4] 3 shows diagrammatically a sequence of light pulses occurring in operation of the light source of FIG. 2; [Diagram 5] 3 shows diagrammatically a sequence of light pulses occurring in operation of the light source of FIG. 2; [Figure 6] 3 is a diagram showing an example of a manipulator used in the light source of FIG. 2. [Figure 7] FIG. 1 shows a block diagram of an example of an apparatus for irradiating a material sample. [Figure 8]3 shows a schematic representation of a sequence of light pulses that may be produced by a particular implementation of a light source according to the invention; [Figure 9] 3 shows a schematic representation of a sequence of light pulses that may be produced by a particular implementation of a light source according to the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] The light source of Figure 1 includes a pulse generator 11 for providing a first sequence of light pulses 13. The first sequence of light pulses 13 includes a first number of light pulses within a predetermined period of time. The light source of Figure 1 also includes a manipulator 15 capable of receiving the first sequence of light pulses 13. The manipulator 15 is configured to generate a second sequence of light pulses 17 from the first sequence of light pulses 13. The second sequence of light pulses 17 includes a second number of light pulses within a predetermined period of time, the second number being different from the first number.

[0057] The second sequence of optical pulses 17 is provided to a nonlinear optical element 19. The nonlinear optical element 19 may be, for example, a nonlinear optical fiber, such as a microstructured optical fiber, and the nonlinear optical element 19 may be configured to generate a sequence of broadband or supercontinuum optical pulses from the second sequence of optical pulses 17.

[0058] Microstructured optical fibers are known in the art, and generally include a longitudinally extending array of features, one or more of which have a different refractive index than the material surrounding the feature. The array of features acts to guide the light propagated by the fiber. Microstructured optical fibers include a core region and a cladding region, where the cladding region typically includes an array of features, and the features typically include voids. Different types of microstructured fibers can operate by different physical mechanisms. For example, in some microstructured fibers, the longitudinally extending array of features provides a photonic band gap such that light cannot exist in the cladding and is therefore confined to the core, and in other microstructured fibers, the longitudinally extending array of features provides an index guiding mechanism to confine light to the core, similar to total internal reflection in conventional fibers. Microstructured fibers also rely on other mechanisms. Microstructured fibers can have hollow or solid cores. For example, photonic band gap type microstructured fibers often have hollow cores.

[0059] Light pulses propagating in gas-filled hollow-core microstructured fibers can generate supercontinuums extending into the ultraviolet (UV) region. Since the light pulses propagate mainly in areas free of solid material, the strong pulse peak power has little effect on the degradation of the fiber material compared to solid-core fibers. However, a window is often placed to contain gas within the fiber (core), and this window can also be subject to degradation from high peak power pulses. This degradation can also be kept at a low level by distributing the pulse energy over a larger number of pulses.

[0060] The pulses in the first sequence of light pulses 13 may occur regularly over time. Thus, the pulses in the first sequence of light pulses 13 may occur at a pulse repetition rate R. In some examples, the predetermined period may be equal to n*T, where n is a natural number such as 1, 2, 3, ...., where the pulses in the first sequence of light pulses occur regularly over time. T may be the inverse of the pulse repetition rate R of the pulses in the first sequence of light pulses 13.

[0061] In some examples, the predetermined period may be equal to T / n, where n is greater than 1, such that the predetermined period is shorter than the time interval between two successive pulses of the first sequence of light pulses 13.

[0062] The second sequence of optical pulses 17 can be generated such that more optical pulses occur within the same time period. Thus, the second number of optical pulses can be greater than the first number of optical pulses. The second sequence of optical pulses 17 is provided to a nonlinear optical element 19, which expands the pulses, thereby generating broadband or supercontinuum optical pulses that are output from the nonlinear optical element 19 with the optical pulses of the sequence.

[0063] Because the second number of optical pulses is preferably greater than the first number of optical pulses, using the second sequence of optical pulses 17 to generate broadband or supercontinuum light in the nonlinear optical fiber provides the advantage that the peak power of the pulses in the second sequence of optical pulses can be maintained at a level that does not damage the nonlinear optical element 19, while still allowing the broadband or supercontinuum output of the nonlinear optical element to be at a high power level. That is, by increasing the number of pulses of the second sequence of optical pulses received by the nonlinear element in a given period of time, the total optical power delivered to the nonlinear element in that period of time can be increased without having to increase the peak power of any individual pulse.

[0064] 2 also includes a pulse generator 11, a manipulator 15, and a nonlinear optical element 19. The pulse generator 11 includes a laser oscillator 21, an amplifier 23, and a pulse picker 25.

[0065] The laser oscillator 21 can be configured to generate an initial sequence of optical pulses 27 having a defined repetition rate. Figure 3 shows a schematic representation of a portion of the initial sequence of optical pulses 27 in a pulse train diagram as a function of power P over time t.

[0066] The initial sequence of light pulses 27 may be amplified by amplifier 23, which increases the power level of the pulses in the initial sequence of light pulses 27. After amplification, the initial sequence of light pulses 27 is provided to a pulse picker 25, which may selectively pick out pulses from the initial sequence of light pulses 27. The pulse picker 25 may be, for example, an acousto-optical modulator or an electro-optical modulator.

[0067] An example of a first sequence of light pulses 13 output by the pulse picker 25 is shown diagrammatically in FIG. 4 in the form of a pulse train diagram. As can be seen by comparison with FIG. 3, the pulse picker 25 is configured to supply only one of the five pulses of the initial sequence of light pulses 27 to the manipulator 15. The remaining pulses may be absorbed in an optical dump arranged in the pulse picker 25. Thus, in the described example, the first sequence of light pulses 13 has a repetition rate that is reduced by a factor of five with respect to the repetition rate of the initial sequence of light pulses 27. A reduction of the repetition rate by any factor, such as, for example, 2, 3 or 4, is also possible. The pulse picker 25 can also be configured to "pick" pulses randomly from the initial sequence of light pulses 27, thereby generating a first sequence of light pulses 13 that does not have a defined repetition rate.

[0068] As can be seen with respect to Fig. 4, the first sequence of light pulses 13 comprises a first number of light pulses within a predetermined period T. For example, the predetermined period can be assumed to be n times the inverse of the pulse repetition rate R of the pulses of the first sequence of light pulses 13. As shown in Fig. 4, if n=1, then T=1 / R. This means that there is one pulse within the period T in the first sequence of light pulses 13 according to the example of Fig. 4.

[0069] The first sequence of light pulses 13 is provided to a manipulator 15 configured to generate a second sequence of light pulses 17 from the first sequence of light pulses 13 . FIG. 5 also shows, in a pulse train diagram, an example of a second sequence of light pulses 17 generated from the first sequence of light pulses 13 of FIG. 4. As can be seen in FIG. 5, the manipulator 15 generates from the pulses 29 in the first sequence 13 a burst of pulses 31 consisting of two or more pulses having a short time delay between each other. Such a time delay is also called a burst-to-burst pulse interval. Thus, per period, say T, the number of light pulses in the second sequence of light pulses 17 is greater than the number of light pulses in the first sequence of light pulses 13. Such a burst of pulses 31 can be detected as a single pulse with a detector having an integration time that exceeds the burst duration, such that the detector cannot resolve individual pulses within the burst 31.

[0070] In systems for optical analysis, such as spectroscopy or optical coherence tomography systems, with a detector having an integration time that exceeds the burst duration, one spectrum is recorded from the analyzed sample within the burst duration. Thus, the light source effectively provides a high power supercontinuum to the analyzed sample, making it suitable for use in the analysis of weakly reflective or transmissive samples.

[0071] The detector may detect the burst 31 as a relatively long single pulse of high energy, especially if it contains multiple closely spaced pulses. The detector integration time may therefore be longer than the duration of the burst 31, but shorter than the time T between successive bursts 31.

[0072] A measure of the duration of a burst may be, for example, the full width at half maximum (FWHM) of the intensity or power signal of the burst 31. The FWHM of the burst 31 may correspond, for example, to the duration between half the maximum power or intensity value of the leading flank of the first pulse in the burst and half the maximum power or intensity value of the trailing flank of the last pulse. The burst duration is denoted as At1.

[0073] Autocorrelation / deconvolution techniques can measure the individual pulse profiles. 5, the time between individual pulses of pulse burst 31 is shown as At2, which is the time interval between the pulse peaks of the pulses within the pulse burst. If the pulses within a pulse burst are regularly spaced, then the inverse of At2, i.e., 1 / At2, corresponds to the repetition rate of the pulses within the burst.

[0074] The duration At3 between pulse bursts 31 can correspond to the time interval between the peaks of the pulse burst envelope 31, which is in principle equal to the time difference between the peaks of the first pulses of each pulse burst 31. The inverse of At3, 1 / At3, corresponds to the pulse burst repetition rate at which the pulse bursts are regularly spaced apart.

[0075] FIG. 5 also shows the time width At4 between pulse bursts, which can be called the "inter-burst time interval" and can be considered as the time difference between the FWHMs points of opposite sides of successive burst pulse envelopes.

[0076] The pulse bursts 31 can be considered to have a "power cycle", which can correspond to At1 divided by At3 (At1 / At3). The power cycle can be expressed as a percentage. The value of the power cycle is related to the number of pulses in each pulse burst, which is, of course, related to the configuration of the manipulator 15.

[0077] In certain embodiments of the present invention, the pulse burst power cycle is less than or equal to a selected value, which may be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%.

[0078] In certain embodiments of the present invention, the pulse burst power cycle is greater than or equal to a selected value, which may be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%.

[0079] All reasonable combinations of the above are considered within the scope of the present invention. For example, the power cycle can be below 80% and above 50%. In certain embodiments of the invention, the ratio of the number of pulses in the second sequence shown in FIG. 5 to the number of pulses in the first sequence shown in FIG. 4 may be greater than or equal to a selected value, which may be 2, 4, 6, 8, 10, 20, 50, 100, or 500.

[0080] In certain embodiments of the invention, the ratio At3 / At2 may be a selected value, such as 5, 10, 25, 50, 100, or 1000 or greater. Again, all sensible, ie, not physically meaningless, combinations of the above embodiments describing selected values ​​and ranges thereof are within the scope of the present invention.

[0081] In another non-illustrated example, the manipulator 15 may be configured to generate the second sequence of light pulses 17 such that the second sequence of light pulses 17 has a second repetition rate that is higher than the first repetition rate of the pulses 29 in the first sequence 13. For example, the repetition rate may be two or four times higher.

[0082] For example, the manipulator 15 can be configured to insert a pulse burst 31 between two pulse bursts 31 shown in FIG. 5, thereby increasing the repetition rate of the pulse bursts from that shown in FIG.

[0083] The manipulator 15 comprises a time delay device 33 and an amplifier 35. An exemplary embodiment of the time delay device 33 is described with respect to Fig. 6. The time delay device 33 comprises an optical splitter 37 configured to split each pulse 29 of the first sequence 13 into a given number N of pulses, in the example described, N being equal to 4. This generates subsequences 39, 41, 43, 45 of N=4 optical pulses.

[0084] The time delay device 33 further includes N=4 optical paths of different optical lengths. The pulse splitter 37 is configured to feed each of the four subsequences of optical pulses 39-45 into one of the optical paths 47-53. The optical paths 47-53 are realized by optical fibers. Specifically, in this embodiment, each optical path 47-53 includes a fiber of a defined length extending between an output port of the optical splitter 37 and an input port of the optical coupler 55. In the first optical path 47, no additional delay line is inserted. In the second optical path 49, one additional delay line 57 is inserted. The delay line 57 consists of a fiber of a defined length. In the third optical path 51, two delay lines 57 are inserted, and in the fourth optical path 53, three delay lines 57 are inserted. The second optical path 49 is therefore longer than the first optical path 47 by one time the length of the delay line 57. The third optical path 51 is twice as long as the length of the delay line 57, compared to the first optical path 47. The fourth optical path 53 is three times as long as the length of the delay line 57, compared to the first optical path 47.

[0085] The first subsequence 39 of light pulses traveling along the first optical path 47 arrives at the optical coupler 55 earlier than the second subsequence 41 traveling through the second optical path 49. The third subsequence 43 of light pulses traveling through the third optical path 51 is further delayed relative to the first and second subsequences of light pulses. Additionally, the fourth subsequence 45 of light pulses is further delayed as the pulses of the fourth subsequence 45 travel down the fourth optical path 53 using three delay lines 57.

[0086] A combiner 55 combines subsequences of light pulses 39-45 originating from different optical paths 47-53, thereby generating a second sequence of light pulses 17 in which the input pulses from the different optical paths are delayed with respect to each other, so that the second sequence 17 may comprise bursts of pulses 31 (see also FIG. 5). By varying the number of optical paths and their lengths it is possible to generate different bursts 51 or to increase the repetition rate of the first sequence of light pulses 13.

[0087] After the generated second sequence of optical pulses 17 has passed through the amplifier 35, it is fed into a nonlinear optical element 19 which includes or consists of a highly nonlinear fiber 61. Nonlinear effects occurring in the fiber 61 broaden the spectral bandwidth of the pulses, resulting in a broadband or supercontinuum spectrum.

[0088] As described above, the optical paths 47 to 53 can be formed by optical fibers of the same length, with one delay line inserted in the second optical path 49, two delay lines 57 inserted in series in the third optical path 51, and three delay lines 57 inserted in series in the fourth optical path 53.

[0089] Alternatively, the four optical paths 47 to 53 may be formed by four optical fibers of different lengths. As used herein, the term "light" refers not only to visible light, but also to light in the non-visible wavelength range, including, for example, light in the infrared (IR) or ultraviolet (UV) wavelength range.

[0090] The broadband or supercontinuum optical spectrum produced by the nonlinear optical element 19 may comprise a continuous spectrum or may comprise a spectrum having bands of very closely spaced wavelengths.

[0091] The broadband spectrum generated in the nonlinear fiber may be a supercontinuum spectrum. The allocation of the light source elements 21-25, 33-35, 61 to the components 11, 15, 19 as shown in Fig. 2 can be seen from a formal point of view, other types of allocations can also be made. For example, the light source of Fig. 2 can be realized using three modules. The first module may include a laser oscillator 21.

[0092] The second module, which may be considered an amplifier or preamplifier module, includes one or more amplifiers, such as amplifier 23 and a further amplifier, with a pulse picker 25 and / or a time delay device 33 sandwiched between the two amplifiers. In some embodiments, the time delay device 33 may also be placed before the one or more amplifiers. The pulse picker 25 is preferably between the two amplifiers. Preferably, in embodiments including both a pulse picker 25 and a time delay device 33, the pulse picker 25 is placed before the time delay device 33 and both are placed between the two amplifiers.

[0093] The third module may be considered a booster module and includes amplifier 35 and nonlinear optical element 19. In some embodiments, a preamplifier may be placed before amplifier 35. Optionally, if this preamplifier is present in the third module, the second amplifier placed in the second module after time delay device 33 may be omitted.

[0094] In some embodiments, each of the modules is contained in a separate housing, which can be connected to each user using optical fibers. 7 shows a block diagram of an example of an apparatus 63 for analyzing a material sample. The apparatus 63 comprises a light source 65, in accordance with a particular embodiment of the present invention, for illuminating a material sample, and a detector 67 for detecting light scattered from or transmitted through the illuminated material sample. The detector 67 preferably has an integration time that is longer than the duration of a burst provided by the light source 65 and smaller than the time span between two successive bursts.

[0095] FIG. 8(a) shows, as an example, two successive pulses generated by a pulse generator. By using several arms of the first manipulator and the delays provided by them, as shown in FIG. 8(b), it is possible to obtain a successive pulse train, each train having a pulse within a predetermined period. These pulses are then amplified, as shown in FIG. 8(c), using one or more amplifiers placed after the first manipulator, while the peak power is kept below a predetermined maximum level, in particular to increase the total power delivered while avoiding accelerated degradation of the nonlinear optical element. The amplification can provide that the total optical power provided to the nonlinear optical element can be increased for the pulse train, as shown in FIG. 8(a) and FIG. 8(b). This allows the generation of high-power supercontinuum pulses without using very high peak powers that would rapidly degrade the nonlinear optical element.

[0096] As shown in FIG. 8(c), a detector that can be used to detect a supercontinuum pulse generated from an amplified pulse train can have an integration time longer than a predetermined time interval, and therefore the integration time can be longer than the time length of the pulse train. The detector detects one supercontinuum pulse while each pulse in the pulse train can generate an individual supercontinuum pulse. Thus, the detected supercontinuum pulse includes the contributions provided by the individual supercontinuum pulses, and the detected supercontinuum pulse can therefore have a high total power and a large spectral power density or spectral energy density.

[0097] Figure 9 shows another way to generate the train pulses shown in Figure 8(c). That is, the initial sequence of optical pulses shown in Figure 9(a) can be amplified by an amplifier placed after the pulse generator and before the first manipulator, as shown in Figure 9(b). Such a sequence has a peak power that exceeds a predefined maximum level, i.e. the damage threshold of the nonlinear optical element, but this is not the case after the manipulator, which increases the repetition rate of the initial sequence of optical pulses shown in Figure 9(c).

[0098] In some embodiments, the above-described embodiments do not include a nonlinear element, and such a pulse or burst of pulses is output without being spectrally broadened by a nonlinear element.

[0099] Some embodiments and additional features of the present invention are summarized in the following list of items. 1. A pulse generator for providing a first sequence of light pulses, said first sequence of light pulses having a first number of light pulses within a predetermined period of time, the pulse generator comprising: a light emitting source for generating optical pulses; A modulator in communication with the light source for increasing or decreasing the first number of optical pulses supplied by the pulse generator within the predetermined period; A manipulator optically downstream of the pulse generator and optically communicating with the pulse generator, configured to generate the second sequence of optical pulses from the first sequence of optical pulses, the second sequence of optical pulses having a second number of optical pulses increased within the predetermined period, the second number being greater than the first number, and a manipulator; In response to a pulse generator operating in the manipulator, the second sequence of optical pulses includes bursts of optical pulses having a time interval TB between bursts, and one burst includes consecutive pulses having a time TBP therebetween, TBP < TB, preferably TBP < TB / 2, a light source.

[0100] 2. The light source according to item 1, wherein the first sequence of optical pulses includes consecutive pulses having a time T therebetween, and TBP < TB < T. 3. Further including a non-linear optical element optically communicating with the manipulator downstream of the manipulator, and generating a burst of spectrally broadened pulses for receiving and spectrally broadening the pulses, the light source according to any one of items 1 or 2.

[0101] 4. The light source according to any one of items 1 to 3, wherein the light source is configured such that TBP can be maintained substantially the same even when TB changes. 5. The modulator includes an optical modulator, the optical modulator optically communicating with the light source and being located optically downstream of the light source, the light source according to any one of items 1 to 4.

[0102] 6. The light source according to item 5, wherein the modulator includes an acousto-optic modulator. 7. The light source according to any one of items 1 to 4, wherein the modulator electrically modulates the light source.

[0103] 8. The light source according to any one of items 1 to 7, wherein the light emitting source includes a laser diode for generating a pulse. 9. The light source according to any one of items 1 to 7, wherein the light emitting source includes a mode-locked fiber laser.

[0104] 10. The light source according to any one of items 1 to 9, wherein the pulse generator can provide an optical pulse having a maximum repetition rate RMAX and a corresponding time TMIN between pulses, and the light source can generate the burst of pulses where TBP < TMIN.

[0105] 11. The light source according to any one of items 1 to 10, wherein the manipulator includes a pulse splitter configured to split the received pulse into N divided pulses. The light source according to any one of items 1 to 10, wherein the manipulator is configured to provide different time delays to at least some of the N divided optical pulses.

[0106] 12. The light source according to item 11, wherein the manipulator includes a pulse combiner (55) configured to combine the divided pulses. 13. The light source according to item 11 or 12, wherein the manipulator includes N optical paths having different optical lengths, and the pulse splitter is configured to supply each of the N divided pulses of the optical pulse to one of the N optical paths.

[0107] 14. The light source according to any one of items 1 to 13, including at least one amplifier optically arranged between the light emitting source of the pulse generator and the manipulator. 15. The light source according to any one of items 3 to 14, including at least one amplifier optically arranged between the manipulator and the non-linear optical element to amplify the pulse before being supplied to the non-linear optical element.

[0108] 16. The light source according to item 15, wherein the light source is configured to amplify the pulse such that the peak power of the amplified pulse remains below a predetermined power threshold level, and the threshold level is selected to reduce optical damage to the nonlinear element.

[0109] 17. The light source according to item 14 or 15, wherein the light source is configured to amplify the pulse such that the peak power of the amplified pulse is substantially the same, or, if not the same, the pulses are controlled such that the value of TBP is different and / or the pulses of the burst with different values of TB are included, so that the pulses are below a threshold level, particularly a predetermined maximum level, and the pulses are amplified in the absence of control.

[0110] 18. The light source according to any one of items 3 to 17, wherein the nonlinear optical element is a nonlinear optical fiber, particularly a microstructure optical fiber. 19. A light source for providing pulses at a repetition rate R and at a corresponding time T between pulses, a pulse picker optically downstream of the light source and optically communicating with the light source for receiving the pulses and providing pulses having a reduced repetition rate RRED, where RRED < R, a manipulator optically downstream of the pulse picker and optically communicating with the pulse picker for receiving the pulses having the repetition rate RRED and providing pulses having an increased repetition rate RINC, where RRED > R, A light source comprising: In response to the light source operating during the manipulator, the light source outputs a burst of pulses, particularly a burst of pulses received from the manipulator, the burst having a time TB between the bursts, and the burst includes pulses having a time TBP between the pulses of the burst, where TBP < TB < T, and preferably TBP < TB.

[0111] 20. The light source described in item 19, further comprising a nonlinear optical element optically downstream of and in optical communication with the manipulator for receiving pulses having the repetition rate RINC and spectrally broadening such pulses, wherein the generated burst of pulses is a burst of spectrally broadened pulses.

[0112] 21. A light source kit comprising the light source according to any one of items 1 to 20, wherein the manipulator is a first manipulator disposed in a first module detachable from the light source, the light source kit further comprising at least one second manipulator configured to generate a third sequence of light pulses from the first sequence of light pulses; the second manipulator is disposed within a second module configured to replace the first module after removal of the first module from the light source; A light source kit, wherein when the second manipulator replaces the first manipulator, the third sequence of pulses includes the bursts of pulses having the time TB between bursts and the time TBP between the successive pulses of a burst.

[0113] 21. A light source kit comprising the light source according to any one of items 1 to 20, wherein the manipulator (15) is a first manipulator disposed in a first module detachable from the light source, the light source kit further comprising at least one second manipulator configured to generate a third sequence of light pulses from the first sequence of light pulses; A light source kit, wherein the second manipulator is disposed within a second module configured to replace the first module after removal of the first module from the light source.

[0114] 22. An apparatus for irradiating a material sample, in particular a material process, comprising: A light source according to any one of items 1 to 20, a holder for a material sample, the holder holding the material sample such that the light emitted from the nonlinear optical element of the light source is irradiated onto the material sample; and / or a detector, preferably having an integration time longer than the duration of a burst provided by the light source.

[0115] 23. Use of a light source according to any one of items 1 to 20, or use of a light source according to any one of items 1 to 10 for carrying out optical analysis, such as spectroscopic analysis, of a sample material. 24. A method for performing spectroscopic analysis of a material sample, comprising: Using a light source according to any one of items 1 to 20, or using a light source according to any one of items 1 to 10 to irradiate a material sample; In particular, detecting light from the material sample using a detector having an integration time longer than the duration of a pulse or burst of pulses provided by the light source. [Explanation of symbols]

[0116] 11: Pulse generator 13: First sequence of light pulses 15: Manipulator 17: Second sequence of light pulses 19: Nonlinear optical elements 21: Laser oscillator 23: Amplifier 25: Pulse Picker 27: Initial sequence of light pulses 29: Pulse 31: Burst of Pulses 33: Time Delay Device 35: Amplifier 37: Optical splitter 39: First subsequence of light pulses 41: Second subsequence of light pulses 43: Third subsequence of light pulses 45: Fourth subsequence of light pulses 47: First optical path 49: Second optical path 51: 3rd optical path 53: 4th optical path 55: Optical coupler 57: Delay line 59: Optical fiber 61: Nonlinear optical fiber 63:Equipment 65: Light source 67: Detector T: Period t: time P: Power

Claims

1. a pulse generator (11) for providing a first sequence of light pulses (13), said first sequence of light pulses (13) comprising a first number of light pulses within a predetermined period of time; a manipulator (15) configured to generate a second sequence of light pulses (17) from the first sequence of light pulses (13), the second sequence of light pulses (17) having a second number of light pulses within the predetermined period, the second number being different from the first number; a nonlinear optical element (19) arranged to receive said second sequence of optical pulses (17); A light source comprising:

2. the manipulator (15) is configured to generate a burst of pulses (31) comprising at least two pulses from a single pulse (29) of the first sequence of light pulses (13), said burst of pulses having a time delay between said at least two pulses. The light source of claim 1 .

3. The nonlinear optical element (19) is a nonlinear optical fiber (61), in particular a microstructured optical fiber, the second sequence of optical pulses generating a broadband spectrum or a supercontinuum when propagating through the nonlinear optical fiber (61).

3. A light source according to claim 1 or 2.

4. at least one amplifier (35) is arranged between the manipulator (15) and the nonlinear optical element (17) for amplifying the pulses of the second sequence (17) of optical pulses before feeding them to the nonlinear optical element (19); 4. A light source according to claim 1, 2 or 3.

5. The manipulator (15) a pulse splitter (37) configured to split each pulse of the first sequence of light pulses into a given number N of pulses, thereby generating N subsequences of light pulses (39, 41, 43, 45) comprising a first subsequence of light pulses (39) and a further subsequence of N-1 light pulses (41, 43, 45), wherein the manipulator (15) is configured to individually delay each of the N-1 subsequences of light pulses (41, 43, 45) with respect to the first subsequence of light pulses (39); a pulse combiner (55) configured to combine the first subsequence of optical pulses (39) and the individually delayed subsequences of N-1 optical pulses (41, 43, 45) thereby generating the second sequence of optical pulses (17); Equipped with A light source according to any one of claims 1 to 4.

6. The manipulator (15) comprises N optical paths (47, 49, 51, 53) having different optical lengths; the pulse splitter (37) is configured to provide each of the subsequences of N optical pulses (39, 41, 43, 45) to one of the N optical paths (47, 49, 51, 53); 6. The light source of claim 5.

7. The optical paths (47, 49, 51, 53) are formed by optical fibers.

7. The light source of claim 6.

8. the pulse generator (11) comprises an optical pump source (21), in particular a pulsed laser; and / or At least one amplifier (23) is arranged between the optical pump source (21) of the pulse generator (11) and the manipulator (15); and / or a pulse picker (25) disposed between the optical pump source (21) of the pulse generator (11) and the manipulator (15); A light source according to any one of claims 1 to 7.

9. the light source comprises a detector for detecting, in particular for sampling, at least a portion of the light pulses of the second sequence of light pulses (17) before they are input to the nonlinear optical element (19), At least one parameter of the second sequence of light pulses (17) is controlled based on a signal obtained from the detector. A light source according to any one of claims 1 to 8.

10. a controller for controlling operation of at least one controllable element of the light source based on a signal obtained from detection of the first sequence of light pulses (13) or a portion of the second sequence of light pulses (17), The controllable element is The pulse generator (11), an amplifier (35) disposed between the manipulator (15) and the nonlinear optical element (17); an amplifier of the pulse generator (11); a pulse picker (25) disposed between the optical pump source (21) of the pulse generator (11) and the manipulator (15); A light source according to any one of claims 1 to 9.

11. 1. An apparatus for spectroscopic analysis of a material sample, comprising: A light source (65) according to any one of claims 1 to 10, a detector (67) for detecting light from the material sample during an integration time, the detector (67) being positionable such that the material sample can be illuminated by light emitted from the nonlinear optical element of the light source (65) and light from the material sample can be detected by the detector (67); An apparatus comprising:

12. the integration time of the detector (67) exceeds the duration of the burst of pulses (31) generated by the light source (65); 12. The apparatus of claim 11.

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