Method and system for broadening output spectrum of mode-locked femtosecond laser and femtosecond laser

Abstract

The invention provides a method and a system for widening an output spectrum of a mode-locked femtosecond laser and the femtosecond laser, and relates to the technical field of mode-locked femtosecond lasers. The widening method comprises the following steps: fitting a gain spectrum curve of a laser gain crystal to obtain a gain spectrum fitting curve about wavelength; fitting the output rate curve of the output mirror based on a preset shape to obtain an output rate fitting curve about the wavelength; determining a comprehensive gain spectrum curve about the wavelength according to the gain spectrum fitting curve and the output rate fitting curve; adjusting the output rate fitting curve to enable the laser spectrum width of the comprehensive gain spectrum curve to meet a preset width; and determining the adjusted output rate fitting curve as a target output rate fitting curve, so that an output mirror prepared through the target output rate fitting curve outputs an output spectrum meeting a preset width. According to the invention, the mode-locked femtosecond laser can output an output spectrum with a wide laser spectrum width.

Description

Technical Field

[0001] The present invention relates to the technical field of mode-locked femtosecond lasers. Specifically, it relates to a method and system for broadening the output spectrum of a mode-locked femtosecond laser, and a femtosecond laser. Background Art

[0002] A mode-locked femtosecond laser is a laser device that can output laser pulses with a pulse width in the femtosecond order of magnitude ( ). Due to the extremely narrow laser pulse width, the peak power of the femtosecond laser pulse can easily reach megawatts (MW), gigawatts (GW) or even higher magnitudes. Such an extremely high peak pulse power enables the femtosecond laser to generate an extremely strong electric field, so that the mode-locked femtosecond laser can be widely used in various application fields.

[0003] Since the laser pulse width satisfies (Q is the laser pulse energy, P is the peak pulse power, and is the laser pulse width), at the same laser pulse energy, the narrower the laser pulse width, the higher the peak power of the instantaneous femtosecond laser pulse can be. Therefore, the laser pulse width is an important parameter for measuring the performance of femtosecond lasers.

[0004] According to the uncertainty principle ( is the laser spectral width, and const is a constant related to the central wavelength), it can be known that the wider the laser spectral width, the narrower the laser pulse width can be, and thus the higher the peak power of the instantaneous femtosecond laser pulse can be.

[0005] Therefore, how to enable the mode-locked femtosecond laser to output an output spectrum with a relatively wide laser spectral width is a technical problem to be solved by the present invention.

[0006] The content of the background art section is only the technology known to the applicant and does not of course represent the prior art in this field. Summary of the Invention

[0007] The present invention provides a method and system for broadening the output spectrum of a mode-locked femtosecond laser, and a femtosecond laser, which are used to solve the technical problem of how to enable the mode-locked femtosecond laser to output an output spectrum with a relatively wide laser spectral width.

[0008] According to one aspect of the present invention, the present invention provides a method for broadening the output spectrum of a mode-locked femtosecond laser, including: fitting the gain spectrum curve of a laser gain crystal to obtain a gain spectrum fitting curve with respect to wavelength; fitting the output rate curve of an output mirror based on a preset shape to obtain an output rate fitting curve with respect to wavelength, wherein the preset shape is that the output rate at the central wavelength is the lowest and the output rate gradually increases away from the central wavelength; determining a comprehensive gain spectrum curve with respect to wavelength according to the gain spectrum fitting curve and the output rate fitting curve; adjusting the output rate fitting curve so that the laser spectral width of the comprehensive gain spectrum curve meets a preset width; and determining the adjusted output rate fitting curve as the target output rate fitting curve so that the output mirror prepared through the target output rate fitting curve outputs an output spectrum meeting the preset width.

[0009] According to some embodiments of the present invention, fitting the gain spectrum curve of a laser gain crystal to obtain a gain spectrum fitting curve with respect to wavelength includes: fitting the gain spectrum curve by the point plotting method or the standard function fitting method to obtain the gain spectrum fitting curve.

[0010] According to some embodiments of the present invention, the standard function is a Gaussian function. Fitting the gain spectrum curve by the point plotting method or the standard function fitting method to obtain the gain spectrum fitting curve includes: fitting the gain spectrum curve based on the Gaussian function to obtain a quasi-Gaussian type gain spectrum fitting curve, including: determining the gain spectrum fitting curve based on the Gaussian function by using the wavelength parameter, the central wavelength parameter, the normalized intensity of the central wavelength parameter, and the full width at half maximum parameter of the gain spectrum fitting curve.

[0011] According to some embodiments of the present invention, fitting the output rate curve of an output mirror based on a preset shape includes: fitting the output rate curve based on the super-Gaussian function to obtain an output rate fitting curve with the preset shape, including: determining the output rate fitting curve based on the super-Gaussian function by using the wavelength parameter, the central wavelength parameter, the output rate parameter corresponding to the central wavelength parameter, the spectral full width at half maximum parameter of the output rate fitting curve, and the order of the super-Gaussian distribution.

[0012] According to another aspect of the present invention, the present invention provides a femtosecond laser. The femtosecond laser includes a mode-locked femtosecond laser, and the mode-locked femtosecond laser at least includes an output mirror prepared through the target output rate fitting curve as described above.

[0013] According to another aspect of the present invention, the present invention further provides a system for broadening the output spectrum of a mode-locked femtosecond laser, including a curve fitting module and a curve adjustment module. The curve fitting module fits the gain spectrum curve of the laser gain crystal to obtain a gain spectrum fitting curve with respect to wavelength; fits the output rate curve of the output mirror based on a preset shape to obtain an output rate fitting curve with respect to wavelength, where the preset shape is that the output rate is the lowest at the central wavelength and gradually increases away from the central wavelength; and determines a comprehensive gain spectrum curve with respect to wavelength according to the gain spectrum fitting curve and the output rate fitting curve. The curve adjustment module adjusts the output rate fitting curve so that the laser spectral width of the comprehensive gain spectrum curve meets a preset width, and determines the adjusted output rate fitting curve as the target output rate fitting curve so that the output mirror prepared by the target output rate fitting curve outputs an output spectrum meeting the preset width.

[0014] According to some embodiments of the present invention, the curve fitting module fits the gain spectrum curve by the point plotting method or the standard function fitting method to obtain the gain spectrum fitting curve.

[0015] According to some embodiments of the present invention, the standard function is a Gaussian function, and the curve fitting module fits the gain spectrum curve based on the Gaussian function to obtain a gain spectrum fitting curve of a quasi-Gaussian type, including: the curve fitting module determines the gain spectrum fitting curve based on the Gaussian function by using a wavelength parameter, a central wavelength parameter, the normalized intensity of the central wavelength parameter, and the full width at half maximum parameter of the gain spectrum fitting curve.

[0016] According to some embodiments of the present invention, the curve fitting module fits the output rate curve based on a super-Gaussian function to obtain an output rate fitting curve with a preset shape, including: the curve fitting module determines the output rate fitting curve based on the super-Gaussian function by using a wavelength parameter, a central wavelength parameter, the output rate parameter corresponding to the central wavelength parameter, the spectral full width at half maximum parameter of the output rate fitting curve, and the order of the super-Gaussian distribution.

[0017] According to another aspect of the present invention, the present invention further provides an electronic device. The electronic device includes: one or more processors; a storage device for storing one or more programs, and when the one or more programs are executed by the one or more processors, the one or more processors are enabled to implement the method for broadening the output spectrum of the mode-locked femtosecond laser as described above.

[0018] According to another aspect of the present invention, the present invention further provides a non-volatile computer-readable storage medium. A computer program is stored on the storage medium, and when the computer program is executed by a processor, it can implement the method for broadening the output spectrum of the mode-locked femtosecond laser as described above.

[0019] According to another aspect of the present invention, the present invention also provides a computer program product. The computer program product includes: a computer program stored on a computer-readable storage medium; the computer program includes program instructions, when the program instructions are executed by a computer, causing the computer to execute the method for broadening the output spectrum of a mode-locked femtosecond laser as described above.

[0020] Beneficial effects By fitting the gain spectrum curve of the laser gain crystal, the present invention can obtain a gain spectrum fitting curve with respect to wavelength. By fitting the output rate curve of the output mirror based on a preset shape, an output rate fitting curve with respect to wavelength can be obtained. According to the gain spectrum fitting curve and the output rate fitting curve, a comprehensive gain spectrum curve with respect to wavelength can be determined. The present invention also adjusts the output rate fitting curve, so that the laser spectral width of the comprehensive gain spectrum curve meets a preset width, and determines the adjusted output rate fitting curve as the target output rate fitting curve, which can make the output mirror prepared by the target output rate fitting curve output an output spectrum that meets the preset width.

[0021] By specifically designing the output rate fitting curve of the output mirror, the present invention can make the curve of the output rate of the output mirror with respect to wavelength compensate with the gain spectrum curve of the laser gain crystal, thereby effectively increasing the laser spectral width of the output spectrum of the mode-locked femtosecond laser, and further realizing the broadening of the output spectrum of the mode-locked femtosecond laser to improve the performance of the mode-locked femtosecond laser. Description of the drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0023] Figure 1 Shows a schematic structural diagram of an existing mode-locked femtosecond laser; Figure 2 Shows a schematic flowchart of the broadening method according to an embodiment of the present invention; Figure 3 Shows a schematic diagram of a gain spectrum fitting curve according to an embodiment of the present invention; Figure 4a Shows a schematic diagram of a traditional output spectrum; Figure 4b Shows a schematic diagram of an output spectrum according to an embodiment of the present invention; Figure 4c Shows a schematic diagram of another output spectrum according to an embodiment of the present invention; Figure 5 Shows another structural schematic diagram of an existing mode-locked femtosecond laser; Figure 6 Shows a comparison schematic diagram of the output spectrum of an embodiment of the present invention; Figure 7 Shows a comparison schematic diagram of the output rate of an embodiment of the present invention; Figure 8 Shows a structural schematic diagram of the broadening system of an embodiment of the present invention.

[0024] Explanation of reference numerals: Mode-locked femtosecond laser 1; laser gain crystal 11; first plane mirror 12; second plane mirror 13; third plane mirror 14; first concave mirror 15; second concave mirror 16; traditional output mirror 17.

[0025] Broadening system 2; curve fitting module 21; curve adjustment module 22. Detailed implementation manners

[0026] Next, in combination with the accompanying drawings in the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

[0027] Figure 1 Shows a structural schematic diagram of an existing mode-locked femtosecond laser. As Figure 1 shown, the mode-locked femtosecond laser includes a laser gain crystal, a total reflection mirror, an output mirror, and other related optical devices ( Figure 1 not shown in the figure). After the relevant optical devices are optically aligned, the laser will oscillate back and forth between the laser gain crystal, the total reflection mirror, and the output mirror. When the laser is reflected by the output mirror each time, a certain proportion of the laser will pass through the output mirror for output (i.e., Figure 1 the output light shown in the figure). And because a part of the laser is output through the output mirror, there will be a certain power loss, and the lost power will be supplemented by the gain of the laser gain crystal, and then it will be reflected by the total reflection mirror to the output mirror again for laser output. By operating repeatedly in this way, the mode-locked femtosecond laser can be in a stable operating state of continuously outputting femtosecond laser.

[0028] At present, the laser gain crystal of a mode-locked femtosecond laser generally selects an ultrafast crystal with a relatively wide inherent emission spectrum (such as a fluorescence spectrum > 3 nm, and the typical emission spectrum shape is Gaussian-like). In addition, a broadband reflection film will be set on the total reflection mirror and the output mirror so that the mode-locked femtosecond laser can output an output spectrum with a relatively wide laser spectral width. Moreover, a saturable absorber can be added or the Kerr lens effect can be introduced into the mode-locked femtosecond laser, so that multiple wavelengths within the reflection spectrum of the laser gain crystal can operate simultaneously within the mode-locked femtosecond laser through these optical devices or physical effects, obtaining an output spectrum with a relatively wide laser spectral width, and then a relatively narrow laser pulse width can be obtained.

[0029] However, the inventors of the present invention have found that although the emission spectrum of the current laser gain crystal is relatively wide (theoretically, the output spectrum output by the mode-locked femtosecond laser will not exceed the width of the fluorescence spectrum of the laser gain crystal), in fact, the output spectrum output by the mode-locked femtosecond laser is much narrower than the spectral width of the laser gain crystal, resulting in limited spectral potential of the laser gain crystal and increasing the laser spectral width of the mode-locked femtosecond laser.

[0030] The inventors have also found that the output rate of the current output mirror of the mode-locked femtosecond laser for different wavelength components within the crystal gain band of the laser gain crystal is the same, so that the proportion of the output light output by different wavelength components after passing through the output mirror is the same. And because the gain curve of the laser gain crystal with respect to wavelength is also Gaussian-like (that is, the gain in the central wavelength part is relatively high, and the gain gradually decreases away from the central wavelength), the output spectrum of the output mirror is also Gaussian-like. That is to say, the output mirror of the current mode-locked femtosecond laser limits the laser spectral width of the output spectrum of the femtosecond laser.

[0031] Based on this, according to one aspect of the present invention, the present invention provides a method for broadening the output spectrum of a mode-locked femtosecond laser, which can enable the mode-locked femtosecond laser to output an output spectrum with a relatively wide laser spectral width.

[0032] Figure 2 The flowchart showing the broadening method of the embodiment of the present invention is as follows. As Figure 2 shown, the broadening method may include steps S100 - S500.

[0033] Exemplarily, the broadening method may be executed by a broadening system for the output spectrum of a mode-locked femtosecond laser with computing capabilities.

[0034] According to the exemplary embodiment, in step S100, the broadening system fits the gain spectral curve of the laser gain crystal to obtain a gain spectral fitting curve with respect to wavelength.

[0035] For example, a mode-locked femtosecond laser includes at least a laser gain crystal and an output mirror. The gain spectral curve of the laser gain crystal is generally Gaussian-like. The broadening system can obtain a Gaussian-like gain spectral fitting curve with respect to wavelength by fitting the gain spectral curve of the laser gain crystal.

[0036] It can be understood here that a Gaussian-like curve in optics can refer to a curve whose shape is similar to that of a Gaussian function (bell curve) (such as a gain spectral curve, a spectral response curve, or an output rate curve, etc.). For example, the shape of the Gaussian-like gain spectral fitting curve with respect to wavelength can be such that the gain corresponding to the central wavelength parameter at the peak of the emission spectrum is the highest (i.e., the spectral intensity is the highest), and the gain gradually decreases as the central wavelength parameter is deviated from (i.e., the spectral intensity gradually decreases).

[0037] Optionally, in step S100, the broadening system can fit the gain spectral curve by the point plotting method or the standard function fitting method to obtain the gain spectral fitting curve.

[0038] For example, the point plotting method can discretize the continuous curve of the gain spectrum into equally spaced scatter points with respect to wavelength and record the abscissa and ordinate values of each scatter point (linear interpolation can be performed if necessary) to form an array that can be operated on by a computer. The standard function fitting method can fit the gain spectral curve by standard mathematical functions (such as a super-Gaussian function, a polynomial function, a Lorentz function, etc.), compare the fitted function with the original curve, and use the least squares method to evaluate the fitting result.

[0039] Optionally, in step S100, the standard function can be a Gaussian function. The broadening system can fit the gain spectral curve based on the Gaussian function to obtain a Gaussian-like gain spectral fitting curve.

[0040] The broadening system can determine the gain spectral fitting curve based on the Gaussian function using the wavelength parameter, the central wavelength parameter, the normalized intensity of the central wavelength parameter, and the full width at half maximum parameter of the gain spectral curve.

[0041] For example, the Gaussian-like gain spectral fitting curve can be: ; where is the gain spectral fitting curve, is the normalized intensity of the central wavelength parameter, is the Euler number, with an approximate value of 2.718, is the wavelength parameter, is the central wavelength parameter corresponding to the peak of the emission spectrum, is the full width at half maximum parameter of the gain spectral fitting curve.

[0042] Figure 3 A schematic diagram showing the gain spectrum fitting curve of an embodiment of the present invention.

[0043] As Figure 3 shown, the gain spectrum fitting curve can be in a shape where the gain corresponding to the central wavelength parameter of the emission spectrum peak is the highest (i.e., the spectral intensity is the highest), and the gain gradually decreases (i.e., the spectral intensity gradually decreases) away from the central wavelength parameter.

[0044] According to an exemplary embodiment, in step S200, the broadening system fits the output rate curve of the output mirror based on a preset shape to obtain an output rate fitting curve with respect to wavelength. The preset shape is that the output rate at the central wavelength is the lowest, and the output rate gradually increases away from the central wavelength.

[0045] For example, in order to make the full width at half maximum of the output spectrum of the mode-locked femtosecond laser wider (i.e., the laser spectral width of the output spectrum is wider), and to enable more output of the wavelength components on both sides far from the central wavelength parameter, the broadening system designs the output rate curve of the output mirror accordingly.

[0046] Through curve fitting design, the broadening system can obtain an output rate fitting curve in a shape where the output rate at the central wavelength parameter is the lowest and the output rate gradually increases away from the central wavelength parameter.

[0047] It can be understood here that as long as the curve satisfies the shape where the output rate at the central wavelength parameter is the lowest and the output rate gradually increases away from the central wavelength parameter, it can be used as a trial curve for the output rate fitting curve, and the present invention does not limit this.

[0048] Optionally, in step S200, the broadening system can fit the output rate curve based on a super-Gaussian function to obtain an output rate fitting curve with a preset shape.

[0049] For example, the broadening system determines the output rate fitting curve based on the super-Gaussian function using the wavelength parameter, the central wavelength parameter, the output rate parameter corresponding to the central wavelength parameter, the spectral full width at half maximum parameter of the output rate curve, and the order of the super-Gaussian distribution.

[0050] For example, the output rate fitting curve can be: ; where is the output rate fitting curve, is the output rate corresponding to the central wavelength parameter, is the Euler number, with an approximate value of 2.718, is the wavelength parameter, is the central wavelength parameter corresponding to the peak of the emission spectrum, is the spectral full-width at half maximum parameter of the output rate fitting curve, and p is the order of the super-Gaussian distribution.

[0051] According to the exemplary embodiment, in step S300, the broadening system determines a comprehensive gain spectral curve with respect to wavelength based on the gain spectral fitting curve and the output rate fitting curve.

[0052] For example, the comprehensive gain spectral curve can be the product of the gain spectral fitting curve and the output rate fitting curve.

[0053] Exemplarily, the comprehensive gain spectral curve can be: ; Wherein, is the comprehensive gain spectral curve, is the gain spectral fitting curve, is the output rate fitting curve.

[0054] Here, it can be understood that the comprehensive gain spectral curve is the spectral intensity curve finally output after different wavelength components pass through the laser gain crystal and the output mirror. That is, the comprehensive gain spectral curve can characterize the output spectrum of the mode-locked femtosecond laser.

[0055] In step S400, the broadening system adjusts the output rate fitting curve so that the laser spectral width of the comprehensive gain spectral curve meets a preset width.

[0056] In step S500, the broadening system determines the adjusted output rate fitting curve as the target output rate fitting curve so that the output mirror output prepared through the target output rate fitting curve outputs an output spectrum that meets the preset width.

[0057] For example, by adjusting the design parameters of the output rate fitting curve, the broadening system can simulate the comprehensive gain spectral curve (i.e., the output spectrum of the mode-locked femtosecond laser) under ideal conditions.

[0058] Exemplarily, the broadening system can obtain the laser spectral width that meets the preset width (such as as large as possible) through numerical simulation calculation, so that it can determine the corresponding output rate fitting curve according to the design parameters of the output rate fitting curve corresponding thereto, and determine it as the target output rate fitting curve.

[0059] According to the exemplary embodiment, the layer film design scheme of the output mirror (for the output rate design of the output mirror) can be determined through the target output rate fitting curve, and then the corresponding output mirror can be prepared industrially according to this layer film design scheme. The output mirror prepared based on this target output rate fitting curve can realize a comprehensive gain spectral curve with a wider output spectrum, and further can realize the broadening of the output spectrum of the mode-locked femtosecond laser, thereby improving the performance of the mode-locked femtosecond laser.

[0060] Exemplarily, the broadening system can simulate the comprehensive gain spectral curve under ideal conditions by changing the spectral full width at half maximum parameter of the output rate fitting curve and the order p of the super-Gaussian distribution.

[0061] It can be understood here that the broadening system can also determine the full width at half maximum parameter and the output spectrum corresponding to a certain required comprehensive gain spectral curve by selecting the appropriate spectral full width at half maximum parameter of the output rate fitting curve and the order p of the super-Gaussian distribution.

[0062] Figure 4a Fig. shows a schematic diagram of a conventional output spectrum; Figure 4b Fig. shows a schematic diagram of an output spectrum according to an embodiment of the present invention; Figure 4c Fig. shows another schematic diagram of an output spectrum according to an embodiment of the present invention.

[0063] As Figure 4a shown, the conventional output spectrum adopts an output rate curve with a fixed output rate, and the output rates of different wavelength components passing through the output mirror are the same. The conventional output spectrum almost completely coincides with the conventional gain spectral curve ( Figure 4a the dotted line in the middle is the conventional output spectrum, and the smooth curve is the conventional gain spectral curve). As Figure 4a shown, in this case, the laser spectral width (i.e., the full width at half maximum) of the output spectrum is 25 nm.

[0064] As Figure 4b shown, the gain spectral fitting curve is of a Gaussian-like shape, and the output rate fitting curve has the lowest output rate at the central wavelength parameter and gradually increases with the output rate away from the central wavelength parameter. The design parameters corresponding to this output rate fitting curve include: p = 3, . As Figure 4b shown, in this case, the laser spectral width (i.e., the full width at half maximum) of the output spectrum is 40 nm.

[0065] As Figure 4c shown, the gain spectral fitting curve is of a Gaussian-like shape, and the output rate fitting curve has the lowest output rate at the central wavelength parameter and gradually increases with the output rate away from the central wavelength parameter. The design parameters corresponding to this output rate fitting curve include: p = 4, . As Figure 4c shown, in this case, the laser spectral width (i.e., the full width at half maximum) of the output spectrum is 50 nm.

[0066] According to Figure 4a , Figure 4b and Figure 4cIt can be seen that, compared with the output mirror of the conventional design with the same output rate for different wavelength components, the present invention can freely adjust the shape of the output spectrum (i.e., adjust the integrated gain spectrum curve) and the laser spectral width (i.e., the full width at half maximum) by adjusting the output rate fitting curve. And, as Figure 4c shown, by appropriately adjusting the design parameters corresponding to the output rate fitting curve, an output spectrum with a laser spectral width doubled compared to the conventional design can be obtained.

[0067] According to another aspect of the present invention, the present invention also provides a femtosecond laser. According to an exemplary embodiment, the femtosecond laser can be a mode-locked femtosecond laser. The mode-locked femtosecond laser includes an output mirror, and the output mirror is prepared based on the target output rate fitting curve described above.

[0068] Figure 5 shows another structural schematic diagram of an existing mode-locked femtosecond laser. As Figure 5 shown, the mode-locked femtosecond laser 1 can be a titanium sapphire mode-locked femtosecond laser based on Kerr lens mode locking.

[0069] According to an exemplary embodiment, as Figure 5 shown, the mode-locked femtosecond laser 1 can include a laser gain crystal 11, a first plane mirror 12, a second plane mirror 13, a third plane mirror 14, a first concave mirror 15, a second concave mirror 16, and a conventional output mirror 17.

[0070] The laser gain crystal 11 can be a titanium sapphire laser gain crystal. The light-passing surface of the laser gain crystal 11 is not coated and is placed in the optical path at the Brewster angle to reduce the surface reflection loss. The first plane mirror 12, the second plane mirror 13, and the third plane mirror 14 are all plane mirrors, and the first plane mirror 12 can be arranged on a movable optical platform.

[0071] The reflectivities of the first plane mirror 12, the second plane mirror 13, the third plane mirror 14, the first concave mirror 15, and the second concave mirror 16 for different wavelengths are all greater than 99.5%, and they are all negative chirped mirrors, so as to supplement the positive dispersion during the multi-wavelength mode-locked operation of the femtosecond laser. The conventional output mirror 17 is an output mirror with an output rate of 3%.

[0072] As an embodiment, the conventional output mirror 17 is replaced with an output mirror prepared based on the target output rate fitting curve described above (hereinafter referred to as a super-Gaussian output mirror). The conventional output spectrum corresponding to the conventional output mirror 17 and the super-Gaussian output spectrum corresponding to the super-Gaussian output mirror provided by the present invention are respectively tested.

[0073] For example, as Figure 5As shown, the optical path of the laser can be adjusted by adjusting the first plane mirror 12, the second plane mirror 13, the third plane mirror 14, the first concave mirror 15, the second concave mirror 16, and the conventional output mirror 17, so that the laser can perform direct current oscillation in the cavity. At this time, the output spectrum is a single-wavelength spectrum corresponding to the central wavelength parameter of the crystal. When the distance between the laser gain crystal 11 and the first concave mirror 15 is adjusted and the first plane mirror 12 is pushed, the Kerr lens mode locking effect will be triggered. In this case, the femtosecond laser will operate in the femtosecond pulse mode locking state and output a wide spectrum of multiple wavelengths through the conventional output mirror 17. The conventional output spectrum corresponding to the conventional output mirror 17 can be obtained through the spectrum measuring device.

[0074] After replacing the conventional output mirror 17 with the super-Gaussian output mirror prepared based on the target output rate fitting curve described above, based on the same principle, the super-Gaussian output spectrum corresponding to the super-Gaussian output mirror provided by the present invention can be obtained.

[0075] Figure 6 A comparison schematic diagram of the output spectra of the embodiments of the present invention is shown; Figure 7 A comparison schematic diagram of the output rates of the embodiments of the present invention is shown.

[0076] As Figure 6 shown, the laser spectral width (i.e., full width at half maximum) of the super-Gaussian output spectrum is significantly wider than that of the conventional output spectrum. For example, the laser spectral width of the super-Gaussian output spectrum is about 225 nm, while the laser spectral width of the conventional output spectrum is about 98 nm. In addition, according to Figure 6 it can be seen that the proportion of the spectral components on both sides of the super-Gaussian output spectrum has also increased significantly.

[0077] As Figure 7 shown, in the conventional output mirror 17, the output rates of different wavelengths are almost the same (both about 3%). The super-Gaussian output mirror is only 3% near the central wavelength parameter, and the other parts are higher than 3%. Moreover, the theoretical value and the measured value of the output rate of the super-Gaussian output mirror are relatively close, indicating that the current coating process can preferably prepare the super-Gaussian output mirror based on the target output rate fitting curve, and the present invention is applicable to industrial production.

[0078] Through the above embodiments, the present invention can obtain a gain spectrum fitting curve with respect to wavelength by fitting the gain spectrum curve of the laser gain crystal. By fitting the output rate curve of the output mirror based on a preset shape, an output rate fitting curve with respect to wavelength can be obtained. According to the gain spectrum fitting curve and the output rate fitting curve, a comprehensive gain spectrum curve with respect to wavelength can be determined. The present invention also adjusts the output rate fitting curve, so that the laser spectral width of the comprehensive gain spectrum curve meets a preset width, and determines the adjusted output rate fitting curve as the target output rate fitting curve, so that the output mirror prepared by the target output rate fitting curve outputs an output spectrum that meets the preset width.

[0079] Through the targeted design of the output rate fitting curve of the output mirror, the present invention can make the curve of the output rate of the output mirror with respect to wavelength compensate with the gain spectrum curve of the laser gain crystal, so as to effectively increase the laser spectral width of the output spectrum of the mode-locked femtosecond laser, and further realize the broadening of the output spectrum of the mode-locked femtosecond laser to improve the performance of the mode-locked femtosecond laser.

[0080] Without changing the original structure of the mode-locked femtosecond laser, the present invention can only perform fitting design on the output rate curve of the output mirror in combination with the gain spectrum curve, so that the gain of different wavelength components after passing through the laser gain crystal and the output mirror tends to be flat, effectively broadening the output spectrum of the mode-locked femtosecond laser, and further obtaining femtosecond laser pulses with narrower laser pulse widths.

[0081] Compared with the prior art spectral broadening methods of replacing the laser gain crystal with a wider emission spectrum and inserting a nonlinear broadening crystal in the cavity, the present invention does not need to replace the laser gain crystal, nor does it need to add additional devices in the cavity. Only the target output rate fitting curve needs to be determined by combining the output rate curve of the output mirror with the gain spectrum fitting curve. Through the layer film design of the output mirror by the target output rate fitting curve, the broadening of the output spectrum of the mode-locked femtosecond laser can be realized. The present invention has the characteristics of simple structure, low cost, and easy industrial implementation, and has good cost performance and practical value.

[0082] According to another aspect of the present invention, the present invention provides a system for broadening the output spectrum of a mode-locked femtosecond laser.

[0083] Figure 8 The structural schematic diagram of the broadening system showing the embodiments of the present invention is shown.

[0084] According to an exemplary embodiment, as Figure 8 shown, the broadening system 2 may include a curve fitting module 21 and a curve adjustment module 22.

[0085] According to an exemplary embodiment, the curve fitting module 21 fits the gain spectral curve of the laser gain crystal to obtain a gain spectral fitting curve with respect to wavelength.

[0086] For example, a mode-locked femtosecond laser includes at least a laser gain crystal and an output mirror. The gain spectral curve of the laser gain crystal is generally Gaussian-like. By fitting the gain spectral curve of the laser gain crystal, the curve fitting module 21 can obtain a Gaussian-like gain spectral fitting curve with respect to wavelength.

[0087] It can be understood here that a Gaussian-like curve in optics can refer to a curve (such as a gain spectral curve, a spectral response curve, or an output rate curve, etc.) whose shape is similar to that of a Gaussian function (bell curve). For example, the shape of the Gaussian-like gain spectral fitting curve with respect to wavelength can be such that the gain is highest (i.e., the spectral intensity is highest) at the central wavelength parameter corresponding to the peak of the emission spectrum, and the gain gradually decreases (i.e., the spectral intensity gradually decreases) away from the central wavelength parameter.

[0088] Optionally, the curve fitting module 21 can fit the gain spectral curve by the point plotting method or the standard function fitting method to obtain the gain spectral fitting curve.

[0089] For example, the point plotting method can discretize the continuous curve of the gain spectrum into equally spaced scatter points with respect to wavelength and record the abscissa and ordinate values of each scatter point (linear interpolation can be performed if necessary) to form an array that can be operated on by a computer. The standard function fitting method can fit the gain spectral curve with a standard mathematical function (such as a super-Gaussian function, a polynomial function, a Lorentz function, etc.), compare the fitted function with the original curve, and use the least squares method to evaluate the fitting result.

[0090] Optionally, the standard function can be a Gaussian function. The curve fitting module 21 can fit the gain spectral curve based on the Gaussian function to obtain a Gaussian-like gain spectral fitting curve.

[0091] The curve fitting module 21 can determine the gain spectral fitting curve based on the Gaussian function using the wavelength parameter, the central wavelength parameter, the normalized intensity of the central wavelength parameter, and the full width at half maximum parameter of the gain spectral curve.

[0092] For example, the Gaussian-like gain spectral fitting curve can be: ; where is the gain spectral fitting curve, is the normalized intensity of the central wavelength parameter, is the Euler number, with an approximate value of 2.718, is the wavelength parameter, is the central wavelength parameter corresponding to the peak of the emission spectrum, is the full width at half maximum parameter of the gain spectrum fitting curve.

[0093] As Figure 3 shown, the gain spectrum fitting curve can be in a shape where the gain corresponding to the central wavelength parameter of the peak of the emission spectrum is the highest (i.e., the spectral intensity is the highest), and the gain gradually decreases (i.e., the spectral intensity gradually decreases) away from the central wavelength parameter.

[0094] According to the exemplary embodiment, the curve fitting module 21 fits the output rate curve of the output mirror based on a preset shape to obtain an output rate fitting curve with respect to wavelength. The preset shape is that the output rate at the central wavelength is the lowest, and the output rate gradually increases away from the central wavelength.

[0095] For example, in order to make the full width at half maximum of the output spectrum of the mode-locked femtosecond laser wider (i.e., the laser spectral width of the output spectrum is wider), and to enable more output of the wavelength components on both sides away from the central wavelength parameter, the curve fitting module 21 designs the output rate curve of the output mirror accordingly.

[0096] Through curve fitting design, the curve fitting module 21 can obtain an output rate fitting curve in a shape where the output rate at the central wavelength parameter is the lowest, and the output rate gradually increases away from the central wavelength parameter.

[0097] It can be understood here that as long as the curve satisfies the shape where the output rate at the central wavelength parameter is the lowest and the output rate gradually increases away from the central wavelength parameter, it can be used as a trial curve for the output rate fitting curve, and the present invention places no restrictions on this.

[0098] Optionally, the curve fitting module 21 can fit the output rate curve based on a super-Gaussian function to obtain an output rate fitting curve with a preset shape.

[0099] For example, the curve fitting module 21 determines the output rate fitting curve based on the super-Gaussian function using the wavelength parameter, the central wavelength parameter, the output rate parameter corresponding to the central wavelength parameter, the spectral full width at half maximum parameter of the output rate curve, and the order of the super-Gaussian distribution.

[0100] For example, the output rate fitting curve can be: ; where, is the output rate fitting curve, is the output rate corresponding to the central wavelength parameter, is the Euler number, with an approximate value of 2.718, is the wavelength parameter, is the central wavelength parameter corresponding to the peak of the emission spectrum, is the spectral full-width at half maximum parameter for the output rate fitting curve, and p is the order of the super-Gaussian distribution.

[0101] According to the exemplary embodiment, the curve fitting module 21 determines a comprehensive gain spectral curve with respect to wavelength based on the gain spectral fitting curve and the output rate fitting curve.

[0102] For example, the comprehensive gain spectral curve can be the product of the gain spectral fitting curve and the output rate fitting curve.

[0103] Exemplarily, the comprehensive gain spectral curve can be: ; where is the comprehensive gain spectral curve, is the gain spectral fitting curve, is the output rate fitting curve.

[0104] Here, it can be understood that the comprehensive gain spectral curve is the spectral intensity curve finally output after different wavelength components pass through the laser gain crystal and the output mirror. That is, the comprehensive gain spectral curve can characterize the output spectrum of the mode-locked femtosecond laser.

[0105] The curve adjustment module 22 adjusts the output rate fitting curve so that the laser spectral width of the comprehensive gain spectral curve meets a preset width.

[0106] The curve adjustment module 22 determines the adjusted output rate fitting curve as the target output rate fitting curve so that the output spectrum with a preset width is output through the output mirror prepared by the target output rate fitting curve.

[0107] For example, by adjusting the design parameters of the output rate fitting curve, the curve adjustment module 22 can simulate the comprehensive gain spectral curve in an ideal situation (i.e., the output spectrum of the mode-locked femtosecond laser).

[0108] Exemplarily, the curve adjustment module 22 can obtain the laser spectral width that meets the preset width (such as as large as possible) through numerical simulation calculation, so as to determine the corresponding output rate fitting curve according to the design parameters of the output rate fitting curve corresponding thereto, and determine it as the target output rate fitting curve.

[0109] According to the exemplary embodiment, the layer film design scheme of the output mirror (for the output rate design of the output mirror) can be determined through the target output rate fitting curve, and then the corresponding output mirror can be prepared industrially according to the layer film design scheme. The output mirror prepared based on the target output rate fitting curve can realize a comprehensive gain spectral curve with a wider output spectrum, and further can realize the broadening of the output spectrum of the mode-locked femtosecond laser, thereby improving the performance of the mode-locked femtosecond laser.

[0110] Exemplarily, the curve adjustment module 22 simulates the spectral full width at half maximum (FWHM) parameter of the output rate curve of the fitting curve by changing the output rate and the order p of the super-Gaussian distribution, and can simulate the integrated gain spectral curve under ideal conditions.

[0111] It can be understood here that the curve adjustment module 22 can also determine the FWHM parameter and the output spectrum corresponding to a certain required integrated gain spectral curve by selecting the appropriate spectral FWHM parameter of the output rate curve and the order p of the super-Gaussian distribution.

[0112] Figure 4a Fig. shows a schematic diagram of a conventional output spectrum; Figure 4b Fig. shows a schematic diagram of an output spectrum according to an embodiment of the present invention; Figure 4c Fig. shows another schematic diagram of an output spectrum according to an embodiment of the present invention.

[0113] As Figure 4a shown, the conventional output spectrum adopts an output rate curve with a fixed output rate, and the output rates of different wavelength components passing through the output mirror are the same. The conventional output spectrum almost completely coincides with the conventional gain spectral curve ( Figure 4a the dash-dot line is the conventional output spectrum, and the smooth curve is the conventional gain spectral curve). As Figure 4a shown, in this case, the laser spectral width (i.e., the FWHM) of the output spectrum is 25 nm.

[0114] As Figure 4b shown, the gain spectral fitting curve is in the shape of a quasi-Gaussian type, and the output rate fitting curve has the lowest output rate at the central wavelength parameter and gradually increases with the output rate away from the central wavelength parameter. The design parameters corresponding to the output rate fitting curve include: p = 3, . As Figure 4b shown, in this case, the laser spectral width (i.e., the FWHM) of the output spectrum is 40 nm.

[0115] As Figure 4c shown, the gain spectral fitting curve is in the shape of a quasi-Gaussian type, and the output rate fitting curve has the lowest output rate at the central wavelength parameter and gradually increases with the output rate away from the central wavelength parameter. The design parameters corresponding to the output rate fitting curve include: p = 4, . As Figure 4c shown, in this case, the laser spectral width (i.e., the FWHM) of the output spectrum is 50 nm.

[0116] According to Figure 4a , Figure 4b and Figure 4cIt can be seen that, compared with the output mirror of the conventional design with the same output rate for different wavelength components, the present invention can freely adjust the shape of the output spectrum (i.e., adjust the comprehensive gain spectrum curve) and the laser spectral width (i.e., the full width at half maximum) by adjusting the output rate fitting curve. And, as Figure 4c shown, by appropriately adjusting the design parameters corresponding to the output rate fitting curve, an output spectrum with a laser spectral width doubled compared to the conventional design can be obtained.

[0117] Through the above embodiments, the present invention can fit the gain spectrum curve of the laser gain crystal to obtain a gain spectrum fitting curve with respect to wavelength. By fitting the output rate curve of the output mirror based on a preset shape, an output rate fitting curve with respect to wavelength can be obtained. According to the gain spectrum fitting curve and the output rate fitting curve, a comprehensive gain spectrum curve with respect to wavelength can be determined. The present invention can also adjust the output rate fitting curve so that the laser spectral width of the comprehensive gain spectrum curve meets a preset width, and determine the adjusted output rate fitting curve as the target output rate fitting curve, so that the output mirror prepared by the target output rate fitting curve outputs an output spectrum that meets the preset width.

[0118] By specifically designing the output rate fitting curve of the output mirror, the present invention can make the curve of the output rate of the output mirror with respect to wavelength compensate with the gain spectrum curve of the laser gain crystal, so as to effectively increase the laser spectral width of the output spectrum of the mode-locked femtosecond laser, and further realize the broadening of the output spectrum of the mode-locked femtosecond laser to improve the performance of the mode-locked femtosecond laser.

[0119] The present invention can, without changing the original structure of the mode-locked femtosecond laser, only fit and design the output rate curve of the output mirror in combination with the gain spectrum curve, so that the gains of different wavelength components after passing through the laser gain crystal and the output mirror tend to be flat, effectively broaden the output spectrum of the mode-locked femtosecond laser, and further obtain femtosecond laser pulses with a narrower laser pulse width.

[0120] Compared with the spectral broadening methods in the prior art that use a laser gain crystal with a wider emission spectrum or insert a nonlinear broadening crystal in the cavity, the present invention does not need to replace the laser gain crystal, nor does it need to add additional devices in the cavity. Only the target output rate fitting curve needs to be determined by combining the output rate curve of the output mirror with the gain spectrum fitting curve. By performing a coating design on the output mirror through the target output rate fitting curve, the broadening of the output spectrum of the mode-locked femtosecond laser can be realized. The present invention has the characteristics of simple structure, low cost, and easy industrial implementation, and has good cost performance and practical value.

[0121] According to another aspect of the present invention, the present invention further provides an electronic device. The electronic device includes: one or more processors; a storage device for storing one or more programs, which when executed by the one or more processors, enable the one or more processors to implement the method for broadening the output spectrum of a mode-locked femtosecond laser as described above.

[0122] According to another aspect of the present invention, the present invention further provides a non-volatile computer-readable storage medium. A computer program is stored on the storage medium, and when the computer program is executed by a processor, it can implement the method for broadening the output spectrum of a mode-locked femtosecond laser as described above.

[0123] According to another aspect of the present invention, the present invention further provides a computer program product. The computer program product includes: a computer program stored on a computer-readable storage medium; the computer program includes program instructions, which when executed by a computer, cause the computer to execute the method for broadening the output spectrum of a mode-locked femtosecond laser as described above.

[0124] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions of the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for broadening the output spectrum of a mode-locked femtosecond laser, characterized in that: The mode-locked femtosecond laser comprises at least a laser gain crystal and an output mirror, and the broadening method comprises: Fitting the gain spectrum curve of the laser gain crystal to obtain a gain spectrum fitting curve with respect to wavelength; Fitting the output rate curve of the output mirror based on a preset shape to obtain an output rate fitting curve with respect to wavelength, wherein the preset shape is such that the output rate at the center wavelength is the lowest and the output rate away from the center wavelength gradually increases; Determining a comprehensive gain spectrum curve with respect to wavelength according to the gain spectrum fitting curve and the output rate fitting curve; Adjusting the output rate fitting curve so that the laser spectrum width of the comprehensive gain spectrum curve meets a preset width; The adjusted output rate fitting curve is determined as the target output rate fitting curve, so that the output mirror prepared by the target output rate fitting curve outputs an output spectrum that meets the preset width.

2. The widening method according to claim 1, characterized in that: The step of fitting the gain spectrum curve of the laser gain crystal to obtain a gain spectrum fitting curve with respect to wavelength comprises: The gain spectrum curve is fitted by a point plotting method or a standard function fitting method to obtain the gain spectrum fitting curve.

3. The widening method according to claim 2, characterized in that: The standard function is a Gaussian function, and fitting the gain spectrum curve by a point plotting method or a standard function fitting method to obtain the gain spectrum fitting curve comprises: Fitting the gain spectrum curve based on the Gaussian function to obtain a Gaussian-like gain spectrum fitting curve includes: The gain spectrum fitting curve is determined based on a Gaussian function using a wavelength parameter, a center wavelength parameter, a normalized intensity of the center wavelength parameter, and a half-width parameter of the gain spectrum fitting curve.

4. The widening method according to claim 1, characterized in that: The fitting of the output rate curve of the output mirror based on the preset shape comprises: Fitting the output rate curve based on a super-Gaussian function to obtain an output rate fitting curve having the preset shape includes: The output rate fitting curve is determined based on the super Gaussian function using wavelength parameters, center wavelength parameters, output rate parameters corresponding to the center wavelength parameters, spectral half-width parameters of the output rate fitting curve, and the order of super Gaussian distribution.

5. A femtosecond laser, characterized in that: The femtosecond laser comprises a mode-locked femtosecond laser, and the mode-locked femtosecond laser comprises at least an output mirror prepared by a target output rate fitting curve; Wherein, the target output rate fitting curve is obtained based on the broadening method described in any one of claims 1-4.

6. A system for broadening the output spectrum of a mode-locked femtosecond laser, characterized in that: The mode-locked femtosecond laser comprises at least a laser gain crystal and an output mirror, and the broadening system comprises: A curve fitting module is configured to fit the gain spectrum curve of the laser gain crystal to obtain a gain spectrum fitting curve with respect to the wavelength; fit the output rate curve of the output mirror based on a preset shape to obtain an output rate fitting curve with respect to the wavelength, wherein the preset shape is that the output rate at the center wavelength is the lowest and the output rate away from the center wavelength gradually increases; and determine a comprehensive gain spectrum curve with respect to the wavelength according to the gain spectrum fitting curve and the output rate fitting curve; A curve adjustment module adjusts the output rate fitting curve so that the laser spectrum width of the comprehensive gain spectrum curve meets a preset width, and determines the adjusted output rate fitting curve as a target output rate fitting curve so that the output mirror prepared by the target output rate fitting curve outputs an output spectrum that meets the preset width.

7. The widening system according to claim 6, characterized in that: The curve fitting module fits the gain spectrum curve by using a point plotting method or a standard function fitting method to obtain the gain spectrum fitting curve.

8. The widening system according to claim 7, characterized in that: The standard function is a Gaussian function, and the curve fitting module fits the gain spectrum curve based on the Gaussian function to obtain a Gaussian-type gain spectrum fitting curve, including: The curve fitting module determines the gain spectrum fitting curve based on a Gaussian function using a wavelength parameter, a center wavelength parameter, a normalized intensity of the center wavelength parameter, and a half-width parameter of the gain spectrum fitting curve.

9. The widening system according to claim 6, characterized in that: The curve fitting module fits the output rate curve based on a super-Gaussian function to obtain an output rate fitting curve having the preset shape, including: The curve fitting module determines the output rate fitting curve based on the super Gaussian function using wavelength parameters, center wavelength parameters, output rate parameters corresponding to the center wavelength parameters, spectral half-width parameters of the output rate fitting curve, and the order of super Gaussian distribution.

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