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

Abstract

The present invention provides a method and system for broadening the output spectrum of a mode-locked femtosecond laser, and a femtosecond laser, which relate to the technical field of mode-locked femtosecond lasers. The broadening method includes: fitting the gain spectral curve of a laser gain crystal to obtain a gain spectral 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; determining a comprehensive gain spectral curve with respect to wavelength according to the gain spectral fitting curve and the output rate fitting curve; adjusting the output rate fitting curve so that the laser spectral width of the comprehensive gain spectral curve meets a preset width; and determining the adjusted output rate fitting curve as a target output rate fitting curve, so that the output mirror prepared through the target output rate fitting curve outputs an output spectrum with a preset width. The present invention can enable the mode-locked femtosecond laser to output an output spectrum with a relatively wide laser spectral 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 the megawatt (MW), gigawatt (GW) or even higher order of magnitude. 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 instantaneous peak power of the femtosecond laser 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 instantaneous peak power of the femtosecond laser can be.

[0005] Therefore, how to make the mode-locked femtosecond laser 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 in 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 make the mode-locked femtosecond laser 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 spectral curve of a laser gain crystal to obtain a gain spectral 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 spectral curve with respect to wavelength according to the gain spectral fitting curve and the output rate fitting curve; adjusting the output rate fitting curve so that the laser spectral width of the comprehensive gain spectral 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 by 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 spectral curve of a laser gain crystal to obtain a gain spectral fitting curve with respect to wavelength includes: fitting the gain spectral curve by a point plotting method or a standard function fitting method to obtain a gain spectral fitting curve.

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

[0012] According to another aspect of the present invention, the present invention provides a femtosecond laser, and the femtosecond laser includes a mode-locked femtosecond laser, and the mode-locked femtosecond laser at least includes an output mirror prepared by 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 through the target output rate fitting curve outputs an output spectrum that meets 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 quasi-Gaussian type gain spectrum fitting curve, including: the curve fitting module determines the gain spectrum 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 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 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.

[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, the computer is made to execute the method for broadening the output spectrum of a mode-locked femtosecond laser as described above.

[0020] Beneficial effects

[0021] In the present invention, by fitting the gain spectral curve of a laser gain crystal, a gain spectral fitting curve with respect to wavelength can be obtained. By fitting the output rate curve of an output mirror based on a preset shape, an output rate fitting curve with respect to wavelength can be obtained. According to the gain spectral fitting curve and the output rate fitting curve, a comprehensive gain spectral 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 spectral curve meets a preset width. Determining the adjusted output rate fitting curve as the target output rate fitting curve can make the output mirror prepared through the target output rate fitting curve output an output spectrum that meets the preset width.

[0022] In the present invention, through targeted design of the output rate fitting curve of the output mirror, the curve of the output rate of the output mirror with respect to wavelength can be made to compensate with the gain spectral 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

[0023] 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 following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 Shows a schematic structural diagram of an existing mode-locked femtosecond laser;

[0025] Figure 2 Shows a schematic flow chart of the broadening method in the embodiment of the present invention;

[0026] Figure 3 Shows a schematic diagram of the gain spectral fitting curve in the embodiment of the present invention;

[0027] Figure 4a Shows a schematic diagram of a traditional output spectrum;

[0028] Figure 4b Shows a schematic diagram of an output spectrum in the embodiment of the present invention;

[0029] Figure 4c Schematic diagram showing another output spectrum of an embodiment of the present invention;

[0030] Figure 5 Schematic diagram showing another structural diagram of an existing mode-locked femtosecond laser;

[0031] Figure 6 Schematic comparison diagram of the output spectrum of an embodiment of the present invention;

[0032] Figure 7 Schematic comparison diagram of the output rate of an embodiment of the present invention;

[0033] Figure 8 Schematic structural diagram showing the broadening system of an embodiment of the present invention.

[0034] Explanation of reference numerals:

[0035] 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; conventional output mirror 17.

[0036] Broadening system 2; curve fitting module 21; curve adjustment module 22. Detailed implementation manners

[0037] 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 fall within the protection scope of the present invention.

[0038] Figure 1 Schematic diagram showing a structural 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 and output (i.e., Figure 1 the output light shown in the figure). Since a part of the laser passes through the output mirror and outputs, 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.

[0039] Currently, 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 reflective film is set on the total reflector and the output mirror so that the mode-locked femtosecond laser can output an output spectrum with a relatively wide laser spectral width. Also, a saturable absorber can be added or the Kerr lens effect can be introduced in the mode-locked femtosecond laser, so that multiple wavelengths within the reflection spectrum of the laser gain crystal can operate simultaneously in 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.

[0040] However, the inventors of the present invention 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.

[0041] The inventors 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 ratio of the output light output by different wavelength components after passing through the output mirror is the same. And since 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, the current output mirror of the mode-locked femtosecond laser limits the laser spectral width of the output spectrum of the femtosecond laser.

[0042] Based on this, on the one hand 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.

[0043] 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.

[0044] Exemplarily, the broadening method may be executed by a system for broadening the output spectrum of a mode-locked femtosecond laser with computing capabilities.

[0045] 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.

[0046] 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 of a quasi-Gaussian type. By fitting the gain spectral curve of the laser gain crystal, the broadening system can obtain a quasi-Gaussian type gain spectral fitting curve with respect to wavelength.

[0047] It can be understood here that a quasi-Gaussian type curve in optics can refer to a curve whose shape is similar to that of a Gaussian function (bell-shaped curve) (such as a gain spectral curve, a spectral response curve, or an output rate curve, etc.). For example, the shape of the quasi-Gaussian type gain spectral fitting curve with respect to wavelength can be such that the gain corresponding to the central wavelength parameter of the highest peak of the emission spectrum is the highest (i.e., the spectral intensity is the highest), and the gain gradually decreases as it moves away from the central wavelength parameter (i.e., the spectral intensity gradually decreases).

[0048] 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.

[0049] 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 horizontal and vertical coordinate values of each scatter point (linear interpolation can be performed if necessary), forming 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.

[0050] 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 quasi-Gaussian type gain spectral fitting curve.

[0051] 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.

[0052] For example, the quasi-Gaussian type gain spectral fitting curve can be:

[0053] ;

[0054] 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 highest peak of the emission spectrum, is the full width at half maximum parameter of the gain spectral fitting curve.

[0055] Figure 3 A schematic diagram showing the gain spectrum fitting curve of an embodiment of the present invention.

[0056] 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.

[0057] 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.

[0058] 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 broadening system designs the output rate curve of the output mirror accordingly.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] For example, the output rate fitting curve can be:

[0064] ;

[0065] Wherein, 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.

[0066] According to the exemplary embodiment, in step S300, the broadening system determines a comprehensive gain spectrum curve with respect to wavelength based on the gain spectrum fitting curve and the output rate fitting curve.

[0067] For example, the comprehensive gain spectrum curve can be the product of the gain spectrum fitting curve and the output rate fitting curve.

[0068] Exemplarily, the comprehensive gain spectrum curve can be:

[0069] ;

[0070] where, is the comprehensive gain spectrum curve, is the gain spectrum fitting curve, is the output rate fitting curve.

[0071] It can be understood here that the comprehensive gain spectrum 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 spectrum curve can characterize the output spectrum of the mode-locked femtosecond laser.

[0072] In step S400, the broadening system adjusts the output rate fitting curve so that the laser spectral width of the comprehensive gain spectrum curve meets a preset width.

[0073] In step S500, the broadening system 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.

[0074] For example, by adjusting the design parameters of the output rate fitting curve, the broadening system can simulate the comprehensive gain spectrum curve under ideal conditions (i.e., the output spectrum of the mode-locked femtosecond laser).

[0075] 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 according to the design parameters of the corresponding output rate fitting curve, the corresponding output rate fitting curve can be determined and determined as the target output rate fitting curve.

[0076] 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 achieve a comprehensive gain spectral curve with a relatively wide output spectrum, and then the broadening of the output spectrum of the mode-locked femtosecond laser can be realized, thereby improving the performance of the mode-locked femtosecond laser.

[0077] 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 curve of the output rate fitting curve and the order p of the super-Gaussian distribution.

[0078] 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.

[0079] 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 another schematic diagram of an output spectrum according to an embodiment of the present invention.

[0080] As Figure 4a shown, this traditional output spectrum uses 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 traditional output spectrum almost completely coincides with the traditional gain spectral curve ( Figure 4a The dotted line in the middle is the traditional output spectrum, and the smooth curve is the traditional 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.

[0081] 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 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.

[0082] As Figure 4cAs shown, the gain spectrum fitting curve is of a quasi-Gaussian shape, and the output rate fitting curve has the lowest output rate at the central wavelength parameter and gradually increases with the distance 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., full width at half maximum) of the output spectrum is 50 nm.

[0083] According to Figure 4a , Figure 4b and Figure 4c it can be known that, compared with the output mirror of the traditional 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., 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 traditional design can be obtained.

[0084] 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 fabricated based on the target output rate fitting curve described above.

[0085] 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 Kerr-lens mode-locked titanium-sapphire femtosecond laser.

[0086] 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 traditional output mirror 17.

[0087] 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.

[0088] The reflectivities of the first planar mirror 12, the second planar mirror 13, the third planar 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-locking operation of the femtosecond laser. The traditional output mirror 17 is an output mirror with an output rate of 3%.

[0089] As an embodiment, the traditional output mirror 17 is replaced with an output mirror prepared based on the target output rate fitting curve described above (hereinafter referred to as the super-Gaussian output mirror). The traditional output spectrum corresponding to the traditional output mirror 17 and the super-Gaussian output spectrum corresponding to the super-Gaussian output mirror provided by the present invention are respectively tested.

[0090] For example, as Figure 5 shown, by adjusting the first planar mirror 12, the second planar mirror 13, the third planar mirror 14, the first concave mirror 15, the second concave mirror 16, and the traditional output mirror 17, the optical path of the laser can be adjusted 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 crystal center wavelength parameter. When the distance between the laser gain crystal 11 and the first concave mirror 15 is adjusted and the first planar mirror 12 is pushed, the Kerr lens mode-locking effect will be triggered. In this case, the femtosecond laser will run to the femtosecond pulse mode-locking state and output a multi-wavelength wide spectrum through the traditional output mirror 17. The traditional output spectrum corresponding to the traditional output mirror 17 can be obtained through the spectrum measuring device.

[0091] After replacing the traditional 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.

[0092] Figure 6 Schematic diagram for comparing the output spectra of the embodiments of the present invention; Figure 7 Schematic diagram for comparing the output rates of the embodiments of the present invention.

[0093] 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 traditional output spectrum. For example, the laser spectral width of the super-Gaussian output spectrum is about 225 nm, while that of the traditional 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.

[0094] As Figure 7As shown, in the traditional output mirror 17, the output rates of different wavelengths are almost the same (both about 3%). While for the super-Gaussian output mirror, it is only 3% near the central wavelength parameter, and it is higher than 3% in other parts. 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.

[0095] Through the above embodiments, the present invention can obtain the gain spectrum fitting curve about the 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, the output rate fitting curve about the wavelength can be obtained. According to the gain spectrum fitting curve and the output rate fitting curve, the comprehensive gain spectrum curve about the wavelength can be determined. The present invention also adjusts the output rate fitting curve to make the laser spectral width of the comprehensive gain spectrum curve meet the 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 can output an output spectrum that meets the preset width.

[0096] 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 about the 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.

[0097] Without changing the original structure of the mode-locked femtosecond laser, the present invention only needs to fit and design 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 a narrower laser pulse width.

[0098] Compared with the prior art methods for broadening the spectrum by replacing the laser gain crystal with a wider emission spectrum or 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. It only needs to determine the target output rate fitting curve by combining the output rate curve of the output mirror with the gain spectrum fitting curve. By performing layer film design on the output mirror through this 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.

[0099] 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.

[0100] Figure 8 Schematic structural diagram of the broadening system showing an embodiment of the present invention.

[0101] According to an example embodiment, as Figure 8 shown, the broadening system 2 may include a curve fitting module 21 and a curve adjustment module 22.

[0102] According to an example 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.

[0103] For example, the 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 of a Gaussian-like type. 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.

[0104] 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-shaped curve). For example, the shape of the Gaussian-like gain spectral fitting curve with respect to wavelength can be such that the gain is the highest (i.e., the spectral intensity is the 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.

[0105] 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.

[0106] 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 super-Gaussian functions, polynomial functions, Lorentz functions, etc.), compare the fitted function with the original curve, and use the least squares method to evaluate the fitting result.

[0107] 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.

[0108] 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.

[0109] For example, the Gaussian-like gain spectral fitting curve can be:

[0110] ;

[0111] Wherein, is the gain spectrum 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.

[0112] As Figure 3 shown, the gain spectrum fitting curve can have a shape where 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.

[0113] 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 the wavelength. The preset shape is that the output rate is the lowest at the central wavelength, and the output rate gradually increases away from the central wavelength.

[0114] 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.

[0115] Through curve fitting design, the curve fitting module 21 can obtain an output rate fitting curve with a shape where the output rate is the lowest at the central wavelength parameter and gradually increases away from the central wavelength parameter.

[0116] It can be understood here that as long as the curve satisfies the shape where the output rate is the lowest at the central wavelength parameter and 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.

[0117] 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.

[0118] 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.

[0119] For example, the output rate fitting curve can be:

[0120] ;

[0121] Wherein, is the output rate fitting curve, is the output rate corresponding to the central wavelength parameter, is the Euler's 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.

[0122] According to the exemplary embodiment, the curve fitting module 21 determines the comprehensive gain spectrum curve with respect to the wavelength based on the gain spectrum fitting curve and the output rate fitting curve.

[0123] For example, the comprehensive gain spectrum curve can be the product of the gain spectrum fitting curve and the output rate fitting curve.

[0124] Exemplarily, the comprehensive gain spectrum curve can be:

[0125] ;

[0126] Wherein, is the comprehensive gain spectrum curve, is the gain spectrum fitting curve, is the output rate fitting curve.

[0127] It can be understood here that the comprehensive gain spectrum 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 spectrum curve can characterize the output spectrum of the mode-locked femtosecond laser.

[0128] The curve adjustment module 22 adjusts the output rate fitting curve so that the laser spectral width of the comprehensive gain spectrum curve meets the preset width.

[0129] 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 the preset width is output through the output mirror prepared by the target output rate fitting curve.

[0130] For example, by adjusting the design parameters of the output rate fitting curve, the curve adjustment module 22 can simulate the comprehensive gain spectrum curve in the ideal case (i.e., the output spectrum of the mode-locked femtosecond laser).

[0131] Exemplarily, the curve adjustment module 22 can calculate, through numerical simulation, a laser spectral width that meets a preset width (such as as large as possible), so as to determine a 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.

[0132] According to the exemplary embodiment, through the target output rate fitting curve, a film layer design scheme of the output mirror (for designing the output rate of the output mirror) can be determined, and then, industrially, the corresponding output mirror can be prepared according to this film layer design scheme. The output mirror prepared based on the target output rate fitting curve can achieve a comprehensive gain spectral curve with a relatively wide output spectrum, and further can achieve the broadening of the output spectrum of the mode-locked femtosecond laser, thereby improving the performance of the mode-locked femtosecond laser.

[0133] Exemplarily, the curve adjustment module 22 can simulate an ideal comprehensive gain spectral curve by changing the spectral full width at half maximum parameter of the output rate curve of the output rate fitting curve and the order p of the super-Gaussian distribution.

[0134] It can be understood here that the curve adjustment module 22 can also determine the full width at half maximum parameter and the output spectrum corresponding to a required comprehensive gain spectral curve by selecting appropriate spectral full width at half maximum parameters of the output rate curve and the order p of the super-Gaussian distribution.

[0135] 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 another schematic diagram of an output spectrum according to an embodiment of the present invention.

[0136] As Figure 4a shown, the traditional output spectrum uses 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 traditional output spectrum almost completely coincides with the traditional gain spectral curve ( Figure 4a The dotted line in the middle is the traditional output spectrum, and the smooth curve is the traditional 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.

[0137] 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 the output rate gradually increases away from the central wavelength parameter, and the design parameters corresponding to this output rate fitting curve include: p = 3, . As Figure 4bAs shown, in this case, the laser spectral width (i.e., full width at half maximum) of the output spectrum is 40 nm.

[0138] As Figure 4c shown, the gain spectral fitting curve is in the shape of a quasi-Gaussian type, and the output rate fitting curve is such that the output rate is the lowest at the central wavelength parameter and gradually increases away from the central wavelength parameter. And 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., full width at half maximum) of the output spectrum is 50 nm.

[0139] According to Figure 4a , Figure 4b and Figure 4c it can be known that, compared with the output mirror of the traditional 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 spectral curve) and the laser spectral width (i.e., 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 traditional design can be obtained.

[0140] Through the above embodiments, the present invention can obtain a gain spectral fitting curve with respect to wavelength by fitting the gain spectral 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. The comprehensive gain spectral curve with respect to wavelength can be determined according to the gain spectral fitting curve and the output rate fitting curve. The present invention can also make the laser spectral width of the comprehensive gain spectral curve meet a preset width by adjusting the output rate fitting curve, 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.

[0141] 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 spectral 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 can achieve the broadening of the output spectrum of the mode-locked femtosecond laser to improve the performance of the mode-locked femtosecond laser.

[0142] The present invention can, without changing the original structure of the mode-locked femtosecond laser, only perform a fitting design on the output rate curve of the output mirror in combination with the gain spectral 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 broaden the output spectrum of the mode-locked femtosecond laser, and further can obtain femtosecond laser pulses with a narrower laser pulse width.

[0143] Compared with the prior art spectral broadening methods that involve replacing the laser gain crystal with a wider emission spectrum laser gain crystal and inserting a nonlinear broadening crystal into the cavity, the present invention does not require replacing the laser gain crystal, nor does it need to add additional devices in the cavity. It only needs to determine the target output rate fitting curve by combining the output rate curve of the output mirror with the gain spectrum fitting curve. By performing thin film design on the output mirror according to this target output rate fitting curve, the spectral broadening of the mode-locked femtosecond laser output can be achieved. The present invention has the characteristics of simple structure, low cost, and easy industrial implementation, and has good cost performance and practical value.

[0144] According to another aspect of the present invention, the present invention also 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 the mode-locked femtosecond laser as described above.

[0145] According to another aspect of the present invention, the present invention also 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.

[0146] 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, which when executed by a computer, cause the computer to execute the method for broadening the output spectrum of the mode-locked femtosecond laser as described above.

[0147] Finally, it should be noted that the above are only the 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, for those skilled in the art, they 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 in 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 at least includes a laser gain crystal and an output mirror, and the broadening method includes: Fitting the gain spectral curve of the laser gain crystal to obtain a gain spectral 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, where 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 spectral curve with respect to wavelength according to the gain spectral fitting curve and the output rate fitting curve; Adjusting the output rate fitting curve so that the laser spectral width of the comprehensive gain spectral curve meets a preset width; Determining 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.

2. The broadening method according to claim 1, characterized in that The fitting the gain spectral curve of the laser gain crystal to obtain a gain spectral fitting curve with respect to wavelength includes: Fitting the gain spectral curve by the point plotting method or the standard function fitting method to obtain the gain spectral fitting curve.

3. The widening method according to claim 2, characterized in that The standard function is a Gaussian function, and the fitting the gain spectral curve by the point plotting method or the standard function fitting method to obtain the gain spectral fitting curve includes: Fitting the gain spectral curve based on the Gaussian function to obtain a gain spectral fitting curve of a quasi-Gaussian type, including: Determining 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 fitting curve.

4. The broadening method according to claim 1, characterized in that The fitting the output rate curve of the output mirror based on a preset shape includes: Fitting the output rate curve based on a 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 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.

5. A femtosecond laser, characterized in that, The femtosecond laser includes a mode-locked femtosecond laser, and the mode-locked femtosecond laser at least includes an output mirror prepared by the target output rate fitting curve; wherein, the target output rate fitting curve is obtained based on the broadening method according to 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 at least includes a laser gain crystal and an output mirror, and the broadening system includes: A curve fitting module that fits the gain spectral curve of the laser gain crystal to obtain a gain spectral 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 at the central wavelength is the lowest and the output rate gradually increases away from the central wavelength; and determines a comprehensive gain spectral curve with respect to wavelength according to the gain spectral 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 spectral 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 through the target output rate fitting curve outputs an output spectrum meeting the preset width.

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

8. The widening system according to claim 7, characterized in that, The standard function is a Gaussian function. The curve fitting module fits the gain spectral curve based on the Gaussian function to obtain a Gaussian-like gain spectral fitting curve, including: The curve fitting module determines the gain spectral 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 spectral fitting curve.

9. The widening system according to claim 6, characterized in that, The curve fitting module fits the output rate curve based on the super-Gaussian function to obtain the output rate fitting curve with the preset shape, including: The curve fitting module determines the output rate fitting curve based on the super-Gaussian function by using the 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.

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