CN117353143A - Femtosecond laser and mode locking method thereof - Google Patents
Femtosecond laser and mode locking method thereof Download PDFInfo
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- CN117353143A CN117353143A CN202311246423.7A CN202311246423A CN117353143A CN 117353143 A CN117353143 A CN 117353143A CN 202311246423 A CN202311246423 A CN 202311246423A CN 117353143 A CN117353143 A CN 117353143A
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
- H01S3/1106—Mode locking
- H01S3/1112—Passive mode locking
- H01S3/1115—Passive mode locking using intracavity saturable absorbers
- H01S3/1118—Semiconductor saturable absorbers, e.g. semiconductor saturable absorber mirrors [SESAMs]; Solid-state saturable absorbers, e.g. carbon nanotube [CNT] based
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Abstract
The application discloses a femtosecond laser and a mode locking method of the femtosecond laser. The femtosecond laser comprises a gain crystal, a pumping source and a resonant cavity, and the femtosecond laser further comprises: at least one light control switch arranged in the optical path of the laser light path of the femtosecond laser; and the driver loads a preset driving signal to the light control switch so as to enable the femtosecond laser to start a femtosecond pulse operation mode and maintain the operation of the femtosecond pulse operation mode. According to the method, the driver loads the drive signal with the specific frequency to the light control switch, so that the femtosecond laser can be excited to be converted into the femtosecond pulse operation mode from the direct-current operation mode, the starting of the femtosecond pulse operation mode is completed under the condition that mechanical movement is not needed, and the problems that a resonator for starting the femtosecond pulse operation mode is detuned and the starting state is inconsistent in a mechanical movement mode are avoided; and by continuously loading the drive signal to the light control switch, the femtosecond laser can continuously maintain the femtosecond pulse operation mode without being interfered by other factors.
Description
Technical Field
The application relates to the technical field of femtosecond lasers, in particular to a femtosecond laser and a mode locking method of the femtosecond laser.
Background
The femtosecond laser can output an ultra-narrow laser pulse sequence with a certain time interval, and is a pulse laser capable of periodically transmitting laser with a pulse width of femtosecond magnitude. The femtosecond laser has the advantages of narrow pulse width, high peak power, multiple spectral components and the like, so that the femtosecond laser is widely applied to the technical fields of leading edge scientific research, high-end industrial processing, minimally invasive medical treatment and the like.
The femtosecond laser generated by the femtosecond laser is realized based on a mode locking technology. Current mode locking techniques generally include kerr lens mode locking techniques and saturable absorber (SESAM) mode locking techniques.
The femtosecond laser includes two modes of operation: a direct current operation mode and a femtosecond pulse operation mode. However, the inventors of the present application have found that kerr lens mode locking is an important way of achieving the femtosecond pulsed mode of operation for current femtosecond lasers. However, the mode locking mode requires additional mechanical motion to trigger the operation of the femtosecond pulse, and the operation state of the femtosecond pulse is extremely easy to be disturbed by the environment, thus the operation is stopped, and the operation is difficult to maintain well.
The inventors therefore believe that the initiation and maintenance of the femtosecond pulsed operation mode of a femtosecond laser is a technical problem that needs to be studied.
Disclosure of Invention
The application discloses a femtosecond laser and a mode locking method of the femtosecond laser. The method is used for solving the problems of starting and maintaining a femtosecond pulse operation mode of the current femtosecond laser based on the Kerr lens mode locking technology.
One aspect of the present application provides a femtosecond laser. The femtosecond laser comprises a gain crystal, a pumping source and a resonant cavity, and the femtosecond laser further comprises: at least one light control switch arranged in the optical path of the laser light path of the femtosecond laser; and the driver loads a preset driving signal to the light control switch so as to enable the femtosecond laser to start a femtosecond pulse operation mode and maintain the operation of the femtosecond pulse operation mode.
According to some embodiments of the present application, at least one light control switch is disposed within the resonant cavity perpendicular to the laser light path; wherein, the surface of the light control switch is provided with an antireflection layer.
According to some embodiments of the present application, at least one optical control switch is disposed within the resonant cavity of the femtosecond laser at the brewster angle.
According to some embodiments of the present application, the light control switch is an acousto-optic control switch; the driving frequency of the preset driving signal is as follows:
wherein f a For the drive frequency, c is the speed of light and L is the quantity related to the cavity length of the resonant cavity.
According to some embodiments of the present application, the light control switch is an electro-optic control switch; the driving frequency of the preset driving signal is as follows:
wherein f b For the drive frequency, c is the speed of light and L is the quantity related to the cavity length of the resonant cavity.
According to another aspect of the present application, a mode locking method based on a femtosecond laser is provided. The femtosecond laser comprises a gain crystal, a pumping source, a resonant cavity and a driver, wherein at least one light control switch is arranged in a laser path of the femtosecond laser, and the mode locking method based on the femtosecond laser comprises the following steps: the driver loads a preset driving signal to the light control switch so as to enable the femtosecond laser to start in a femtosecond pulse operation mode; the driver continuously loads a preset driving signal to the light control switch so that the femtosecond laser continuously operates in a femtosecond pulse operation mode.
According to some embodiments of the present application, at least one light control switch is disposed within a resonant cavity of a femtosecond laser; wherein, the surface of the light control switch is provided with an antireflection layer.
According to some embodiments of the present application, at least one optical control switch is disposed within the resonant cavity of the femtosecond laser at the brewster angle.
The light control switch is an acousto-optic control switch according to some embodiments of the present application; under the condition that the light control switch is an acousto-optic control switch, the driving frequency of a preset driving signal is as follows:
wherein f a For the driving frequency, c is the speed of light and L is the quantity related to the cavity length of the resonant cavity.
According to some embodiments of the present application, the light control switch is an electro-optic control switch; in the case that the light control switch is an electro-optical control switch, the driving frequency of the preset driving signal is:
wherein f b For the driving frequency, c is the speed of light and L is the quantity related to the cavity length of the resonant cavity.
According to the technical scheme, the driver loads the drive signal with the specific frequency to the light control switch, so that the femtosecond laser can be excited to be converted into the femtosecond pulse operation mode from the direct-current operation mode, the starting of the femtosecond pulse operation mode is completed under the condition that mechanical movement is not needed, and the problems that a resonator for starting the femtosecond pulse operation mode is detuned and inconsistent in initial state and the like are avoided; and by continuously loading the drive signal to the light control switch, the femtosecond laser can continuously maintain the femtosecond pulse operation mode without being interfered by other factors.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 shows a schematic diagram of a prior art Kerr lens mode-locked femtosecond laser;
FIG. 2 shows a schematic diagram of a femtosecond laser of an example embodiment of the application;
FIG. 3 shows another schematic diagram of a femtosecond laser of an example embodiment of the application;
FIG. 4 shows a schematic diagram of signals acquired by an oscilloscope according to an example embodiment of the present application;
FIG. 5 shows a schematic diagram of the output power of a femtosecond laser according to an example embodiment of the application;
fig. 6 shows a flow chart of a mode locking method of an example embodiment of the present application.
Reference numerals illustrate:
a continuous laser pump source A; a first plano-concave mirror B; cr is ZnS crystal C; a second plano-concave mirror D; a planar high-reflection mirror E; bai Bao stone chips F; an output coupling mirror G; an optical coupling system H.
A gain crystal 1; a pump source 2; a chirped mirror 3; a chirped mirror 4; a chirped mirror 5; an output mirror 6; a prism pair 7; a prism pair 8; a chirped mirror 9; a light control switch 10; a driver 11; a high-speed photodetector 12.
Detailed Description
Example embodiments will now be described more fully with reference to the accompanying drawings. However, the exemplary embodiments can be embodied in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the example embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and thus a repetitive description thereof will be omitted.
The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the disclosed aspects may be practiced without one or more of the specific details, or with other methods, components, materials, apparatus, etc. In these instances, well-known structures, methods, devices, implementations, materials, or operations are not shown or described in detail.
Furthermore, the terms "comprise" and "have," as well as any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those listed steps or elements but may include other steps or elements not listed or inherent to such process, method, article, or apparatus.
The terms first, second and the like in the description and in the claims of the present application and in the above-described figures, are used for distinguishing between different objects and not for describing a particular sequential order.
The following description of the embodiments of the present application, taken in conjunction with the accompanying drawings, will clearly and fully describe the technical aspects of the present application, and it will be apparent that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.
The pulse width of the laser pulse emitted by the femtosecond laser can be several femtoseconds to several hundred femtoseconds (femtosecond unit English is fs, 1fs=10) -15 s) whose repetition frequency can be generally from a few tens of MHz to a few GHz.
Femtosecond lasers have wide applications, which can play an important role in the fields of medicine, industry, scientific research, safety detection, and the like. For example, in the scientific field, the femtosecond laser can be used for material surface analysis, spectrum analysis, biochemical research, quantum physical research and the like, and can also be used for manufacturing ultra-fast electric pulses, terahertz radiation and the like; in the field of industrial processing, the femtosecond laser can be used for micromachining, such as processing tiny parts, marking, cutting and the like, and can also be used for manufacturing solar cells, LED lamps and the like, and the femtosecond laser can also utilize the high peak power of the femtosecond laser to realize the cold processing of materials, so that the thermal influence in the processing process is minimized; in the medical field, femtosecond lasers are used in ophthalmic surgery such as LASIK, cornea implantation, etc.
And the femtosecond laser generated by the femtosecond laser is realized based on a mode locking technology. The mode locking technology refers to a technology for generating extremely short-time laser pulses in a femtosecond laser, and the laser pulses can reach the magnitude of femtosecond.
Current mode locking techniques generally include kerr lens mode locking techniques and saturable absorber (SESAM) mode locking techniques.
The saturable absorber mode-locking technique does not require the introduction of external signals (e.g., drive signals for modulators, etc.) to the femtosecond laser to generate pulses, which typically uses light waves in the laser cavity to cause a change in a device within the laser cavity that in turn causes a change in the light within the cavity. The device typically used is a saturable absorber, the transmissivity of which is related to the light intensity. The saturable absorber can behave differently when light passes through, depending on the intensity of the light. An ideal saturable absorber absorbs light at low intensities and passes through it when the intensity is high enough.
However, the inventors have found that the saturable absorber mode locking technique requires a saturable absorber device to assist in achieving the output of the femtosecond laser, and that there are several practical problems with the saturable absorber device: if the corresponding speed of the device is slow, a narrower laser pulse width is difficult to obtain; the laser is easy to damage, needs to be replaced at regular time, and is difficult to realize high-power laser output; the supply of devices is relatively difficult and the cost is high; poor device-to-device uniformity, etc.
The Kerr lens mode locking technology realizes mode locking by utilizing the photophysical effect in a medium, so that no additional auxiliary device is needed, and compared with the saturable absorber mode locking technology, the Kerr lens mode locking technology has the characteristics of high response speed, easiness in generating femtosecond laser with narrow pulse width, low cost, high reliability and the like.
For example, for a femtosecond laser with the pulse width of less than 30fs (such as a titanium precious stone femtosecond laser), only the kerr lens mode locking technology can realize the mode locking of the femtosecond laser.
For the femtosecond laser, the femtosecond laser has two operation modes, one is a direct current operation mode and the other is a femtosecond pulse operation mode. In the direct current operation mode, the femtosecond laser is in a direct current operation state, and the output light is continuous light; if the femtosecond laser is started in a specific starting manner, the femtosecond laser can be caused to jump from a direct current operation mode to a femtosecond pulse operation mode. In the femtosecond pulse operation mode, the output light of the femtosecond laser is a femtosecond pulse laser.
In the prior art, a method for starting a femtosecond pulse operation mode of a femtosecond laser generally forms instantaneous impact by pushing or rotating an optical device of the femtosecond laser and the like in a mechanical mode, so as to excite a kerr lens effect in the femtosecond laser.
For example, FIG. 1 shows a schematic diagram of a prior art Kerr-lens mode-locked femtosecond laser. As shown in fig. 1, the kerr lens mode-locked femtosecond laser includes: the laser comprises a continuous laser pumping source A, a first flat concave mirror B, cr, a ZnS crystal C, a second flat concave mirror D, a flat high-reflection mirror E, a Bai Bao stone chip F, an output coupling mirror G and an optical coupling system H.
According to the structure and the optical path in fig. 1, laser emitted by the continuous laser pumping source a is focused to a Cr ZnS crystal C through an optical coupling system H, laser emitted by the Cr ZnS crystal C is incident to a second concave mirror D, the second concave mirror D reflects the laser back to a plane high-reflection mirror E, the plane high-reflection mirror E reflects the laser back in the original path, and focuses the laser to the Cr ZnS crystal C through the second concave mirror D for gain, then reaches a first concave mirror B and is reflected by the first concave mirror B to a Bai Bao stone sheet F, after passing through the Bai Bao stone sheet F, a part of the laser is reflected back by an output coupling mirror G in the original path, gain is further obtained in the Cr ZnS crystal C through the first concave mirror B, and another part of the laser is output by the output coupling mirror G. The Kerr lens mode locking can be realized by fine-tuning Cr: znS crystal C and second flat concave mirror D and slightly pushing plane high-reflection mirror E.
The femtosecond laser can realize Kerr lens mode locking by fine-tuning a Cr-ZnS crystal, a second flat concave mirror and a light pushing plane high-reflection mirror. However, the inventors have found that the mode locking method has the following problems: after being pushed for many times, the lens is easy to loosen to cause the detuning of the femtosecond laser; the consistency of the impact formed by multiple mechanical pushing/moving is difficult to ensure, and the problem of inconsistent running state after each start is easily caused.
In addition, the inventors have found that when the femtosecond laser is started in the femtosecond pulse operation mode, the femtosecond laser is operated in the femtosecond pulse operation mode all the time without any interference. The physical process of the Kerr lens mode locking effect is very easy to jump back to the direct current operation mode under the influence of external environment disturbance (such as mechanical vibration, airflow, temperature and humidity change and the like). In this case, the femtosecond laser can only be re-excited into the femtosecond pulse operation mode again by a specific starting manner.
Accordingly, the inventors believe that the current mode locking methods of femtosecond lasers remain to be improved with respect to the scheme of initiation and maintenance of the femtosecond pulse operation mode of the femtosecond laser.
Based on this, an aspect of the present application provides a femtosecond laser. At least one light control switch is arranged in the femtosecond laser, a drive signal with specific frequency is loaded to the light control switch through a driver, and the femtosecond laser can be directly excited to be converted into a femtosecond pulse operation mode from a direct current operation mode, so that the starting of the femtosecond pulse operation mode is completed without mechanical movement, and the problems of detuning of a resonator, inconsistent initial state and the like when the femtosecond pulse operation mode is started in a mechanical movement mode are avoided; and by continuously loading the drive signal to the light control switch, the femtosecond laser can continuously maintain the femtosecond pulse operation mode without being interfered by other factors.
Fig. 2 shows a schematic diagram of a femtosecond laser according to an exemplary embodiment of the application.
Illustratively, the femtosecond laser includes, but is not limited to, a solid state laser, a disk laser, a slab laser, a fiber laser, and the like, which is not limited in this application. It will be appreciated here that the femtosecond laser can be tuned to achieve kerr lens mode-locked operation.
According to an example embodiment, as shown in fig. 2, a femtosecond laser includes a gain crystal 1, a pump source 2, and a resonant cavity. The resonant cavity is internally provided with a chirp mirror 3, a chirp mirror 4, a chirp mirror 5 and an output mirror 6 with proper dispersion quantity, or is provided with a prism pair 7 and a prism pair 8, or is provided with a combination of the chirp mirror and the prism pair so as to meet the requirement of dispersion in the resonant cavity when the femtosecond pulse laser operates.
Illustratively, the resonant cavity may be a combination of the chirped mirror 3, the chirped mirror 4, the chirped mirror 5 and the chirped mirror 6, or may be a combination of the chirped mirror 3, the chirped mirror 4, the output mirror 6, the prism pair 7, the prism pair 8 and the chirped mirror 9.
According to an exemplary embodiment, the femtosecond laser further comprises at least one light control switch 10 and a driver 11, as shown in fig. 2.
The light control switch 10 is disposed in the optical path of the femtosecond laser optical path. The driver 11 loads a preset driving signal to the light control switch 10 to cause the femtosecond laser to start the femtosecond pulse operation mode and maintain the operation of the femtosecond pulse operation mode.
For example, the light control switch 10 may be an acousto-optic control switch or an electro-optic control switch (e.g., a combination of an electro-optic modulator and a polarizer). The light control switch 10 has a sufficiently fast response speed to be able to respond quickly to a preset drive signal that it is loaded with.
The preset driving signal is preset according to the user requirement. The type of preset drive signal includes, but is not limited to, a standard sine wave, a triangular wave, a square wave, and the like. Under the drive of a preset drive signal, the femtosecond laser can be periodically opened and closed by controlling the light control switch. The frequency of opening and closing the light control switch is the same as the repetition frequency of the output of the femtosecond laser pulse.
Optionally, as shown in fig. 2, the femtosecond laser further includes a high-speed photodetector 12 for detecting a repetition frequency of the femtosecond laser in the femtosecond pulse operation mode.
Optionally, as shown in fig. 2, at least one optical control switch 10 is disposed within the resonant cavity perpendicular to the laser light path, and the surface of the optical control switch 10 is provided with an anti-reflection layer. For example, the anti-reflection layer is an anti-reflection film.
Or, alternatively, at least one optical control switch 10 is disposed within the cavity of the femtosecond laser at the brewster angle. For example, by adjusting the angle of the optical control switch 10, losses associated with devices inserted within the cavity may be minimized.
Fig. 3 shows another schematic diagram of a femtosecond laser of an example embodiment of the application.
As shown in fig. 3, the number of the light control switches 10 may also be 2. By the arrangement, the femtosecond pulse operation mode of the femtosecond laser can be excited more accurately under the control of a plurality of light control switches. It will be appreciated here that in the case where a plurality of optical control switches are provided, a specific pulse phase delay is required between the plurality of optical control switches so that the femtosecond pulsed laser can smoothly pass through the respective optical control switches with the specific pulse phase delay.
The driving frequency of the preset driving signal may be determined by detection by the high-speed photodetector 12 or may be determined by calculation by a preset formula.
Optionally, in the case that the light control switch is an acousto-optic control switch, the driving frequency of the preset driving signal is:
wherein f a For the drive frequency, c is the speed of light and L is the quantity related to the cavity length of the resonant cavity. For example, when the resonant cavity of the femtosecond laser is a line cavity, L is the cavity length of the line cavity; when the resonant cavity of the femtosecond laser is a ring cavity, L is 1/2 of the cavity length of the ring cavity.
Optionally, in the case where the light control switch is an electro-optical control switch, the driving frequency of the preset driving signal is:
wherein f b For the drive frequency, c is the speed of light and L is the quantity related to the cavity length of the resonant cavity. For example, when the resonant cavity of the femtosecond laser is a line cavity, L is the cavity length of the line cavity; when the resonant cavity of the femtosecond laser is a ring cavity, LIs 1/2 of the cavity length of the annular cavity.
When the preset driving signal of the driver 11 is loaded to the light control switch 10, the femtosecond laser can be started from the direct current operation mode to the femtosecond pulse operation mode instantaneously, and the femtosecond pulse operation mode of the femtosecond laser can be not interfered by the external environment under the condition that the preset driving signal is continuously loaded to the light control switch 10, so that the operation of the femtosecond pulse operation mode can be maintained.
Example embodiment
As shown in fig. 2, the femtosecond laser is a solid femtosecond laser based on kerr lens mode locking, a resonant cavity of the solid laser is a linear cavity, and the femtosecond laser is adjusted to a state capable of realizing femtosecond pulse operation.
The repetition rate of the femtosecond laser in the operation mode of the femtosecond pulse can be detected by the high-speed photodetector 12 to be 80.64MHz.
The light control switch 10 is an acousto-optic control switch, such as a fused quartz crystal, having a response frequency of about 40MHz. The optical control switch 10 is disposed within the cavity at a brewster angle such that the insertion loss of devices within the cavity is minimized.
The driving frequency of the preset driving signal is 40.32MHz by frequency division calculation according to the repetition frequency detected by the high-speed photodetector 12.
FIG. 4 shows a schematic diagram of signals acquired by an oscilloscope according to an example embodiment of the present application; fig. 5 shows a schematic diagram of the output power of the femtosecond laser of an example embodiment of the present application.
As shown in fig. 4, the driver 11 loads a preset driving signal having a driving frequency of 40.32MHz to the acousto-optic control switch.
Fig. 4 shows the femtosecond laser pulse signal and the acousto-optic driving signal collected by the oscilloscope. As shown in fig. 4, at the moment when the acousto-optic control switch is loaded with a preset driving signal, an oscilloscope signal acquired by an oscilloscope connected with the high-speed photodetector 12 is converted from a direct-current waveform into a pulse waveform (a femtosecond laser pulse signal as shown in fig. 4). Therefore, the characteristic that the femtosecond laser is switched into the femtosecond pulse operation mode to generate the femtosecond laser pulse at the moment that the acousto-optic control switch is loaded with a preset driving signal can be obtained.
The frequency of the preset driving signal loaded to the acousto-optic control switch is doubled with that of the femtosecond laser pulse signal after the femtosecond laser is started, and the phase difference of the preset driving signal and the femtosecond laser pulse signal is a fixed value. As shown in fig. 5, the femtosecond laser is instantaneously changed from the direct current operation mode to the femtosecond pulse operation mode, and the output power of the femtosecond laser is also significantly changed.
As shown in fig. 5, in the case of continuously loading the preset driving signal to the acousto-optic control switch, the pulse operation state of the femtosecond laser can be continuously maintained for more than 24 hours without being influenced by other external environments.
Through the above-mentioned example embodiments, when the femtosecond pulse operation mode is started, the optical device in the resonant cavity does not need to perform mechanical motion, so that compared with the traditional scheme of pushing/moving/rotating the optical device to start the femtosecond pulse operation mode, the femtosecond laser has higher reliability, can reduce the risk of detuning of the resonant cavity in the femtosecond laser, and improves the consistency of the operation state in the femtosecond laser. According to the method, the preset driving signal is loaded to the light control switch through continuous loading, so that the anti-interference capability of the femtosecond pulse operation mode of the femtosecond laser can be improved, and the environment adaptability of the femtosecond laser is obviously improved.
Another aspect of the present application provides a method of mode locking a femtosecond laser. The mode locking method can load a specific-frequency driving signal to the optical control switch through a driver, and can directly excite the femtosecond laser to be converted into a femtosecond pulse operation mode from a direct-current operation mode, so that the starting of the femtosecond pulse operation mode is completed without mechanical movement, and the problems of detuning of a resonator, inconsistent initial state and the like when the femtosecond pulse operation mode is started in a mechanical movement mode are avoided; and by continuously loading the drive signal to the light control switch, the femtosecond laser can continuously maintain the femtosecond pulse operation mode without being interfered by other factors.
Fig. 6 shows a flow chart of a mode locking method of an example embodiment of the present application. As shown in fig. 6, the mode locking method includes steps S100 to S200. The mode locking method may be performed by a femtosecond laser, for example.
Illustratively, the femtosecond laser includes, but is not limited to, a solid state laser, a disk laser, a slab laser, a fiber laser, and the like, which is not limited in this application. It will be appreciated here that the femtosecond laser can be tuned to achieve kerr lens mode-locked operation.
According to an example embodiment, a femtosecond laser includes a gain crystal, a pump source, and a resonant cavity. The resonant cavity is internally provided with a chirped mirror and an output mirror with proper dispersion quantity, or is provided with a prism pair, or is provided with a combination of the chirped mirror and the prism pair so as to meet the requirement of dispersion in the resonant cavity when the femtosecond pulse laser operates. The resonant cavity may be a combination of a plurality of chirped mirrors, or a combination of chirped mirrors and prism pairs, for example.
According to an example embodiment, the femtosecond laser further comprises at least one light control switch and a driver.
In step S100, the driver loads a preset driving signal to the light control switch to start the femtosecond laser in the femtosecond pulse operation mode.
In step S200, the driver continuously loads the preset driving signal to the light control switch to continuously operate the femtosecond laser in the femtosecond pulse operation mode.
For example, when the preset driving signal of the driver is loaded to the light control switch, the femtosecond laser can be started from the direct-current operation mode to the femtosecond pulse operation mode instantaneously, and the femtosecond pulse operation mode of the femtosecond laser can be not interfered by the external environment under the condition that the preset driving signal is continuously loaded to the light control switch, so that the operation of the femtosecond pulse operation mode can be maintained.
Illustratively, the light control switch may be an acousto-optic control switch or an electro-optic control switch (e.g., a combination of an electro-optic modulator and a polarizer). The light control switch has a sufficiently fast response speed to be able to respond quickly to the preset drive signal it is loaded with.
The preset driving signal is preset according to the user requirement. The type of preset drive signal includes, but is not limited to, a standard sine wave, a triangular wave, a square wave, and the like. Under the drive of a preset drive signal, the femtosecond laser can be periodically opened and closed by controlling the light control switch. The frequency of opening and closing the light control switch is the same as the repetition frequency of the output of the femtosecond laser pulse.
Optionally, the femtosecond laser further comprises a high-speed photodetector for detecting a repetition frequency of the femtosecond laser in the femtosecond pulse operation mode.
Optionally, at least one light control switch is disposed within the resonant cavity perpendicular to the laser light path, and a surface of the light control switch is provided with an anti-reflection layer. For example, the anti-reflection layer is an anti-reflection film.
Or, alternatively, at least one optical control switch is disposed within the cavity of the femtosecond laser at the brewster angle. For example, by adjusting the angle of the optical control switch, losses associated with devices inserted within the cavity may be minimized.
The driving frequency of the preset driving signal may be determined by detection by the high-speed photodetector 12 or may be determined by calculation by a preset formula.
Optionally, in the case that the light control switch is an acousto-optic control switch, the driving frequency of the preset driving signal is:
wherein f a For the drive frequency, c is the speed of light and L is the quantity related to the cavity length of the resonant cavity. For example, when the resonant cavity of the femtosecond laser is a line cavity, L is the cavity length of the line cavity; when the resonant cavity of the femtosecond laser is a ring cavity, L is 1/2 of the cavity length of the ring cavity.
Optionally, in the case where the light control switch is an electro-optical control switch, the driving frequency of the preset driving signal is:
wherein f b For the drive frequency, c is the speed of light and L is the quantity related to the cavity length of the resonant cavity. For example, when the resonant cavity of the femtosecond laser is a line cavity, L is the cavity length of the line cavity; when the resonant cavity of the femtosecond laser is a ring cavity, L is 1/2 of the cavity length of the ring cavity.
Through the above-mentioned example embodiments, the mode locking method of the femtosecond laser provided by the application does not need to perform mechanical movement on the optical device in the resonant cavity when the femtosecond pulse operation mode is started, and compared with the traditional scheme of pushing/moving/rotating the optical device to start the femtosecond pulse operation mode, the mode locking method has higher reliability, can reduce the risk of detuning of the resonant cavity in the femtosecond laser, and improves the consistency of the operation state in the femtosecond laser. According to the method, the preset driving signal is loaded to the light control switch through continuous loading, so that the anti-interference capability of the femtosecond pulse operation mode of the femtosecond laser can be improved, and the environment adaptability of the femtosecond laser is obviously improved.
Finally, it should be noted that the foregoing description is only a preferred embodiment of the present application, and is not intended to limit the present application, and although the detailed description of the present application is given with reference to the foregoing embodiment, it will be obvious to those skilled in the art that various modifications may be made to the technical solutions of the foregoing embodiments, or that equivalents may be substituted for some of the technical features thereof. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.
Claims (10)
1. A femtosecond laser comprising a gain crystal, a pump source, and a resonant cavity, the femtosecond laser further comprising:
at least one light control switch arranged in the light path of the femtosecond laser light path;
and the driver loads a preset driving signal to the light control switch so as to enable the femtosecond laser to start a femtosecond pulse operation mode and maintain the operation of the femtosecond pulse operation mode.
2. The femtosecond laser according to claim 1, wherein said at least one light control switch is disposed within said cavity perpendicular to said laser light path;
wherein, the surface of light control switch is provided with the anti-reflection layer.
3. The femtosecond laser according to claim 1, wherein said at least one light control switch is disposed within a cavity of said femtosecond laser at brewster angle.
4. The femtosecond laser according to claim 1, wherein the light control switch is an acousto-optic control switch;
the driving frequency of the preset driving signal is as follows:
wherein f a For the driving frequency, c is the speed of light and L is the quantity related to the cavity length of the resonant cavity.
5. The femtosecond laser according to claim 1, wherein the light control switch is an electro-optical control switch;
the driving frequency of the preset driving signal is as follows:
wherein f b For the driving frequency, c is the speed of light and L is the quantity related to the cavity length of the resonant cavity.
6. A mode locking method based on a femtosecond laser, wherein the femtosecond laser comprises a gain crystal, a pumping source, a resonant cavity and a driver, and at least one light control switch is arranged in a laser path of the femtosecond laser, the method comprises:
the driver loads a preset driving signal to the light control switch so as to enable the femtosecond laser to start in a femtosecond pulse operation mode;
the driver continuously loads the preset driving signal to the light control switch so as to enable the femtosecond laser to continuously operate in the femtosecond pulse operation mode.
7. The method of claim 6, wherein the at least one light control switch is disposed within a resonant cavity of the femtosecond laser perpendicular to the laser light path;
wherein, the surface of light control switch is provided with the anti-reflection layer.
8. The method of claim 6, wherein the at least one light control switch is disposed within a resonant cavity of the femtosecond laser at a brewster angle.
9. The method of claim 6, wherein the light control switch is an acousto-optic control switch;
when the light control switch is the acousto-optic control switch, the driving frequency of the preset driving signal is as follows:
wherein f a For the driving frequency, c is the speed of light, and L is the quantity related to the cavity length of the resonant cavity.
10. The method of claim 6, wherein the light control switch is an electro-optic control switch;
in the case that the light control switch is the electro-optical control switch, the driving frequency of the preset driving signal is:
wherein f b For the driving frequency, c is the speed of light, and L is the quantity related to the cavity length of the resonant cavity.
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