A femtosecond laser mode-locking state detection method and system

Abstract

The present invention relates to the field of laser state detection, and specifically discloses a femtosecond laser mode-locked state detection method and system, wherein the sampling frequency of a data acquisition card is configured so that the effective sampling number is greater than a preset sampling number threshold; the data acquisition card performs several continuous samplings, and obtains several sampling values ​​each time, and in each continuous sampling, the data acquisition card samples at least once in each sampling cycle; the corresponding peak-valley values ​​are calculated according to the several sampling values ​​obtained by each continuous sampling; if the difference between any two peak-valley values ​​is less than a first difference threshold, and the difference between each peak-valley value and a standard peak-valley value is less than a second difference threshold, then it is determined that the laser is mode-locked, otherwise it is determined that the laser is not mode-locked. The present invention uses period mismatch and peak-valley values ​​to determine the mode-locked state, and has low requirements on the sampling frequency of the data acquisition card, thereby effectively saving the cost of the detection system, while reducing the difficulty of output processing and improving detection efficiency.

Description

Technical Field

[0001] The present invention relates to the field of laser state detection, and in particular to a femtosecond laser mode-locking state detection method and system. Background Art

[0002] Most femtosecond lasers are realized through mode locking. Whether the laser has completed mode locking or not has a fundamental difference in the laser peak power. Usually, when the laser is not mode locked, the peak power of the laser is relatively low, while after mode locking, the peak power of the laser will be hundreds of times higher than that of the non-mode locked state, and the peak power will be very stable. Therefore, accurately judging whether the femtosecond laser has completed mode locking is the key to the use of the laser.

[0003] The current method of judgment is mainly based on frequency. Figure 1 This is a schematic diagram of the structure of the existing femtosecond laser mode-locking state detection system. First, the approximate period and pulse width of the laser are known (usually given in the manufacturer's information). The laser emits laser light, and a very small proportion of the light is irradiated to the photodetector through a partial reflector, and the optical signal is converted into an electrical signal. The electrical signal is collected by a data acquisition card, and the period or pulse width of the light is restored through data processing. It is compared with the known laser period or pulse width to determine whether the laser has completed mode locking and give different status indications.

[0004] This method relies on high-speed photoelectric detectors and high-speed data acquisition cards for data acquisition. Figure 2 This is a schematic diagram of the sampling data points of the existing data acquisition card. Usually, the acquisition frequency of the data acquisition card is more than 10 times the frequency of the laser output waveform to collect enough values ​​to determine the laser cycle, and then determine whether the laser is in the mode-locked state. This puts higher requirements on the data acquisition card and data processing. The price of the whole set of products is very expensive, resulting in a high cost for detecting the mode-locked state of the femtosecond laser. Summary of the invention

[0005] To solve the above problems, the present invention provides a method and system for detecting the mode-locked state of a femtosecond laser, which utilizes period mismatch to obtain peak-to-valley values, and detects the stability and accuracy of the peak-to-valley values ​​to determine the mode-locked state of the laser. The method has low requirements on the sampling frequency of a data acquisition card, thereby effectively saving the cost of the detection system, while reducing the difficulty of output processing and improving detection efficiency.

[0006] In a first aspect, the technical solution of the present invention provides a method for detecting a femtosecond laser mode-locking state, comprising the following steps:

[0007] The sampling frequency of the data acquisition card is configured so that the effective sampling number is greater than a preset sampling number threshold, and the sampling frequency is less than the laser output waveform frequency, and the two are not integer multiples;

[0008] The data acquisition card performs several continuous samplings, runs several sampling cycles in each continuous sampling, and samples at least once in each sampling cycle to obtain several sampling values ​​in each continuous sampling;

[0009] Calculate the corresponding peak and valley values ​​according to a number of sampling values ​​obtained by each continuous sampling;

[0010] If the difference between any two consecutively sampled peak-to-valley values ​​is less than the first difference threshold, and the difference between each peak-to-valley value and the standard peak-to-valley value is less than the second difference threshold, the laser is determined to be mode-locked, otherwise the laser is determined to be not mode-locked.

[0011] In an optional implementation, configuring the sampling frequency of the data acquisition card so that the effective sampling number is greater than a preset sampling number threshold specifically includes:

[0012] Calculate the laser output waveform frequency;

[0013] Set the initial sampling frequency of the data acquisition card;

[0014] Calculate the greatest common divisor between the laser output waveform frequency and the initial sampling frequency;

[0015] Calculate the effective sampling number = initial sampling frequency / the greatest common divisor;

[0016] Determine whether the effective sampling number is greater than the preset sampling number threshold. If so, configure the data acquisition card with the initial sampling frequency. Otherwise, adjust the sampling frequency of the data acquisition card until the effective sampling number is greater than the preset sampling number threshold, and configure the data acquisition card with the final sampling frequency.

[0017] In an optional implementation, configuring the sampling frequency of the data acquisition card so that the effective sampling number is greater than a preset sampling number threshold specifically includes:

[0018] Calculate the laser output waveform frequency;

[0019] Set the initial sampling frequency of the data acquisition card;

[0020] Calculate the lowest common multiple between the laser output waveform frequency and the initial sampling frequency;

[0021] Calculate the effective sampling number = the lowest common multiple / laser output waveform frequency;

[0022] Determine whether the effective sampling number is greater than the preset sampling number threshold. If so, configure the data acquisition card with the initial sampling frequency. Otherwise, adjust the sampling frequency of the data acquisition card until the effective sampling number is greater than the preset sampling number threshold, and configure the data acquisition card with the final sampling frequency.

[0023] In an optional implementation, the data acquisition card performs several continuous samplings, specifically including:

[0024] Configure continuous sampling parameters, including the duration of each sampling, the interval between two consecutive continuous samplings, and the number of continuous samplings;

[0025] The data acquisition card performs continuous sampling several times according to the configured continuous sampling parameters.

[0026] In an optional implementation, the data acquisition card samples at least once in each sampling cycle thereof, specifically including:

[0027] Set the sampling times of the data acquisition card in each sampling cycle;

[0028] Set the sampling period of the data acquisition card according to the sampling frequency of the data acquisition card and the number of samples in each sampling period;

[0029] Set the sampling time point in each sampling cycle;

[0030] The data acquisition card samples at least once in each sampling cycle according to the set sampling time point.

[0031] In an optional implementation, the sampling time points of the data acquisition card in each sampling cycle include a sampling peak time point and a sampling valley time point.

[0032] In an optional implementation, the corresponding peak-to-valley values ​​are calculated according to a number of sampling values ​​obtained by each continuous sampling, specifically including:

[0033] Filter out the maximum and minimum values ​​from a number of sample values;

[0034] The difference between the maximum and minimum values ​​is used to obtain the corresponding peak-to-valley values.

[0035] In a second aspect, the technical solution of the present invention provides a femtosecond laser mode-locking state detection system, including a reflector, a photodetector, a data acquisition card and a data processing terminal;

[0036] The laser emits laser light which enters the photodetector through the reflector. The photodetector converts the optical signal into an electrical signal and outputs it to the data acquisition card. The data acquisition card performs data acquisition and transmits the acquired data to the data processing terminal. The system executes any of the above-mentioned methods for detecting the mode-locked state of a femtosecond laser.

[0037] In an optional embodiment, the system further includes an indicator light, which is connected to a data processing terminal, and the data processing terminal controls the state of the indicator light according to the detection result.

[0038] A femtosecond laser mode-locking state detection method and system provided by the present invention has the following beneficial effects compared with the prior art: a plurality of continuous samplings are performed on the basis that the sampling frequency of the data acquisition card is less than the frequency of the laser output waveform to achieve period mismatch, and the peak-to-valley values ​​are calculated using a plurality of points continuously collected each time, and then the laser mode-locking state is determined according to the stability and accuracy of the peak-to-valley values. The present invention obtains the peak-to-valley values ​​by period mismatch, and determines the laser mode-locking state by detecting the stability and accuracy of the peak-to-valley values, and has low requirements on the sampling frequency of the data acquisition card, thereby effectively saving the cost of the detection system, while reducing the difficulty of output processing and improving the detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 It is a schematic diagram of the structure of an existing femtosecond laser mode-locking state detection system.

[0041] Figure 2 It is a schematic diagram of sampling data points of existing data acquisition cards.

[0042] Figure 3 The present invention provides a schematic flow chart of a method for detecting a femtosecond laser mode-locking state.

[0043] Figure 4 It is a schematic diagram of sampling data points of the data acquisition card of the present invention. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0046] This embodiment provides a femtosecond laser mode-locking state detection system. Figure 1The existing femtosecond laser mode-locking state detection systems shown have the same structure, including a reflector, a photodetector, a data acquisition card and a data processing terminal.

[0047] The laser emits laser light and enters the photodetector through the reflector. The photodetector converts the optical signal into an electrical signal and outputs it to the data acquisition card. The data acquisition card performs data acquisition and transmits the acquired data to the data processing terminal. The system executes a femtosecond laser mode-locking state detection method to detect the laser mode-locking state. The existing femtosecond laser mode-locking state detection method restores the period or pulse width of the light, compares it with the known laser period or pulse width, and determines whether the laser has completed mode-locking. The femtosecond laser mode-locking state detection method executed in this embodiment uses period mismatch to obtain peak-to-valley values, and determines the laser mode-locking state by detecting the stability and accuracy of the peak-to-valley values. The sampling frequency requirement of the data acquisition card is low, thereby effectively saving the cost of the detection system, while reducing the difficulty of output processing and improving detection efficiency.

[0048] The femtosecond laser mode-locking state detection method implemented by the system includes configuring the sampling frequency of the data acquisition card so that the effective sampling number is greater than the preset sampling number threshold, the sampling frequency is less than the laser output waveform frequency, and the two are not integer multiples; the data acquisition card performs several continuous samplings, runs several sampling cycles in each continuous sampling, and samples at least once in each sampling cycle to obtain several sampling values ​​in each continuous sampling; the data processing terminal calculates the corresponding peak-valley values ​​according to the several sampling values ​​obtained by each continuous sampling; if the difference between the peak-valley values ​​of any two continuous samplings is less than the first difference threshold, and the difference between the peak-valley value of each time and the standard peak-valley value is less than the second difference threshold, it is determined that the laser is mode-locked, otherwise it is determined that the laser is not mode-locked. The detailed steps of the femtosecond laser mode-locking state detection method will be described in detail in the subsequent embodiments.

[0049] The system of this embodiment also includes an indicator light, which is connected to a data processing terminal. The data processing terminal controls the state of the indicator light according to the detection result. For example, if the state is a mold locking state, a green light is on, otherwise a red light is on.

[0050] Figure 3It is a schematic flow chart of a method for detecting the mode-locked state of a femtosecond laser provided by an embodiment of the present invention, which uses a method of period mismatch + peak-to-valley value judgment to realize the judgment of the mode-locked state of the laser. The light of the laser is irradiated onto a high-speed photodetector, and data is collected through a conventional data acquisition card. The acquisition cycle of the data acquisition card is mismatched with the cycle of the laser, and the time of data collection is lengthened. The peak and valley values ​​of the laser can be found, and the peak-to-valley value data can be used to determine whether the laser is in a mode-locked state. This method greatly reduces the requirements for the data acquisition card, and also reduces the difficulty of output processing. Usually, the acquisition rate of the data acquisition card will be within 10 times of the laser cycle, and can even be 1 / 100 of the acquisition cycle.

[0051] like Figure 3 As shown, the method includes the following steps.

[0052] S1, configure the sampling frequency of the data acquisition card so that the effective sampling number is greater than the preset sampling number threshold.

[0053] The sampling frequency of this embodiment is less than the laser output waveform frequency, and the two are not integer multiples, so as to avoid collecting repeated sampling values.

[0054] In this embodiment, the sampling frequency of the data acquisition card can be configured in two ways so that the effective sampling number is greater than the preset sampling number threshold. The effective sampling number refers to the number of sampled data without duplication. The effective sampling number can be set larger to obtain more effective sampling data. Accordingly, a larger sampling data threshold is pre-set, for example, the preset sampling number threshold is 400, and the sampling frequency of the data acquisition card is set so that the effective sampling number is greater than 400 to meet the requirements.

[0055] Method 1: (1) Calculate the laser output waveform frequency; (2) Set the initial sampling frequency of the data acquisition card; (3) Calculate the greatest common divisor between the laser output waveform frequency and the initial sampling frequency; (4) Calculate the effective sampling number = initial sampling frequency / the greatest common divisor; (5) Determine whether the effective sampling number is greater than a preset sampling number threshold. If so, configure the data acquisition card with the initial sampling frequency; otherwise, adjust the sampling frequency of the data acquisition card until the effective sampling number is greater than the preset sampling number threshold, and configure the data acquisition card with the final sampling frequency.

[0056] Method 2: (1) Calculate the laser output waveform frequency; (2) Set the initial sampling frequency of the data acquisition card; (3) Calculate the lowest common multiple between the laser output waveform frequency and the initial sampling frequency; (4) Calculate the effective sampling number = the lowest common multiple / laser output waveform frequency; (5) Determine whether the effective sampling number is greater than a preset sampling number threshold. If so, configure the data acquisition card with the initial sampling frequency; otherwise, adjust the sampling frequency of the data acquisition card until the effective sampling number is greater than the preset sampling number threshold, and configure the data acquisition card with the final sampling frequency.

[0057] The formula for calculating the waveform frequency of the laser is f=speed of light / 2L; L is the optical path, which is the product of the refractive index of each material and the distance that the light on the optical path passes through. The final calculated f is usually a number that is at least accurate to a single digit.

[0058] Assume that the laser output waveform frequency is A, and the data acquisition card sampling frequency is B, where A>B, calculate the greatest common divisor C between A and B, then the effective sampling number when the sampling data does not repeat is D=B / C (another method: calculate the least common multiple E of A and B, then the maximum sampling number when the sampling data does not repeat is D=E / A). In order to ensure the accuracy of the sampling data, D needs to be large enough, usually more than 20 data points are required, and the more points, the more realistic the situation is. That is, the greatest common divisor C between A and B needs to be as small as possible (or the least common multiple E needs to be as large as possible). If A and B are in a multiple relationship, the data card will collect the same position point in different cycles each time, so it cannot reflect the peak and valley value data.

[0059] For example, the frequency of the laser output waveform is 50MHz, and the sampling rate of the data acquisition card is 48k (the sampling rate of the data acquisition card refers to the number of samples per unit time, which is consistent with the meaning of the sampling frequency. 48k means that 48*10 samples are collected per unit time. 3 times), the greatest common divisor is 16000, and the number of effective samples is 3. If the sampling rate is changed to 47k, the number of effective samples is 47 data. If the number of samples is further changed to 47.1k, the number of effective samples is 471, which can more accurately collect data at each position in different cycles of the laser.

[0060] This embodiment has lower requirements for the data acquisition card and does not require a sampling frequency of more than 500M / s. The detection can be completed within a range of 100k / s or lower. Generally, the higher the frequency, the better the detection effect.

[0061] S2, the data acquisition card performs several continuous samplings, runs several sampling cycles in each continuous sampling, and samples at least once in each sampling cycle to obtain several sampling values ​​in each continuous sampling.

[0062] This embodiment performs several continuous samplings, each continuous sampling includes several sampling cycles of the data acquisition card, and each sampling cycle is sampled at least once, so that each continuous sampling can obtain several sampling values. Each continuous sampling can obtain at least one peak-valley value, and the peak-valley value of each continuous sampling is compared to determine the laser mode locking state.

[0063] To achieve continuous sampling of the data acquisition card, first configure the continuous sampling parameters, and then the data acquisition card performs continuous sampling several times according to the configured continuous sampling parameters. The continuous sampling parameters include the duration of each sampling, the interval between two adjacent continuous samplings, and the number of continuous samplings. For example, each continuous sampling is 10s, and the interval between two continuous samplings is 15s, which provides 3 continuous samplings.

[0064] The data acquisition card samples at least once in each of its sampling cycles, which can be set according to actual needs, including: setting the number of sampling times of the data acquisition card in each of its sampling cycles; setting the sampling cycle of the data acquisition card according to the sampling frequency of the data acquisition card and the number of sampling times in each sampling cycle; setting the sampling time point in each sampling cycle; the data acquisition card samples at least once in each of its sampling cycles according to the set sampling time point.

[0065] For example, the sampling time points of the data acquisition card in each sampling cycle thereof include a sampling peak time point and a sampling valley time point. Figure 4 This is a schematic diagram of sampling data points of the data acquisition card of the present invention, Figure 4 The blue line in the middle represents the curve of data collection. Two data points (peak value and valley value) are collected at equal intervals in each sampling period. The red line represents the output waveform of the actual laser. After a certain period of collection, the points collected by the blue curve will be collected at different positions of each period on the red curve (as shown by the black circle). By calculating the peak-to-valley values, the peak-to-valley values ​​of the actual red curve can be obtained, and then it can be judged whether the laser is mode-locked.

[0066] S3, calculating corresponding peak-valley values ​​according to a number of sampling values ​​obtained by each continuous sampling.

[0067] For each continuous sampling, the maximum and minimum values ​​are screened out from a number of sampling values, and the maximum and minimum values ​​are subtracted to obtain the corresponding peak-to-valley values.

[0068] S4, if the difference between any two consecutively sampled peak-to-valley values ​​is less than the first difference threshold, and the difference between each peak-to-valley value and the standard peak-to-valley value is less than the second difference threshold, it is determined that the laser is mode-locked, otherwise it is determined that the laser is not mode-locked.

[0069] This embodiment can determine whether it is in a mode-locked state by judging the accuracy of the peak-to-valley value and the difference between the peak-to-valley values. If the difference is not large (the specific data will be calibrated when the equipment leaves the factory), it is considered to be in a mode-locked state. If the difference between the peak-to-valley values ​​each time is small and the peak-to-valley value is close to the calibrated peak-to-valley value, it means that the laser can stably output high-power laser and is in a mode-locked state.

[0070] The above disclosure is only a preferred embodiment of the present invention, but the present invention is not limited thereto. Any non-creative changes that can be thought of by a person skilled in the art, as well as several improvements and modifications made without departing from the principle of the present invention, should fall within the protection scope of the present invention.

Claims

1. A method for detecting the mode-locked state of a femtosecond laser, characterized in that: The following steps are involved: The sampling frequency of the data acquisition card is configured so that the effective sampling number is greater than a preset sampling number threshold, and the sampling frequency is less than the laser output waveform frequency, and the two are not integer multiples; The data acquisition card performs several continuous samplings, runs several sampling cycles in each continuous sampling, and samples at least once in each sampling cycle to obtain several sampling values ​​in each continuous sampling; Calculate the corresponding peak and valley values ​​according to a number of sampling values ​​obtained by each continuous sampling; If the difference between any two consecutively sampled peak-to-valley values ​​is less than the first difference threshold, and the difference between each peak-to-valley value and the standard peak-to-valley value is less than the second difference threshold, it is determined that the laser is mode-locked, otherwise it is determined that the laser is not mode-locked; The sampling frequency of the data acquisition card is configured so that the effective sampling quantity is greater than the preset sampling quantity threshold, specifically including: Calculate the laser output waveform frequency; Set the initial sampling frequency of the data acquisition card; Calculate the greatest common divisor between the laser output waveform frequency and the initial sampling frequency; Calculate the effective sampling number = initial sampling frequency / the greatest common divisor; Determine whether the effective sampling number is greater than a preset sampling number threshold, if so, configure the data acquisition card with an initial sampling frequency, otherwise adjust the sampling frequency of the data acquisition card until the effective sampling number is greater than the preset sampling number threshold, and configure the data acquisition card with a final sampling frequency; Among them, the data acquisition card performs several continuous samplings, including: Configure continuous sampling parameters, including the duration of each sampling, the interval between two consecutive continuous samplings, and the number of continuous samplings; The data acquisition card performs continuous sampling several times according to the configured continuous sampling parameters; The corresponding peak and valley values ​​are calculated based on a number of sampling values ​​obtained by each continuous sampling, specifically including: Filter out the maximum and minimum values ​​from a number of sample values; The difference between the maximum and minimum values ​​is used to obtain the corresponding peak-to-valley values.

2. The method for detecting the mode-locked state of a femtosecond laser according to claim 1, characterized in that: Configure the sampling frequency of the data acquisition card so that the effective sampling number is greater than the preset sampling number threshold, including: Calculate the laser output waveform frequency; Set the initial sampling frequency of the data acquisition card; Calculate the lowest common multiple between the laser output waveform frequency and the initial sampling frequency; Calculate the effective sampling number = the lowest common multiple / laser output waveform frequency; Determine whether the effective sampling number is greater than the preset sampling number threshold. If so, configure the data acquisition card with the initial sampling frequency. Otherwise, adjust the sampling frequency of the data acquisition card until the effective sampling number is greater than the preset sampling number threshold, and configure the data acquisition card with the final sampling frequency.

3. The method for detecting the mode-locked state of a femtosecond laser according to claim 1, characterized in that: The data acquisition card samples at least once in each sampling cycle, including: Set the sampling times of the data acquisition card in each sampling cycle; Set the sampling period of the data acquisition card according to the sampling frequency of the data acquisition card and the number of samples in each sampling period; Set the sampling time point in each sampling cycle; The data acquisition card samples at least once in each sampling cycle according to the set sampling time point.

4. The method for detecting the mode-locked state of a femtosecond laser according to claim 3, characterized in that: The sampling time points of the data acquisition card in each sampling cycle include a sampling peak time point and a sampling valley time point.

5. A femtosecond laser mode-locking state detection system, characterized in that: It includes a reflector, a photoelectric detector, a data acquisition card and a data processing terminal; The laser emits laser light which enters the photodetector through the reflector. The photodetector converts the optical signal into an electrical signal and outputs it to the data acquisition card. The data acquisition card performs data acquisition and transmits the acquired data to the data processing terminal. The system executes the femtosecond laser mode locking state detection method described in any one of claims 1 to 4.

6. The femtosecond laser mode-locking state detection system according to claim 5, characterized in that: The system also includes an indicator light, which is connected to a data processing terminal, and the data processing terminal controls the state of the indicator light according to the detection result.

Images