CN114367735A - A method for measuring transient temperature in ultrafast laser micromachining - Google Patents

Abstract

A method for measuring the transient temperature of ultrafast laser micromachining includes such steps as providing a ultrafast laser micromachining unit, high-precision machining and collecting synchronization system, spectrum collecting system and specimen shape observing system. The processing and collecting high-precision synchronization system enables the time zero point of the material processing start to be accurately calibrated, the ultrafast laser micromachining device is utilized to carry out laser ultrafast pulse processing on the interior of the material, then the blackbody radiation spectrum at any time (nanosecond magnitude) after the processing start is collected by the spectrum collection system, and the temperature at the time is calculated by drawing. In the research process, the morphology of the processed part can be observed by using a morphology observation system, so that the research work of measuring the temperature of the material after the ultrafast laser processing is completed.

Description

A method for measuring transient temperature in ultrafast laser micromachining

technical field

The invention utilizes the technology of spectral measurement, and is a measurement method for measuring the temperature of the processed material processed by the ultrafast laser.

Background technique

As the quality control of laser processing workpieces has become more and more accurate and fast in recent years, more and more technological innovations have emerged in laser processing temperature measurement in terms of method and accuracy. These include, for example: Langmuir probe method, laser-induced plasma emission spectroscopy, time-resolved projection method, pump detection method, and blackbody radiation method. At present, the most mature methods are mainly the Langmuir probe method using vacuum electrode bias measurement and the laser-induced plasma emission spectroscopy method using Boltzmann spectrogram. These temperature measurement methods are of great significance to the quality monitoring of laser processing. Laser pulse power, repetition frequency, pulse width, wavelength and other technical parameters can affect the calculation of material temperature.

The black body radiation spectrum is a distribution law function of the photon energy distribution formed after the material radiates photons. This distribution law function is also called Planck's formula. Since the distribution law function has an exponential term corresponding to the temperature, the temperature can be measured by capturing the black body radiation spectrum. The black body radiation method has been used in medical temperature measurement, equipment temperature monitoring, aviation, automobile, navigation and other fields for a long time.

In 2004, C.W.Carr et al. first observed the blackbody radiation spectrum in the laser-induced processing of materials such as DKDP (potassium dideuterium phosphate), sapphire, and fused silica using nanosecond laser pulses. In the subsequent work, the research group also tried femtosecond laser induced DKDP crystals, and observed a spectrum dominated by nonlinear second harmonics.

Compared with the energy level spectrum, the black body radiation spectrum method was discovered late, mainly because the black body radiation spectrum has no competitive advantage compared with the energy level spectrum, but the black body radiation spectrum method does not require energy level information. An emission spectrum exists in all environments, which is of extraordinary significance for fast temperature measurement of various materials and various environments. In order to measure the blackbody radiation spectrum of ultrafast laser processing, a device that can detect the blackbody radiation spectrum of the ultrafast laser processing inside the material is needed, so as to use the Planck formula to calculate the temperature. In order to measure the temperature change in the nanosecond order of the processing part, it is necessary to measure the measurement of the black body radiation spectrum with the corresponding precision. The nanosecond scale is very limiting for ICCD operation, due to the inevitable delay of photocathode switching on for ICCD operation. For example, we use ultrafast laser pulses to act on the inside of 1cm × 1cm × 1mm dielectric fused silica, When the blackbody radiation spectrum reaches the inside of the spectrometer, the ICCD has not turned on the photocathode, and 20 nanoseconds have elapsed until the ICCD turns on the photocathode, so the time zero measured by the ICCD is actually the blackbody radiation spectrum of the material at 20 nanoseconds. Therefore, it is necessary to design a device that is calibrated for the zero point of the processing time, so as to ensure that the photocathode is just opened when the laser processing action reaches the material and corresponds to the zero point of time. From the above, there is a need to provide a method for measuring the transient temperature of ultrafast laser micromachining using the blackbody radiation method.

SUMMARY OF THE INVENTION

The purpose of the invention is to solve the problem of measuring the transient temperature of materials after ultrafast laser micromachining. By utilizing the physical phenomenon that ultrafast laser induces materials to generate black body radiation spectrum, a method for measuring the temperature of materials after ultrafast laser processing is proposed by using a black body radiation method. processing device. The method is simple in structure, easy to build, and safe and reliable in operation. It can complete the collection of blackbody radiation spectra of a series of nanosecond-scale moments inside various materials processed by single-pulse ultrafast laser processing. Non-linear fitting can calculate the temperature at the corresponding time. If there is a time domain evolution requirement, the temperature change curve can also be completed.

The technical solution of the present invention is as follows:

A method for measuring the transient temperature of ultrafast laser micromachining, comprising an ultrafast laser micromachining device, characterized in that the system further comprises: a processing and acquisition high-precision synchronization system, a spectrum acquisition system, and a sample morphology observation system;

The ultrafast laser micromachining device includes an ultrafast laser, a dichroic mirror that reflects the ultrafast laser, a microscope objective lens that focuses the ultrafast laser to the material processing area, a three-dimensional mechanical motion stage, and a stage placed on the stage. sample. The ultrafast laser emitted from the ultrafast laser is reflected into the microscope objective through the dichroic mirror, and then focused into the interior of the sample by the microscope objective to realize single-pulse processing.

The high-precision synchronization system for processing and acquisition includes a photodiode for acquiring partially reflected laser light, an oscilloscope containing at least two channels, and a signal delay generator. A part of the laser pulse reflected from the surface of the material is received by the photodiode and transmitted to the oscilloscope through the wire. At the same time, the ultrafast laser is turned on and the trigger signal of the switch guides the ICCD to turn on the photocathode for spectral sampling. The ICCD photocathode switch signal is connected to the signal delay generator through a wire and then connected to the oscilloscope. There will be a delay in the waveforms of the two signals. Calibration time zero.

The spectrum acquisition system includes a half mirror that reflects the black body radiation spectrum while ensuring imaging, a lens, a spectrometer, and an ICCD sampling device. The transflector reflects the signal into the lens, and then focuses it to the aperture of the spectrometer. After that, the blackbody radiation signal can be collected every n (n can be set arbitrarily) nanoseconds. Then it is used as a graph software to fit the black body radiation spectrum signal at each moment by Planck's formula, and the fitting parameters can calculate the temperature at each acquisition moment.

The sample topography observation system includes an illumination system and a CCD image acquisition device. Turn on the lighting system, and collect the topography of the processing part of the material through the CCD, so that the effect of processing can be further understood.

Compared with the prior art, the technical effect of the present invention is as follows:

The present invention utilizes the relationship between the blackbody radiation and the temperature of the material processed by the ultrafast laser, and is different from other spectral line measurement methods. The processing transient temperature of materials with various properties can be measured.

The invention has stable performance, and provides a reliable and efficient way to accurately measure the temperature of the material after ultrafast laser processing at the nanosecond level.

Description of drawings

Figure 1 is a schematic diagram of a method for measuring the transient temperature of ultrafast laser micromachining

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited accordingly.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of a method for measuring the transient temperature of ultrafast laser micromachining. As shown in the figure, the present invention is a device for measuring ultrafast laser micromachining, including: a high-precision synchronization system for processing and acquisition, a spectrum Acquisition system, sample morphology observation system.

The ultrafast laser micromachining device includes an ultrafast laser 1, a dichroic mirror 3 that reflects the ultrafast laser, a microscope objective 4 that focuses the ultrafast laser to the material processing area, a three-dimensional mechanical motion stage 6, and a Sample 5 on the stage.

The processing and acquisition high-precision synchronization system includes a photodiode 15 for acquiring partially reflected laser light, an oscilloscope 12 including at least two channels, and a signal delay generator 11 .

The spectrum acquisition system includes a half mirror 7 that reflects the blackbody radiation spectrum while ensuring imaging, a lens 9 , a spectrometer 10 , and an ICCD sampling device 16 .

The sample topography observation system includes an illumination system 14 and a CCD image acquisition device 13 .

The specific steps of the measurement method are:

The first step is to calibrate the time zero of the acquired signal. The ultrafast laser 2 emitted from the ultrafast laser 1 is reflected by the dichroic mirror 3 into the microscope objective lens 4, and is focused into the interior of the sample 5 by the microscope objective lens 4. At the moment of single-pulse processing, a part of it will be reflected from the surface of the material. The pulse of the laser is received by the photodiode 15 and transmitted to the oscilloscope through the wire. At the same time, the ultrafast laser is turned on and the trigger signal of the switch instructs the ICCD acquisition system 16 to turn on the photocathode for spectral sampling. The photocathode switch signal of the ICCD acquisition system 16 is connected to the signal delay generator 11 and then to the oscilloscope 12 through a wire. The waveforms of the two signals will have a delay. By adjusting the delay amount of the signal delay generator 11, the two signals The rising edge of the waveform coincides, thereby calibrating the time zero.

In the second step, the ultrafast laser 2 is reflected into the microscope objective 4 through the dichroic mirror 3, and is focused to the interior of the sample 6 by the microscope objective lens. The sample is fixed on the stage 5, and the three-dimensional stage 5 can move , to achieve single-pulse precision machining. After the processing, the black body radiation 8 is collected by the microscope objective lens 4, passes through the dichroic mirror 3, and is reflected by the half mirror 7 into the lens 9, and then focused to the aperture of the spectrometer 10. n (n can be set arbitrarily) black body radiation signal is collected once in nanoseconds. Then it is used as a graph software to fit the black body radiation spectrum signal at each moment by Planck's formula, and the fitting parameters can calculate the temperature at each acquisition moment.

In the third step, after the processing is completed, the lighting system 14 can be turned on, and the topography of the processing part of the material can be collected by the CCD image acquisition device 13, so that the processing effect can be further understood.

Claims (4)

1. A method for measuring ultrafast laser micro-processing transient temperature comprises an ultrafast laser micro-processing device, a processing and collecting high-precision synchronization system, a spectrum collecting system and a sample morphology observation system; the processing and collecting high-precision synchronization system comprises a photodiode (15) for collecting part of reflected laser, an oscilloscope (12) comprising at least two channels and a signal delay generator (11); the spectrum acquisition system comprises a half-transmitting and half-reflecting mirror (7), a lens (9), a spectrometer (10) and an ICCD sampling device (16); the sample appearance observation system comprises an illumination system (14) and a CCD image acquisition device (13); the ultrafast laser micromachining device comprises an ultrafast laser (1), a dichroic mirror (3) for reflecting the ultrafast laser, a microscope objective (4) for focusing the ultrafast laser to a material processing area, a three-dimensional mechanical motion objective table (6) and a sample (5) placed on the objective table; the method is characterized by comprising the following specific steps:

calibrating the time zero point of the collected signal: ultrafast laser (2) emitted from an ultrafast laser (1) is reflected into a microscope objective (4) through a dichroic mirror (3) and is focused into a sample (5) through the microscope objective (4), at the moment of single-pulse processing, a pulse of a part of laser is reflected through the surface of the sample (5) and is received by a photodiode (15) and transmitted to an oscilloscope (12) through a lead, and simultaneously when the ultrafast laser is turned on, an ICCD acquisition system (16) is guided to turn on a photocathode to perform spectrum sampling through a trigger signal of a switch; an ICCD acquisition system (16) is connected with a signal delay generator (11) through a lead and then is connected with an oscilloscope (12), so that a time zero point is calibrated by means of signal representation;

processing: ultrafast laser (2) is reflected to a microscope objective (4) through a dichroic mirror (3) and is focused into a sample (6) through the microscope objective, the sample is fixed on an objective table (5), and the three-dimensional objective table (5) moves to realize single-pulse precision machining;

and thirdly, after the processing is finished, black body radiation light (8) reflected by the sample (6) is collected by the microscope objective (4), penetrates through the dichroic mirror (3), is reflected by the semi-transparent semi-reflecting mirror (7) to enter the lens (9), and then is focused to a diaphragm opening of the spectrometer (10), and then black body radiation signals are collected once every n nanoseconds, and a Planck formula is utilized for fitting to obtain the temperature at each collection time.

2. The method for measuring the ultrafast laser micro machining transient temperature according to claim 1, further comprising turning on an illumination system (14) to collect the morphology of the machining site of the material through a CCD image collecting device (13).

3. The method of measuring ultrafast laser micro process transient temperature of claim 1, wherein: the semi-transparent and semi-reflective mirror (7) is parallelly arranged on the dichroic mirror (3), and the light outlet of the semi-transparent and semi-reflective mirror (7) is connected with the lens (9) through a cage structure to ensure collimation.

4. The method of measuring ultrafast laser micro process transient temperature of claim 1, wherein: in the step I, the rising edges of the waveforms of the two signals are overlapped by adjusting the delay amount of the signal delay generator (11), so that the time zero point is calibrated.

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