CN112229538B - Device and method for measuring temperature of femtosecond laser processing material based on thermodynamics method - Google Patents
Device and method for measuring temperature of femtosecond laser processing material based on thermodynamics method Download PDFInfo
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- CN112229538B CN112229538B CN202010964042.2A CN202010964042A CN112229538B CN 112229538 B CN112229538 B CN 112229538B CN 202010964042 A CN202010964042 A CN 202010964042A CN 112229538 B CN112229538 B CN 112229538B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F19/00—Calibrated capacity measures for fluids or fluent solid material, e.g. measuring cups
Abstract
The invention discloses a device and a method for measuring the material temperature in a femtosecond laser processing process. The method is suitable for temperature measurement in the process of processing materials by femtosecond laser. The device is simple, convenient to operate, and the measurement is accurate reliable. The device design utilizes the basic principle of thermodynamics, the heat generated by the femtosecond laser is obtained through conversion by measuring the total energy of the femtosecond laser pulse entering the cavity and the work done by gas in the processing process, and the temperature in the material removing process is further calculated. The device has good gas tightness, can accurately capture, and generates the volume of gas instant expansion in the process of femtosecond laser processing. By integrating the measurements, the accuracy and reliability of the measurements is improved. The design of the upper air valve and the lower air valve ensures that the internal pressure of the cavity is standard atmospheric pressure in the processing process, thereby providing convenience for the calculation of a subsequent formula.
Description
Technical Field
The invention relates to a gas volume measurement and collection technology, in particular to an experimental device and a method for measuring the removal temperature of a material in a femtosecond laser processing process.
Background
How to measure the temperature of a material during femtosecond laser processing has been a difficulty. And the measurement of the temperature during the material removal by laser has guiding significance for the femtosecond laser processing of the material. The existing femtosecond laser processing thermodynamic process, namely a dual-temperature model (TTM), describes the temperature evolution process when laser acts on the surface of a material, but few experiments prove the correctness of the theory convincingly. Because the theoretical predicted material temperature is difficult to measure effectively. The device provided by the invention can verify the existing theory.
The existing technical scheme is divided into two types. One is the black body radiation method (appl. Optics.55 (13), 8347-8351 (2016)) which estimates the temperature of a material by measuring the black body radiation spectral curve inside quartz glass using planck's equation fitting. The method can only be used for measuring the temperature in the transparent material, and the measuring equipment is required to have nanosecond-level time resolution measuring capability, so that the measuring difficulty is higher. Another method is to deduce the processing temperature of the material by measuring the electron density at the surface of the material by pump probing. The pumping detection method has poor measurement accuracy. In addition, the measuring instruments of the two methods are expensive, and have high requirements on the time resolution of the instruments.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a device and a method for measuring the temperature of a femtosecond laser processing material based on a thermodynamic method, wherein gas generated during processing is captured in time through two sensitive gas valves, and the volume of the generated gas is measured through a piston. And (4) calculating by a formula to obtain the temperature in the material processing process. The device has the advantages of simple measurement method, high precision, no requirement on time resolution, relatively cheap instrument and device, simple structure, convenient and safe operation and suitability for femtosecond lasers with different wavelengths.
The invention is composed of a processing cavity and a gas volume measuring cylinder. The bottom of the cavity is provided with a bottom cover with good air tightness. The bottom cover is provided with an air valve which can be used for air inlet when the bottom cover is cooled after processing. And a gas valve is arranged at the part of the cavity body, which is connected with the measuring cylinder, and is used for capturing gas in the process of processing and generating gas. The amount of trapped gas is measured by the piston. And this device can measure gas accumulation volume to reach more accurate measuring effect.
The concrete technical scheme of the invention is as follows:
a temperature measuring device for a femtosecond laser processing material based on thermodynamics is characterized by comprising a cavity for placing a material to be measured, a gas measuring cylinder, an upper gas valve and a lower gas valve;
the bottom of the cavity is provided with a bottom cover, the bottom cover is provided with an air inlet, the air inlet is connected with a lower air valve, the upper part of the cavity is provided with an air outlet, the air outlet is communicated with a gas measuring cylinder through the upper air valve, and a piston with air tightness can slide in the gas measuring cylinder; and light-transmitting glass is arranged on the side surface of the cavity.
The light-transmitting glass is optical glass which is transparent to the wavelength of femtosecond laser and can be replaced.
The gas measuring cylinder is provided with volume scales.
The method for measuring the temperature by using the device for measuring the temperature of the material processed by the femtosecond laser based on thermodynamics comprises the following steps:
a. opening the bottom cover, placing the material to be detected on the bottom cover, and aligning the processing surface with the light-transmitting window;
b. closing the bottom cover to ensure the air tightness of the cavity and the gas measuring cylinder, and reading the current degree of the piston in the gas measuring cylinder;
c. aligning a light-passing window to the femtosecond laser, focusing a femtosecond laser objective lens on a material to be processed, and opening light to control the pulse number and the pulse interval for measurement;
d. when the number of pulses is N, recording the degrees of the pistons at the moment, and calculating the difference of the degrees of the pistons at two times to obtain a volume V;
e. calculating the temperature T of the material to be measured during processing, wherein the formula is as follows:
T＝(U-P*V)*V m /(C m *V)，
wherein U is the laser pulse energy, cm is the gas molar heat capacity, vm is the gas molar volume at standard atmospheric pressure, and P is the standard atmospheric pressure.
The working principle of the invention is as follows:
during measurement, the bottom cover of the device is opened, the material is placed into the cavity, and the processing surface is aligned to the light-transmitting glass. And closing the bottom cover and checking the air tightness of the device. When the femtosecond laser is turned on to process the material, when the femtosecond laser is used for phosgenating the material, the pressure intensity in the cavity is increased due to the gasification of the material, the upper valve is pushed open due to the action of the pressure intensity, and the gas enters the measuring cylinder. When the femtosecond light action is finished, the gasified material begins to be condensed, then the pressure in the cavity is reduced, the upper valve is closed, the lower valve is opened at the moment, and the external air enters the cavity through the lower valve. The pressure in the cavity is ensured to be stable to the standard atmospheric pressure. The device retains the information of the gas volume through the design of the double-valve direction, so that the device has no requirement on time resolution. The degree of the piston is more considerable by measuring a plurality of pulses. The accuracy of the measurement is increased.
Because the device needs to convert the measured quantity by using a formula, the formula is explained, and the process based on the action of the femtosecond laser and the material is material gasification and phase explosion. And the basic principle of thermodynamics:
U＝Q+W
wherein U is internal energy, Q is heat, and W is work. The energy provided by N pulsed femtosecond lasers acting on the material is U, the volume expansion produced by material gasification and phase explosion does work as W, and then:
U＝Q+PV
v is the measurement volume and P is the standard atmospheric pressure, assuming that at the instant the laser is acting on the material, all the heat of the material is concentrated in the vaporized material (this approximation does not hold true for picosecond light with a substantial presence of thermal effects in the crystal lattice). According to the gas heat capacity formula, the material temperature is as follows:
c is the heat capacity of the part of gas, the molar volume of the gas is Vm under a standard condition, the molar heat capacity of the gasification of the material is Cm, and then the heat capacity of the part of gas is as follows:
the material temperature can be obtained by combining the above formula, wherein V is the gas volume measured by the device:
compared with the prior art, the invention has the following beneficial effects: the device is specially used for measuring the removal temperature of the material when the femtosecond laser with any wavelength processes the material. The device is used for special optical glass which is easy to replace when passing through a light-passing window of a femtosecond laser beam, and is transparent to a selected femtosecond laser waveband. The device has good gas tightness and ensures the gas volume accuracy of the captured material. Because the design of the double gas valves records the change of the gas volume, the change of the gas volume can reflect the instant energy information. The measurement is more accurate. Compared with the existing method, the device has no requirement on time resolution, and is cheaper. The method is simple, convenient to operate and stable in performance, and provides an efficient, reliable and accurate way for measuring the temperature of the material in the femtosecond laser processing process.
Drawings
FIG. 1 is a schematic structural diagram of a thermodynamics-based femtosecond laser processing material temperature measuring device
FIG. 2 is a view showing a state in which the material vaporizing upper gas valve is opened, and FIG. 2 (a) is a schematic view showing a direction of gas flow; fig. 2 (b) is a schematic diagram of the valve opening when the gasification material is cooled, and the arrow indicates the gas flow direction.
Detailed Description
The invention is further described below with reference to the drawings and examples, but the scope of protection of the invention should not be limited thereby.
Referring to fig. 1, fig. 1 shows an apparatus for measuring a material temperature during a femtosecond laser process, in which gas valves are formed at the top and bottom of a chamber of the apparatus to sensitively trap gas generated during a process of gasification and maintain a pressure of the chamber.
The device comprises a device main body and a bottom cover, wherein the device main body comprises a light-transmitting window, an upper air valve and a gas measuring cylinder. The light-transmitting window is positioned on the side surface of the cavity. The upper air valve is connected with the cavity and the gas measuring cylinder, and a piston 4 is arranged in the gas measuring cylinder 3 and used for measuring the volume of gas. The bottom cover 1 is provided with a lower air valve 6 which is used for connecting the air inlet cavity and the gas measuring cylinder 3 together to ensure the air tightness. The side surface of the cavity is provided with a light-transmitting glass 8. A piston 4 is provided in the gas measuring cylinder 3 for measuring the volume of collected gas.
The device cavity comprises a bottom cover 1 of the cavity, a cavity 2, an upper valve 5, a lower valve 6, a material 7 to be measured, a light-transmitting glass 8 cavity on the side surface of the cavity and an incident femtosecond laser 9. The gas measuring part of the device comprises a gas measuring cylinder 3 and a piston 4 in the measuring cylinder.
When measurement is needed, the bottom cover 1 of the cavity is opened to place the material 7 into the cavity, and the surface to be processed faces the light-transmitting glass 8. And (3) closing the bottom cover 1, covering the cavity by hands, and if the piston of the cavity is increased by 4 degrees, indicating that the air tightness of the cavity is good. When the cavity is cooled, the piston 4 is read. The cavity clear glass 8 is aligned to the femtosecond laser 9 while the focus is adjusted to the surface of the material 7. And introducing N pulsed femtosecond lasers. Piston 4 readings were observed to increase at this time, and the piston degrees were read at this time. The difference value of the degrees of the pistons obtained twice is V.
Reading out the total energy U of the incident femtosecond light based on the parameters of the femtosecond laser or by using a power meter, and then substituting V/N into the formula:
in (1). The temperature at which the femtosecond laser processes the material can be obtained.
Claims (3)
1. A temperature measuring method of a temperature measuring device of a femtosecond laser processing material based on thermodynamics comprises a cavity (2) for placing a material to be measured, a gas measuring cylinder (3), an upper gas valve (5) and a lower gas valve (6); the bottom of the cavity (2) is provided with a bottom cover (1), the bottom cover (1) is provided with an air inlet, the air inlet is connected with a lower air valve (6), the upper part of the cavity (2) is provided with an air outlet, the air outlet is communicated with the gas measuring cylinder (3) through an upper air valve (5), and a piston (4) with air tightness can slide in the gas measuring cylinder (3); the side surface of the cavity (2) is provided with light-transmitting glass (8); the method is characterized by comprising the following steps:
a. opening the bottom cover, placing the material to be detected on the bottom cover, and aligning the processing surface with the light-transmitting window;
b. closing the bottom cover to ensure the air tightness of the cavity and the gas measuring cylinder, and reading the degree of the piston in the gas measuring cylinder at the moment;
c. aligning a light-passing window to the femtosecond laser, focusing a femtosecond laser objective lens on a material to be processed, and opening light to control the pulse number and the pulse interval for measurement;
d. when the number of pulses is N, recording the degrees of the pistons at the moment, and calculating the difference of the degrees of the pistons at two times to obtain a volume V;
e. calculating the temperature T of the material to be measured during processing, wherein the formula is as follows:
T＝(U-P*V)*V m /(C m *V)，
wherein U is the laser pulse energy, cm is the gas molar heat capacity, vm is the gas molar volume at standard atmospheric pressure, and P is the standard atmospheric pressure.
2. The temperature measurement method according to claim 1, characterized in that: the light-transmitting glass (8) is optical glass which is transparent to the wavelength of femtosecond laser and can be replaced.
3. The temperature measuring method according to claim 1, characterized in that: the gas measuring cylinder (3) is provided with volume scales.
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| EP0402830A1 (en) * | 1989-06-15 | 1990-12-19 | Siemens Nixdorf Informationssysteme Aktiengesellschaft | Method for controlling temperature course at soldering points during laser soldering |
| CN202770534U (en) * | 2012-09-04 | 2013-03-06 | 徐州工程学院 | Temperature field measuring device in laser processing process based on LabView |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP4309213B2 (en) * | 2003-09-05 | 2009-08-05 | 株式会社東芝 | Heat transfer analysis method, heat transfer analysis program, and heat transfer analysis device |
| FR2897687B1 (en) * | 2006-02-17 | 2008-09-26 | Commissariat Energie Atomique | METHOD AND DEVICE FOR CHARACTERIZING, BY ACTIVE PYROMETRY, A THIN-LAYER MATERIAL ARRANGED ON A SUBSTRATE |
| DE102007030398A1 (en) * | 2007-06-29 | 2009-01-02 | Trumpf Laser- Und Systemtechnik Gmbh | Device and method for monitoring the temperature and / or a temperature-dependent characteristic of an optical element |
| JP5426115B2 (en) * | 2008-06-10 | 2014-02-26 | アルバック理工株式会社 | Thermophysical property measurement method |
| WO2015156119A1 (en) * | 2014-04-10 | 2015-10-15 | 三菱電機株式会社 | Laser processing device and laser processing method |
| CN105675161A (en) * | 2016-01-19 | 2016-06-15 | 河南理工大学 | Method for measuring temperature of laser processing workpiece via thermocouple |
| US10729497B2 (en) * | 2016-06-20 | 2020-08-04 | University Of North Texas | Laser-assisted machining (LAM) of non-monolithic composite bone material |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0402830A1 (en) * | 1989-06-15 | 1990-12-19 | Siemens Nixdorf Informationssysteme Aktiengesellschaft | Method for controlling temperature course at soldering points during laser soldering |
| CN202770534U (en) * | 2012-09-04 | 2013-03-06 | 徐州工程学院 | Temperature field measuring device in laser processing process based on LabView |
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