JP3430531B2 - Light marking device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser marking device using a spatial light modulator.

[0002]

2. Description of the Related Art A laser marking device using a liquid crystal spatial light modulator as a variable mask is under development. In this device, the two-dimensional optical switching effect of the liquid crystal spatial light modulator is used to directly display the pattern to be marked on the liquid crystal spatial light modulator as grayscale information. Next, the laser illuminates the liquid crystal spatial light modulator, and the lens images the pattern on the sample surface. In this way, the portion of the sample surface on which the pattern is imaged is vaporized and engraved by the heat of the laser. (For example,
(JP-A-60-174671, JP-A-1-76564)

[0003]

However, in the conventional laser marking device, most of the light is blocked because the light and shade pattern displayed on the liquid crystal spatial light modulator is used as an aperture mask, and the light utilization efficiency is reduced. There was a problem of being low. For this reason, when the total area of the pattern to be marked is small, such as a small character string or a line image, a high output laser light source is required, and the production efficiency of the laser marking device is significantly reduced.

The present invention is intended to solve such a problem, and an object thereof is to provide a laser marking device which has a high light utilization efficiency and is capable of high-quality pattern marking.

[0005]

A first optical marking device of the present invention is a coherent light source, at least one spatial light modulator for controlling a wave front of a beam emitted from the coherent light source, and the spatial light modulator. An optical marking device having a Fourier transform lens for irradiating a surface of a sample with a beam whose wavefront is controlled by means, at least means for inputting pattern data to be reproduced, means for generating random number data, and Fourier transform The step of creating complex amplitude data to be displayed on the spatial light modulator includes the step of multiplying the pattern data to be reproduced by the random number data, and the Fourier transform of the obtained data. Fourier transform by means of means for obtaining, and means for recording complex amplitude data in the spatial light modulating means, A means for determining the maximum spatial frequency in the pattern data to be reproduced, a means for adjusting the diameter of the beam emitted from the coherent light source according to the maximum spatial frequency of the pattern to be reproduced, and means for adjusting the number of repeated exposures are provided. It is characterized by being

In the second optical marking device of the present invention, the means for recording the complex amplitude data is means for determining the maximum spatial frequency in the pattern data to be reproduced, and the means for recording the complex amplitude data according to the maximum spatial frequency in the pattern to be reproduced. An optical system as a means for adjusting the beam diameter emitted from the coherent light source, a means for adjusting the number of repetitive exposures, a control device as a means for adjusting the output of the coherent light source, a drive power source, and the spatial light modulator. A liquid crystal spatial light modulator and its drive circuit are provided as a means for recording complex amplitude data.

[0007]

[0008]

[0009]

[0010]

[0011]

The details of the present invention will be described below with reference to Examples.

(Embodiment 1) FIG. 1 shows the configuration of a laser marking device of the present invention. The beam emitted from the laser light source 101 becomes parallel light expanded by the optical system 102 and enters the phase modulation type liquid crystal spatial light modulator 103. And
By the action of the phase distribution displayed on the liquid crystal spatial light modulator,
The phase of the beam wavefront is two-dimensionally modulated. By subjecting the modulated wavefront to Fourier transform by the lens 104, a predetermined pattern is imaged and reproduced on the surface of the sample 105. A portion of the sample surface irradiated with the laser light is evaporated or altered by heat, and a pattern is imprinted. In FIG. 1, 1
Reference numeral 06 is a laser drive power source, 107 is a drive circuit for the liquid crystal spatial light modulator, and 108 is a control device for controlling them. Characters and patterns to be marked are input from the input device 109. In this embodiment, a YAG laser having a wavelength of 1.064 μm is used as a light source.

The optical system 102 is a beam collimator with a variable magnification, and according to a signal from the controller 108,
It has a function of adjusting the diameter of the beam incident on the liquid crystal spatial light modulator 103. As a configuration of the optical system 102, for example, a configuration as shown in FIG. 2 can be considered. Control device 10
The beam magnification is set by moving the stage that supports the lens group according to the signal from 8 and adjusting the inter-lens distance (d ₁ , d ₂ in the figure).

The liquid crystal spatial light modulator used in this embodiment has an ECB (electric field control birefringence) mode liquid crystal panel with antiparallel alignment, and only the phase is linearly changed to 2π without changing the amplitude of light. Can be modulated above (51st Autumn Meeting, 26
aH-10 (1990)). This liquid crystal spatial light modulator is provided with a TFT (thin film transistor) in each pixel and can be rewritten at least at a video rate by an active matrix driving method. The number of pixels is 128 × 128, the pixel pitch is 80 μm × 80 μm, and the aperture ratio is 50%.
On the surface of the substrate on which the laser is incident, the display region is provided with a dereflective coating and the non-display region is provided with a dereflective coating. Figure 4 shows the phase modulation characteristics of the liquid crystal spatial light modulator.
Shown in. The ECB mode liquid crystal panel modulates only the phase of the polarization component parallel to the director of the liquid crystal. Therefore, a linearly polarized YAG laser was used as the light source, and the polarization direction of the emitted beam was made parallel to the director of the liquid crystal.

In the marking device of the present invention, one-dimensional or two-dimensional printing is possible.
The dimensional phase distribution is displayed on the liquid crystal spatial light modulator, and the pattern is reproduced from this phase distribution. This is a big difference from the conventional method in which the liquid crystal spatial light modulator is used as a simple aperture mask. Below, as the phase distribution recorded in the liquid crystal spatial light modulator, the kinoform (IBM J. Res. Dev., 1
3, 150-155 (1969)) as an example, the features of the present invention will be described in terms of (1) reduction of speckle noise in a reproduction pattern and (2) improvement of light utilization efficiency.

First, a brief description will be given of how to create kinoform data. The random phase distribution is superimposed on the image data given as the amplitude distribution, and the Fourier transform is performed to extract only the phase component of the Fourier transform image. The quantized phase component is kinoform data, which is displayed on the liquid crystal spatial light modulator. If this kinoform is illuminated with collimated laser light, a reproduced image can be obtained behind the liquid crystal spatial light modulator. However, since speckle noise is conspicuous, it is difficult to use this reproduced image as it is for the purpose of marking.

In the present invention, the reproduced image quality is improved by integrating the reproduced image from the kinoform to lower the speckle contrast (Optical Union Symposium '92, p.25-26). . It has been found that a binary phase of 0 and π has a sufficient effect on the random image to be superimposed on the original image when creating the kinoform data. According to this method, the intensity error due to the phase jump and the intensity error due to the characteristic variation between the pixels of the liquid crystal spatial light modulator can be absorbed, so that a reproduced image with high image quality can be obtained.

However, in order to effectively use the energy of the laser, it is necessary to consider the relationship between the beam diameter for illuminating the liquid crystal spatial light modulator and the kinoform size. '92
This is not mentioned at all in the collection of papers, p.25-26).

The present invention presents a method for determining the diameter of the reproduction beam in consideration of the maximum spatial frequency contained in the original image and a specific means for realizing it, for the purpose of improving the light utilization efficiency.

First, the experimental facts that form the basis of the present invention will be described. FIG. 5 shows the relationship between the reproducing beam diameter (1 / e ² ) and the kinoform size. The intensity distribution of the reproduction beam is Gaussian. 3 levels of light utilization efficiency (99%,
90%, 80%), and the corresponding beam diameter w
(10 mm, 15 mm, 20 mm) was selected and a reproduction experiment was conducted to investigate the relationship between speckle contrast and the number of integrals (FIG. 6). As a result, it has been found that the speckle contrast (variation in intensity) increases as the beam diameter decreases (the light utilization efficiency increases). Further, in order to examine the resolution after integration, a fine stripe pattern (cycle: 2 sample points) was reproduced and its intensity distribution was measured. From this measurement, it was found that the narrower the beam diameter (the higher the light utilization efficiency), the more difficult it was to distinguish between black and white stripes. As an example, the integration number is 50
The result at the time of is shown in FIG.

From these experimental results, the diameter of the reproduction beam is determined in consideration of the maximum spatial frequency included in the original image, and (1) the laser output is adjusted to prevent overexposure. It can be understood that the energy of can be used to the maximum extent, and that (2) the engraving with the same quality can be realized regardless of the reproduction beam diameter by adjusting the number of integrations.

Specific means for realizing this method will be shown below. FIG. 3 shows the configuration of the control device 108 used in this embodiment. It should be noted that the control circuit 301 sends a control signal to each circuit as necessary in order to efficiently execute the following processing at the same timing.

The image data input from the input device 109 is converted into dot matrix data by the font ROM 302 and then stored in the input buffer 203 (if the dot matrix data has been given from the beginning). The data of one frame is read from the buffer to the memory 306. On the other hand, the random number generation circuit 304 randomly generates binary data (1 and -1 in this embodiment). This binary data is stored in the memory 305 as a set for each number equal to the number of dots of the image data.

The data of the memories 305 and 306 are multiplied by each dot by the multiplication circuit 308 and stored in the memory 309. This data is converted into a two-dimensional complex fast Fourier transform circuit 3
Fourier transform is performed at 10 and the complex amplitude data is stored in the memory 311.
Save to. The arctangent calculation circuit 312 extracts the phase data from this data, and the quantization calculation circuit 313 quantizes (16 gradations in this embodiment) to create kinoform data. This data is stored in the output buffer 314, and the drive circuit 107 of the liquid crystal spatial light modulator is stored for each frame.
Send to.

The control device of this embodiment can calculate one kinoform (128 × 128 dots) in about 30 ms. The kinoform is rewritten at almost the video rate according to the response of the liquid crystal spatial light modulator, and the trigger signal is sent to the power source 107 for driving the laser in synchronization with this.
Pulse the YAG laser.

As described above, by determining the reproduction beam diameter in consideration of the maximum spatial frequency included in the image data, the energy of the reproduction beam can be utilized most effectively. Here, the determination circuit 207 causes the memory 206 to
The maximum spatial frequency included in the image data is determined. Then, a signal corresponding to the determination result is sent to the optical system 102 in FIG. 1 and the control circuit 301 in FIG. 3 to adjust the beam expansion ratio and set the number of repeated exposures. For example, when the maximum spatial frequency included in the image data is high, the reproduction beam diameter is 20 mm (light utilization efficiency 80
%), The number of repeated exposures is set to 30, and when the maximum spatial frequency included in the image data is low, the reproduction beam diameter is set to 10 mm (light utilization efficiency 99%) and the number of repeated exposures is set to 50.

Further, the result of determination of the maximum spatial frequency contained in the image data is fed back to the laser driving power source of FIG. 1 to adjust the laser output. That is, by reducing the reproduction beam diameter and lowering the laser output, overexposure is prevented and laser energy is effectively used.

According to the present invention, the reproduction beam diameter and the integration number (the number of repeated exposures) are determined in consideration of the maximum spatial frequency included in the image data to be imprinted.
(1) Make the most effective use of laser energy,
(2) It has become possible to realize high-quality markings that are not affected by speckle noise.

[0029]

The following effects are produced by the laser marking device of the present invention.

(1) By reproducing the pattern from the phase distribution displayed on the phase modulation type liquid crystal spatial light modulator, the pattern can be marked with extremely high light utilization efficiency.

(2) It is possible to engrave a pattern with extremely high light use efficiency while adjusting the reproduction beam diameter and ensuring a required pattern resolution.

(3) By adjusting the number of integrations (the number of repeated exposures), it is possible to perform high-quality marking with little intensity variation, regardless of the reproduction beam diameter.

[Brief description of drawings]

FIG. 1 is a side view showing a configuration of a marking device of the present invention.

FIG. 2 is a plan view showing the configuration of a collimating optical system with variable magnification.

FIG. 3 is a diagram showing a configuration of a control device used in the marking device of the present invention.

FIG. 4 is a diagram showing a phase modulation characteristic of a liquid crystal spatial light modulator.

FIG. 5 is a diagram showing a relationship between a reproduction beam diameter and a kinoform size.

FIG. 6 is a diagram showing the relationship between speckle contrast and the number of integrals.

FIG. 7 is a diagram showing a reproduced image (after integration) of a stripe pattern.

[Explanation of symbols]

101 laser light source 102 Optical system 103 Phase modulation type liquid crystal spatial light modulator 104 Fourier transform lens 105 samples 106 laser drive power supply 107 Liquid crystal spatial light modulator driving circuit 108 Control device 109 input device 201 lens 202 lens 203 lens 301 control circuit 302 font ROM 303 input buffer 304 number generation circuit 305 memory 306 memory 307 Judgment circuit 308 Multiplier circuit 309 memory 310 Fast Fourier Transform Circuit 311 memory 312 arctangent calculation circuit 313 Quantization arithmetic circuit 314 output buffer

Continued Front Page (56) References Amako Atsushi, et al. Recording and reproduction of kinoforms by liquid crystal spatial light modulator, Optics, March 10, 1992, Volume 21, No. 3, pp. 155-156 (58) ) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 27/46 B23K 26/00 JISST file (JOIS)

Claims (2)

(57) [Claims] 1. A coherent light source, at least one spatial light modulator that controls the wavefront of a beam emitted from the coherent light source, and a beam whose wavefront is controlled by the spatial light modulator is applied to the surface of the sample. An optical marking device having a Fourier transform lens, comprising at least means for inputting pattern data to be reproduced, means for generating random number data, and means for executing Fourier transform, and displaying on the spatial light modulator. The step of creating the complex amplitude data includes a step of multiplying the random number data by the pattern data to be reproduced, and a step of performing Fourier transform on the obtained data by means of executing the Fourier transform, The means for recording complex amplitude data in the spatial light modulator is the maximum spatial circumference of the pattern data to be reproduced. A light having a means for determining the number, a means for adjusting the diameter of the beam emitted from the coherent light source according to the maximum spatial frequency of the pattern to be reproduced, and a means for adjusting the number of repeated exposures. Marking device. 2. The means for recording the complex amplitude data comprises:
Means for determining the maximum spatial frequency in the pattern data to be reproduced, optical system as means for adjusting the beam diameter emitted from the coherent light source according to the maximum spatial frequency of the pattern to be reproduced, and means for adjusting the number of repeated exposures A controller and a drive power source as means for adjusting the output of the coherent light source, and a liquid crystal spatial light modulator and its drive circuit as means for recording complex amplitude data in the spatial light modulator. The optical marking device according to claim 1, which is characterized in that.