Nanosecond laser rubbing-based transparent material surface latent fingerprint visualization method

Abstract

The invention relates to a transparent material surface latent fingerprint visualization method based on nanosecond laser rubbing. Belongs to the field of fingerprint extraction. Comprising the following steps that a transparent material plate with latent fingerprints on one side is placed above a metal substrate, and the surface of the fingerprints faces upwards; a laser beam penetrates through the transparent material, is focused on the metal substrate and performs multi-line scanning, and when the metal substrate absorbs laser energy, the surface is heated and melted, and because the surface of the transparent material above is attached to the metal substrate, the melted material is attached to the combined surface of the transparent material and the metal substrate. The energy loss caused in the process that the laser penetrates through the latent fingerprint lines is more than that of the finger gap area, so that the temperature of the metal surface below the fingerprint area is lower than that of the finger gap area, the adhesion amount of melt is reduced, the contrast ratio of the fingerprint area and the finger gap area is enhanced, and the fingerprint is displayed. Compared with an existing latent fingerprint enhanced display technology, the method is more convenient to operate and free of pollution, and the extracted fingerprints are easy to store. The method is expected to be applied to the criminal investigation field.

Description

Technical Field

[0001] The invention relates to the technical field of fingerprint extraction, and in particular to a method for visualizing latent fingerprints on a transparent material surface based on nanosecond laser rubbing, which has potential application prospects in the field of criminal investigation. Background Art

[0002] When a finger touches an object, the sweat and oil secreted from the finger usually adhere to the surface of the object, leaving marks on the surface that cannot be observed by the naked eye - latent fingerprints. Human fingerprints have different characteristics that remain unchanged throughout life. Based on these characteristics, fingerprint traces, as the "first evidence", play a vital role in the case handling process. Transparent materials are widely used in daily life. For example, windows and water cups are very easy to leave latent fingerprints, so the extraction of latent fingerprints on the surface of transparent materials is crucial to case detection. However, due to its transparency, the background of latent fingerprints is the background of the surrounding environment, which is relatively complex, and fingerprints on the surface of transparent materials are not easy to extract. At present, the methods for visualizing latent fingerprints mostly use chemical and biological solvents. For example, in the Chinese patent (202410523055.4), a PVP / PVA-Nin composite nanofiber membrane, a method for preparing and displaying fingerprints are proposed, so that the outline of latent fingerprints can be displayed. However, this type of method generally has problems such as the solution used has a certain toxicity, which harms the operator's body; the chemical reaction takes time, which affects the efficiency of case handling; the storage time is short, and the visible fingerprints are easily destroyed. Most of the environmentally friendly methods do not mention their applicability on the surface of transparent materials. For example, a method for fingerprint extraction using femtosecond laser is proposed in a Chinese patent (201810202353.8). This method realizes the transfer of fingerprints on metal surfaces to glass using femtosecond lasers, but this method obviously cannot achieve the extraction of fingerprints on the surface of transparent materials. Therefore, it is urgent to develop a new latent fingerprint visualization technology for latent fingerprints on the surface of transparent materials. Since latent fingerprints can reduce the laser energy on the metal surface, thereby affecting the amount of melt adhesion, a method for visualization of latent fingerprints on the surface of transparent materials based on nanosecond laser rubbing is proposed. This method is suitable for the visualization of latent fingerprints on transparent surfaces. The method is simple to operate, efficient, low-cost, non-toxic and pollution-free. More importantly, the displayed fingerprints have the advantages of abrasion resistance and long storage time. Therefore, this method has a high application value in the field of criminal investigation. Summary of the invention

[0003] The purpose of the present invention is to provide a method for visualizing latent fingerprints on the surface of transparent materials based on nanosecond laser rubbing, so as to realize efficient and pollution-free visualization of latent fingerprints on the surface of transparent materials, and the visualized fingerprints are easy to preserve. The existence of latent fingerprints can reduce the laser energy on the metal surface, thereby affecting the amount of molten material adhesion. By adjusting the laser parameters, the latent fingerprints on the surface of transparent materials can be quickly visualized. The method has potential application prospects in the field of criminal investigation.

[0004] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0005] A method for visualizing latent fingerprints on the surface of a transparent material based on nanosecond laser rubbing, characterized in that it comprises the following steps:

[0006] (1) Obtaining latent fingerprints: Gently press your finger on the surface of a transparent material to obtain a sample with latent fingerprints on the surface;

[0007] (2) Laser irradiation treatment: Place the sample with latent fingerprints on top of the metal substrate with the fingerprint facing upwards and place it on the sample stage. Set parameters on the computer program and use the laser beam for multi-line scanning. The high transmittance of the transparent material to the laser allows the laser beam to pass through the sample and focus on the metal substrate. When the metal substrate absorbs the laser energy, the surface will quickly heat up and melt. Because the transparent material fits the metal substrate, the molten material will adhere to the junction surface of the two. Since the transparency of the fingerprint pattern area is lower than that of the finger joint area, the energy loss caused by the laser penetrating the latent fingerprint pattern will be greater than that of the finger joint area, making the metal surface temperature below the fingerprint pattern area lower than that of the finger joint area, so that the amount of molten material attached to the fingerprint pattern area is less than that to the finger joint area, thereby enhancing the contrast between the fingerprint pattern area and the finger joint area, and the fingerprint can be revealed. The laser irradiation parameters include: average laser power of 13.3W, laser scanning speed of 1000mm / s, distance between adjacent laser scanning lines of 0.03mm, laser wavelength of 1064nm, laser pulse width of 250ns, laser repetition frequency of 100kHz, and laser energy Gaussian distribution;

[0008] Furthermore, the transparent material in step (1) is a light-transmitting material such as glass, acrylic, or fused quartz.

[0009] Furthermore, the latent fingerprint described in step (1) is mainly composed of sweat and grease, which can change the laser transmittance of transparent materials.

[0010] Furthermore, the metal base material described in step (1) and step (2) is stainless steel, zinc, aluminum, brass, etc.

[0011] Furthermore, the presence of the latent fingerprint in step (2) reduces the laser energy on the metal surface, mainly because the latent fingerprint has a lower light transmittance than transparent materials and blocks the laser to a certain extent.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] The present invention proposes a method for visualizing latent fingerprints on the surface of transparent materials based on nanosecond laser rubbing, which provides a solution for latent fingerprint visualization in the field of criminal investigation. The existence of latent fingerprints can reduce the laser energy on the metal surface, thereby affecting the amount of molten material adhesion. The method is suitable for latent fingerprint visualization on the surface of transparent materials and has the following advantages:

[0014] 1. Non-toxic and pollution-free, will not cause harm to the human body.

[0015] 2. The fingerprints revealed by this method are not easy to erase and can be preserved for a long time.

[0016] 3. Easy to operate, efficient and low-cost, it has high application value in the field of criminal investigation.

[0017] 4. The original latent fingerprint will not be destroyed and the fingerprint can be extracted multiple times. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide further understanding of the present invention and constitute a part of this application. The illustrative examples of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0019] Figure 1 It is a schematic diagram of the operation of a method for visualizing latent fingerprints on a transparent material surface based on nanosecond laser rubbing provided by the present invention;

[0020] Figure 2 This is a schematic diagram of a method for visualizing latent fingerprints on a transparent material surface based on nanosecond laser rubbing provided by the present invention;

[0021] Figure 3 is the original latent fingerprint digital photo of the glass surface involved in Example 1 of the present invention;

[0022] Figure 4 It is a digital photo of the fingerprint of the original latent finger on the glass surface involved in Example 1 of the present invention, which is printed on the interface between glass and stainless steel after being irradiated by laser;

[0023] Figure 5 It is a digital photo of the fingerprint after wiping that appears after irradiation according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0025] Taking typical glass as the upper transparent material and stainless steel as the lower metal substrate as an example, the implementation process and beneficial effects of the method for visualizing latent fingerprints on the surface of a transparent material based on nanosecond laser rubbing proposed by the present invention are explained.

[0026] Embodiment 1:

[0027] (1) Obtaining latent fingerprints: Gently press your finger on the glass surface to obtain a sample with latent fingerprints on the surface;

[0028] (2) Laser irradiation treatment: Place the glass sample with latent fingerprints on the stainless steel substrate with the fingerprint facing upward. Place it on the sample stage, set parameters on the computer program and use the laser beam for multi-line scanning. The laser irradiation parameters include: average laser power of 13.3W, laser scanning speed of 1000mm / s, distance between adjacent laser scanning lines of 0.03mm, laser wavelength of 1064nm, laser pulse width of 250ns, laser repetition frequency of 100kHz, laser energy Gaussian distribution, and use digital equipment to take pictures to obtain digital photos.

[0029] See also Figure 3 and Figure 4 As shown in the figure, there are the original latent fingerprint digital photos on the glass surface of this embodiment and the fingerprint digital photos of the original latent fingerprint on the glass surface after laser irradiation on the glass and stainless steel joint surface. It can be found that the clarity of the deposited fingerprint after laser irradiation is much higher than that of the original latent fingerprint, which can meet the fingerprint extraction needs in the field of criminal investigation.

[0030] See also Figure 5 As shown, it is a digital photo of the deposited fingerprint after irradiation in this embodiment after being wiped. It can be found that the fingerprint after wiping is still clear, can avoid secondary damage, and is easier to preserve.

[0031] It can be seen from the test results that the method proposed in the present invention can quickly and conveniently make latent fingerprints on the surface of transparent materials clearly visible, and clear fingerprint patterns can still be revealed after a simple wipe.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made to the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for visualizing latent fingerprints on transparent material surfaces based on nanosecond laser rubbing, characterized in that: The following steps are involved: (1) Obtaining latent fingerprints: Gently press the surface of a transparent material plate with your finger to obtain a sample with latent fingerprints on the surface; (2) Laser irradiation treatment: Place a transparent material plate with latent fingerprints on top of a metal substrate, with the fingerprint facing upward. Place the sample on a sample stage, set parameters on a computer program, and use a laser beam to perform multi-line scanning. The high transmittance of the transparent material to the laser allows the laser beam to pass through the sample and focus on the metal substrate. When the base metal absorbs the laser energy, the surface will quickly heat up and melt. Because the transparent material fits the metal substrate, the molten material will adhere to the junction of the two. Since the transparency of the fingerprint pattern area is lower than that of the finger gap area, the energy loss caused by the laser penetrating the latent fingerprint pattern will be greater than that of the finger gap area, causing the metal surface below the fingerprint pattern area to be damaged. The surface temperature is lower than that of the finger joint area, so that the amount of molten material attached to the fingerprint pattern area is less than that of the molten material attached to the finger joint area, thereby enhancing the contrast between the fingerprint pattern area and the finger joint area, and the fingerprint can be revealed. The fingerprint revealed by the method is not easy to be erased, has a long storage time, and will not damage the original fingerprint during operation. The original fingerprint can be extracted multiple times. The laser irradiation parameters include: an average laser power of 13.3W, a laser scanning speed of 1000mm / s, a distance between adjacent laser scanning lines of 0.03mm, a laser wavelength of 1064nm, a laser pulse width of 250ns, a laser repetition frequency of 100kHz, and a Gaussian distribution of laser energy.

2. The method for visualizing latent fingerprints on the surface of a transparent material based on nanosecond laser rubbing according to claim 1, characterized in that: The transparent material described in step (1) is any light-transmitting material selected from the group consisting of glass, acrylic, and fused quartz.

3. The method for visualizing latent fingerprints on the surface of a transparent material based on nanosecond laser rubbing according to claim 1, characterized in that: The latent fingerprints described in step (1) are mainly composed of sweat and grease.

4. The method for visualizing latent fingerprints on the surface of a transparent material based on nanosecond laser rubbing according to claim 1, characterized in that: The metal base material described in step (2) is any one of stainless steel, zinc, aluminum, and brass.

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