A method for visualizing latent fingerprints on transparent material surface based on nanosecond laser lifting

Abstract

The present application relates to a kind of transparent material surface latent fingerprint visualization method based on nanosecond laser transfer printing.It belongs to the field of fingerprint extraction.It includes the following steps: the transparent material plate with latent fingerprint on one side is placed above metal base, fingerprint surface upward.Laser beam is focused on metal base through transparent material and carries out multi-line scanning, when metal base absorbs laser energy, surface temperature melts, because the surface of transparent material above is in contact with metal base, molten material will be attached to the joint surface of both.The energy loss caused by the process of laser penetrating latent fingerprint ridge will be more than the area of finger gap, so that the temperature of metal surface below fingerprint area is lower than the area of finger gap, thereby reducing the attachment amount of molten material, enhancing the contrast of fingerprint area and finger gap area, and the fingerprint is revealed.Compared with existing latent fingerprint enhancement and visualization technology, the present application is more convenient to operate, pollution-free, and the extracted fingerprint is easy to save.It is expected to be applied in criminal investigation field.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fingerprint extraction, in particular to a method for visualizing latent fingerprints on the surface of transparent materials based on nanosecond laser transfer printing, which has potential application prospects in the field of criminal investigation. BACKGROUND

[0002] When a finger contacts an object, the sweat and sebum secreted on the finger will usually adhere to the surface of the object, leaving an invisible mark, i.e. latent fingerprints, on the surface of the object. Human fingerprints have different and lifelong characteristics, and based on these characteristics, the fingerprint trace, as the "first evidence", plays a crucial role in the investigation process. Transparent materials are widely used in daily life, such as windows, water cups, etc., which are prone to leave latent fingerprints. Therefore, the extraction of latent fingerprints on the surface of transparent materials is crucial for case investigation, but due to its transparency, the background of the latent fingerprints is the background of the surrounding environment, which is relatively complex, and the fingerprints on the surface of transparent materials are not easy to extract. At present, the method for visualizing latent fingerprints mostly uses chemical and biological solvents. For example, a PVP / PVA-Nin composite nanofiber membrane, its preparation and a method for visualizing fingerprints are proposed in Chinese patent (202410523055.4), which makes the latent fingerprint profile visible. However, this type of method generally has the problems of toxic solution, harm to the operator's body, time-consuming chemical reaction, affecting the efficiency of the case, short preservation time, and easily damaged visualized fingerprints. The environmentally friendly method is mostly not mentioned in the applicability on the surface of transparent materials. For example, a method for realizing fingerprint extraction using femtosecond laser is proposed in Chinese patent (201810202353.8), which realizes the transfer printing of metal surface fingerprints onto glass using femtosecond laser, but this method obviously cannot realize 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 the latent fingerprints can reduce the laser energy on the metal surface, thereby affecting the adhesion amount of the molten material, a method for visualizing latent fingerprints on the surface of transparent materials based on nanosecond laser transfer printing is proposed. This method is suitable for the visualization of latent fingerprints on transparent surfaces, and has the advantages of simple operation, high efficiency, low cost, non-toxicity and non-pollution. More importantly, the visualized fingerprints have the advantages of abrasion resistance and long preservation time. Therefore, this method has high application value in the field of criminal investigation. SUMMARY

[0003] The present application aims to provide a method for visualizing latent fingerprints on the surface of transparent materials based on nanosecond laser transfer printing, to realize the efficient and non-polluting visualization of latent fingerprints on the surface of transparent materials, and the visualized fingerprints are easy to preserve. The principle of using the existence of latent fingerprints to reduce the laser energy on the metal surface, thereby affecting the adhesion amount of the molten material, is used. By adjusting the laser parameters, the latent fingerprints on the surface of transparent materials are quickly visualized. This method has potential application prospects in the field of criminal investigation.

[0004] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0005] A method for visualizing latent fingerprints on transparent material surfaces based on nanosecond laser imprinting, characterized by comprising 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: The sample with latent fingerprints is placed on a metal substrate with the fingerprint side facing up. The sample is placed on a sample stage, and the parameters are set on the computer program and a laser beam is used 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 heat up and melt rapidly. Because the transparent material is in contact with the metal substrate, the molten material will adhere to the interface between the two. Since the transparency of the fingerprint pattern area is worse 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. This makes the temperature of the metal surface below the fingerprint pattern area lower than that of the finger gap area, so that the amount of molten material adhering to the fingerprint pattern area is less than that adhering to the finger gap area, which enhances the contrast between the fingerprint pattern area and the finger gap area, and the fingerprint is revealed. The laser irradiation parameters include: an average laser power of 13.3W, a laser scanning speed of 1000mm / s, a distance of 0.03mm between adjacent laser scanning lines, a laser wavelength of 1064nm, a laser pulse width of 250ns, a laser repetition frequency of 100kHz, and a Gaussian distribution of laser energy.

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

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

[0010] Furthermore, the metal substrate material mentioned in step (2) of step (1) is stainless steel, zinc, aluminum, brass, etc.

[0011] Furthermore, the presence of latent fingerprints in step (2) reduces the laser energy on the metal surface, mainly because latent fingerprints have poor light transmittance compared to transparent materials, which will block the laser to some extent.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] The application provides a method for visualizing latent fingerprints on the surface of transparent materials based on nanosecond laser transfer printing, and provides a solution for latent fingerprint development in the field of criminal investigation. The method is suitable for developing latent fingerprints on the surface of transparent materials, and has the following advantages:

[0014] 1. Non-toxic and non-polluting, and harmless to human body.

[0015] 2. The developed fingerprint is not easy to be erased and has a long storage time.

[0016] 3. Simple operation, high efficiency and low cost, and high application value in the field of criminal investigation.

[0017] 4. The original latent fingerprint is not damaged, and the fingerprint can be extracted multiple times. BRIEF DESCRIPTION OF DRAWINGS

[0018] The drawings described herein are used to provide further understanding of the application, and constitute a part of the application. The schematic examples of the application and the description thereof are used to explain the application, and do not constitute an improper limitation on the application.

[0019] Figure 1 It is a method for visualizing latent fingerprints on the surface of transparent materials based on nanosecond laser transfer printing provided by the application;

[0020] Figure 2 It is a principle diagram of the method for visualizing latent fingerprints on the surface of transparent materials based on nanosecond laser transfer printing provided by the application;

[0021] Figure 3 It is a digital photo of the original latent fingerprint on the surface of glass involved in example 1 of the application;

[0022] Figure 4 It is a digital photo of the fingerprint on the glass and stainless steel combined surface after laser irradiation of the original latent fingerprint on the surface of glass involved in example 1 of the application;

[0023] Figure 5 It is a digital photo of the fingerprint after wiping the developed fingerprint after irradiation involved in example 1 of the application. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the application more clear and explicit, the application is further described in detail below with reference to the drawings and examples.

[0025] The implementation process and beneficial effects of the method for visualizing latent fingerprints on the surface of transparent materials based on nanosecond laser transfer printing provided by the application are described by taking typical glass as the upper transparent material and stainless steel as the lower metal substrate as examples.

[0026] Example 1:

[0027] (1) Obtaining latent fingerprints: gently press the 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 up. Place it on the sample stage, set the parameters on the computer program and use the laser beam for multi-line scanning. The laser irradiation parameters include: laser average power is 13.3 W, laser scanning speed is 1000 mm / s, the distance between adjacent laser scanning lines is 0.03 mm, laser wavelength is 1064 nm, laser pulse width is 250 ns, laser repetition frequency is 100 kHz, laser energy is Gaussian distribution, use digital equipment to take pictures, and obtain digital photos.

[0029] Referring to Figure 3 and Figure 4 , it is shown that the original latent fingerprint digital photo of the glass surface and the fingerprint digital photo of the glass surface after laser irradiation of the original latent fingerprint on the glass and stainless steel combined surface. It can be found that the deposited fingerprint after laser irradiation has a much higher clarity than the original latent fingerprint, which can meet the fingerprint extraction requirements in the field of criminal investigation.

[0030] Referring to Figure 5 , it is shown that the fingerprint digital photo after wiping the deposited fingerprint after irradiation in this example. It can be found that the fingerprint after wiping is still clear, which can avoid secondary damage and is easier to save.

[0031] From the test results, it can be seen that the method proposed by the present application can quickly and conveniently clearly show the latent fingerprints on the surface of transparent materials, and the clear fingerprint lines can still be shown after simple wiping.

[0032] The above only describes the preferred examples of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made to the present application shall be included in the protection scope of the present application.

Claims

1. A method for visualizing latent fingerprints on transparent material surfaces based on nanosecond laser lifting, characterized in that, The method comprises the following steps: (1) obtaining latent fingerprints: gently press the surface of a transparent material plate with a finger to obtain a sample with latent fingerprints on the surface; the transparent material is glass; (2) laser irradiation treatment: place the transparent material plate with latent fingerprints above a metal substrate, the metal substrate material is stainless steel, the fingerprint surface faces upward, place the sample on a sample stage, set parameters on a computer program and perform multi-line scanning using a laser beam, utilize the high transmittance of the transparent material to the laser to make the laser beam pass through the sample and focus on the metal substrate, when the substrate metal absorbs the laser energy, the surface will quickly heat and melt, because the transparent material is attached to the metal substrate, the molten material will adhere to the combined surface of the two, since the transparency of the fingerprint line area is poorer than that of the interdigital area, the energy loss caused by the laser penetrating the latent fingerprint line area is more than that of the interdigital area, the temperature of the metal surface below the fingerprint line area is lower than that of the interdigital area, so that the adhesion amount of the molten material in the fingerprint line area is less than that in the interdigital area, the contrast between the fingerprint line area and the interdigital area is enhanced, and the fingerprint is revealed, the laser irradiation parameters include: the average laser power is 13.3 W, the laser scanning speed is 1000 mm / s, the distance between adjacent laser scanning lines is 0.03 mm, the laser wavelength is 1064 nm, the laser pulse width is 250 ns, the laser repetition frequency is 100 kHz, and the laser energy is in Gaussian distribution.

2. The method for visualizing latent fingerprints on transparent material surface based on nanosecond laser lifting according to claim 1, characterized in that: The main components of the latent fingerprints in step (1) are sweat and grease.

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