Method of subsurface inscription on lab grown diamonds

Abstract

The disclosure provides a method (100) of subsurface inscription on a lab grown diamond without causing structural damage to the surrounding crystal. The method includes steps of providing (101) a laser marking system having a marking apparatus, a motorized element and a control unit and providing (103) a lab grown diamond sample on a motorized element. Then the method then includes generating (105) an optical beam by a laser unit, and adjusting (107) the beam in a beam expander followed by attenuating (109) the expanded beam in a modulator coupled to optical elements. Then, the scanning area is defined (111), and optical output is guided (113) at the focal point through a focusing lens. The method includes moving (115) the sample with reference to the focal point, thereby producing the subsurface inscription.

Description

METHOD OF SUBSURFACE INSCRIPTION ON EAB GROWN DIAMONDSCROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority to Indian Patent Application No. 20241079446 entitled METHOD OF SUBSURFACE INSCRIPTION ON LAB GROWN DIAMONDS filed on 18 October, 2024.FIELD OF THE INVENTION

[0002] The present invention generally relates to laser system and more particularly relates to method and laser system to mark lab grown diamonds.DESCRIPTION OF THE RELATED ART

[0003] The emergence of lab-grown diamonds has revolutionized the diamond industry, offering a sustainable and ethically responsible alternative to mined diamonds. Lab- grown diamonds are chemically and optically the same as natural diamonds, traditional gemological observations and instrumentation are not able to make the difference between them. As this industry continues to expand, the importance of traceability in lab- grown diamonds cannot be overstated. Thus, the inscription techniques are necessary to easily distinguish between the lab grown and mined diamonds.

[0004] There are different inscription techniques, but the drawback of physically marking gems on their surface is that these markings will be lost if the gem is cut or polished. Even more concerning is the possibility of surface marks being manipulated or fraudulently altered. Among the different inscription techniques, laser marking has been known for a long time in the gemstone industry. The laser marking technique mainly relies on the characteristics of the laser beam that is focused on the polished surface of the diamond. The selection of laser beam parameters such as average power or energy per pulse, wavelength, pulse duration, frequency, and laser spot or output beam diameter are crucial to ensure the penetration of the laser beam at the sub-surface without damaging the surface of the diamond crystal.

[0005] Previous research works faced a challenge in inscribing diamonds, specifically in developing a method that could effectively penetrate the laser into the sub-surface of extremely hard diamonds without causing damage to the diamond's surface. Previousefforts have exclusively concentrated on marking natural diamonds or jewelery diamonds, with no research conducted on laser subsurface marking for lab-grown diamonds. Additionally, working on lab-grown diamond seed crystals presented difficulties due to their very small size, especially when compared to gem-grade diamonds. The majority of diamond seed crystals used have a thickness of approximately 500 pm or less than 1000 pm. Attempting laser marking at a depth on these seeds generally led to surface damage.

[0006] Although lasers were previously used for altering the surface of diamond as illustrated in a United States patent application US4336439A and 4,028,532 were focused on engraving the sub-surface of diamond but did not focus on the issues such as graphitization or microcracks during inscription. An alternative work on using laser energy for diamond processing was disclosed in U.S. Patent No. 3,537,198. However, this method failed to address the challenge of effectively controlling both the depth of laser penetration and the size of the engraved lines. Yet another application US4467172A discloses a method to engrave gem diamonds by laser, but the work mostly focused only on surface marking techniques. In European Patent EP1855556A1, authentication codes were inscribed at a depth below the surface of the gemstone. WO2023039224A1 discloses a system for laser inscribing a gemstone, a computer in communication with a first light source and a second light source, and a laser generator to create an inscription on the gemstone.

[0007] However, the above mentioned references did not report any works on adjusting laser pulse parameters for precise sub-surface marking or at depths of a lab grown diamond seed crystals. Specifically, there have been no reported efforts to inscribe readable QR codes beneath the surface of a diamond seed crystal without causing structural damage. The invention proposes to mitigate some of the problems discussed above, as illustrated further with reference to the description and drawings.SUMMARY OF THE INVENTION

[0008] According to one embodiment of the present subject matter, a method of adjusting operating parameters of a laser pulse on a lab grown diamond while inducing a subsurface inscription without causing structural damage is disclosed. The method includes the steps of providing a laser marking system. In various embodiments, the lasermarking system includes a marking apparatus having at least a laser unit with a femtosecond pulsed laser, a beam expander, at least one modulator coupled to a pair of optical elements, at least one focusing lens and fitted with a visible range camera, a motorized element connected to a control unit configured to control at least one operating parameter. Next step includes providing a lab grown diamond sample on the motorized element. This step is followed by generating an optical beam by the laser unit after adjusting a first set of operating parameters. The next step includes adjusting output beam from the laser unit in the beam expander, thereby expanding size of output beam while concurrently decreasing divergence. This step is followed by attenuating optical output from the beam expander in the modulator coupled to optical elements, thereby regulating a second set of operating parameters. Further step includes, defining the scanning area of the sample by a visible range camera within the visible spectrum followed by guiding optical output from the modulator coupled to optical elements towards the sample at the focal point through at least one focusing lens. The final step includes moving the sample position in X, Y or Z directions with reference to the focal point along a pre-programmed trajectory, thereby producing the subsurface inscription. In various embodiments, providing the laser marking system comprises executing program instructions provided via a keyboard, a graphic input device, or wired or wireless communication configured to adjust focus and to move the three- axis stage along the pre-programmed trajectory to produce the inscription.

[0009] In various embodiments, the femtosecond pulsed laser is a titanium- sapphire crystal. In various embodiments, adjusting the first set of operating parameters comprises regulating a laser wavelength or a pulse width or a laser power or a repetition rate or a laser fluence. In various embodiments, generating an optical beam comprises generating laser wavelength in the range 650 nm to 1100 nm, the pulse width of 100 fs or more, the laser power of 10 - 50mW, the repetition rate is 10 kHz or higher frequency, or the laser fluence is 2.55+0.5 J / cm2. In various embodiments, regulating the second set of operating parameters include adjusting output beam size or a scanning speed in the range 0.5 - 3.0 mm / s. In various embodiments, the focusing lens has a focal length of at least 10 mm and a numerical aperture of 0.25. In various embodiments, the output beam size is 15 pm or less.

[0010] In various embodiments, the method is configured to inscribe the sample with a thickness of at least 300 pm. In various embodiments, the method is configured to produce laser marking at a depth of at least 200 pm below the surface of the sample. In various embodiments, the method is configured to inscribe single character size in the range of 30- 60 pm. In various embodiments, the method is configured to inscribe a two- dimensional logo, a three dimensional logo, an alphanumeric code, or a quick response barcode on a subsurface plane of the sample.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:

[0012] FIG. 1: represents a method of adjusting operating parameters of a laser pulse on a lab grown diamond while inducing a subsurface inscription without causing structural damage.

[0013] FIG. 2: represents a laser marking system for producing subsurface inscription on a lab grown diamond sample.

[0014] FIG. 3A: Images showing laser inscription of a QR code

[0015] FIG. 3B: Images showing laser inscription of a Logo

[0016] FIG. 3C: Images showing laser inscription of Alphanumeric codes

[0017] FIG. 4A: SEM image showing a logo "INCENT" engraved on and below the surface of a lab grown diamond sample

[0018] FIG. 4B: Optical image showing a logo "INCENT" with varying scanning speeds and laser fluence.

[0019] FIG. 4C: Optical image showing a logo at a laser fluence of 2.55 J / cm2and a scan speed of 1 mm / s.

[0020] FIG. 4C: Graphical representation of Raman spectroscopy measurement at a laser fluence of 2.55 J / cm2and a scan speed of 1 mm / s.

[0021] FIG. 5A: Optical image of a QR code engraved 200 pm below the diamond seed surface.

[0022] FIG. 5B: Graphical representation of Raman spectroscopy measurement of the QR code engraved 200 pm below the diamond seed surface.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.

[0024] Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of "a", "an", and "the" include plural references. The meaning of "in" includes "in" and "on." Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.

[0025] The present subject matter discloses a method of subsurface inscription on a lab grown diamond without causing structural damage.

[0026] The method of subsurface inscription on lab grown diamond without causing structural damage is further disclosed with reference to the drawings. As illustrated in FIG. 1, the method 100 of includes the steps of providing 101 a laser marking system 200 followed by providing 103 a lab grown diamond sample on a motorized element 213. Next step includes generating 105 an optical beam by the laser unit. Adjusting the optical beam and attenuating the optical output beam takes place in steps 107 and 109, respectively. This is followed by defining 111 of the scanning area and guiding 113 optical input towards the sample at a focal point by moving 115 the sample position.

[0027] In various embodiments, the method 100 of adjusting operating parameters of a laser pulse includes the step of providing 101 the laser marking system 200. The laser marking system 200 for producing subsurface inscription on a lab grown diamond sample 217 is illustrated in FIG. 2, according to embodiments of the present subjectmater. The laser marking system 200 includes a marking apparatus 201, a motorized element and a 213 control unit 215.

[0028] In various embodiments, the marking apparatus 201 is configured to generate an output beam for producing subsurface inscription of a lab grown diamond sample 217. The marking apparatus 201 includes at least a laser unit 203, a beam expander 205, at least one modulator 207 coupled to a pair of optical elements 209, at least one focusing lens 211 and fited with a visible range camera 219. In one embodiment, the optical elements include pair of optical mirrors for focusing the laser beam onto the objective lens. In various embodiments, the laser unit is configured to produce optical output. In various embodiments, the laser unit 203 may include a housing encasing the laser source positioned within cavity of an optical resonator.

[0029] In various embodiments of the method, generating 105 an optical beam by the laser unit comprises providing a femtosecond pulsed laser. In one embodiment, the femtosecond pulsed laser is a titanium- sapphire crystal. In various embodiments, the laser unit 203 may include a first pair of optical elements coupled with mechanical shuter, configured to receive radiation from a acoustic-optical unit and guiding radiation towards a harmonic generator. In various embodiments, the laser unit 203 may include a second pair of optical elements configured to receive and guide optical output from the harmonic generator out of the laser unit 203. In various embodiments, the optical output form the laser unit 203 is received by the beam expander 205. In various embodiments, this step enables adjusting a first set of operating parameters such as a laser wavelength or a pulse width or a laser power or a repetition rate or a laser fluence. In various embodiments, generating an optical beam comprises generating the laser wavelength in the range 650 nm to 1100 nm, the pulse width of 100 fs or more, the laser power is 10 - 50m W, the repetition rate is 10 kHz or higher frequency, the laser fluence is 2.55±0.5 J / cm2.

[0030] In various embodiments, the next step 107 of the method 100 includes adjusting output beam from the laser unit 203 in the beam expander 205. In various embodiments, the optical output form the laser unit 203 is received by the beam expander 205. In various embodiments, the beam expander 205 includes a plurality of lenses, configured to deflect expanded output beam from the laser unit 203 towards the modulator 207,thereby expanding size of output beam while concurrently decreasing divergence. In various embodiments, output beam the beam expander 205 is received by the modulator 207.

[0031] In various embodiments, the method 100 includes attenuating 109 optical output from the beam expander 205 in the modulator 207 coupled to optical elements 209. In various embodiments, this step enables regulating a second set of operating parameters. In various embodiments, the second set of operating parameters include adjusting output beam diameter or a scanning speed. In one embodiment, the scanning speed ranges within 0.5 - 3.0 mm / s. In various embodiments, the output beam size is 15 pm or less.

[0032] In various embodiments, the method 100 includes providing 110 the lab grown diamond sample 217 on the motorized element 213. In various embodiments, the motorized element 213 is configured to optimize sample position at a focal point of the output beam. In various embodiments, the motorized element 213 comprises a sample positioning stage configured to move and adjust the sample position in X, Y or Z directions. In various embodiments, the method 100 further includes defining 111 the scanning area of the sample 217 by a visible range camera 219 within the visible spectrum. In various embodiments, the visible range camera 219 is configured to optically determine scanning area of the sample and to capture real time image of the sample.

[0033] In various embodiments, the method 100 includes guiding 113 optical output from the modulator 207 coupled to optical elements 209 towards the sample 217 at the focal point through at least one focusing lens 211. In one embodiment, the focusing lens has a focal length of at least 10 mm and a numerical aperture of 0.25. In various embodiments, the method 100 further includes moving 115 the sample position in X, Y and Z directions with reference to the focal point along a pre-programmed trajectory, thereby producing the subsurface inscription.

[0034] In various embodiments, the method 100 includes providing the laser marking system 200 with the control unit 215 configured to control at least one operating parameter. In various embodiments, the control unit 215 includes a computer having at least one processor and memory, communicably connected to the marking apparatus 201 and the motorized element 213. In various embodiments, the control unit includes aregulator configured to control the function of the marking apparatus 201, and an intensity of optical output from the laser unit 203 through a radiation channel. The control unit 215 further include a function generator configured to provide signal to the marking apparatus 201 to penetrate the sample 217 with output beam to a predetermined depth. The control unit 215 also includes a visible image processing module configured to receive real-time image from the visible range camera 219 and to extract visible image data to carry out inscription along the pre-programmed trajectory. In various embodiments, providing the laser marking system comprises executing program instructions provided via a keyboard, a graphic input device, or wired or wireless communication configured to adjust focus and to move the three- axis stage along the pre-programmed trajectory to produce the inscription.

[0035] In various embodiments, the method 100 of the present invention is configured to inscribe a two dimensional logo, a three dimensional logo, an alphanumeric code, a quick response barcode on a subsurface plane of the sample. In one embodiment, the method is configured to produce laser marking at a depth of at least 200 pm below the surface of the sample. In another embodiment, the method is configured to inscribe the sample with a thickness of at least 300 pm.

[0036] The method of the present invention has many advantages as set for the herein. The method of the present invention enables to achieve a controlled depth of penetration of optical laser beam from the surface of the diamond sample by employing an optical system with a short focal length, resulting in a pinpoint-focused spot size characterized by high energy density. The invention also ensures that lab-grown diamonds meet quality standards and are genuine. The method offers a comprehensive and certifiable system that can track the journey of lab-grown diamonds from their creation to the final product, enhancing consumer trust and confidence. The method enables inscription at sub surface of diamond sample without leaving visible signs of alteration at the sub surface level marking the method suitable for applications where product authenticity and anticounterfeiting measures are required. The method enables laser inscription of a custom- made logo, alphanumeric codes or QR codes of relatively small size beneath the surface, without causing any microstructural damage to the diamond surface. The QR code, once inscribed, may be read by an optical scanner, providing the entire information about the lab-grown diamond.EXAMPLES:Example- 1: Set Up for Laser Marking of Lab Grown Diamonds

[0037] The key components used in the laser system included a marking apparatus, a motorized element and a control unit. A schematic representation of a laser marking system for producing subsurface inscription is shown in the FIG. 2. The marking apparatus further included beam expanders, modulators, visible range camera and objective lens.-Laser unit: The Ultra-short pulse (on the order of 10‘15seconds) laser system used consisted of a solid-state Ti: Sapphire laser that emits a beam with an 800 nm wavelength and had tunable range of wavelength in the range of 650 nm to 1100 nm. This system generates pulses with durations ranging from 35 to 120 fs with a repetition rate of up to 10 kHz. The number of pulses was controlled by using a fast mechanical shutter. Experiments were conducted at laser fluences ranging from 1.27 to 5.10 J / cm2for single pulses with a 100 fs duration. The focal spot size of the beam was 10 pm at 1 / e of the maximum intensity with M2of 1.3 for all experiments.- Beam Expander: The apparatus further included a beam expander placed after the laser source. The beam expanders and reducers adjusted the diameter of the laser beam before it reached the focusing optics and helped in controlling the size of the focus spot and the depth of focus. The beam expander (Edmund Optics 5X Beam Expander) used in the set-up had a magnification of 5X with an input aperture of 1.8 mm and an output aperture of 9 mm. The beam expander had a wavelength range of 700 - 1100 nm (optimized for 800 nm). The beam expander increased the diameter of the laser beam, typically up to a diameter of 9 mm. It was observed that this expansion improved the collimation of the beam and allowed for better focusing of the laser beam.- Modulator: The expanded beam was passed through a Spatial Light Modulator (Thor Labs Exulus-HD2 SLM) with a highly stable phase control with minimal flickering. The SLM used was a Reflective 2D Phase Only Spatial Light Modulators (SLMs) with a resolution of 1920 x 1200 (WUXGA), an operating Wavelength - 400 - 850 nm. The SLM was used to modulate the phase, amplitude and polarization of the expanded laser beam and shaped the laser beam for any distortions. This ensured that the beam is correctly focused on the sub surface of the diamond without any aberrations. An additional mirror was placed after the SLM just to ensure that the modulated laser beam maintained optimal properties before entering the objective lens.- Objective lens: The objective lens (RMS20X-PF 20X Olympus Microscope Fluorite Objective) then precisely focused the modulated and expanded laser beam to a beam diameter less than 15 pm. The objective lens used had a numerical aperture of 0.5 NA, 2.1 mm WD. The 20X lens ensured the beam is tightly focused enabling high-definition micro engravings such as QR codes and Logos.- Visible range camera: A charge -coupled device (CCD) camera was fitted in the apparatus for accurate positioning and focusing of the laser beam on the sample.- Sample: The material used in our investigation was a single crystal diamond seed with a dimension of 10 X 10 X 0.5 mm.- Motorized element: Polished diamond samples were mounted on a high precision controlled three- axis (X, Y, Z) positioning stage for moving the diamond surface in relation to the focused point. The positioning stage was mounted with a specially designed vacuum fixture so as to hold the diamond surface flat and in position under the high energy laser beam.-Control unit: The control unit managed the operational parameters of the laser and ensured that the laser operated within the required settings to produce the ultra-short femtosecond pulses. The control unit further regulate and determine the pulse width, wavelength, repetition rate and pulse energy. The system used for machining could be operated manually or by using an Aerobasic program running in the Aerotech CNC operator environment. Aerobasic is a proprietary Aerotech CNC language which was based on G-code but also allows for I / O, simple logic and control flow. All the output laser parameters were manually controlled through the laser driver software, FCAP ULI software and Aerotech CNC operator interface. The manual control enabled fine tuning of the inscription power, set arbitrary polarisation states and move the three- axis (X, Y, Z) positioning stage as per requirement. Stage movements were regulated either from the GUI controls or immediate G-code command line in the CNC operator interface. Whilst manual control was useful for setting properties like initial laser parameters, the machining operations were performed using an aerobasic program.Example- 2: Adjusting Operating Parameters of a Laser Pulse Sample preparation: Before the experiment, the sample was cleaned in an ultrasonic bath with 0.5M sodium hydroxide (NaOH) solution for about 20 min. The diamond seed was positioned perpendicular to the laser beam and subjected to irradiation at varying scanning speeds,ranging from 0.5 mm / s to 3 mm / s. The focal spot size of the beam was 10 pm at 1 / e of the maximum intensity with M2 of 1.3 for all experiments.

[0038] Once the diamond seed sample was cleaned and placed on the fixture, the laser beam from Ti: sapphire femtosecond laser was passed through a beam expander followed by the modulator coupled to lenses and focused on the sample surface using a quartz objective lens with the help of camera. The specific laser parameters used for engraving logos and alphanumeric codes are provided in the table below.Table 1: The Specific Laser Parameters Used For Engraving Logos And Alphanumeric Codes:

[0039] The intensity distribution of the incident Gaussian laser beam was calculated as given in equation (1).Here, (x — xc) and (y — yc) are the distances from the centre of the laser beam located at (xc. yc), <n0is the beam radius. The peak fluence (O) is calculated as given in equation (2).Ep is the pulse energy, expressed as the average power divided by the repetition rate.

[0040] The ablation threshold of diamond ranges from 2 to 4 J / cm2, depending on the type of laser used. The experiment focused on fluence levels below or within the ablationthreshold, specifically ranging from 1.27 to 5.10 J / cm2Using a tightly focused laser beam, logos, alphanumeric codes, and QR codes were inscribed on the subsurface of single -crystal diamond seeds at depths of 200 nm and 100 nm.

[0041] For 3D marking from the focus, multiple depth was moved along the Z axis to create the 3D effect. The Z stage for the movement of laser was critical. The overlap distance between the depth movements also needed to be set in the software (Aerotech CNC). For each Z axis movement a pulse overlap of 1 micrometre was required. Also, the pulse energy increased with increase in depth from the focus. The difference in operating laser parameters used for a three dimensional inscription, logo or a quick response barcode on a subsurface plane of the sample are provided in the table below.Table 2: Difference in Operating Laser Parameters for a Three Dimensional Inscription, Logo or a Quick Response BarcodeExample- 3: Surface Morphology Analysis

[0042] The laser beam was focused on the targeted area below the surface at around 200 pm. The femtosecond laser pulses when focused on the sample created structural changes such as graphitic phase formation. These microstructures were opaque to visible light and were detected using optical instruments such as a 10X magnification lens, even if they were inscribed at a depth of a few 100 pm below the surface. The size of the inscription in this case for the logo “InCenf ’ was around 100 pm x 60 pm and for the QR code was 500 pm x 500 pm and Alphanumeric code was around 75 pm x 500 pm as shown in FIG. 3.

[0043] The surface morphology was investigated using a secondary electron microscope, as shown in FIG. 4A. This figure shows the logo "INCENT" engraved on and below the surface. However, only the surface engraving is visible under SEM, indicating that the laser beam does not affect the surface when focused below it. In contrast, FIG. 4B shows an optical image where surface and subsurface markings were visible and identifiable. During the experiment, it was observed that lowering the scanning speed below Imm / s can damage the surface, as the laser interacts with the material for a longer time. Therefore, higher scanning speeds was preferred to achieve subsurface inscription with minimal surface impact.

[0044] FIG. 4D shows the Raman spectrum used to study the structural modifications in the diamond caused by a laser fluence of 2.55 J / cm2and a scan speed of 1 mm / s. The corresponding optical image is presented in FIG. 4C. This indicated that the diamond structure remains unaltered up to a depth of 100 pm, as evidenced by the absence of any significant spectral changes in the Raman spectrum. However, at a depth of 200 pm, a weak peak was observed at approximately 1595 cm '. corresponding to the G-band characteristic of graphitic structures. This suggested potential laser-induced graphitization at this depth while the diamond peak remains, indicating a coexistence of diamond and sp2bonded carbon. Furthermore, alphanumeric codes were inscribed beneath the diamond seed at a depth of 100 pm. The analysis of these inscribed regions revealed similar findings, suggesting that the diamond structure remains largely unaffected by the laser inscription process up to a depth of 100 pm. From the above investigation it was concluded that for inscribing logos and alphanumeric at subsurface of diamond seeds at any depth an optimum laser fluence should be 2.55+0.5 ] / cml with scanning speed Imm / s. The effective number of pulses was 10.Example- 3: Engraving QR Code.

[0045] To further investigate the limitations of laser inscription within diamond seeds, a QR code measuring 0.5 mm x 0.5 mm was inscribed at a depth exceeding 200 pm. Due to the intricate structure of the QR code within a small area, precise positioning and Spatial Light Modulator (Thor Labs Exulus-HD2 SLM) lens were required to eliminate spherical aberration and ensure accurate inscription of each individual array. To minimize potential damage or distortion to the QR code structure, the scanning speedwas increased from 0.5 mm / s to 5 mm / s, keeping all other parameters same. This adjustment aimed to reduce the interaction time between the laser pulses and the diamond seed. FIG. 5A presents an optical image of the inscribed QR code with a laser fluence of 5.10 J / cm2and a scan speed of 2.5 mm / s. The corresponding Raman spectrum, depicted in FIG. 5B, exhibits similar results to those observed previously. These findings suggest that the diamond structure remains largely intact even after inscribing a complex code beneath the surface at this depth. Using a suitable optical reading device, the inscribed QR code was successfully read from its subsurface location within the diamond seed. The retrieved code gave access to the complete production process data for the lab- grown diamond seed. The selection and optimization of laser inscription parameters are crucial and depend on the desired outcome. Therefore, different parametric combinations have been optimized to achieve specific inscription objectives. Therefore, it was concluded that for inscribing QR Codes at subsurface of diamond seeds at any depth an optimum laser fluence should be 5.10±0.5 J / cm2 with scanning speed 2.5 mm / s. The effective number of pulses was found to be 4.

[0046] Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed herein. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the system and method of the present invention disclosed herein without departing from the spirit and scope of the invention as described here and as set forth in the claims attached herewith.

Claims

We claim:

1. A method (100) of adjusting operating parameters of a laser pulse on a lab grown diamond while inducing a subsurface inscription without causing structural damage, the method comprising steps of: providing (101) a laser marking system (200), the laser marking system comprising a marking apparatus (201) having at least a laser unit with a femtosecond pulsed laser (203), a beam expander (205), at least one modulator (207) coupled to a pair of optical elements (209), at least one focusing lens (211) and fitted with a visible range camera (219), a motorized element (213) connected to a control unit (215) configured to control at least one operating parameter; providing (103) a lab grown diamond sample (217) on the motorized element (213); generating (105) an optical beam by the laser unit (203) after adjusting a first set of operating parameters; adjusting (107) output beam from the laser unit (203) in the beam expander (205), thereby expanding size of output beam while concurrently decreasing divergence; attenuating (109) optical output from the beam expander (205) in the modulator (207) coupled to optical elements (209), thereby regulating a second set of operating parameters; defining (111) the scanning area of the sample (217) by a visible range camera (219) within the visible spectrum; guiding (113) optical output from the modulator (207) coupled to optical elements (209) towards the sample (217) at the focal point through at least one focusing lens (211); and moving (115) the sample position in X, Y or Z directions with reference to the focal point along a pre-programmed trajectory, thereby producing the subsurface inscription.

2. The method as claimed in claim 1, wherein the femtosecond pulsed laser is a titanium- sapphire crystal.

3. The method as claimed in claim 1, wherein adjusting the first set of operating parameters comprises regulating a laser wavelength or a pulse width or a laser power or a repetition rate or a laser fluence.

4. The method as claimed in claim 3, wherein generating (105) an optical beam comprises generating laser wavelength in the range 650 nm to 1100 nm, the pulse width of 100 fs or more, the laser power of 10 - 50mW, the repetition rate is 10 kHz or higher frequency, or the laser fluence is 2.55+0.5 J / cm2.

5. The method as claimed in claim 1, wherein regulating the second set of operating parameters include adjusting output beam size or a scanning speed in the range 0.5 - 3.0 mm / s.

6. The method as claimed in claim 1, wherein the method is configured to inscribe the sample with a thickness of at least 300 pm.

7. The method as claimed in claim 1, wherein the method is configured to produce laser marking at a depth of at least 200 pm below the surface of the sample.

8. The method as claimed in claim 1, wherein the method is configured to inscribe single character size in the range of 30- 60 pm.

9. The method as claimed in claim 1, wherein the focusing lens has a focal length of at least 10 mm and a numerical aperture of 0.25.

10. The method as claimed in claim 1, wherein the output beam size is 15 pm or less.

11. The method as claimed in claim 1, wherein the method is configured to inscribe a two-dimensional logo, a three dimensional logo, an alphanumeric code, or a quick response barcode on a subsurface plane of the sample.

12. The method as claimed in claim 1, wherein providing the laser marking system comprises executing program instructions provided via a keyboard, a graphic input device, or wired or wireless communication configured to adjust focus and to move the three- axis stage along the pre-programmed trajectory to produce the inscription.

Images