Laser system for detecting a corneal ablation threshold using spectral analysis of the laser-induced plasma and detection methods

Abstract

A laser system for detecting a corneal ablation threshold potential by means of spectral analysis, comprising a sample module (4), a femtosecond laser transmitter module (1), and a laser focusing module (2), characterized in that the laser system further comprises a spectral analysis module (3), wherein the sample module (4) serves to receive a corneal sample, the femtosecond laser transmitter module (1) serves to transmit a laser beam, the laser focusing module (2) serves to focus the laser beam onto the sample module (4), and the spectral analysis module (3) serves to perform spectral analysis of a laser-induced plasma light signal and to detect a corneal ablation threshold potential, and wherein the femtosecond laser transmitter module (1) transmits a laser beam which, after focusing by the laser focusing module (2), appears on the corneal sample of the sample module (4), wherein the corneal sample, after laser induction, laser-induced plasma light signal emitted,which is sent via the laser focusing module (2) to the spectral analysis module (3) so that the spectral analysis module (3) performs a spectral analysis of the laser-induced plasma light signal and a detection of the corneal ablation threshold potential, wherein the spectral analysis module (3) is configured to determine, by analyzing the spectral information of the laser focusing points, whether the laser is focused on the cornea or other substances, taking into account that the spectrum produced by corneal tissue is different from the spectrum produced by other substances in contact with the cornea.

Description

TECHNICAL AREA The present invention relates to the technical field of laser eye surgery technology, in particular a femtosecond laser system for detecting an ablation threshold by means of spectral analysis and a detection method for a corneal ablation threshold. STATE OF THE ART Over the past 10 years, the field of femtosecond laser eye surgery has developed rapidly due to its improved ablation accuracy and minimal side effects. Femtosecond laser eye surgery offers the best clinical prospects, and femtosecond laser corneal transplantation and femtosecond laser corneal keratomileusis are already being used in practice. To achieve optimal surgical results, the femtosecond laser pulse energy used in surgery should be as close as possible to the corneal laser ablation threshold and only slightly higher. Therefore, accurate real-time measurement of the femtosecond laser corneal ablation threshold is a crucial requirement for surgical applications. Measuring the corneal laser ablation threshold using a scattered light signal can be achieved in the laboratory. However, the scattered light is typically positioned orthogonally to the incident laser beam, and its lower intensity means it must be observed and measured against a dark background. This makes scattered light measurement difficult to apply in actual surgical procedures. A more common method for detecting a femtosecond laser corneal ablation threshold involves measuring it using a laser-induced plasma light signal. The principle is to monitor the laser-induced plasma light signal in the direction perpendicular to the ablation laser using a photomultiplier tube. During the gradual increase in the incident ablation laser energy, the presence of a laser-induced plasma light signal is simultaneously monitored.When a laser-induced plasma light signal occurs, the corresponding incident ablation laser energy is the laser energy at the threshold value. In this method, the detection light signal is in the parallel direction of an ablation light; therefore, the method can be used in actual surgery, but there is a problem regarding the accuracy of the measurement.Since in actual surgery the ablation threshold of an optical element that is in close contact with the cornea is very close to the ablation threshold of the cornea, and the human cornea is only half a millimeter thick, it is likely that, due to the occurrence of a deviation in the exact focusing, the ablation threshold of the optical element can be considered as the ablation threshold of the cornea; that is, the threshold measured by focusing the laser on the optical element that is in close contact with the cornea is erroneously regarded as the ablation threshold of the cornea. DE 103 23 422 A1 describes a device for measuring an optical breakthrough triggered in tissue below a tissue surface by a treatment laser radiation that focuses a laser surgical device in a treatment focus located in the tissue, wherein the device has a detection beam path with optics in which the optics couple radiation emanating from the tissue below the tissue surface into the detection beam path, and a detector device is arranged downstream of the detection beam path which generates a detection signal that indicates the spatial extent and / or location of the optical breakthrough in the tissue. US Patent 2007 / 0078447 A1 describes a method and device for photoablation. Photoablation occurs at the interface between a material with a higher ablation energy limit and a material with a lower ablation energy limit. The method and device utilize a laser beam with a beam energy density of less than the higher ablation energy limit and greater than or equal to the lower ablation energy limit. When the laser beam is directed at the interface, the material with the lower ablation energy limit is removed, while the material with the higher ablation energy limit remains largely intact. US Patent 2013 / 0274725 A1 describes a device for processing material from a component. This device includes a pulsed processing laser, a focusing lens, a beam deflection unit, a control unit, and a confocal detection unit. The laser radiation intensity is variable. An imaging unit is also present, which detects structures on the component using electromagnetic radiation. The electromagnetic radiation from the imaging unit is directed onto the component via the beam deflection unit through the focusing lens. An evaluation unit compares the position of the laser beam focus detected by the imaging unit with the position of the laser beam focus determined by the detection unit. Hui Sun et al. “Femtosecond Laser Corneal Ablation Threshold: Dependence on Tissue Depth and Laser Pulse Width”; Lasers in Surgery and Medicine 39:654-658 (2007) describe the investigation of ablation thresholds in corneal samples from pigs using three diode-pumped solid-state ultrashort pulse lasers for a systematic investigation of the interactions between ultrashort pulse lasers and tissue. CONTENT OF THE PRESENT INVENTION The aim of the present invention is to overcome the technical shortcomings of the existing femtosecond laser system, namely that the corneal ablation threshold cannot be accurately measured in real time, to improve the measurement accuracy and to provide a femtosecond laser system for detecting an ablation threshold by means of spectral analysis. To achieve the aforementioned objective, the present invention employs the following technical solution: On the one hand, the present invention provides a femtosecond laser system for detecting an ablation threshold by means of spectral analysis, comprising a sample module, a femtosecond laser transmitter module, and a laser focusing module, wherein the present invention further comprises a spectral analysis module; and wherein the sample module serves to receive a corneal sample; and wherein the femtosecond laser transmitter module serves to transmit a laser beam; and wherein the laser focusing module serves to focus the laser beam onto the sample module; and wherein the spectral analysis module serves to perform spectral analysis of a laser-induced plasma light signal and to detect a corneal ablation threshold;and wherein the femtosecond laser transmitter module sends a laser beam which, after focusing by the laser focusing module, appears on the corneal sample of the sample module, wherein the corneal sample, after laser induction, emits a laser-induced plasma light signal which is sent via the laser focusing module to the spectral analysis module so that the spectral analysis module performs a spectral analysis of the laser-induced plasma light signal and a detection of the corneal ablation threshold, wherein the spectral analysis module (3) is configured to determine, by analyzing the spectral information of the laser focusing points, whether the laser is focused on the cornea or other substances, taking into account that the spectrum produced by corneal tissue is different from the spectrum produced by other substances in contact with the cornea. In some embodiments, the spectral analysis module comprises a laser-induced plasma light signal receiver and an analysis unit, wherein the laser-induced plasma light signal receiver receives a laser-induced plasma light signal generated by excitation of the corneal sample and transmits it to the analysis unit, and wherein the analysis unit performs a spectral analysis of the laser-induced plasma light signal. In some embodiments, the receiving unit for laser-induced plasma light signals is a near-infrared filter for filtering the laser beam. In some embodiments, the laser focusing module comprises an incident laser light intensity adjustment device, a beam expander and a dichroic mirror arranged sequentially along the laser incident light path, and a converging lens arranged between the dichroic mirror and the sample module; wherein, after light intensity adjustment by the incident laser light intensity adjustment device, the laser beam is expanded via the beam expander and, after expansion, strikes the dichroic mirror, from which the expanded laser is reflected onto the converging lens, which focuses the laser beam onto the sample module. In some embodiments, the incident laser light intensity adjustment device is composed of a half-wave plate and a polarizer. In some embodiments, the converging lens has a numerical aperture of 0.12 and a magnification factor of five. In some embodiments, the femtosecond laser transmitter module (1) comprises a scanning unit (105), a femtosecond laser oscillator, a stretcher, a regeneration amplifier and a compressor, wherein for a laser beam generated by the femtosecond laser oscillator a pulse width is extended via the stretcher, then an amplification of the single pulse energy is performed via the regeneration amplifier, a compression of the pulse width is performed via the compressor and emission is performed via the scanning unit. In some embodiments, the scanning unit is a two-dimensional XY scanning mirror. Accordingly, the present invention further provides a method for detecting a corneal ablation threshold by means of spectral analysis, comprising the following steps: S0: Initiation; S1: Sending a laser beam through a femtosecond laser transmitter module; S2: Processing the laser beam through a laser focusing module, such that the laser beam is focused onto a corneal sample of a sample module and the corneal sample generates a laser-induced plasma light signal by excitation; S3: Receiving and sending the laser-induced plasma light signal through the focusing module to the spectral analysis module; S4: Spectral analysis of the laser-induced plasma light signal and detection of a corneal ablation threshold by the spectral analysis module. In some embodiments, step S2 comprises the following steps: S20: Initiation; S21: Adjusting the light intensity of the laser beam by means of an incident laser light intensity adjustment device; S22: Expanding the laser beam by means of a beam expander; S23: Reflecting the expanded laser beam through a dichroic mirror onto a converging lens; S24: Focusing the laser beam through the converging lens onto the corneal sample of the sample module. The present invention has the following advantages: by means of a spectral analysis of the laser-induced plasma light signal, the present invention determines a corneal ablation threshold, thus realizing the advantage of accurately determining the laser ablation threshold of the cornea in real time during surgery. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 shows a block diagram of a femtosecond laser system for detecting a corneal laser ablation threshold by means of signal analysis according to the present invention. Fig. 2 shows a detailed embodiment of a femtosecond laser system for detecting a corneal laser ablation threshold by means of signal analysis according to the present invention. Fig. 3 shows a detailed embodiment of the femtosecond laser transmitter module in the femtosecond laser system for detecting a corneal laser ablation threshold by means of signal analysis according to the present invention. Fig. 4 shows a flowchart of a method for detecting a corneal laser ablation threshold by means of spectral analysis according to the present invention. Fig. 5 shows a process flowchart of the laser focusing in the method for detecting a corneal laser ablation threshold by means of spectral analysis according to the present invention. Reference symbol list 1 Femtosecond laser transmitter module 2 Laser focusing module 3 Spectral analysis module 4 Sample module 101 Femtosecond laser oscillator 102 Extender 103 Regeneration amplifier 104 Compressor 105 Scanning unit 201 Incident laser light intensity adjustment device 202 Beam expander 203 Dichroic mirror 204 Converging lens 301 Receiver unit for laser-induced plasma light signals 302 Analysis unit DETAILED DESCRIPTION In conjunction with figures and detailed embodiments, the present invention will be explained in more detail below to clarify its objective, technical solutions, and advantages. It is understood that the detailed embodiments described here serve only to illustrate the present invention and do not constitute a limitation of the invention. The key technical aspects of the present invention lie in precisely determining, by analyzing the spectral information of the laser focusing points, whether the laser is focused on the cornea or other materials, based on the fact that the spectrum generated by corneal tissue and that generated by other substances in contact with the cornea are completely different. This allows for the determination of a femtosecond laser corneal ablation threshold. The present invention achieves this by means of a femtosecond laser equipped with an additional plasma spectral analysis unit, enabling the precise determination of a femtosecond laser corneal ablation threshold in real time. See Fig. 1. Fig. 1 shows a block diagram of a femtosecond laser system for detecting a corneal laser ablation threshold by means of signal analysis according to the present invention. The present invention comprises the following modules: a femtosecond laser transmitter module 1, a laser focusing module 2, a spectral analysis module 3, and a sample module 4. The femtosecond laser transmitter module 1 emits a laser beam, which is focused by the laser focusing module 2 onto the sample module 4 such that the corneal sample on the sample module 4 emits a laser-induced plasma light signal under laser induction. This signal is transmitted via the laser focusing module 2 to the spectral analysis module 3, enabling the spectral analysis module 3 to perform a spectral analysis of the laser-induced plasma light signal and to detect the corneal ablation threshold.When the corneal ablation threshold is detected, the femtosecond laser transmitter module 1 sends a laser to ablate the corneal samples. Preferably, the femtosecond laser system for detecting a corneal laser ablation threshold by means of signal analysis according to the present invention further comprises a notification module which is connected to the spectral analysis module 3 to output a notification when the corneal ablation threshold is reached. See Fig. 2. Fig. 2 shows a detailed embodiment of a femtosecond laser system for detecting a corneal laser ablation threshold by means of signal analysis according to the present invention. The present invention comprises a laser transmitter module 1, a laser focusing module 2, a spectral analysis module 3, and a sample module 4. The laser focusing module 2 comprises an incident laser light intensity adjustment device 201, a beam expander 202, and a dichroic mirror 203, arranged sequentially along the laser incident light path, and a converging lens 204 located between the dichroic mirror 203 and the sample module 4. After light intensity adjustment by the incident laser light intensity adjustment device 201, the laser beam is expanded via the beam expander 202 and, after expansion, emerges onto the dichroic mirror 203, from which the expanded laser is reflected onto the converging lens 204, which focuses the laser onto the sample module 4. Preferably, the incident laser light intensity adjustment device 201 is composed of a half-wave plate and a polarizer. Preferably, the converging lens 204 has a numerical aperture of 0.12 and a magnification factor of five. The spectral analysis module 3 comprises a laser-induced plasma light signal receiver 301 and an analysis unit 302. The laser-induced plasma light signal receiver 301 receives a laser-induced plasma light signal generated by exciting the corneal sample and transmits it to the analysis unit 302, the analysis unit 302 performing a spectral analysis of the laser-induced plasma light signal and detecting a corneal ablation threshold. Preferably, the receiving unit for laser-induced plasma light signals 301 is a near-infrared filter for filtering the laser beam. The detailed operating process of the present embodiment is as follows: a laser emitted by the femtosecond laser transmitter module 1 is expanded via the beam expander 202 after a light intensity adjustment by the incident laser light intensity adjustment device 201 and after expansion appears on the dichroic mirror 203, from which the expanded laser is reflected onto the converging lens 204, which focuses the laser onto the corneal samples of the sample module 4. Under the influence of an excitation, the corneal samples of the sample module 4 generate a laser-induced plasma light signal, which is transmitted via the converging lens 204 and the dichroic mirror 203 to a near-infrared wave filter of the spectral analysis module 3, wherein the near-infrared wave filter filters the laser refracted by the dichroic mirror 203, and wherein only the laser-induced plasma light signal is allowed to pass through the infrared wave filter and be sent to the analysis unit 302, which performs a spectral analysis of the laser-induced plasma light signal, analyzes whether the laser is focused on the cornea, and detects a corneal ablation threshold. See Fig. 3, in a detailed embodiment of a femtosecond laser transmitter module 1 in the femtosecond laser system for detecting a corneal laser ablation threshold by means of signal analysis according to the present invention, the femtosecond laser transmitter module 1 comprises a scanning unit 105, a femtosecond laser oscillator 101, a stretcher 102, a regeneration amplifier 103 and a compressor 104, wherein for a laser beam generated by the femtosecond laser oscillator 101 a pulse width is extended via the stretcher, then an amplification of the single pulse energy is carried out via the regeneration amplifier 103, a compression of the pulse width is carried out via the compressor 104 and emission is carried out via the scanning unit 105. Preferably, the scanning unit 105 is a two-dimensional XY scanning device. Preferably, the laser transmitter in the present invention can be a fully fixed femtosecond laser with chirped-pulse amplification. The femtosecond seed source is a commercial product from the Austrian company HIGHQ. The pulse width of the femtosecond laser is 180 fs, the repetition rate is 90 MHz, and the average power is 90 mW. To save space, a holographic transmission volume grating is used as both a stretcher and a compressor. The stretcher extends a seed source light beam from 180 femtoseconds to 20 picoseconds and directs it through a magneto-optical isolator into the regeneration amplifier. The laser beam moves back and forth in the regeneration amplifier approximately 100 times, with the individual pulse energy gradually increasing to its maximum value and then being emitted from the regeneration amplifier through the magneto-optical isolator.The laser beam emitted from the regeneration amplifier, which undergoes energy amplification, has its pulse width compressed from 20 picoseconds back to 500 femtoseconds via the compressor. The laser beam operates in a basic transverse mode, with a mass factor greater than 1.5. A scanning and focusing system converges the laser beam within the corneal samples, achieving a focus diameter of 5 micrometers. This allows for rapid scanning in the X and Y directions and precise adjustment of the focusing depth in the Z direction. See Fig. 4. Fig. 4 shows a flowchart of a method for detecting a corneal laser ablation threshold by means of spectral analysis according to the present invention. The method is implemented by the laser system for detecting an ablation threshold by means of spectral analysis of the present invention. The method is implemented in detail by the following steps: Performing step S1: Sending a laser beam through a femtosecond laser transmitter module. A laser oscillator of the femtosecond laser transmitter module generates a laser beam, whereby the pulse width is stretched by the stretcher, then the single-pulse energy is amplified by the regeneration amplifier, the pulse width is compressed by the compressor, and the beam is emitted by the scanning unit. Performing step S2: Processing the laser beam through a laser focusing module so that the laser beam is focused onto a corneal sample from a sample module, causing the corneal sample to generate a laser-induced plasma light signal upon excitation. This is implemented in detail by the following steps in the flowchart according to Fig. 5: Adjusting the light intensity of the laser beam by an incident laser light intensity adjustment device (step S21); expanding the laser beam by a beam expander (step S22); reflecting the expanded laser beam through a dichroic mirror onto a converging lens (step S23); focusing the laser beam through the converging lens onto the corneal sample of the sample module (step S24), causing the cornea to generate a laser-induced plasma light signal upon excitation. Performing step S3: Receiving and sending the laser-induced plasma light signal through the focusing module to the spectral analysis module. Performing step S4: Spectral analysis of the laser-induced plasma light signal and detection of a corneal ablation threshold by the spectral analysis module. Using the single-pulse femtosecond laser realized by the system and method of the present invention, corneal tissue is etched, and the resulting spectrum is observed using a laser-induced plasma. Only the corneal tissue contains such elements; the spectrum of the laser-induced plasma light signal generated by other substances (such as the lubricating fluids used in surgery or the optical components in close contact with the cornea during surgery) does not contain such elements. The foregoing embodiments of the present invention do not limit the scope of protection of the present invention. All further corresponding modifications and variants based on the technical concept of the present invention shall be considered to be covered by the scope of protection of the claims of the present invention.

Claims

A laser system for detecting a corneal ablation threshold potential by means of spectral analysis, comprising a sample module (4), a femtosecond laser transmitter module (1), and a laser focusing module (2), characterized in that the laser system further comprises a spectral analysis module (3), wherein the sample module (4) serves to receive a corneal sample, the femtosecond laser transmitter module (1) serves to transmit a laser beam, the laser focusing module (2) serves to focus the laser beam onto the sample module (4), and the spectral analysis module (3) serves to perform spectral analysis of a laser-induced plasma light signal and to detect a corneal ablation threshold potential, and wherein the femtosecond laser transmitter module (1) transmits a laser beam which, after focusing by the laser focusing module (2), appears on the corneal sample of the sample module (4), wherein the corneal sample, after laser induction, laser-induced plasma light signal emitted,which is sent via the laser focusing module (2) to the spectral analysis module (3) so that the spectral analysis module (3) performs a spectral analysis of the laser-induced plasma light signal and a detection of the corneal ablation threshold potential, wherein the spectral analysis module (3) is configured to determine, by analyzing the spectral information of the laser focusing points, whether the laser is focused on the cornea or other substances, taking into account that the spectrum produced by corneal tissue is different from the spectrum produced by other substances in contact with the cornea. Laser system for detecting a corneal ablation threshold potential by means of spectral analysis according to claim 1, characterized in that the spectral analysis module (3) comprises a receiving unit for laser-induced plasma light signals (301) and an analysis unit (302), wherein the receiving unit for laser-induced plasma light signals (301) receives a laser-induced plasma light signal generated by excitation of the corneal sample and sends it to the analysis unit (302), and wherein the analysis unit (302) performs a spectral analysis of the laser-induced plasma light signal. Laser system for detecting a corneal ablation threshold potential by means of spectral analysis according to claim 2, characterized in that the receiving unit for laser-induced plasma light signals (301) is a near-infrared filter for filtering the laser beam. Laser system for detecting a corneal ablation threshold potential by means of spectral analysis according to claim 1, characterized in that the laser focusing module (2) comprises an incident laser light intensity adjustment device (201), a beam expander (202) and a dichroic mirror (203) arranged sequentially along the laser incident light path, and a converging lens (204) arranged between the dichroic mirror (203) and the sample module (4), wherein the laser beam, after a light intensity adjustment by the incident laser light intensity adjustment device (201), is expanded via the beam expander (202) and, after expansion, strikes the dichroic mirror (203), from which the expanded laser is reflected onto the converging lens (204), which focuses the laser beam onto the sample module (4). Laser system for detecting a corneal ablation threshold potential by means of spectral analysis according to claim 1, characterized in that the incident laser light intensity adjustment device (201) is composed of a half-wave plate and a polarizer. Laser system for detecting a corneal ablation threshold potential by means of spectral analysis according to claim 1, characterized in that the converging lens (204) has a numerical aperture of 0.12 and a magnification factor of five. Laser system for detecting a corneal ablation threshold potential by means of spectral analysis according to claim 1, characterized in that the femtosecond laser transmitter module (1) comprises a scanning unit (105), a femtosecond laser oscillator (101), a stretcher (102), a regeneration amplifier (103) and a compressor (104), wherein for a laser beam generated by the femtosecond laser oscillator (101) a pulse width is extended via the stretcher (102), then an amplification of the single pulse energy is carried out via the regeneration amplifier (103), a compression of the pulse width is carried out via the compressor (104) and an emission is carried out via the scanning unit (105). Laser system for detecting a corneal ablation threshold potential by means of spectral analysis according to claim 7, characterized in that the scanning unit (105) is a two-dimensional XY scanning mirror.

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