BR-102024017550-A2 - Sensor for direct measurement of laser pulse duration for pigment removal.

Abstract

Sensor for measuring the duration of laser pulses for pigment removal covering wavelengths in the range of 1064 nm (from Nd:YAG lasers) or in the range of 694 – 755 nm (corresponding to ruby and alexandrite lasers), in the nanosecond range or in the range of hundreds of picoseconds (in Q-switched mode) through direct firing in the sampling area of the device, with filtering of the optical signal, allowing the reading of the pulse temporal profile (single pulse mode) or the pulse train (multiple pulse mode) on a high-bandwidth (≥ 250 MHz) and high-sampling-rate (≥ 2 Gs/s) oscilloscope. The present invention allows the analysis of the temporal profile of high-energy pulses, both unitary and in the form of pulse trains, which would damage most photodiodes in photoconductive or photovoltaic mode, in tattoo removal equipment, allowing quality control of commercially available devices and verification of failures in the optical system of the equipment.

Inventors

• JERRFY CRISTIAN GANDIN

Assignees

• JERRY CRISTIAN GANDIN

Dates

Publication Date

20260310

Application Date

20240827

Claims (5)

1. 1. “Sensor for direct measurement of laser pulse duration for pigment removal” consisting of a metallic body (1), composed of multiple parts in order to facilitate assembly and/or maintenance, equipped with an entry window (3) for the laser beam whose temporal profile will be analyzed, including a sintered glass diffuser (7) and an optical barrier filter (8), characterized by a unitary device, for direct measurement of high-energy, low-pulse-duration laser beams fired at its sampling window (3), composed of a diffuser (7) and attenuator, optical filter (8), photodiode (9), electrical power supply (battery) (10) and built-in electrical noise filter, allowing analysis of the generated electrical signal on an oscilloscope;
2. 2. “Device” according to claim 1, characterized by a short pulse duration light measurement circuit using PIN type photodiodes (9) reverse biased by an internal battery and located in its own support (11) as per circuitry shown in FIGURE 5;
3. 3. “Device” according to claim 1 or 2 characterized by containing in its own body (1) the sintered glass diffuser (7), which also acts as a beam attenuator, sized for measuring laser pulses typically used in tattoo and micropigmentation removal;
4. 4. “Device” according to claim 1 or 2 characterized by employing an internally incorporated optical barrier filter (8) in order to allow measurements only in the indicated wavelength range, in addition to preserving the photodiode (9) if an attempt is made to measure an intense laser at a wavelength outside the sensitivity range of the component.
5. 5. “Device” according to claim 1 or 2 characterized by having the physical arrangement shown in FIGURE 1, FIGURE 2, FIGURE 3 and, in longitudinal section, in FIGURE 4, allowing it to be fixed, through the eyelets (2), in universal supports, both in the vertical and horizontal positions, and to receive shots directly in its sampling window (3), even at high cadences and energies on the order of a few Joules without being damaged and without allowing dispersion or lateral reflection of the beam, improving safety for the operator of the device.

Description

Field of Invention [001] The present invention relates to a dedicated type sensor for measuring the pulse duration of Q-switched or similar lasers, with a minimum duration of about 100 ps (picoseconds) up to hundreds of μs (microseconds), especially commercial Nd:YAG Q-switched lasers with applications in the area of lasers for removing artificially implanted pigments in the human body, such as in the case of tattoos and micropigmentation (with emission at 1064 nm), in a safe manner for the professional. [002] The sensor, depending on the type of photodiode used in its construction, which have distinct spectral working ranges, can also measure the pulse duration of alexandrite lasers (755 nm), ruby lasers (694 nm) and those generated from the 1064 nm laser using a potassium titanyl phosphate (KTP) crystal, resulting in a 532 nm beam. [003] The sensor consists of a device that allows high-energy pulses (from 200 mJ to 3 J) to be performed directly on the measurement window (3), without the need for attenuators or the use of reflection techniques. The device described here must be connected directly to a wideband (>250 MHz) and high sampling rate (>2 Gs/s) oscilloscope to capture the electrical pulse directly proportional to the duration of the laser pulse, recording it graphically (FIGURE 8) and allowing measurements through the use of cursors. Fundamentals of the invention [004] Although the use of photodiodes is common and fundamental in the state of the art for both energy measurement (within a range up to junction saturation) and time measurement, mainly through configurations that exploit the photoconductive effects of the reverse-biased junction, dedicated devices that allow the direct measurement of the temporal profile of high-energy laser beams, such as those used for tattoo removal, are not found in the literature or on the market. In order to use some sensors available on the world market to measure the duration of any high-energy laser pulses, we need to use attenuators, such as scatterers and/or neutral absorber filters (which attenuate optical intensities in wide ranges of the light spectrum). Or we should perform indirect beam sensing, reflecting it off a distant screen so that some of the reflected and scattered light, with a much lower intensity than the original beam, reaches the photodiode without damaging or saturating it in a way that would impair the visualization of the sampled pulse shape on an oscilloscope. [005] The techniques mentioned above are generally employed in optical laboratories that deal with the measurement of key laser parameters through the association of various optical devices and components, requiring a controlled, isolated environment where everyone present in the room uses personal protective equipment, such as safety glasses certified for the laser's operating wavelength and with a high attenuation factor (OD > 4). Techniques such as reflection to attenuate the intensity of incident light in commercial pulse duration measurement sensors are especially critical for use in environments not prepared or certified for laser metrology, since they expose the environment and people who may be present or suddenly enter the room to potentially damaging light, especially to the retina, from the high-power laser. [006] Therefore, as previously stated, measuring the temporal profile, which includes both the short duration of unit pulses of tattoo removal lasers generated using Q-switched or similar techniques, and identifying pulse trains using generic sensors available on the market, is quite difficult and dangerous to perform, especially when measurements are made in the field. [007] In addition to the limitation described in the previous paragraph, commercial sensors are designed for measurements across the entire sensitivity range of the photodiode, which often has the semiconductor wafer directly exposed in the sampling window. This makes the sensor nonspecific and subject to interference from beams originating from nonlinear optical phenomena and, consequently, with wavelengths different from the fundamental wavelength. For this reason, the sensor that is the subject of this patent application employs an integrated optical bandpass filter, aiming to allow the incidence of light with only wavelengths of interest for measuring the temporal profile on the photodiode. [008] Without the need for diffusers, attenuators, barriers, filters or even a prepared environment for measurements, the object of the invention allows the direct measurement of the temporal profile of laser pulses as intense as those with a few Joules of energy, keeping the output window of the commercial tattoo removal laser directed directly to the sampling window (3) of the sensor, avoiding reflections and potentially dangerous light escape. This procedure allows measurements to be carried out in the field quickly, practically and safely. [009] Furthermore, measuring the temporal profile of laser beams us