BR-202024017551-U2 - Photoacoustic sensor arrangement for measuring the energy of short laser pulses used for tattoo removal.

Abstract

This device comprises a sensor employing a piezoelectric crystal, in the form of a commercial loudspeaker, coupled to a broad-spectral-band light-absorbing surface made of vulcanized rubber, allowing the generation of an electrical pulse with an amplitude directly proportional to the energy dissipated by the laser in the short interval of its emission in Q-switched mode. The present invention enables the manufacture of efficient and low-cost sensors capable of integrating the energy generated by pulse trains originating from passively switched cavities, frequently used in lasers for the removal of pigments implanted in the human body. Connected to a dedicated interpreter or oscilloscope, this sensor allows for quick, efficient, and accessible measurement for operators of pigment removal lasers, ensuring greater safety and performance for patients.

Inventors

• JERRY CRISTIAN GANDIN

Assignees

• JERRY CRISTIAN GANDIN

Dates

Publication Date

20260310

Application Date

20240827

Claims (2)

1. 1. PHOTOACOUSTIC SENSOR ARRANGEMENT FOR MEASURING THE ENERGY OF SHORT LASER PULSES USED FOR TATTOO REMOVAL, characterized by being a portable, small-sized device with a cylindrical metal body (1) housing a 50 mm diameter piezoelectric speaker with the face composed of the brass disc (5) covered by a black vulcanized rubber disc (4) used as an absorbent barrier for laser beams directed at the sampling window (A) and with electrical signal output via a female BNC type connector (3).
2. 2. PHOTOACOUSTIC SENSOR ARRANGEMENT FOR MEASURING THE ENERGY OF SHORT LASER PULSES USED FOR TATTOO REMOVAL, characterized by a photoacoustic signal capture device as per the previous claim, composed of threaded metal parts that make up the housing (1) of the device, facilitating maintenance and replacement of components and use of the sensor in universal laboratory supports.

Description

Field of invention [001] The present utility model consists of a sensor for measuring the energy of short-duration laser pulses (on the order of nanoseconds), typically used for tattoo removal, through the photoacoustic effect of light interacting with a highly absorptive surface for a wide range of wavelengths. The device, therefore, falls within the field of optical and electronic instrumentation for professional applications (sensors and/or measuring instruments), involving knowledge of physics and electrical and electronic engineering. Fundamentals of the invention [002] Since the creation of the first laser light emitting device in 1960 by Theodore Harold Maimann, the need arose to measure the intensity of this light for sizing its applications, especially in the medical field, and determining the efficiency of the generation process. Therefore, since then, several patents have been published for laser light sensors and measurement systems employing a wide variety of techniques. As examples, we have the use of polarized photodiodes in the photoconductive mode for direct light detection as described in US patent 3,687,558 of August 1972, or calorimetric methods that determine the energy of the laser pulse by heating an optically absorptive panel where several directly polarized diodes are thermally coupled, as stated in US patent 4,436,437 of March 1984. [003] One way, however, of measuring the energy of short-duration, high-intensity laser pulses involves exploiting the photoacoustic effect generated from the photodisruption of a small portion of an optically absorbent target coupled to a piezoelectric transducer. The idea of implementing sensing through a piezoelectric transducer is not original, which is why the present invention is being presented as a utility model. The presentation of the sensor and its constructive arrangement for the specific application of measuring the energy of Q-switched Nd:YAG laser pulses for tattoo removal, however, is original, possessing inventive activity and technical application. [004] The principles of laser pulse measurement using a piezoelectric transducer are cited in US Patent 5,048,969, published in September 1991, invented by Dason et al. In short, the measurement occurs when the laser pulse is absorbed by a coating on the sensing target and promotes a thermal expansion that conducts an ultrasonic elastic pulse on the piezoelectric transducer. The transducer output is an electrical voltage pulse (measured in V), whose peak voltage (Vpp) is recorded and has a directly proportional relationship and, according to studies done with prototypes of the present utility model, is linearly correlated to the energy of the pulsed laser beam. [005] Taking advantage of the photoacoustic effect of the laser interaction with the piezoelectric transducer coating simplifies the resolution of some classic problems in sensing short and ultrashort pulses, such as the speed of capturing the resulting electrical signals for integration. This is quite significant when using photodiodes that allow the capture of the laser pulse and its sensing in a way that is faithful to the pulse's temporal profile, that is, it provides electrical signals with the same duration as the optical pulse. When measuring pulses from Nd:YAG Q-switched tattoo removal lasers, we obtain signals with a duration of 6 to 20 ns, whose digital electronic processing requires very high-speed and high-cost circuits or precisely using analog peak & hold circuits, whose assembly and implementation are also critical, since the system behaves like an RF circuit. In the generation of the photoacoustic effect, the inertia of the piezoelectric transducer itself and the elastic (compressible) behavior of the surrounding air promote an "integration" of the pulse, providing an electrical signal directly proportional to the laser energy, but with a duration approximately 20,000 times longer, facilitating detection and recording by less critical and less expensive electrical circuits. [006] Sensors employing thermal methods, such as thermopiles and calorimeters, also allow the acquisition of signals directly proportional to the laser pulse energy and with long duration, which also facilitates the recording of the electrical signal. However, the high thermal inertia of these sensors leads to a longer delay in obtaining the result and makes it impossible to sense unitary pulses at high firing rates (up to 10 Hz). In addition, since the energy density of a tattoo removal laser pulse is very high, damage to the coating of thermal sensors is common, and they do not promote a very efficient transfer of energy in the form of heat for pulses of very short duration (on the order of nanoseconds). [007] Although patents exist related to laser pulse energy measurement devices employing piezoelectric transducers, commercially available, user-friendly models are not readily available. Most of these devices are academic application models, used