Measuring the power of a laser is a challenge. We can converge the laser energy onto the sensor and measure the resulting temperature rise, or use the power of a known partial beam to measure the laser being measured. For the first option, the laser must be switched (transferred) from the normal propagation path, so it cannot be used in production. Of these two options, if faced with extremely high power lasers for applications such as metal cutting and soldering, it is easy to burn the sensor because of "handicap". According to James Consulting, researchers at the National Institute of Standards and Technology (NIST) are clearly aware of these challenges and have recently designed a system to measure laser power in the high kilowatt range (up to 500 kW). They use a mirror to intercept and reflect 99.9% of the beam so that the beam can continue to perform its original function. This device is roughly the size of a shoebox and accurately counteracts the error to measure the force of the impact photon (radiation pressure, a 100 kW beam, approximately 330 mg). But this method is not compatible with laser beams of much lower magnitude, so NIST researchers have designed a completely different sensing solution. Instead of measuring the tiny laser forces that impinge on the mirror, they designed a conceptually simple "smart mirror" scheme (Figure 1). The new design is both compact and suitable for embedding in the light path, so it does not interfere with the use of the laser, which is a big advantage in practical applications. Figure 1. In this smart mirror prototype, the laser is reflected from the highly reflective surface of the Bragg mirror silicon in the middle of the black plastic ring. At the heart of this sensor is a MEMS-based capacitor assembly consisting of two identical plates, each with a width of approximately 20 mm and an interval of 42.5 um (Figure 2). The upper silicon plate sensing element is attached to the peripheral silicon ring by three narrow spiral supports (width 265 um, thickness 380 um, length 45 mm), which is fabricated as a distributed Bragg mirror, one A high reflectivity mirror made of alternating layers of silicon and silicon dioxide. Unlike conventional mirrors, by tuning the spacing and distribution of alternating layers, it is able to achieve maximum reflectance at the desired wavelength. Figure 2 shows a schematic of the MEMS sensing mirror system (a) and the sensor prototype photo produced (b) The coupled upper and lower silicon plates can suppress common mode mechanical noise, such as vibration or tilt, because they can do the same (or very close) motion. Researcher John Lehman commented: "If the device is physically moved or vibrated, both plates move together, so the net force on the silicon plate is primarily radiation pressure without any environmental impact." The laser that is projected onto the upper silicon plate creates a force that moves closer to the lower silicon plate and changes the capacitance of the entire assembly; the spacing between the two silicon plates is directly related to the photon pressure. To measure changes in capacitance, the prototype device uses open-loop signal processing to measure weight (Figure 3). Figure 3 is a simplified block diagram showing the optical force applied to variable capacitor C1. The optical bridge-related AC bridge signal is measured by a lock-in amplifier and a servo controller can be added for closed-loop control of the C1 electrode spacing. The open loop arrangement is highly non-linear. Careful characterization is required to determine the initial zero quiescent state to properly measure the sensor's response to laser power. To enhance performance, they plan to use a closed-loop zero-indicator method, which is common in high-performance measurements, using a servo controller to electrostatically deflect the sensing silicon plate to a preset bias point. Then, as the spacing between the two silicon plates is reduced, the servo controller adjusts the biasing force to return the MEMS spring and silicon plate to their original zero position. Although the closed-loop architecture requires additional circuitry, it provides better performance and eliminates some sources of error, such as sensor spring constants. Their proof-of-concept device operates with an open-loop using a 250 W laser. The response time is less than 20 ms and the noise floor is 2.5 W/√Hz. The researchers made it clear that the study is still in its early stages. In addition to circuit noise, many second and third order error factors need to be considered and calibrated to improve sensitivity and stability (including air dielectric constant). Through further research, they hope to create a sensing system that can be used for power from 1 W to 1 kW. The power measurement subsystem can even be packaged in the laser system and optical path for continuous real-time readout, resulting in significant real-world benefits. Brake Pad For Kia,Brake Pads For Kia,Ceramic Brake Pad For Kia,Auto Spare Parts For Kia Hengshui Zhongcheng Friction Material Co.,Ltd. , https://www.hszcbrake.com