Polygon Mirror Research Articles

Design and analysis of polygonal mirror-based scan engines for improved spatial frequency modulation imaging.

Spatial frequency modulation imaging (SPIFI) is a structured illumination single pixel imaging technique that is most often achieved via a rotating modulation disk. This implementation produces line images with exposure times on the order of tens of milliseconds. Here, we present a new architecture for SPIFI using a polygonal scan mirror with the following advances: (1) reducing SPIFI line image exposure times by 2 orders of magnitude, (2) facet-to-facet measurement and correction for polygonal scan design, and (3) a new anamorphic magnification scheme that improves resolution for long working distance optics.

275–305 GHz FM-CW Radar 3D Imaging for Walk-Through Security Body Scanner

Imaging using millimeter waves (MMW) and terahertz (THz) waves can help inspect hazardous materials hidden beneath clothing in a non-contact and non-invasive manner. A 3D terahertz imaging system for security gate applications in the 275–305 GHz range was developed and experimentally demonstrated to detect concealed objects carried by pedestrians. This system performs 3D measurements by combining depth detection using frequency-modulated continuous wave (FM-CW) radar, vertical scanning of the detection spot using a 1D high-speed mechanical beam scanner, and horizontal movement of the irradiated area and detection spot as the pedestrian walks. The high-speed beam scanner comprises an F-Theta telecentric lens and a polygon mirror. It has a vertical line scan rate of 142 lines/s and spatial resolution of ~10 mm, consistent with the design value, and a depth resolution of ~7 mm, which is 40% larger than the theoretical value estimated from the FM-CW radar principle. The depth-dependent lateral distortion in 3D images, known as telecentricity, measured using the body scanner imaging system, was also evaluated. Consequently, images with the same magnification were obtained at a range of more than 500 mm of focus depth. Finally, the detection of concealed objects carried by pedestrians was demonstrated, showing that the system can work for a pedestrian walking at speeds from 4 km/h to 7 km/h.

Analysis of optimal detection range performance of LiDAR systems applying coaxial optics

In this study, the optimal detection range performance of a LiDAR system employing coaxial optics is analyzed. On analyzing laser beam diameter, beam divergence angle, light-receiving area, and receiving light intensity, the optimal detection range was exhibited when the collimator focal length was 6.5 mm, the laser-beam divergence angle was 1.23 mrad, and the hole of the receiving mirror was 1.4 mm. Furthermore, the maximum deviation of the optical scan angles with respect to the mechanical angles of the polygon mirror and the MEMS mirror were analyzed as -0.99° and +4.54° in the x-axis and y-axis directions, respectively.

Output Characterization of 220 nm Broadband 1250 nm Wavelength-Swept Laser for Dynamic Optical Fiber Sensors.

Broadband wavelength-swept lasers (WSLs) are widely used as light sources in biophotonics and optical fiber sensors. Herein, we present a polygonal mirror scanning wavelength filter (PMSWF)-based broadband WSL using two semiconductor optical amplifiers (SOAs) with different center wavelengths as the gain medium. The 10-dB bandwidth of the wavelength scanning range with 3.6 kHz scanning frequency was approximately 223 nm, from 1129 nm to 1352 nm. When the scanning frequency of the WSL was increased, the intensity and bandwidth decreased. The main reason for this is that the laser oscillation time becomes insufficient as the scanning frequency increases. We analyzed the intensity and bandwidth decrease according to the increase in the scanning frequency in the WSL through the concept of saturation limit frequency. In addition, optical alignment is important for realizing broadband WSLs. The optimal condition can be determined by analyzing the beam alignment according to the position of the diffraction grating and the lenses in the PMSWF. This broadband WSL is specially expected to be used as a light source in broadband distributed dynamic FBG fiber-optic sensors.

Fast-sweeping continuous wave quantum cascade laser operating in an external cavity with polygon mirror.

We report a continuous wave room temperature quantum cascade laser operating in an external cavity in the Littrow configuration with a 10-facet polygon mirror rotating at 24,000 RPM. The quantum cascade laser emission is swept across ∼1520 - 1625 cm-1 wavenumber range in less than ∼45 µs with a sweep repetition rate of 4 kHz. The measured maximum output power at the laser gain maximum, 15°C and 0.86 A driving current is ∼90 mW; the estimated average output power across the 45 µs wavenumber sweep is ∼50 mW. Through its sweep, the laser emits on the sequential Fabry-Perot longitudinal modes of the laser chip cavity with the mode separation of ∼0.5 cm-1. The linewidth of the emitting modes is less than ∼0.05 cm-1. Spectral measurements of the infrared absorption features of a 10 µm thick layer of acetophenone and water vapor in the air have demonstrated the capability of obtaining spectral data in less than 45 µs.

Optomechanical Analysis and Design of Polygon Mirror-Based Laser Scanners

Polygon Mirror (PM)-based scanning heads are one of the fastest and most versatile optomechanical laser scanners. The aim of this work is to develop a multi-parameter opto-mechanical analysis of PMs, from which to extract rules-of-thumbs for the design of such systems. The characteristic functions and parameters of PMs scanning heads are deduced and studied, considering their constructive and functional parameters. Optical aspects related to the kinematics of emergent laser beams (and of corresponding laser spots on a scanned plane or objective lens) are investigated. The PM analysis (which implies a larger number of parameters) is confronted with the corresponding, but less complex aspects of Galvanometer Scanners (GSs). The issue of the non-linearity of the scanning functions of both PMs and GSs (and, consequently, of their variable scanning velocities) is approached, as well as characteristic angles, the angular and linear Field-of-View (FOV), and the duty cycle. A device with two supplemental mirrors is proposed and designed to increase the distance between the GS or PM and the scanned plane or lens to linearize the scanning function (and thus to achieve an approximately constant scanning velocity). These optical aspects are completed with Finite Element Analyses (FEA) of fast rotational PMs, to assess their structural integrity issues. The study is concluded with an optomechanical design scheme of PM-based scanning heads, which unites optical and mechanical aspects—to allow for a more comprehensive approach of possible issues of such scanners. Such a scheme can be applied to other types of optomechanical scanners, with mirrors or refractive elements, as well.

Fabrication of Medical Titanium Alloy Microhole Array Substrates Based on High-Speed Polygon Mirror

Fabrication of Medical Titanium Alloy Microhole Array Substrates Based on High-Speed Polygon Mirror

Non-back-reflecting polygon scanner with applications in surface cleaning.

Polygon mirror scanners are attracting considerable interest owing to their rapid speed and large scanning area. Here, we focused on the back-reflection effect of the polygon scanner. A new polygon scanner system was designed based on a geometric analysis. The final equations for the design express the position of the laser beam source having the largest scanning length without the reflected beam traveling back to the fiber. The proposed system performed a raster scan on an area. Additionally, a paint stripping experiment was conducted to demonstrate the potential use of our scanner in commercial laser cleaning applications.

Accelerating laser processes with a smart two-dimensional polygon mirror scanner for ultra-fast beam deflection

Abstract In laser processing, the possible throughput is directly scaling with the available average laser power. To avoid unwanted thermal damage due to high pulse energy or heat accumulation during MHz-repetition rates, energy distribution over the workpiece is required. Polygon mirror scanners enable high deflection speeds and thus, a proper energy distribution within a short processing time. The requirements of laser micro processing with up to 10 kW average laser powers and high scan speeds up to 1000 m/s result in a 30 mm aperture two-dimensional polygon mirror scanner with a patented low-distortion mirror configuration. In combination with a field programmable gate array-based real-time logic, position-true high-accuracy laser switching is enabled for 2D, 2.5D, or 3D laser processing capable to drill holes in multi-pass ablation or engraving. A special developed real-time shifter module within the high-speed logic allows, in combination with external axis, the material processing on the fly and hence, processing of workpieces much larger than the scan field.

High Throughput Laser Drilling with High Power Lasers Using a Two-Dimensional Polygon Mirror Scanner

High Throughput Laser Drilling with High Power Lasers Using a Two-Dimensional Polygon Mirror Scanner

Time–space conversion spectral analysis for the nanosecond fluorescent processes of organic–inorganic compounds

Time-resolved spectral measurements were conducted by using a continuous-wave laser and a CCD-based spectrometer. A spinning polygon mirror swung both the excitation laser beam and fluorescent rays, in the process of which a temporal change in the fluorescent spectrum was converted to a spatial distribution. The temporal resolution could be adjusted in the nano- and micro-second ranges by changing the rotation rate of the mirror. In comparison with the conventional pulsed-laser spectrometry, a higher sensitivity is attainable due to the slow features of the devices, i.e., continuous excitation by the laser and a long exposure time (1 s) of the CCD. The usefulness and reliability of the constructed system were demonstrated by spectral measurements of an organic–inorganic hybrid phosphor, which exhibited both a rapid fluorescent decay of organic ligands and a long-lasting afterglow of metal ions.

High-Speed and Cost-Effective Reflective Terahertz Imaging System Using a Novel 2D Beam Scanner

Nondestructive THz imaging technology is a promising technology in several industrial applications such as process monitoring and quality control. To further popularize the application of this technique in the industry, we developed photonics-based devices such as a dual-mode laser, uni-travelling carrier photodiode, and Schottky-barrier diode that enable the realization of a compact, low-cost, multifunctional continuous wave (CW) THz system. To develop CW THz reflective imaging systems with these devices, a telecentric f-θ lens and novel two-dimensional (2D) beam scanner were developed. A high-speed, low-cost 2D reflector with a 4-sided polygon mirror, a brushless DC (BLDC) motor rotating at approximately 2,990 revolutions per minute (RPM) and a stepping motor was designed to ensure that a THz image sized 500 × 400 pixels could be scanned in approximately 2 s. However, it is difficult to maintain a constant speed in high-speed rotating BLDC motors. The measured maximum deviation is approximately 0.7%, which results in distorted images. To compensate for this distortion, a sync signal reflector was designed to monitor the real-time RPM of the BLDC motor. Using the novel 2D beam scanner and sync signal reflector, the distorted images could be corrected simply, enabling the development of a 2D THz reflective imaging system using a single emitter and detector; this system could exhibit a higher speed and was more cost effective than the existing system. Although further improvements to photonics-based THz technologies are necessary, we believe that these efforts will begin an era of THz technologies as a widely used industrial technique.

Design of a six-degree-of-freedom geometric errors measurement system for a rotary axis of a machine tool

This paper proposes a new kind of non-contact optical measurement system, which combines with a polygon mirror and a conical lens to achieve the purpose of simultaneously measuring six-degree-of-freedom (6 DOF) geometric errors for a rotary axis of a machine tool. At the beginning, we used the Zemax software to construct the proposed optical structure and observe the change of light spots on the detectors. Then, we built the proposed optical structure on the Matlab software by using the skew-ray tracing method, which used to present the actual condition of light spot change and compare with the simulation results. Then, we designed the appropriate fixtures to place the system structure on a rotary axis in a laboratory environment. After completing the laboratory-built prototype, we analyzed the effects of different geometric errors on the detectors at different angular positions of a rotary axis of a machine tool. The proposed measurement system simultaneously measured 6 DOF geometric errors of the rotary axis, and the experimental results were compared with those of two dial gauges by using the measurement method of ISO 230–7. The experimental results show that the maximum deviation ranges of the radial motion error in X axis, the radial motion error in Y axis, the tilt motion error around X, and the tilt motion error around Y are ±4.7 µm, ±6.0 µm, ±3.6 arcsec, and ±8.1 arcsec, respectively.

A compact and portable laser radioactive decontamination system using passive Q-switched fiber laser and polygon scanner

We designed a compact and portable laser radioactive decontamination system using a passive Q-switched fiber laser and a polygon scanner. The passive Q-switched fiber laser produced average power of 15 W at a repetition rate of 60 kHz. The scanner system contained a 12-sided spinning polygon mirror driven by a DC motor. By varying the spinning speed of the polygon mirror, we achieved a processing speed of up to 88,500 mm/s. This system was demonstrated to be very efficient for radioactive decontamination on surfaces of various metals: stainless steel, brass, iron, and aluminum.

Minimization of mixed-color image noise caused by shape error of polygonal mirror in color-laser printing system

A color-laser printing system consisting of a tandem laser scanning unit uses four laser diodes and a single polygonal mirror (PM) to expose light onto four photo-conductive drums. In this study, we developed a method to reduce periodical image noise, which is mainly generated during scanning by shape errors in a PM, during color mixing of a color-laser scanning system. Through fundamental optical and image analyses, the horizontal dot shift induced by shape errors in the PM was expected to generate visible image noise with a period of 2.8 mm. In addition, the dominant cause of the horizontal dot shift was the peak-to-valley error and the pyramidal angle of each mirror. In order to reduce the periodical image noise (moire) in color mixing, a horizontal-synchronization detection-optics layout was proposed, and its effectiveness was verified through image-printing experiments.

A Study on Performance Improvement of Polygon Mirror Scanner Motor

Electric machines for printers require good noise and vibration performance. The polygon mirror scanner motor is an important component of the laser beam printer because it is used to reflect the laser beam of the polygon mirror. Hence, many studies on the improvement of noise and vibration of polygon mirror scanner motor have been carried out. These noise and vibration are classified into electromagnetic, aerodynamic, and structural. Electromagnetic noise and vibration is mainly caused by large cogging torque and non-sinusoidal back EMF. To improve the cogging torque the back EMF of a polygon mirror scanner motor simultaneously, an unequal air-gap model is proposed. To analyze the performance of different models, finite element analysis is applied. To minimize the cogging torque of the proposed model under the limited conditions, the optimal design is performed. As a result of the optimization, the cogging torque and torque ripple were reduced by 47.7% and 23.4%, respectively, while the back EMF and average torque were maintained. The experiment was performed to verify the optimal design results. The experimental results showed that the radial and axial vibration of the optimal model decreased 7.3 times and 3.6 times, respectively, in the 14.2 kHz band.

Structure factors and charge-density study of diamond at 800 K

The structure factors of diamond were determined by synchrotron radiation X-ray powder diffraction at 800 K at sin θ/λ ≤ 2.2 Å−1 reciprocal resolution. The structure factors were estimated using six powder profiles measured on beamline BL02B2 at SPring-8 (Hyogo, Japan). A high reciprocal resolution at sin θ/λ ≤ 2.2 Å−1 was required to reveal the temperature dependence of the charge density, due to the high Debye temperature of θD = 1860 K of diamond. Wide 2θ angle data with the highest counting statistics are crucial for accurate data analysis. The periodic noise of every six-pixel step was observed in the highest counting statistics imaging plate (IP) data scanned by a BAS2500 IP scanner. It was found that the noise originated from the six-sided polygonal mirror in the scanner. The intensity fluctuation at every six-pixel step was also found in the Fourier series expansion of the powder profiles. The ratio of the maximum fluctuation was estimated as 0.4% by summing all six-pixel step data. The powder profiles were corrected by multiplying the ratios. The intensity fluctuation in the background region was reduced to less than 50% of the uncorrected data. The weak 888 Bragg reflection, with an intensity of 0.005% of that of the 111 Bragg reflection at 800 K, was readily observed in the corrected data. Finally, the structure factors determined at 800 K were successfully applied to a charge-density study by multipole modelling. The reliability factors and multipole parameters at 800 K are in agreement with those at 300 K. The differences in the charge density at the bond midpoint and ∇2ρ at the bond-critical point were less than 1% and 2%, respectively.

High-speed time-domain characterization method for polygon scanners

Two major advantages of polygon scanners over galvano scanners are their fast scanning speed and linear scanning motion. However, a polygon scanner has a fundamental problem associated with the irregularity of its structure due to unequal facet-to-facet angles. Conventional methods rely on geometrical measurements of the polygon mirror structure; though accurate, they are time-consuming and do not show other scanning errors in the real beam scanning action. We propose a simple and fast time-domain characterization method that can show the structural defects of a polygon mirror as well as other scanning jitter that exists only when it is in motion. A laser beam's optical power passing through a slit is measured using a fast detector and digitizer. By analyzing repeated pulse patterns in the data, we can estimate facet-to-facet angles and other scanning jitter of a polygon mirror. Our proposed method is experimentally demonstrated by measuring three polygon mirrors with 12 facets.

Passively Q-switched laser based on Nd:YAG/YAG Polygonal Active Mirror with timing jitter improvement

Abstract We demonstrate a passively Q-switched laser based on Polygonal Active Mirror (PAM). Cr:YAG with different initial transmittance were used as saturable absorber (SA). To improve the output timing jitter, an intracavity aperture was used. Without the intracavity aperture, the maximum average output power of 726 mW was obtained with SA initial transmittance of 98%, and the corresponding optical-to-optical efficiency was 23.3%. With 92% initial transmittance SA, the maximum slope efficiency of 49.9% was obtained, and the maximum single pulse energy was 132.8 uJ. By applying the intracavity aperture, the output beam quality and timing jitter were improved. With 98% initial transmittance Cr:YAG SA, the beam quality (M2) was improved from 1.40 × 1.22 to 1.33 × 1.19 after applying the aperture, while timing jitter was improved from 18. 4 μ s (31.68%) to 4. 8 μ s (8.61%).

A systematic comparison and evaluation of three different Swept-Source interferometers for eye lengths biometry

This study reviews the development of Swept-Source interferometers and compares systematically three different Swept-Source interferometer designs for biometric measurements of the eye. Principles characteristics, conveniences and accessibilities of the three developed systems are presented.The main difference between the three Swept-Source systems is the method of tuning the wavelength at the broadband optical amplifier.The implementation of a “quasi-phase-continuous method” (QPC) for wavelength tuning led to longer measuring depth but was more time-consuming. The wavelength tuning using a rotating polygon mirror scanner was faster.The wavelength tuning via Fourier Domain Mode Locking (FDML), where the tuning frequency ft of the filter must be matched to the inverse cavity roundtrip time τ, achieved the widest tuning range combined with a rather better resolution and signal to noise ratio (SNR).The swept sources were compared using a fiber-optic based Michelson interferometer setup. Measurements of a self-made human model eye demonstrate excellent capturing of the biometric data, with all interfaces of eye optical components and their contours being clearly detected.