NMC–NMIJ bilateral comparison of millimeter-wave attenuation in WR-15 waveguide band at 50 GHz and 54 GHz

This paper reports on a bilateral comparison of millimeter-wave attenuation in WR-15 waveguide band between the National Metrology Institute of Japan (NMIJ) and the National Metrology Centre, A1STAR (NMC). Different types of attenuation measurement systems were independently developed at both laboratories. The systems are based on a stabilized single-channel intermediate frequency (IF) substitution method at NMIJ, and a dual-channel audio frequency substitution method at NMC. A comparison was carried out at 50 GHz and 54 GHz using a programmable step attenuator fitted with precision coaxial to waveguide adaptors as a traveling standard. Good agreement of the measurement results between both laboratories was verified in the attenuation range up to 60 dB.     

Uncertainty evaluation of the 20 kN m deadweight torque standard machine

A deadweight-type torque standard machine of 20 kN m rated capacity (20 kN m-DWTSM) has been designed and developed by the National Metrology Institute of Japan (NMIJ) at the National Institute of Advanced Industrial Science and Technology (AIST). Each uncertainty contribution comes mainly from the performance of each mechanical part of the 20 kN m-DWTSM. Authors evaluated the uncertainty of the mass of the linkage weights, local acceleration of gravity, influence of air buoyancy on deadweight loading, initial moment-arm length (including CMM measurement and temperature compensation), and sensitivity of the fulcrum. This report deals especially with evaluation of the remaining contributions, namely the influence of arm flexure and reference line variation at the end of the moment-arm on best measurement capability (BMC). Estimation of BMC in the 20 kN m-DWTSM gave a relative expanded uncertainty of less than 7.0 · 10⁻⁵ (k = 2) for the calibration range from 200 N m to 20 kN m.     

Small-capacity deadweight force standard machine compensating loading frame

The Korea Research Institute of Standards and Science (KRISS) has developed a 20 N deadweight force standard machine. The machine consists of a weight stack, a loading frame, a taring system, a main body and a control system. The taring system has the role of compensating the initial force generated by the loading frame. With two motors, a displacement sensor, several limit switches, and a synthetic control system consisting of a programmable logic controller and an operating PC, the machine can be operated almost fully automatically. The machine can generate a compressive force in the range of 0.5–22 N with a relative expanded uncertainty of 1.0 × 10^–4. The machine was compared with a 200 N deadweight force standard machine. In the comparison, the relative deviation was 5.8 × 10^–5, less than the declared expanded uncertainty of the force standard machines, therefore confirming the machine’s accuracy.     

Bilateral comparisons of measurement capabilities for the calibration of low nominal capacity torque measuring devices between NMIJ and PTB in the range from 0.1 N m to 10 N m using different procedures

Bilateral comparisons of the calibration of low nominal capacity torque measuring devices (TMDs) were conducted between NMIJ and PTB for the first time. A 10 N m deadweight torque standard machine (TSM) newly developed at NMIJ was compared with PTB’s two TSMs with nominal capacities of 1 N m and 1 kN m, in the range from 0.1 N m to 10 N m. The transfer measurement devices used had nominal capacities of 1 N m and 10 N m. The comparisons were made using two calibration procedures: one based on the CCM.T-K2 Key Comparison procedure and the other according to the daily calibration procedure adopted at each institute. As a result, the torque realized by the TSM at NMIJ was shown to be equivalent to that realized by the two TSMs at PTB. In addition, it was confirmed that the daily calibration procedures of both institutes yielded consistent results in the calibration of low nominal capacity TMDs.     

Calibration of laser Doppler vibrometer and laser interferometers in high-frequency regions using electro-optical modulator

We proposed a new primary calibration method of a laser Doppler vibrometer (LDV) using the optical modulated excitation of an electro-optical modulator and validated this approach by comparing mechanical modulated excitation with homodyne laser interferometer at the National Metrology Institute of Japan (NMIJ). The velocity sensitivity of the LDV was evaluated with the uncertainty budget at a high-frequency range up to 1 MHz, which is indicated as the upper limit of 50 kHz in ISO (International Organization for Standardization) 16063–41. As the results, we confirmed that velocity sensitivities between optical and mechanical modulated excitations are flat within their uncertainty from 100 Hz up to 1 MHz. Moreover, in order to evaluate the accurate phase shift of the accelerometer up to 20 kHz using optical modulated excitation, we also revealed the reliability of two time shifts between homodyne and heterodyne laser interferometers.     

Uncertainty evaluation of a 10N·m dead weight torque standard machine and comparison with a 1kN·m dead weight torque standard machine

A 10N·m dead weight torque standard machine (10-N·m-DWTSM) has been developed and evaluated since 2006 at the National Metrology Institute of Japan (NMIJ), a part of the National Institute of Advanced Industrial Science and Technology (AIST). Previously, the lengths of a moment arm, made of a low-thermal-expansion alloy (Super Invar), and the sensitivity limit of the fulcrum were evaluated. However, it is known that mechanical parts made of Super Invar vary in size with time. Therefore, the sensitivity limit of the fulcrum should be investigated under real calibration conditions. In this study, the moment arm lengths and the sensitivity limit of the fulcrum were re-evaluated. The moment arm lengths were found to have increased by an average of 6.3 μm in five years. The relative combined standard uncertainty of the moment arm length, w_arm, was re-evaluated in consideration of the uncertainty of the secular length change and was found to be 1.8 × 10⁻⁵. The sensitivity limit of the fulcrum was investigated by using a highly accurate, small-rated-capacity torque measuring device. The relative combined standard uncertainty due to the sensitivity limit of the fulcrum was 2.5 × 10⁻⁵ in the 0.1–10N·m torque range. The uncertainty budget table of the 10-N·m-DWTSM was completed. The relative expanded uncertainty of torque realized by the 10-N·m-DWTSM, W_tsm, was evaluated in the 0.1–10N·m torque range and was found to be 6.6 × 10⁻⁵, with a coverage factor, k, being equal to 2. In addition, the 10-N·m-DWTSM was compared with the existing 1-kN·m-DWTSM at NMIJ by using small-rated-capacity torque measuring devices at 5N·m and 10N·m torque steps. Two loading conditions were adopted in this comparison. The comparison results showed good agreement within the uncertainties in all cases. Thus, the torque realized by the 10-N·m-DWTSM was shown to be equivalent to that achieved by the 1-kN·m-DWTSM.     

100 kN deadweight force standard machine and Evaluation

A deadweight force standard machine is a mechanical structure that generates force by subjecting deadweights to the local gravitational field. The Korea Research Institute of Standards and Science (KRISS) developed and installed a 100 kN deadweight force standard machine for national force standards. It can generate forces from 2 kN to 110 kN in increments of 1 kN. The uncertainty of the force machine was estimated and declared as 2 × 10⁻⁵. This 100 kN deadweight force machine was compared with the 500 kN deadweight force standard machine at KRISS and the 20 kN and 50 kN deadweight force standard machines at the National Metrology Institute of Japan (NMIJ). The measurement results showed good agreement between the deadweight force machines, and the accuracy level of the 100 kN deadweight force machine was verified.     

Application of blue laser direct-writing equipment for manufacturing of periodic and aperiodic nanostructure patterns

This study presents the novel development of low cost, highly efficient blue laser direct-writing equipment for using mask-less laser lithography to manufacture periodic and aperiodic nanostructure patterns. The system includes a long-stroke linear motor precision stage (X, Y), a piezoelectric nano-precision stage (Y, θz), a 3-DOF (degrees of freedom) laser interferometer measurement system, and a blue laser direct-writing optical system. The 3-DOF laser interferometer measurement system gives the control system feedback for displacement (X, Y, θz) of the equipment. The laser processing equipment consists of a blue laser direct-writing optical head, a field-programmable gate array (FPGA) alignment interface, and an optical head servo controller. The optical head operates at a wavelength of 405 nm. Processing the nanostructures on thermo-reaction inorganic resists with precise control of the laser intensity, taking advantage of the threshold effect to exceed the limitations of optical diffraction, and reduces the nanostructure hole size. The equipment can be used to fabricate various periodic nanostructure patterns, aperiodic nanostructure patterns, and two-dimensional patterns. The equipment positioning accuracy is within 50 nm at a speed of 50 mm/s, and the minimum critical dimension can be achieved about 100 nm or so.     

A high performance one-dimensional homodyne encoder and the proof of principle of a novel two-dimensional homodyne encoder

Displacement laser interferometers and interferometric encoders currently are the dominating solutions to the displacement measurement applications which require measurement uncertainties in the order of a few nanometers over hundreds of millimeters of measurement range. But, in comparison with interferometric encoders, to achieve nanometer order or even lower measurement uncertainties, displacement laser interferometers require much stricter environmental control if not vacuum, which will increase their Total Cost of Ownership (TCO). Therefore interferometric encoders are getting more and more preferable. Furthermore, for some applications, the measurement of the out-of-plane displacement is required as well. Therefore, in this work, a one-dimensional interferometric encoder was built and investigated, a novel two-dimensional (one is in-plane, the other one is out-of-plane) interferometric encoder was devised and its principle was proven experimentally. For the one-dimensional encoder, a periodic nonlinearity of ±50 pm with HEIDENHAIN EIB 741 and a periodic nonlinearity of less than ±10 pm with a home built phase meter and off-line Heydemann correction were identified through a comparison measurement with a differential heterodyne interferometer. In addition, this one-dimensional encoder was identified to have a better measurement stability compared to the differential heterodyne interferometer.     

Verification of the positioning accuracy of industrial coordinate measuring machine using optical-comb pulsed interferometer with a rough metal ball target

An optical-comb pulsed interferometer was developed for the positioning measurements of the industrial coordinate measuring machine (CMM); a rough metal ball was used as the target of the single-mode optical fiber interferometer. The measurement system is connected through a single-mode fiber more than 100 m long. It is used to connect a laser source from the 10th floor of a building to the proposed measuring system inside a CMM room in the basement of the building. The repetition frequency of a general optical comb is transferred to 1 GHz by an optical fiber-type Fabry–Pérot etalon. Then, a compact absolute position-measuring system is realized for practical non-contact use with a high accuracy of measurement. The measurement uncertainty is approximately 0.6 μm with a confidence level of 95%.     

Non-contact measurement technique for dimensional metrology using optical comb

This paper proposes a non-contact pulsed interferometer for dimensional metrology using the repetition frequency of an optical frequency comb. A compact absolute-length measuring system is established for practical non-contact measurement based on a single-mode fiber interferometer. The stability and accuracy of the measurements are compared with those from a commercial incremental laser interferometer. The drifts of both systems have the same tendency and a maximum difference is approximately 0.1 μm. Subsequently, preliminary absolute-length measurements up to 1.5 m were measured. The signal-to-noise ratios of the small signals are improved by a frequency-selective amplifier. It is apparent that the noise is rejected, and the intensity of the interference fringes is amplified, achieving a maximum standard deviation of measurement approximately 1 μm. The proposed technique can provide sufficient accuracy for non-contact measurement in applications such as a simple laser-pulse tracking system.     

Measurement of highly reflective surface shape using wavelength tuning Fizeau interferometer and polynomial window function

In this study, a 5N − 4 phase shifting algorithm comprising a polynomial window function and a discrete Fourier transform is developed to measure interferometrically the surface shape of a silicon wafer, with suppression of the coupling errors between the higher harmonics and the phase shift error. A new polynomial window function is derived on the basis of the characteristic polynomial theory by locating five multiple roots on the characteristic diagram. The characteristics of the 5N − 4 algorithm are estimated with respect to the Fourier representation in the frequency domain. The phase error of the measurements performed using the 5N − 4 algorithm is discussed and compared with those of measurements obtained using other conventional phase shifting algorithms. Finally, the surface shape of a 4-in. silicon wafer is measured using the 5N − 4 algorithm and a wavelength tuning Fizeau interferometer. The accuracy of the measurement is discussed by comparing the amplitudes of the crosstalk noise calculated by other algorithms. The uncertainty of the entire measurement was 34 nm, better than that of any other conventional phase shifting algorithms.     

Stable mounting of beamsplitters for an interferometer

The Basic Angle Monitoring (BAM) system for satellite GAIA (2012–2018) will measure variation on the angle between the lines-of-sight between two telescopes with 2.5 prad uncertainty. It is a laser-interferometer system consisting of two optical benches with a number of mirrors and beamsplitters. The optical components need to be stable with respect to each other within 0.17 pm in position and 60 nrad in angle during measurements over a period of 6 h with 0.1 mK thermal stability. This paper aims at finding the most suitable mounting plane of the fused silica beamsplitters mounted onto the silicon carbide optical bench in the BAM system. These beamsplitters must be clamped mechanically. Based on a force stability analysis, mounting in the plane of light is a more stable solution than mounting on the reflective surface. However, when making a conceptual design the difficulty is making a design which has sufficient alignment stability to survive launch vibrations and a cool-down trajectory is more difficult.     

Simultaneous interferometric measurement of the absolute thickness and surface shape of a transparent plate using wavelength tuning Fourier analysis and phase shifting

The absolute optical thickness and surface shape of optical devices are considered as the fundamental characteristics when designing optical equipment. The thickness and surface shape should be measured simultaneously to reduce cost. In this research, the absolute optical thickness and surface shape of a 6–mm-thick fused silica transparent plate of diameter 100 mm was measured simultaneously by a three-surface Fizeau interferometer. A measurement method combining the wavelength tuning Fourier and phase shifting technique was proposed. The absolute optical thickness that corresponds to the group refractive index was determined by wavelength tuning Fourier analysis. At the beginning and end of the wavelength tuning, the fractional phases of the interference fringes were measured by the phase shifting technique and optical thickness deviations with respect to the ordinary refractive index and surface shape were determined. These two kinds of optical thicknesses were synthesized using the Sellmeier equation for the refractive index of fused silica glass, and the least square fitting method was used to determine the final absolute optical thickness distribution. The experimental results indicate that the all the measurement uncertainties for the absolute optical thickness and surface shape were approximately 3 nm and 35 nm, respectively.     

Diagonal in space of coordinate measuring machine verification using an optical-comb pulsed interferometer with a ball-lens target

This paper presents a new optical method of coordinate measuring machine (CMM) verification. The proposed system based on a single-mode fiber optical-comb pulsed interferometer with a ball lens of refractive index 2 employed as the target. The target can be used for absolute-length measurements in all directions. The laser source is an optical frequency comb, whose repetition rate is stabilized by a rubidium frequency standard. The measurement range is confirmed to be up to 10 m. The diagonals of a CMM are easier to verify by the proposed method than by the conventional artifact test method. The measurement uncertainty of the proposed method is also smaller than that of the conventional method because the proposed measurement system is less affected by air temperature; it achieves an uncertainty of approximately 7 μm for measuring lengths of 10 m. The experimental results show that the measurement accuracy depends on noise in the interference fringe, which arises from airflow fluctuations and mechanical vibrations.     

Effect of silicon nitride coating thickness on fatigue of silicon microbeams

In this paper, two silicon nitride layers with thickness, 0.2 and 0.4 μm, are coated onto single crystal silicon (SCS) in order to achieve Si₃N₄/Si cantilever microbeams. The effect of LPCVD silicon nitride surface coatings on fatigue properties of SCS cantilever microbeams is investigated. Fatigue testing is conducted at both 40 Hz and 100 Hz. Typical S–N (strain amplitude–fatigue cycle) curves of the beams are achieved and correlated fatigue failure modes are investigated. It is found that thinner Si₃N₄ coating of 0.2 μm results in better fatigue lives of Si₃N₄/Si beams than thicker Si₃N₄ coating of 0.4 μm. Both thinner and thicker coated beams have major fatigue crack planes along {1 1 1} planes; however, thicker coated beams possess specific failure mode of delamination, which is not found in thinner coated beams. Delamination reduces the reinforcing effect of thicker Si₃N₄ coating and leads to its shorter fatigue life. For thicker coated beams, fatigue life at 100 Hz is longer than that at 40 Hz. The mechanism for delamination and the effect of cyclic frequency is investigated, and factors for better fatigue life are proposed.     

A differential interferometric heterodyne encoder with 30 picometer periodic nonlinearity and sub-nanometer stability

A differential interferometric heterodyne encoder with spatially separated input beams was developed to minimize periodic nonlinearities resulting from polarization mixing. The laser beams with different frequencies were delivered by two polarization-maintaining fibers to the encoder head. Under laboratory conditions this encoder demonstrated a system stability of 38 pm (standard deviation) and 100 pm over 30 s and 1 h respectively. In a comparison measurement with a differential heterodyne interferometer, this encoder showed periodic nonlinearities of less than 30pm without any additional correction.     

Method for generating and measuring the micro-Newton level forces

A method for generating and measuring the micro-Newton level forces is proposed. In the method, the force is generated and measured as the inertial force acting on a mass. A pneumatic linear bearing is used to realize a linear motion with sufficiently small friction acting on the mass, i.e. the moving part of the linear bearing. The inertial force acting on the mass is calculated from the velocity of the mass, and the velocity is determined highly accurately by means of measuring the Doppler shift frequency of the laser light beam reflecting on the mass using an optical interferometer. To demonstrate the performance of the method, the mechanical properties of a piece of paper have determined with the resolution of 0.5 μN.     

Subpixel edge location method proposed to improve the performance of optical fiber spherical coupling probe during dimensional measurement of micro-cavities with high aspect ratio

A subpixel edge location method based on orthogonal Jacobi–Fourier moments is proposed in this paper to improve the performance of optical fiber spherical coupling probe during dimensional measurement of micro-cavities with high aspect ratio. The effectiveness of the proposed method is proved through the performance test of a micro-hole measuring machine with optical spherical coupling probe. Test results indicate that a blind micro-hole of 400 μm in diameter can be experimentally measured at the depth of 2000 μm with a repeatability of 40 nm and an extremity resolution of 42 nm.