Interferometric Dilatometer Research Articles

Evaluation of dimensional stability of metering truss structure using built-in laser interferometric dilatometer

Dimensional stability in a space telescope is one of the important factors for performing high-resolution observations. The supporting structures between the primary and the secondary mirrors in a space telescope are required to maintain the mirror positions with the proper focus for minimizing the optical alignment error. In orbit, the harsh environment subjects a space telescope to temperature variations that can lead to deformation of those structures and degradation of the telescope’s optical performance. Several approaches are available for achieving high dimensional stability. They include minimizing temperature variations with active thermal control, designing the structure with low thermal expansion materials, and correcting the shape and/or position of the structure with actuators. An optimum combination of these measures is determined based on an accurate evaluation of the dimensional stability of the structures. This paper proposes a displacement measuring interferometer system with a simple, robust, and compact sensor that can monitor the dimensional stability of the precise structure by integrating the sensor into the structure. In this technique, a Fabry–Perot displacement sensor was built into the end of a strut that is a component of a metering truss structure. Two types of truss struts were tested to verify the performance of the proposed technique in measuring thermal expansions. The first one was the prototype that was made of stainless steel (SUS304). The other strut was made of a low thermal expansion ceramic (SiAlON) that is one of the most promising materials for a highly thermo-stable satellite structure. The thermal dimensional stability of these struts was evaluated by using the proposed technique and compared with conventional dilatometers for validating this new technique. The results showed that the technique has similar precision to the conventional measurement system and provide a more convenient and stable measurement system.

Measurement of the thermal expansion coefficient of AISI 420 stainless steel between 20 and 293 K

The accurate measurement of thermal expansion coefficient at low temperatures is fundamental in applications where a high mechanical stability is required over the complete procedure of cooling. Here we report on our measurement of thermal expansion of AISI 420 between 20 and 293K, measured by an interferometric dilatometer.

A novel interferometric dilatometer in the 4–300 K temperature range: thermal expansion coefficient of SRM-731 borosilicate glass and stainless steel-304

We present a newly designed heterodyne interferometric dilatometer for the measurement of the coefficient of thermal expansion of solids in the 4–300 K temperature range. The instrument can measure non-monotonic thermal expansion curves and has an accuracy better than 200 nm across the whole 4–300 K measurement range. The compensation for the misalignment of the interferometer design and the configuration of the sample holder make the instrument suitable to carry out measurements on any kind of sample that can be produced in a bar or rod shape. The measurement of a standard SRM-731 borosilicate glass and an SS-304 sample are presented and compared with literature data.

A high-speed interferometric dilatometer based on the inductive heating of a specimen

A high-speed dilatometer has been designed for high precision measurements of the thermal expansion/contraction of solid samples. The length of the specimens is measured using a differential interference method with a resolution of 0.3 nm. The temperature is controlled by induction heating and gas cooling. The maximum heating rate is about 100 K s−1 and the maximum cooling rate is 50 K s−1. The system enables measurements under different gas atmospheres, including oxygen, up to temperatures of 1600 °C.

A double-pass interferometer for measurement of dimensional changes

A double-pass interferometer was developed for measuring dimensional changes of materials in a nanoscale absolute interferometric dilatometer. This interferometer realized the double-ended measurement of a sample using a single-detection double-pass interference system. The nearly balanced design, in which the measurement beam and the reference beam have equal optical path lengths except for the path difference caused by the sample itself, makes this interferometer have high stability, which is verified by the measurement of a quasi-zero-length sample. The preliminary experiments and uncertainty analysis show that this interferometer should be able to measure dimensional changes with characteristic uncertainty at the nanometer level.

Performance of dilatometer for determining absolute CTE of EUVL LTEMs

An optical heterodyne interferometric dilatometer, which was specially designed to meet the requirements of extreme ultraviolet lithography (EUVL), has been developed. It employs an interferometer to measure the absolute coefficient of thermal expansion (CTE), which means that it directly measures the change in sample length. An examination of its capabilities revealed that it can handle a wide variety of materials with a coefficient of thermal expansion (CTE) ranging from ppm/°C to ppb/°C. In addition, it was found that the reproducibility of CTE measurements ( σ) on low-thermal-expansion materials (LTEM) for EUVL was less than 1 ppb/°C. Thus, it was concluded that this dilatometer would be useful for the precise measurement of the CTEs of EUVL-grade LTEMs.

Interferometric dilatometer for thermal expansion coefficient determination in the 4–300 K range

The measurement of thermal and mechanical properties of materials at cryogenic temperatures gains more and more importance in the field of the application of novel high-tech materials to aerospace industry and in developing scientific instrumentation. We present a simple and inexpensive interferometric dilatometer for the measurement of the thermal expansion of materials in the 4–300 K range. The dilatometer consists of a Michelson tilt-compensated interferometer in which the path difference is given by the variation in length of a sample enclosed in a 4 K cryostat. The compensation for misalignment permits a fast and simple operation routine that configures the instrument as a valuable tool for materials engineering.

음향광변조기를 이용한 고분해능의 헤테로다인 간섭식 열팽창 측정기술

열팽창계수의 정확한 측정은 재료과학이나 공업기술 분야에서 가장 중요한 요구량 중의 하나이다. 음향광변조기(AOM)를 이용한 고분해능 간섭식 열팽창계를 제작하여 성능검사를 하였다. 이 계는 이중광로 헤테로다인 간섭계와 복사열 전기로로 구성되어, 정밀한 변위의 측정과 시료의 신속한 가열 및 냉각이 가능토록 하였다. 또한 레이저의 주파수 안정화를 위하여 2차 맥놀이 주파수를 이용한 3종모드 안정화 He-Ne 레이저를 제작하였으며, 이때의 주파수 안정도는 5<TEX>$\times$</TEX><TEX>$10^{-9}$</TEX>이었다. 제작된 계의 길이 측정은 실온에서 1100k온도영역에서 나노미터 정도의 정밀도를 주었다. The accurate measurements of thermal expansion coefficients is one of the most important techniques required not only in material science but also in industries. A high precision interferometric dilatometer, using acoustic optical modulator, has been constructed and its performance has been tested. The system consists of a double-path optical heterodyne interferometer and a radiant heating furnace. This provides highly accurate length measurement, and allows rapid heating and cooling method for the specimen. A three longitudinal mode frequency stabilized He-Ne laser, using the secondary beat frequency, is constructed. Its stability is found to be <TEX>$5{\times}10^{-9}$</TEX>. The uncertainty in the length measurement is estimated to be of nanometer order in the range between room temperature to 1100 K.

Development of a Laser Interferometric Dilatometer for Measurements of Thermal Expansion of Solids in the Temperature Range 300 to 1300 K

A laser interferometric dilatometer has been developed for measuring linear thermal expansion coefficients of reference materials for thermal expansion in the temperature range 300 to 1300 K. The dilatometer is based on an optical heterodyne interferometer capable of measuring length change with an uncertainty of 0.6 nm. Linear thermal expansion coefficients of silicon were measured in the temperature range 700 to 1100 K. The performance of the present dilatometer was tested by a comparison between the present data and the data measured with the previous version of the present dilatometer and the data recommended by the Committee on Data for Science and Technology (CODATA). The present data agree well with the recommended values over all the temperature range measured. On the other hand, the present values at lower temperatures are in poor agreement with the previous experimental data. The combined standard uncertainty in the present value at 900 K is estimated to be 1.1×10−8 K−1.

Laser interferometric dilatometer applicable to temperature range from 1300 to 2000 K

A laser interferometric dilatometer has been developed for measuring the thermal expansion of high-temperature solids in the temperature range 1300 to 2000 K. The dilatometer consists of a double-path optical heterodyne interferometer, a spectral-band radiation thermometer, and a vacuum chamber with carboncomposite heaters. The performance of the dilatometer has been assessed on the basis of measurements of linear thermal expansion coefficients for glassy carbon. The relative standard deviation of the measured values from those calculated from the fitting polynomial is 0.63 0 over the temperature range investigated. The combined standard uncertainties in the measured values are estimated to be less than 1.3 0 over this range. The process of sample relocation predominantly affects the reproducibility of the experimental results.

Ultra-precise thermal expansion measurements of ceramic and steel gauge blocks with an interferometric dilatometer

Linear thermal expansion coefficients (LTECs) of two kinds of ceramic gauge block (seven in all) and steel gauge blocks (four in all) were measured in the range -10°C to 60°C with an optical heterodyne interferometric dilatometer. The dilatometer has an uncertainty and reproducibility of the order of 1 × 10-9 K-1 in LTEC measurements. LTECs of (9.229 ± 0.011) × 10-6 K-1 were obtained for four 2% Al2O3 partially stabilized zirconia (PSZ) gauge blocks; (9.381 ± 0.003) × 10-6 K-1 for three 99.9% PSZ gauge blocks; and (10.702 ± 0.064) × 10-6 K-1 for four steel gauge blocks. These results are discussed in relation to the compositions and production batches of the gauge blocks.

Examination of Thermal Expansion Uniformity of Glassy Carbon as a Candidate Standard Reference Material for Thermal Expansion Measurements.

The linear thermal expansion coefficients(LTEC) of some different pieces of the grade GC-20SS of glassy carbon produced by Tokai Carbon Co. Ltd. Japan have been measured using both an interferometric dilatometer and a push-rod dilatometer in order to investigate the piece-to-piece and lot-to-lot consistency for thermal expansion. The results indicated that the differences in LTEC in the temperature range -50 to 220 °C for different pieces from the two glassy carbon lots are sufficiently small within ±4×10-8K-1, which is the same order of measurement uncertainty. Thus, no significant thermal expansion divergency exists among different pieces and lots of GC-20SS glassy carbon, this material seems to be a very promising candidate standard reference material for thermal expansion measurement.

Development of a low-temperature laser interferometric dilatometer using a cryogenic refrigerator

A low-temperature laser interferometric dilatometer using a liquid-helium-free cryo- genic refrigerator was developed for the absolute measurement of a linear thermal expansion coefficient with high accuracy. To evaluate the performance of the laser interferometric dilatometer, measure-ments were carried out on a high-purity single crystal of silicon over the temperature range 10^320 K. The measured value of the expansion coefficient was also compared with the recommended value by CODATA. The present result was in good agreement with the recommended value below room temperature, and the deviation from the recommended value was less than0:01 10 ˇ6 K ˇ1 .

Precise Dilatometric Measurements of Silica Glasses.

The linear thermal expansion coefficients (LTEC) of silica glasses produced by the Nippon Glass lnc. Ltd. have been measured in the temperature range 0 ∼50°C using an interferometric dilatometer. The measurement system consists of a double-path optical heterodyne interferometer and a compact vaccum thermal bath controlled by a thermoelectric transducer. Before measuring the silica glass specimens, the reliability checks of the dilatometer were perfomed on silicon and fused silica SRM 739. The resultant estimated maximum uncertainty of the measured LTECs is about±2×10-8K-1. The measurement results indicated that, around room temperature (0∼50°C), only a factor of CI-rich content in silica glass affects the thermal expansion characteristics of the silica glass reducing slightly its absolute values, nevertheless the differences in the LTECs for all of the investigated specimens are sufficiently small within 4×10-8K-1

Thermal expansion of vitreous silica: Correspondence between dilatation curve and phase transitions in crystalline silica

The linear thermal expansion coefficients of fused quartz containing 3 ppm of OH produced by electrical melting of natural quartz powder were measured using an interferometric dilatometer in the temperature range 300–970 K. The data obtained show several maxima and minima, some of which correspond to the phase transitions in crystalline silica. A sharp maximum is observed at 500 K, which corresponds to the α to β transition temperature of cristobalite. Minima at 850 and 580 K correspond to low- to high-temperature phase transitions of crystalline quartz and tridymite, respectively. This correspondence was not observed in synthetic fused silica containing about 800 ppm of OH.

Measurements of linear thermal expansion coefficients of copper SRM 736 and some commercially available coppers in the temperature range 20–300 K by means of an absolute interferometric dilatometer

The thermal expansivities of several grades of copper were measured in the temperature range 20–300 K by means of an absolute laser interferometric dilatometer. The present results for copper standard reference material (NIST; SRM 736) and three commercially available kinds of copper, such as a high-purity copper (99.999% purity), an oxygen-free high-conductivity copper and a tough-pitch copper, show good agreement with the NIST certified values and the CODATA recommended values within 0.09 × 10 −6K −1 over the whole temperature range.

Precise, versatile interferometric dilatometer for room-temperature operation: measurements on some standard reference materials

Precise, versatile interferometric dilatometer for room-temperature operation: measurements on some standard reference materials

Laser interferometric dilatometer at low temperatures: application to fused silica SRM 739

An optical heterodyne interferometer has been combined with a helium flow cryostat to measure the linear thermal expansion coefficient of solids at cryogenic temperatures. The absolute accuracy in length measurement is within a few nanometres. Measurement results on a specimen of fused silica (SRM 739; by US NIST) in the temperature range 6–273 K are presented and compared with some literature data.

Thermal expansion of some advanced ceramics applicable as specimen holders of high Tc superconductors

The thermal expansion of some advanced ceramics and well orientated Bi 2Sr 2-CaCu 2O 8+ x were measured from 10 to 300 K to find suitable substrates with similar levels of thermal expansion to high T c superconductors. The length measurements were based on readings from an interferometric dilatometer with a precision of 5 nm. The thermal expansion and coefficient of thermal expansion of each material are presented in this paper, along with a brief guide to specimen holders.

An interferometric dilatometer for the determination of thermo-optic coefficients of NLO materials

An interferometric dilatometer has been designed for determination of thermo-optic coefficients of millimetric nonlinear optical (NLO) materials. The apparatus is a combination of a modified Mach-Zehnder arrangement for dilation measurements and a Fizeau technique for determination of changes in optical length. Its configuration allows measurements under known conditions of applied electric field. Analysis of the linear thermal expansion coefficient alpha b of a triglycine sulphate (TGS) single crystal around its second-order phase transition is used to evaluate the sensitivity of the interferometer, and measurements performed on a LiNbO3 single crystal exhibit step-like variations of changes in optical length from 20 degrees C to 122 degrees C. These experiments show that an accuracy better than 1*10-6 K-1 is achievable for both dilation and thermo-optic coefficients with this dilatometer, provided that they are not highly temperature-dependent and are under the condition of suitably controlled applied electric field.