Software for correcting the dynamic error of force transducers.

Software which corrects the dynamic error of force transducers in impact force measurements using their own output signal has been developed. The software corrects the output waveform of the transducers using the output waveform itself, estimates its uncertainty and displays the results. In the experiment, the dynamic error of three transducers of the same model are evaluated using the Levitation Mass Method (LMM), in which the impact forces applied to the transducers are accurately determined as the inertial force of the moving part of the aerostatic linear bearing. The parameters for correcting the dynamic error are determined from the results of one set of impact measurements of one transducer. Then, the validity of the obtained parameters is evaluated using the results of the other sets of measurements of all the three transducers. The uncertainties in the uncorrected force and those in the corrected force are also estimated. If manufacturers determine the correction parameters for each model using the proposed method, and provide the software with the parameters corresponding to each model, then users can obtain the waveform corrected against dynamic error and its uncertainty. The present status and the future prospects of the developed software are discussed in this paper.

Time-resolved interferometry of femtosecond-laser-induced processes under tight focusing and close-to-optical breakdown inside borosilicate glass.

We use an interferometric time-resolved observation of a femtosecond-laser pulse (800 nm/45 fs) interaction with glass from 100 fs to 10 ns at spatial lateral resolution down to the wavelength of the pulse. The phase and amplitude images reveal sequence of events after the irradiation of a single ultra-short laser pulse at close-to-threshold intensity when permanent refractive index changes occur. The proposed method is applicable to characterization of the processes induced by tightly focused fs-laser pulses during three-dimensional structuring of glasses and crystals for fundamental studies and optical applications. Generation of carriers, thermal expansion, generation and propagation of shockwaves, and formation of refractive index changes are experimentally observed and resolved in time and space with the highest resolution. Quantitative estimations of the threshold energies of different processes are achieved. The threshold energy of carrier generation is found the same as that of shockwave generation while the threshold energy of refractive index changes was by 40% higher. Application potential of the method is discussed.

Sparse-exposure technique in holographic two-photon polymerization.

Holographic two-photon polymerization is based on a high-speed, low-loss parallel laser irradiation technique inside photosensitive materials using a computer-generated hologram displayed on a liquid crystal spatial light modulator. We demonstrated a sparse exposure technique combining parallel exposure and scanning exposure to improve the fabrication throughput and to achieve simultaneous fabrication of linear structures with different widths. We also demonstrated fabrication of space-variant structures by changing a CGH, as well as parallel fabrication of voxel structures with single femtosecond laser pulse irradiation.

Three-dimensional optical memory using a human fingernail.

We realized optical data storage in a human fingernail. A structural change is recorded by irradiating a focused femtosecond laser pulse and is read out with fluorescent observation by making use of an increased fluorescence intensity. The shape of the structural changes drastically depends on the irradiated pulse energy. The fluorescence spectrum of the structure coincided with the auto-fluorescence spectra of a fingernail and a heated fingernail. It is suggested that the increased fluorescence is most likely caused by a local denaturation of the keratin protein by the femtosecond laser pulse irradiation. We demonstrate that the increased fluorescence effect is useful for reading out three-dimensionally recorded data.