Reducing Thermal Effect on Thermoelectric Thin Films Fabrication Using Mechanical Chopper Coupling with CO2 Laser Ablation

The aim of this experiment was to use mechanical chopper coupling with CO2 laser ablation to reduce thermal effect on thermoelectric thin film fabrication. The average power at 10 W of sealed tube CO2 laser together with the mechanical chopper was used for the thermoelectric (TE) thin film fabrication on silicon substrate in vacuum system. The 1.02 ms of pulse duration with 600 Hz of repetition rate were generated by the optimized speed of chopper at 4500 rpm with 8 channels of circular apertures which were used for the reduction of thermal effect on the bismuth antimony telluride (Bi-Sb-Te) target. The experiment results illustrated the thickness and the thin films fabricated by using 10 seconds of exposure time with the chopper, illustrated the smaller grain size than without the chopper while the thickness increased as the exposure time increased at constant speed of chopper. The output efficiency referred to the ratio of the thickness per target lost in unit time which increased from 19.6 to 181.8 μm/g per hour, due to the increase of the exposure time with the chopper while without the chopper resulted in 55.0 μm/g per hour caused by the higher temperature raise on the thermoelectric target which affected to the as-deposited thin films and the re-evaporation occurred. In this experiment, the chopper speed was measured by the digital tachometer, the target loss was analyzed by the digital analytical balance and the morphology of the 600 tilted surface of thin film was characterized by scanning electron microscope (SEM).

Design and Performance of a Hadamard Transform Infrared Spectrometer with No Moving Parts

The development of an improved Hadamard transform infrared HT-IR) spectrometer with no moving optical parts is described. This spectrometer is based on a thermo-optic array for the stationary encoding of radiation (TOASTER) fabricated from Nichrome resistance wire. The TOASTER HT-IR instrument utilizes a reversed Czerny-Turner optical mount and relies on entrance focal plane modulation for operation. This design allows the dedispersion optics to be eliminated while still providing for a multiplex advantage. In addition, a conventional mechanical chopper is not needed in this instrument because the TOASTER is used as a natural modulator. The TOASTER HT-IR spectrometer can acquire an infrared spectrum in the range of 2.5 to 11 μm (4000 to 910 cm−1). Its spectral resolution is 0.07 μm (∼7 cm−1 at 1000 cm−1), and, for fifteen spectral resolution elements, the observation window is 0.5 μm (∼48 cm−1 at 1000 cm−1). In addition to the design of the instrument, this communication also examines the thermo-optic switching properties of the Nichrome wire used in the prototype TOASTER. Although the maximum switching speed of the Nichrome wire is governed by its thermal decay time, we show that the TOASTER can be operated faster than this limit by employing a preheating step.

Apparatus for the measurement of the electronic excited-state structure of single crystals using X-ray diffraction

Instrumentation for measuring the X-ray diffraction pattern of optically excited crystals is described. The experiment uses a high-power (~1 W) laser and a single-crystal diffractometer equipped with a helium cryostat (T < 70 K). The laser beam is modulated by a mechanical chopper and the diffraction signal gated in synchronization with the chopper phase. The modulation method is capable of observing small changes (down to about 0.01%) in the structure factors upon excitation of a fraction of the molecules in the crystal, given adequate counting statistics. The technique can be used for relatively long lived electronic excited states (τ ≃ 0.1–10 ms). The optical system is also suitable for time-resolved measurements using the time structure of synchrotron radiation.