Acousto-optic measurements

A planarization monitor has been applied to the copper system to investigate pattern dependencies during copper overburden planarization. Conventional profilometry and a noncontact, acousto-optic measurement tool, the Insite 300, are utilized to quantify the planarization performance in terms of the defined step-height-reduction-ratio (SHRR). Illustrative results as a function of slurry, pad type and process conditions are presented. For a typical stiff-pad copper CMP process, we determined the planarization distance to be approximately 2mm. 

Caruso F, Jory M J, Bradberry G W, Sambies J R and Furiong D N 1998 Acousto-optic surface-piasmon resonance measurements of thin fiims on goid J. AppL Rhys. 83 1023-8... 

In frequency-domain FLIM, the optics and detection system (MCP image intensifier and slow scan CCD camera) are similar to that of time-domain FLIM, except for the light source, which consists of a CW laser and an acousto-optical modulator instead of a pulsed laser. The principle of lifetime measurement is the same as that described in Chapter 6 (Section 6.2.3.1). The phase shift and modulation depth are measured relative to a known fluorescence standard or to scattering of the excitation light. There are two possible modes of detection heterodyne and homodyne detection. 

Gies, D. and Poon, T.-C., Measurement of Acoustic Radiation Pattern in an Acousto-Optic Modulator Proceedings of IEEE SoutheastCon 2002, pp. 441-445. 

There are several measurement techniques that can be considered for use in IR-based instrumentation in the NIR and the mid-IR spectral regions, and these are summarized in Table 4.1. Some of these techniques are classical, as in the case of optical filter-based instruments and scanning monochromators. Others, such as acousto-optically tunable filter (AOTF), have been considered for 15+ years, but are mainly applied to NIR... 

The power outputs of the lasers will be actively stabilized and matched using a system of thermopile power meters (PM) and acousto-optic modulators (AOM s). Spatial filters (SF) will be used to ensure a well defined laser mode at the interaction region. A system of beam scanners will be used to accurately characterize the laser and ion beams at the interaction region and to measure the intersection angles 61. ... 

Figure 2 The stronger component of the 1S-2S two photon transition in deuterium. The signal is the normalised Lyman-a fluorescence observed as a function of the frequency difference between lasers LI and L2 (fig. 1) when LI is locked to the appropriate transition (b2) in 13°Te2. The measured offset frequency is 20 MHz greater than the true value because of the shift introduced by the acousto-optic modulator. The pressure in the deuterium cell was 270 mtorr...

Figure 5. Visible laser stability. The laser power fluctuations using a 488 nm (blue) and 568 nm (red) lasers were determined using a 10x objective and a Chroma red slide. The fluorescence was sequentially measured every 30 sec (400 times) for total time duration of 3.33 hrs. The variation of the peak to peak using 488 nm or 568 nm excitation was approximately 25%. The fluctuating power intensity line suggests that the system scanning and detection devices are yielding large power fluctuations that will affect the illumination of the sample. The Acousto Optical Transmission Filter (AOTF) is probably contributing to this 488-568 nm sinusoidal pattern.

Fig. 2. Schematic diagram of the laser system to be used for a measurement of the 2Si/2 2P3y2 transition frequency in Si (A/2 half wave plate, A/4 quarter wave plate, PBS polarizing beamsplitter, VCO voltage-controlled osciUator, AOM acousto-optic modulator, EOM electro-optic modulator)...

In a PA experiment, the excited-state absorption spectrum is measured. The sample was excited by an amplitude- modulated pump beam and changes in the transmission of a probe beam are measured by lockin amplification of a photoreceiver. The 363-nm line of an argon ion laser at a power density of 30 mW/cm2 was used as the pump beam and a monochromated tungsten white-light source was used as the probe. The pump beam was modulated at 120 Hz by an acousto-optical modulator and the spectra were measured under... 

In one paper by Kirsch and Drennen [62], three experiments were performed on coated tablets. In the first experiment, intact theophylline tablets coated with an ethylcellulose polymer were analyzed by acousto-optic tunable filter (AOTF) spectrometers. Tablets were coated with increasing levels of ethylcellulose to vary the dissolution profiles. After spectra were collected, the dissolutions were run on a U.S.P. Type II dissolution apparatus. The time required for 50% of the drug to enter solution was used as the measure of dissolution rate. Principal component (PC) regression was used to develop the calibration. This gave a SEE of 2.8 min, a coefficient of variation of 0.977, and a SEP of 6.6 min the time to 50% dissolution ranged from 48 to 93 min. 

Sweat, J.A. and Wetzel, D.L. (2001) Near infrared acousto-optic tunable filter based instrumentation for the measurement of dynamic spectra of polymers. Rev. Sci. Instrum., 72 (4), 2153-8. 

The heterodyne measurement is performed as follows. The dye laser excites the trapped ion with frequency (Ol while the fluorescence is observed in a direction of about 54 to the exciting laser beam (see Fig. 2). However, both the observation direction and the laser beam are in a plane perpendicular to the symmetry axis of the trap. Before reaching the ion, a fraction of this laser radiation is removed with a beamsplitter and then frequency shifted (by 137 MHz with an acousto-optic modulator (AOM)) to serve as the local oscillator. The local oscillator and fluorescence radiations are then overlapped and simultaneously focused onto the photodiode where the initial frequency mixing occurs. The frequency difference signal is amplified by a narrow band amplifier and then frequency down-converted to 1 kHz so that it could be analyzed by means of a fast Fourier analyzer (FFT). The intermediate frequency for this mixing of the signal was derived from the same frequency-stable synthesizer which was used to drive the accousto-optic modulator producing the sideband of the laser radiation so that any synthesizer fluctuations are canceled out. 

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