Lasers can significantly advance medical diagnostics and treatment. At high power, they are typically used as cutting
tools during surgery. For lasers that are used as knifes, radiation wavelengths in the far ultraviolet and in the near
infrared spectral regions are favored because tissue has high contents of collagen and water. Collagen has an absorption
peak around 190 nm, while water is in the near infrared around 3,000 nm. Changing the wavelength across the
absorption peak will result in significant differences in laser tissue interactions. Tunable lasers in the infrared that could
optimize the laser tissue interaction for ablation and/or coagulation are not available until now besides the Free Electron
Laser (FEL). Here we demonstrate efficient tissue ablation using a table-top mid-IR laser tunable between 3,000 to
3,500 nm. A detailed study of the ablation has been conducted in different tissues. Little collateral thermal damage has
been found at a distance above 10-20 microns from the ablated surface. Furthermore, little mechanical damage could be
seen in conventional histology and by examination of birefringent activity of the samples using a pair of cross polarizing
filters.
Measurement of the 1/f noise of MEMS devices with sidewall embedded piezoresistors, prototyped for the current study,
are described in the present paper. A modified sample conditioning and pre-amplification setup was employed and the
complete arrangement was kept at 30°C. The 1/f and the 1/Δf noise signals are fully correlated as the underlying
mechanism is the same for both phenomena. The bias voltage of each resistor ranges from zero to Vpp and the device
currents contain 1/f noise due to the DC bias in conjunction with conductivity fluctuations. Accordingly, the AC bias
results in 1/Δf noise centred about the frequency of the sinusoidal. The spectrally resolved analysis of the 1/f and down-converted
1/Δf noise signals was then established with two instances of a digital lock-in amplifier capable of mHz
operation. As both lock-in amplifiers have been locked to a common reference signal, the spectral analyser keeps any
correlation between the two channels. Measurements of the current noise were done over the frequency range 0.0625 Hz
to 2.048 kHz and measurement resolution of about 10-18 V2/Hz is determined by the selected correlator averaging period
in conjunction with the total noise of the instrumentation channels. For a direct comparison with metal-film resistor
technology, sidewall piezoresistors have been replaced by 1 kΩ metal-film resistors for dedicated measurements. The
crossover of the 1/f noise of a full bridge of piezoresistors and their thermal noise will appear below 10 Hz for a bias
voltage smaller than 1V. This is, to our best knowledge, among the best 1/f noise performances for piezoresistors.
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