Darryl A. Keenan

Calibration of sampling oscilloscopes with high-speed photodiodes

We calibrate the magnitude and phase response of equivalent-time sampling oscilloscopes to 110 GHz. We use a photodiode that has been calibrated with our electrooptic sampling system as a reference input pulse source to the sampling oscilloscope. We account for the impedance of the oscilloscope and the reference photodiode and correct for electrical reflections and distortions due to impedance mismatch. We also correct for time-base imperfections such as drift, time-base distortion, and jitter. We have performed a rigorous uncertainty analysis, which includes a Monte Carlo simulation of time-domain error sources combined with error sources from the deconvolution of the photodiode pulse, from the mismatch correction, and from the jitter correction

Covariance-based uncertainty analysis of the NIST electrooptic sampling system

We develop a covariance matrix describing the uncertainty of mismatch-corrected measurements performed on the National Institute of Standards and Technologys electrooptic sampling system. This formulation offers a general way of describing the uncertainties of the measurement system in both the temporal and frequency domains. We illustrate the utility of the approach with several examples, including determining the uncertainty in the temporal voltage generated by the photodiode

Traceable Waveform Calibration With a Covariance-Based Uncertainty Analysis

We describe a method for calibrating the voltage that a step-like pulse generator produces at a load at every time point in the measured waveform. The calibration includes an equivalent-circuit model of the generator that can be used to determine how the generator behaves when it is connected to arbitrary loads. The generator is calibrated with an equivalent-time sampling oscilloscope and is traceable to fundamental physics via the electro-optic sampling system at the National Institute of Standards and Technology. The calibration includes a covariance-based uncertainty analysis that provides the uncertainty at each time in the waveform vector and the correlations between the uncertainties at the different times. From the calibrated waveform vector and its covariance matrix, we calculate pulse parameters and their uncertainties. We compare our method with a more traditional parameter-based uncertainty analysis.

Minimum-phase calibration of sampling oscilloscopes

We describe an algorithm for determining the minimum phase of a linear time-invariant response function from its magnitude. The procedure is based on Kramers-Kronig relations in combination with auxiliary direct measurements of the desired phase response. We demonstrate that truncation of the Hilbert transform gives rise to large errors in estimated phase, but that these errors may be approximated using a small number of basis functions. As an example, we obtain a minimum-phase calibration of a sampling oscilloscope in the frequency domain. This result rests on data obtained by an electrooptic sampling (EOS) technique in combination with a swept-sine calibration procedure. The EOS technique yields magnitude and phase information over a broad bandwidth, yet has degraded uncertainty estimates from dc to approximately 1 GHz. The swept-sine procedure returns only the magnitude of the oscilloscope response function, yet may be performed on a fine frequency grid from about 1 MHz to several gigahertz. The resulting minimum-phase calibration spans frequencies from dc to 110 GHz, and is traceable to fundamental units. The validity of the minimum-phase character of the oscilloscope response function at frequencies common to both measurements is determined as part of our analysis. A full uncertainty analysis is provided

Power measurement standards for high-power lasers: comparison between the NIST and the PTB

We report the results of the first laser high-power measurement comparison between the Physikalisch-Technische Bundesanstalt (PTB, Germany), and the National Institute of Standards and Technology (NIST, USA). Laser power transfer standards were calibrated at both national standards laboratories between 82 W and 127 W at 1.06 µm and between 85 W and 554 W at 10.6 µm. Relative agreement between the standards of the two laboratories was demonstrated to lie between 5 × 10−3 and 7 × 10−3, which is well within the combined uncertainties.

New developments in deep ultraviolet laser metrology for photolithography

Current and future laser measurement services at 157, 193 and 248 nm will be reviewed. Laser power and energy measurements at 193 nm will be presented; electrical calibration issues will be reviewed. We report an overall calibration uncertainty of laser power and energy meters of less than 2%. Characterization measurements for ultraviolet materials also will be discussed.

Measurements of detector nonlinearity at 193 nm

We have developed a measurement system based on a correlation method to characterize the nonlinearity of a detectors response over a large range of laser pulse energy. The system consists of an excimer-laser source, beam-shaping optics, a beam splitter, a monitor detector, a set of optical filters, and the detector under test. Detector nonlinearities as large as 10% or greater over an entire measurement range at an excimer-laser wavelength of 193 nm are observed. The measurement range of the current system is approximately 300 nJ to 50 mJ of laser pulse energy at the detector under test. The typical expanded measurement uncertainty of nonlinearity is 0.6% (k = 2).

193-nm detector nonlinearity measurement system at NIST

To meet the semiconductor industry’s demands for accurate measurements on excimer lasers, we have developed a system using the correlation method to measure the nonlinear response of pulse energy detectors of excimer laser at 193 nm. The response of the detector under test to incident laser pulse energy is compared to the corresponding response of a linear monitor detector. This method solves the difficulties caused by large pulse-to-pulse instability of the excimer laser and delivers measurement results with an expanded uncertainty (k=2) of 0.8 %.

A primary standard for 157 nm excimer laser measurements

Two primary standard calorimeters have been developed for accurate measurements of 157 nm (F2) excimer laser power and energy. The calorimeter specifications and design are discussed. Results from the construction and testing of the calorimeters, control electronics, data acquisition, and N2 purge system are presented. These calorimeters have demonstrated a two‐fold improvement in sensitivity over existing NIST excimer laser calorimeters. The measurement uncertainty from electrical calibrations is a five‐fold improvement over the NIST 193 nm primary standard.

Excimer laser treatment of carbon nanotubes

In this work we examine laser treatment of unaligned bulk nanotube samples as a potentially simple and fast purification method. The effects of laser treatment by a 248 nm excimer laser at various pulse lengths and time of exposure are evaluated to gain control and selectivity for the removal of carbon impurities from nanotube samples.