High-field/high-frequency electron spin resonance ͑ESR͒ offers improved sensitivity and resolution compared to ESR at conventional fields and frequencies. However, most high-field/high-frequency ESR spectrometers suffer from limited mm-wave power, thereby requiring long mm-wave pulses. This precludes their use when relaxation times are short, e.g., in fluid samples. Low mm-wave power is also a major factor limiting the achievable spectral coverage and thereby the multiplex advantage of Fourier

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... ransform ESR ͑FTESR͒ experiments. High-power pulses are needed to perform two-dimensional ͑2D͒ FTESR experiments, which can unravel the dynamics of a spin system in great detail, making it an excellent tool for studying spin and molecular dynamics. We report on the design and implementation of a high-power, high-bandwidth, pulsed ESR spectrometer operating at 95 GHz. One of the principal design goals was the ability to investigate dynamic processes in aqueous samples at physiological temperatures with the intent to study biological systems. In initial experiments on aqueous samples at room temperature, we achieved 200 MHz spectral coverage at a sensitivity of 1.1ϫ10 10 ͱs spins and a dead time of less than 50 ns. 2D-electron-electron double resonance experiments on aqueous samples are discussed to demonstrate the practical application of such a spectrometer.