Abstract
We demonstrate the use of optical pulse-shaping technique in conjunction with difference frequency generation in a non-linear optoelectronic crystal for generating synthesized waveforms at terahertz frequencies. Spectral phase modulations, programmed using Gerchberg-Saxton algorithm and prepared in a spatial light Fourier filter, produce tailored terahertz pulses, including chirped pulses, zero-area pulses, and trains of multiple pulses for tunable narrow-band terahertz radiation up to 2.0 THz.
Highlights
The generation of coherent radiation across the electromagnetic spectrum has enabled the technologies that have a defining impact on life in the 21st century
Using an optoelectronic technique based on semiconductor strip-lines, a spatially and temporally coherent beam of THz radiation from 0.1 to 5 THz can be generated and detected with signal-to-noise ratio (S/N) > 105, while nonlinear optical methods based on optical rectification have generated 50 fs THz pulses with frequencies from 0.1 to ∼40 THz that are detected with S/N = 1000:1 [5, 6]
We have used non-linear difference frequency mixing of an optical coherent light source to produce designed THz waveforms
Summary
The generation of coherent radiation across the electromagnetic spectrum has enabled the technologies that have a defining impact on life in the 21st century. The technique of terahertz time domain spectroscopy (THz-TDS) generates broadband, single cycle THz pulses of subpicosecond duration using resonant femtosecond(fs) optical excitation of biased semiconductor strip-lines or nonresonant optical rectification in electro-optic crystals [2, 3, 4]. The coherent detection of the THz electric field is achieved using fs optical gating pulses. The coherent nature of THz-TDS yields a much greater brightness in comparison to thermal sources and optical-gating discriminates against thermal background leading to, in some cases, a signal-to-noise ratio (S/N) approaching 106. The THz pulses are derived from a coherent optical source, enabling synchronized optical excitation useful both for time-resolved spectroscopic studies and two-color schemes for communications, remote sensing, imaging, and signal processing [7, 8, 9]
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