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Ultrashort pulses are capable of processing practically any material with a negligible heat affected zone [1]. For productive industrial applications a pulse duration of about 5 ps is a well established compromise between being faster than the electron-phonon interaction time of the material and being long enough to suppress detrimental effects such as nonlinear interaction with the ablated plasma...
We report a terahertz time-domain spectrometer with 6 THz spectral coverage and 1 GHz resolution which is based on high-speed asynchronous optical sampling. High-speed asynchronous optical sampling is based on two femtosecond lasers with approximately 1 GHz repetition rate. The two lasers are stabilized in their repetition rate to an off-set frequency of approximately 2 kHz. The time delay between...
Coherent zone folded acoustic phonons in terahertz quantum cascade laser (QCL) structures [1] are investigated by high-speed asynchronous optical sampling [2]. This method is based on two Ti:sapphire lasers with repetition rates of ∼1 GHz respectively. The time delay between pump and probe pulse is achieved by an offset in repetition rate of 5kHz. This allows for fast scanning times without moving...
The photo-Dember effect is known as source of impulsive THz radiation after excitation with femtosecond optical pulses. The origin of the emission is the ultrafast separation of electron and holes in strong carrier gradients due to different diffusion coefficients. For a simple semiconductor surface the time dependent polarization is oriented perpendicular to the excited surface which complicates...
We demonstrate a new scheme for generating THz radiation based on the photo-Dember effect in lateral geometry. By micro-structuring a semiconductor surface we achieve strongly enhanced THz emission comparable to high-efficiency externally biased photoconductive emitters.
We present an ultrafast time-domain spectrometer based on high-speed asynchronous optical sampling. A time resolution of 45-fs is obtained at kilohertz scan rates over a 1 ns time-delay window without mechanical moving parts.
We combine high-speed asynchronous optical sampling with semiconductor disk femtosecond laser technology and realize a high-resolution THz time-domain spectrometer without mechanical delay. The system has great potential for size and cost reduction of existing systems.
A terahertz time-domain spectroscopy (THz-TDS) system using an optically pumped semiconductor disk laser and high-speed asynchronous optical sampling is reported. The combination of these techniques holds considerable promise towards a compact and low-cost implementation of THz-TDS. The spectrometer offers a 333 ps time delay window scanned at 10 kHz and delivers more than 1.2 THz spectral coverage...
High-speed asynchronous optical sampling with two offset-locked Ti:sapphire femtosecond oscillators permits time-domain THz spectroscopy with almost 7 THz bandwidth at 1 GHz resolution. The system operates at 2 kHz scan rate without moving mechanical parts. The mean fractional frequency error of absorption lines in a measured water vapor absorption spectrum with respect to the data published in the...
This work reports the time-resolved experimental observation of the acoustic vibrational dynamics in the thin freestanding silicon membranes. The femtosecond time resolved pump-probe experiments are performed using the newly developed high-speed asynchronous optical sampling (ASOPS) method. This method is based on two asynchronously linked femtosecond unidirectional ring lasers of ~1GHz repetition...
We investigate asymmetric split ring resonators (SRR) for the THz frequency range. These SRRs exhibit sharp resonances and strong field localization, which is of potential interest e.g. for biosensing of minute amount of sample material. Our near-field measurements show the local response of the SRRs on a scale much smaller than the resonance wavelength of 320 mum. Fig. 1 depicts the spatially resolved...
In this paper, we have shown that our high-speed ASOPS system approaches the time-delay resolution of conventional time-domain spectroscopy setups while at the same time permitting significantly reduced data acquisition times and eliminating mechanical delay stages. The system may thus fully replace conventional systems in the near future and provide the additional benefit straightforward possibility...
In this paper, a self-referenced Ti:sapphire femtosecond laser frequency combs (FLFC) with 5 GHz repetition rate and 230 pJ of pulse energy is reported. The individual modes of the 5 GHz FLFC are dispersed and recorded in a 2D image using a high-resolution spectrometer. This experiment is an important milestone within ongoing efforts to investigate applications in spectroscopy and arbitrary waveform...
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