G.M.H. Knippels

Optical parametric generation in CGA crystal

Summary form only given. CGA (CdGeAs/sub 2/) crystal is known for its highest second-order nonlinearity (236 pm/V) among any crystals in practical use. It transmits between 2.4 and 18 /spl mu/m and is a perfect candidate for nonlinear-optical frequency conversion in the mid-IR, specifically into the second atmospheric window (8-12 /spl mu/m). In this paper, we report the first demonstration of optical parametric generation in CGA, as well as efficient SHG operation.

Two-color facility based on a broadly tunable infrared free-electron laser and a subpicosecond-synchronized 10-fs-Ti:sapphire laser.

Subpicosecond synchronization between a mirror-dispersion-controlled 10-fs Ti:sapphire laser and the Free-Electron Laser for Infrared Experiments has been achieved. The measured intensity cross correlation between the two lasers is consistent with a jitter of only 400 fs rms. The wide and continuous tunability of the free-electron laser (FEL; 4.2-300mum) combined with ultrashort pulse duration of six optical cycles and high pulse energy of several tens of microjoules makes a series of two-color experiments possible in a previously inaccessible wavelength range. We demonstrate these capabilities by performing a two-color pump-probe experiment to study carrier cooling in GaAs. A FEL tuned from 8 to 17mum is used as the pump, and a synchronized Ti:sapphire laser pulse serves as the probe.

Cavity ring down spectrocopy with a free-electron laser

Abstract A cavity ring down (CRD) absorption experiment is performed with a free-electron laser (FEL) operating in the 10–11 μm region. A short infrared pulse of approximately 20 ns, sliced from the much longer FEL pulse, is used to measure CRD spectra of ethylene in two different ways. First, “ordinary” CRD spectra with a resolution determined by the bandwidth of the FEL (≈ 5 cm−1) are recorded. Second, Fourier transform (FT) CRD spectra with a resolution that is in principle determined by the FT-spectrometer are obtained by analyzing the light exiting the ring down cavity with a FT-spectrometer while the FEL is operated in broadband mode.

Free-electron laser operation and self-amplified spontaneous emission using a step-tapered undulator

Abstract We present an experimental and theoretical evaluation of a new method of enhancing the efficiency and gain of the free-electron laser (FEL) and observations of self-amplified spontaneous emission at start-up of the step-tapered FEL. The stepped undulator is divided into two uniform sections of different deflection strengths, the upstream K 1 and the downstream K 2 , and a step of Δ K = K 2 − K 1 ≈ 0.03 with K 1 K 2 for mid-infrared operation.

Excite-Probe Determination of the Intersubband Lifetime in Wide Gaas/Algaas Quantum-Wells Using a Far-Infrared Free-Electron Laser

A direct excite-probe semiconductor lifetime determination in the picosecond regime has been made for the first time in the far infrared. We have used an RF-linac-pumped free-electron laser to determine the relaxation rate associated with intersubband absorption in GaAs/AlGaAs quantum wells having a subband separation smaller than the optical phonon energy. The measurement yields a relaxation lifetime of 40+or-5 ps. This is compared with a variety of other results obtained with less direct techniques.

Generation of frequency-chirped pulses in the far-infrared by means of a sub-picosecond free-electron laser and an external pulse shaper

The generation of frequency-chirped optical pulses in the far-infrared is reported. The pulses are produced by the free-electron laser FELIX. The chirp is induced by means of an external shaping device consisting of a grating and a telescope. The shaper is based on reflective optics to permit operation in a wide spectral range. The present experiments were made at 8.2 μm wavelength. The fwhm duration of the incident pulse was 0.50 ps, which corresponds to a bandwidth of 2.2%. It has been checked that a linear chirp is produced, for the case that the frequency increases from the leading edge of the pulse to the trailing edge, as well as for the reverse case. This is accompanied by an increase of the fwhm pulse duration which ranges up to 16.5 ps.

Optical Performance Comparison of Argon-Ion and Solid-State Cyan Lasers

Recent advances in biotechnology have created a need for compact, efficient and reliable 488-nm cyan lasers, a trend which has hastened the development of technologies to replace air-cooled argon-ion lasers in biomedical instrumentation applications.

A far-infrared broadband (8.5–37 μm) autocorrelator with sub-picosecond time resolution based on cadmium telluride

A background-free autocorrelator has been developed for measuring the duration of far-infrared laser pulses in the spectral range from 8.5 to 37 μm by using an 840-μm-long wedged cadmium telluride crystal as the second-harmonic generator. Typical intensity second-harmonic autocorrelation traces are given for the wavelengths of 19.7 and 37 μm, indicating FWHM pulse duration of 0.90 and 1.5 ps respectively. An interferometric autocorrelation trace at 18.2 μm has been measured for the first time, and the distortion of autocorrelation traces due to the absorption and re-emission of ambient water vapor is shown at 28 μm.

Observation of superradiance in a short-pulse FEL oscillator

Superradiance has been experimentally studied, in a short-pulse free-electron laser (FEL) oscillator. Superradiance is the optimal way of extracting optical radiation from an FEL and can be characterised by the following scale laws: peak optical power P, scales as the square of electron charge, Q, (P, proportional to Q(2)); the optical pulse duration, sigma(z), scales as the inverse of the square root of the charge, (sigma(z) proportional to 1/root Q); the efficiency, eta, scales as the inverse of optical pulse length (eta proportional to 1/sigma(z) proportional to root Q), which also implies that the relative spectral brightness defined by eta/(sigma(lambda)/lambda) remains constant and close to 0.86. To characterise the properties of the superradiant emission, we have measured the efficiency, optical pulse energy, pulse duration and spectral width as functions of electron beam current and cavity loss for the optimum cavity length detuning. The efficiency has been deduced from measurements of electron beam energy spectra. The optical pulse duration has been determined from second-order autocorrelation measurements and the optical spectra determined using a grating spectrometer. We show that the superradiance in the oscillator has properties similar to that in a high-gain amplifier and discuss the links with spikes created by synchrotron instabilities.

STEP-TAPERED OPERATION OF THE FEL : EFFICIENCY ENHANCEMENT AND TWO-COLOUR OPERATION

We present measurements of the temporal and spectral properties of radiation produced from the step-tapered undulator infrared free-electron lasers (FELs), CLIO in France and FELIX in the Netherlands. Using a two section undulator with independently adjustable deflection parameters, K, the FEL will operate either with an enhanced efficiency and improved spectral properties (with a small positive Delta K step) or simultaneously at two frequencies (for large Delta K). Using a dispersion-free hole output coupler the maximum wavelength difference delta lambda/lambda, has now been extended to more than delta lambda/lambda approximate to 0.6. We also present measurements that show that the FEL FELIX will produce significant power simultaneously at two wavelengths by coherent spontaneous emission when the wavelength is long and the electron bunch is short. The efficiency, spectral and temporal properties have been measured. We show that at the maximum efficiency, Delta K approximate to 0.02, the optical pulses generated are smooth and close to Fourier transform limited. By adjusting Delta K the optical pulse duration can be varied by a factor of 2 or more and sidebands due to synchrotron oscillations can be suppressed.