L. Corner

Cavity-enhanced absorption spectroscopy of methane at 1.73 μm

Abstract The integrated cavity output spectroscopy technique has been applied to the study of methane near 1.73 μm using a tunable diode laser. We have shown that this simple approach produces accurate high resolution spectra and have achieved a detection sensitivity of 1.8×10 −7 cm −1 for mirror reflectivities of 99.84%.

OH detection by absorption of frequency-doubled diode laser radiation at 308 nm

Radiation at 308 nm has been obtained by frequency doubling the output of a commercial diode laser cooled to 165 K. A single pass through a crystal of LiIO3 converted 1 mW of 616 nm radiation to 50 pW of UV, and this was used to detect the OH radical in absorption in a flow tube. Possible extensions of the method for detection of OH in the atmosphere are discussed.

Experimental and theoretical characterisation of rhodium-doped barium titanate

Abstract We present the results of an experimental and theoretical investigation of the properties of rhodium-doped barium titanate (Rh:BaTiO 3 ). In our theoretical analysis we derive an expression for the effective trap density in the three-valence state model, for the first time to our knowledge. We apply this model of photorefraction to the three-valence states of rhodium in Rh:BaTiO 3 , together with additional iron centres, and using this theory and our experimental results we deduce the population densities and some photorefractive parameters of Rh:BaTiO 3 .

Measurements of pressure broadening coefficients of selected transitions in the 2ν5 band of formaldehyde

A tunable diode laser and a low finesse optical cavity are used to probe formaldehyde on four selected rotational transitions within its 2ν5 overtone band around 1.76 μm by cavity enhanced absorption spectroscopy (CEAS). Pressure broadening coefficients for these transitions in the presence of a variety of gases (He, Ne, Ar, Kr, N2, O2 and H2O, and also for CH2O itself) have been determined. The variation in the pressure broadening cross sections with molecular parameters of the colliding partners is discussed in terms of multipole interactions and compared with previous results and with inelastic collision probabilities. For the rare gases the pressure broadening parameters are shown to be strongly correlated with the intermolecular well depth between CH2O and each collider.

Cross sections in the 2ν5 band of formaldehyde studied by cavity enhanced absorption spectroscopy near 1.76 μm

The 2ν5 C–H stretching band of formaldehyde has been studied by cavity enhanced absorption spectroscopy near 1.76 μm using the output of an external cavity diode laser. Strong individual transitions have been spectroscopically identified, and the absorption cross section and air broadening parameter measured for the QR1(10) line at 5676.21 cm−1, a wavenumber at which interference from absorption by atmospheric CH4 and other constituents is minimal. The integrated cross section is found to be 5.7 ± 0.6 × 10−22 cm2 cm−1, and the pressure broadening coefficient for air at 295 K is 3.93 MHz Torr−1 (half width at half maximum of the Lorentzian component). The integrated intensity of the 2ν5 absorption band is found to be a factor of 108 smaller than that of the ν5 fundamental. Implications of these values for the measurement of atmospheric formaldehyde by absorption near 1.76 μm are discussed.

Multi-pulse laser wakefield acceleration: a new route to efficient, high-repetition-rate plasma accelerators and high flux radiation sources

Laser-driven plasma accelerators can generate accelerating gradients three orders of magnitude larger than radio-frequency accelerators and have achieved beam energies above 1 GeV in centimetre long stages. However, the pulse repetition rate and wall-plug efficiency of laser plasma accelerators is limited by the driving laser to less than approximately 1 Hz and 0.1% respectively. Here we investigate the prospects for exciting the plasma wave with trains of lowenergy laser pulses rather than a single high-energy pulse. Resonantly exciting the wakefield in this way would enable the use of different technologies, such as fibre or thin-disc lasers, which are able to operate at multi-kilohertz pulse repetition rates and with wall-plug efficiencies two orders of magnitude higher than current laser systems. We outline the parameters of efficient, GeV-scale, 10 kHz plasma accelerators and show that they could drive compact x-ray sources with average photon fluxes comparable to those of third-generation light source but with significantly improved temporal resolution. Likewise free-electron laser (FEL) operation could be driven with comparable peak power but with significantly larger repetition rates than extant FELs.

Complete characterization of attosecond pulses

We review the requirements for achieving full phase and amplitude characterization of attosecond X-ray pulses and propose several methods for carrying out such measurements. We show via numerical simulation that these techniques are capable of retrieving full field information of attosecond pulses and compare their performance and ease of implementation.

Excitation and Control of Plasma Wakefields by Multiple Laser Pulses

We demonstrate experimentally the resonant excitation of plasma waves by trains of laser pulses. We also take an important first step to achieving an energy recovery plasma accelerator by showing that a plasma wave can be damped by an out-of-resonance trailing laser pulse. The measured laser wakefields are found to be in excellent agreement with analytical and numerical models of wakefield excitation in the linear regime. Our results indicate a promising direction for achieving highly controlled, GeV-scale laser-plasma accelerators operating at multikilohertz repetition rates.

ATF extraction line laser-wire system

The ATF extraction line laser-wire (LW) aims to achieve a micron-scale laser spot size and to verify that micron- scale beam profile measurements can be performed at the International linear collider beam delivery system. Recent upgrades to the LW system are presented together with recent results including the first use of the LW as a beam diagnostic tool.

Laserwire at the Accelerator Test Facility 2 with submicrometer resolution

A laserwire transverse electron beam size measurement system has been developed and operated at the Accelerator Test Facility 2 (ATF2) at KEK. Special electron beam optics were developed to create an approximately 1 x 100 {\mu}m (vertical x horizontal) electron beam at the laserwire location, which was profiled using a 150 mJ, 71 ps laser pulse with a wavelength of 532 nm. The precise characterisation of the laser propagation allows the non-Gaussian transverse profiles of the electron beam caused by the laser divergence to be deconvolved. A minimum vertical electron beam size of 1.07