Optical parametric converter

The femtosecond transient absorption studies were performed with 387 nm laser pulses (1 khz, 150 fs pulse width) from an amplified Ti Sapphire laser system (Model CPA 2101, Clark-MXR Inc). A NOPA optical parametric converter was used to generate ultrashort tunable visible pulses from the pump pulses. The apparatus is referred to as a two-beam setup, where the pump pulse is used as excitation source for transient species and the delay of the probe pulse is exactly controlled by an optical delay rail. As probe (white light continuum), a small fraction of pulses stemming from the CPA laser system was focused by a 50 mm lens into a 2-mm thick sapphire disc. A schematic representation of the setup is given below in Fig. 7.2. 2.0 mm quartz cuvettes were used for all measurements. 

Fig. 7.2 Two-beam experimental setup for femtosecond transient absorption studies using a white light continuum. A commercially available CPA 2101 laser system delivers the pulses. Ultrashort tunable visible pulses are obtained by the NOPA optical parametric converter. A chopper wheel is used to cut every second pump pulse in order to compare the signal with and without the pump. The white light continuum is generated by a sapphire disc. The time delay between the pump and probe pulses is adjusted by the optical delay rail...

Optical parametric converter Optical equivalent of heterod3me effect the mixing of a coherent signal and a beam from a local oscillator takes place in a nonlinear optical crystal and results in foequency difference (downconversion) or their sum (upconversion)... 

Time-resolved fluorescence was used to detect rhodamine 6G (R6G), sulfor-hodamine 101 (SR101), and rhodamine B (RB). A Ti-sapphire laser (800 nm, 50 fs) was used, but the excitation wavelength has been converted to 400 nm (for R6G) or 532 nm (for SR 101 or RB) by an optical parametric amplifier or by second harmonic generation [676], In another report, fluorescence burst detection was used for detection of single chromophore molecules [677]. 

For second harmonic generation (SHG), the tensor is y(2)(—2co co, co) (useful for frequency doubling and parametric down-conversion) while for the linear electrooptic or Pockels71 effect the tensor is y(2)(— co co, 0) (useful for Q-switching of lasers, for phase or amplitude modulators, and for beam deflectors) for optical rectification the tensor is y 2>(0 00, —co) for frequency mixing the tensor is y(2)(— co3 oolr co2) (useful for frequency up-converters, optical parametric oscillators, and spectroscopy). 

Another example of a second-order non-linear process is optical parametric down-conversion. In optical parametric down-conversion, a photon from an input pump (p) wave at frequency lower frequencies ffl and coi. These are termed the signal (s) and idler (i) frequencies, with the convention cOg < coj. Within a photon picture, the OPO can be thought of as a photon splitter. However, it should be made clear that a photon is not really cut into two it is the non-linear action with the incoming high-frequency wave with the NLO material that gives rise to the generation of two new low-frequency waves. 

This is an alternative solution to a tunable laser source in the optical frequency range. Here a powerful single frequency radiation (pump) is parametrically converted into equally powerful coherent radiation tunable over a wide optical frequency range (signal and idler). In its simplest version, which is also the most useful one, it is based on the optical parametric amplification of noise photons of frequencies (Wj and 0)2 provided by the dissociation of a pump photon of frequency o)p such that 0) = 0) + 0D2, the selection of a particular frequency pair being made through the phase-matching condition... 

In the field of solid state physics, one of the most investigated materials is ferroelectric, which has important applications as memory switching [1-4], nonlinear optical communications [5], non-volatile memory devices [6, 7], and many others [8, 9]. Ferroelectrics have also emerged as important materials as (a) piezoelectric transducers, (b) pyroelectric detectors, (c) surface acoustic wave (SAW) devices, and (d) four-phase mixing doublers. Both lithium tantalate and lithium niobate appear to be promising candidates as the key photonic materials for a variety of devices (a) optical parametric oscillators, (b) nonlinear frequency converters, (c) second-order norrlinear optical material, and (d) holography, etc. Many of such devices include important nano-devices [9-11],... 

In recent years there has been a growing interest in the search for materials with large macroscopic second-order nonlinearities [20-22] because of their practical utility as frequency doublers, frequency converters and electro-optic modulators [23] by means of second-harmonic generation, parametric frequency conversion (or mixing) and the electro-optic (EO) effect. They are described by X (2w w, u)), 0, w), respectively. In order to optimize... 

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