Pulse frequency generation

It would be impossible to handle ternary solvent systems such as acetonitrile/ water/methanol or mixtures which contain further additives such as triethyla-mine. Therefore most techniques nowadays use modulated shaped pulses for multiple presaturation or pulse frequency generation (PFG) techniques. With basic hardware, it is then possible to suppress an arbitrary number of solvents. 

Ultrasonic pulses are generated within the sample on the transducer s resonance frequency, pass through sample and are received by the wideband receiver. After received pulse processing in the computer, results analysis is carried out. 

SHG Optical second-harmonic generation [95, 96] A high-powered pulsed laser generates frequency-doubled response due to the asymmetry of the interface Adsorption and surface coverage rapid surface changes... 

Richter L T, Petralli-Mallow T P and Stephenson J C 1998 Vibrationally resolved sum-frequency generation with broad-bandwidth infrared pulses Opt Lett. 23 1594-6... 

There are many specific ways to generate equally spaced tags but they are all based on the same principle of manipulating the rf pulses to generate equally spaced bands of rf radiation in the frequency domain. It is well known that under ordinary conditions, meaning normal levels of nuclear spin excitation, the frequency spectrum of the rf excitation pulse(s) is approximately the Fourier transform of the pulses in the time domain. Thus, a single slice can be generated in the... 

The other consequence of the pulse width is the spread of frequencies generated. The shorter the pulse, the wider will be the spread of frequencies. Because we often want to excite a wide range of frequencies, we need very short pulses (normally in the order of a few microseconds). This gives rise to a so-called sine function (Figure 3.3). 

Initial laser pulse generation is achieved with the use of a twin-tube excimer laser in which one channel is a XeCl laser oscillator dehvering 15-ns, 308-nm, 80-mJ pulses for the driving of two dye lasers needed for difference frequency generation. The second channel is used for amphfication of subpicosecond 308-nm pulses that become pump pulses. 

We performed transient absorption measurements on BP(OH>2 with a spectrometer based on two noncollinearly phase matched optical parametric amplifiers (NOPAs) pumped by an homebuilt regenerative Ti Sapphire laser system or a CPA 2001 (Clark-MXR) [1,7]. The tunable UV pump pulses are generated by frequency doubling the output of one of the NOPAs. The other NOPA provides the visible probe pulses. The cross correlation between pump and probe pulses has a typical width (FWHM) of 40 fs. The sample is a cyclohexane solution of BP(OH)2 pumped through a flow cell with a 120 pm thick channel. 

The double-beam transient absorption spectrometer utilized in this work is described in detail elsewhere [3]. Briefly, the output from a 1 kHz Ti Sapphire laser is frequency quadrupled to generate the 200 nm photolysis pulses. The probe pulses are generated by frequency doubling the output of an optical parametric amplifier (OPA) pumped at 400 nm or by sum-frequency mixing of the OPA output with 400 nm and 800 nm pulses. The sample consisted of a 0.1 mm jet of aqueous KNO3 solution. The acidity of the solutions was adjusted by addition of HN03(aq). 

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