Pulse shaper

The hardware required for PEG work, although commercially available, is not usually included in the basic version of spectrometers. It consists of a gradient accessory, a gradient amplifier, a shielded probehead equipped with a z-gradient coil and a pulse shaper (which in itself is an integral part of the gradient accessory). 

The potential of broadband laser excitation and fs-pulse shaping for different microspectroscopy techniques ranges from pure dispersion compensation (in the case of SHG, THG), to highly functional pulse shaping (in the case of CARS), as summarized in Table 7.2. It is worth mentioning again that all techniques can be implemented in the same approach—broadband laser and pulse shaper. The detection technique of choice is just selected by the corresponding pulse shapes. 

FIGURE 7.7 Usage of the pulse shaper to simplify SPIDER pulse compression, as employed in the SAC-SPIDER method (von Vacano et al. 2006b, 2007). See text for details. 

The added benefit of intrinsic interferometric detection is only a further example of the great flexibility of using the pulse shaper in single-beam nonlinear microspectroscopy. The setup used here for CARS in its variants is, of course, also capable of immediately performing all the other nonlinear microspectroscopies simply by changing the shape of the excitation pulses with computer control. This is shown in the next section, where we discuss a broadband TPF application. 

To demonstrate the versatility of nonlinear microspectroscopy with shaped broadband laser pulses, TPF is chosen as a second example. Remember that TPF can be implemented only by programming the pulse shaper differently and sampling a different wavelength range of the signal spectrum in the same experimental setup. TPF is so far probably the most widely applied nonlinear optical spectroscopy... 

Stobrawa, G., Hacker, M., Feurer, T., Zeidler, D., Motzkus, M., and Reichel, F. 2001. A new high-resolution femtosecond pulse shaper. Appl. Phys. B-Lasers Opt. 72(5) 627-30. 

The ability to cancel all orders of phase distortion gives us an opportunity to evaluate the effect of partial dispersion correction on TPM. In particular, we focus on comparing SOD correction, which can be achieved with a prism pair arrangement, and correction of all orders of phase dispersion using MIIPS. For these measurements we used a pair of prisms in addition to our pulse shaper. With the aid of the pulse shaper, we found the condition for which SOD at the center wavelength was fully eliminated by the prism pair, and only higher-order dispersion was compensated by the pulse shaper. 

Written by an international panel of experts, this volume begins with a comparison of nonlinear optical spectroscopy and x-ray crystallography. The text examines the use of multiphoton fluorescence to study chemical phenomena in the skin, the use of nonlinear optics to enhance traditional optical spectroscopy, and the multimodal approach, which incorporates several spectroscopic techniques in one instrument. Later chapters explore Raman microscopy, third-harmonic generation microscopy, and nonlinear Raman microspectroscopy. The text explores the promise of beam shaping and the use of a broadband laser pulse generated through continuum generation and an optical pulse shaper. 

Using the broadband laser pulse generated through continuum generation and an optical pulse shaper, Vacano and Motzkus (Chapter 7) and Bantus et al. (Chapter 8) demonstrate the substantial untapped potential of this approach for microscopic biological imaging and biochemical analysis. 

Bessel-Thompson Delay Low Pass Filter with Pulse Shaper... 

Experiments were performed using a titanium sapphire laser oscillator capable of producing pulses with bandwidths up to 80 nm FWHM. The output of the oscillator was evaluated to make sure there were no changes in the spectrum across the beam and was compressed with a double prism pair arrangement. The pulse shaper uses prisms as the dispersive elements, two cylindrical concave mirrors, and a spatial light modulator (CRI Inc. SLM-256), composed of two 128-pixel liquid crystal masks in series. The SLM was placed at the Fourier plane [5]. After compression and pulse shaping, 200 pJ pulses were used to interrogate the samples. 

The pulse shaper is a device made of a pair of gratings and lenses, arranged in a zero dispersion compressor, and a liquid crystal modulator placed in the Fourier plane. Liquid crystal arrays allow one to influence independently spectral phase and amplitude with discretization of 128 pixels each. 

Fig.l. The experimental setup containing the pulse shaper, the molecular beam and the computer controlled feedback loop. 

LT, low-temperature housing A, amplifier S, pulse shaper D, discriminator CT, counter T, timer, (b) Principle of the discriminator Vj and V2 are the low and high signal limits... 

An experimental illustration of the GA is shown in Fig. 21. The molecule cyclopentadieny 1-iron-dicarbonyl-chloride was irradiated with pulses of 800 nm radiation that were initially 80 ns long before entering the pulse shaper. The phases of the laser pulses were modified with... 

The amplitude and phase corrections are calculated from the target pulse and the acquired pulse using a TADPOLE measurement, and the new amplitude and phase mask functions are simultaneously rewritten to the pulse shaper. The difference between the measured phase and the target... 

---