Laser scissors

Tiny laser scissors have been used to cut off pieces of chromosomes during cell division. Laser tweezers were then used to move the pieces around the cell and the spindles, as shown in Figure 2. Knowing the force with which the tweezers grasp the chromosomes, scientists can measure the opposing force exerted by the spindles. Scientists hope that learning how spindles function during cell division will help them learn more about diseases related to cell division, such as cancer—a disease in which cells divide uncontrollably. 

Easy availability of ultrafast high intensity lasers has fuelled the dream of their use as molecular scissors to cleave selected bonds (1-3). Theoretical approaches to laser assisted control of chemical reactions have kept pace and demonstrated remarkable success (4,5) with experimental results (6-9) buttressing the theoretical claims. The different tablished theoretical approaches to control have been reviewed recently (10). While the focus of these theoretical approaches has been on field design, the photodissociation yield has also been found to be extremely sensitive to the initial vibrational state from which photolysis is induced and results for (11), HI (12,13), HCl (14) and HOD (2,3,15,16) reveal a crucial role for the initial state of the system in product selectivity and enhancement. This critical dependence on initial vibrational state indicates that a suitably optimized linear superposition of the field free vibrational states may be another route to selective control of photodissociation. 

In 1985 chemists at Rice University in Texas used a high-powered laser to vaporize graphite in an effort to create unusual molecules believed to exist in interstellar space. Mass spectrometry revealed that one of the products was an unknown species with the formula Ceo- Because of its size and the fact that it is pure carbon, this molecule has an exotic shape, which the researchers worked out using paper, scissors, and tape. Subsequent spectroscopic and X-ray measurements confirmed that Ceo is shaped like a hollow sphere with a carbon atom at each of the 60 vertices. Geometrically, buckyball (short for buckminsterfullerene ) is the most symmetrical molecule known. In spite of its unique features, however, its bonding scheme is straightforward. Each carbon is xp -hybridized, and there are extensive delocalized molecular orbitals over the entire structure. 

Hie most thorough and accurate method to debride an ulcer wound is to surgically remove any necrotic tissue. Surgical instruments (scalpel, forceps, scissors, or laser) are used to cut away the dead tissue. Surgical debridement may be associated with bleeding, which can be controlled by direct pressure, electrocautery, or by cauterising the wound with silver nitrate. ... 

The formation and dissociation of chemical bonds is of prime concern in chemistry, and with the advent of ultrafast high-intensity lasers, selective bond dissociation using appropriate laser pulses as molecular tweezers and scissors has received extensive and intense attention. - Theoretical approaches to laser-assisted control of chemical reactions have kept pace and demonstrated remarkable success, with experimental results reinforcing the theoretical ideas. The development of... 

The experimental realization of the optimal initial states is, however, a completely uncharted area. In an earlier paper,we have presented the formulae to obtain field parameters required to achieve these FOISTs, and the optimal control approach may also feasibly and profitably be employed to attain this FOIST, which comprises only three vibrational levels. We however believe that, while the theoretical tools are useful, the central results from our investigation - - are that, instead of putting the entire onus of selective control on a theoretically designed laser pulse that may not be easy to realize in practice, the approach where different vibrational population mixes are experimentally obtained and subjected to readily attainable photolysis pulses, leading to an empirical experimental correlation between selectivity attained for diverse photolysis pulses and initial vibrational population mix used, represents a more promising and desirable alternative. Our results, we hope, will spur experimental tests, and a concerted partnership between field and initial state shaping is required to better realize the chemical dream - of using lasers as molecular scissors and tweezers to control chemical reactions. 

M.W. Berns Lciser scissors and tweezers. Sci. Am. 278(4), 52 (1998) M.E.J. Priese, T.A. Nieminen, N.R. Heckenberg, H. Rubinsztein-Diinlop Alignment and spinning of laser-trapped microscopic pai ticles. Nature 394, 348 (1998)... 

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