Laser Beam Steering

In addition to displays, liquid crystals have also been used extensively in tunable photonic devices, such as optical phased array for laser beam steering, variable optical attenuator (VOA) for telecommunications, tunable-focus lens for camera zoom lens, LC-infiltrated photonic crystal fibers [1,2], diode laser-pumped dye-doped LC laser, just to mention a few. 

In this chapter, we only select four topics to illustrate the potential appUcations of liquid crystals in photonics and their technical challenges. The four representative subjects selected are (1) laser beam steering, (2) variable optical attenuator, (3) tunable-focus lens, and (4) polarization-independent LC devices. 

Active transmitler wiih laser diode and beam steering... 

Figure 15.5 Schematic of instrumental apparatus. The DT/MH-functionalized AgFON was surgically implanted into a rat with an optical window and integrated into a conventional laboratory Raman spectroscopy system. The Raman spectroscopy system consists of a Ti sapphire laser (Acx = 785 nm), band-pass filter, beam-steering optics, collection optics, and a long-pass filterto reject Raleigh scattered light. All of the optics fit on a 4 ft x 10 ft optical table.

Active-steered communication systems include a small laser diode, a collimating lens and beam-steering optics. 

Figure 10. Optical configuration for differentially arranged, thermal lens detected CD. P, beam steering prism M, beam steering mirror BS, polarizing beam splitter HR, half-wave rhomb QR, quarter-wave rhomb L, focusing lens DM, dichroic mirror C, converging sample cell (before probe focus) D, diverging sample cell (after probe focus) PD, aperture/photodiode combination LF, line filter (to isolate the probe laser from extraneous pump radiation). Solid line, probe laser optical path broken line, pump beam path.

The application of bR as protein biochip offered a new possibility in the molecular memory research. As an example of current work, consider the molecular optical memory research underway by Birge and coworkers. Using the purple membrane from the bacterium Halobacterium hajobium, a working optical bistable switch, fabricated in a monolayer by self-assembly, that reliably stores data with 10,000 molecules per bit was realised. The molecule switches in 500 femtoseconds and the actual speed of the memory is currendy limited by how fast you can steer a laser beam to the correct spot on the memoty. 

Implementation of Beam-Steered Laser Marking of Coated and Uncoated Plastics 309... 

Figure 12.3 Acousto optical defelectors (AODs) are used to steer the laser optical tweezer. Left a photograph of the AODs mounted on the optical table. The AODs are fixed to translators that allow fine adjustment of angle and translation with respect to the input laser beam. Right how the laser must enter the AOD at the Bragg angle so that the first order beam (which is the beam used to produce the optical trap) exits aligned with the microscope axis...

Fig. 2 Schematic diagram of laser optical tweezers (LOT) system. (Top panel) An infrared laser beam was steered to trap and move pm-size particles in the focal plane. At a sufficiently large laser intensity, the gradient force dominates over the scattering force. (Lower panel) Membrane tethers are extracted from live cells. Dielectric beads (0.5 pm in diameter) were conjugated with antibodies against integiins and attached to the cell membrane. LOT traps one bead and pulls it away from the cell, as indicated by the arrow. Thin membrane tethers extending from the beads to the cell body appear. Using conventional brightfield microscopy, the tether length and its diameter are measured which, in turn, provide an estimate of the plasma membrane tension.

Lenses and Other Trapping Optics Lenses are required to expand the initial laser beam so that it totally fills the back apermre of the objective lens. Beam expanders can be either bought or constructed for specific use by using individual lenses. The latter allows for the flexibility of a variable output if three lenses are used. Mirrors help to steer the beam. Other optics might be required depending on the specific task. Position detection might be achieved by a variety of techniques with each having its own merits and demerits. An exhaustive treatment of the same can be found in [4]. 

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