Modulation laser light

Laser Light Modulation and Side Band Tuning... 

The light produced by a laser has a much more narrow wavelength than the light of an LED or other light sources (Fig. 15.3). In addition, laser light is coherent, i.e., the photons travel in parallel paths from the source. Lasers made of thin-films are similar to bulk lasers (He-Ne, ruby) except that they are more compact and efficient. Due to the short lifetime of the photons, high-frequency modulations are possible. 

Nowadays, polymeric photoconductors may be used in electrophotography, microfilms, photothermoplastic recording, spatial light modulators, and nonlinear elements. The combination of photosensitivity with high quality electrical and mechanical properties permits the use of such materials in optoelectronics, holography, laser recording and information processes. The applications of the various types of polymers were reported in the final parts of the relevant items in the earlier sections. Here, we will briefly analyze the common features of photoconductive polymer applications. The separate questions of each type have been dealt with in some books and papers [3, 11, 14, 329]. 

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. 

As a method to control wavepackets, alternative to the use of ultra-short pulses, I would like to propose use of frequency-modulated light. Since it is very difficult to obtain a well-controlled pulse shape without any chirp, it is even easier to control the frequency by the electro-optic effect and also by appropriate superposition of several continuous-wave tunable laser light beams. 

When an intense pulse of monochromatic laser light is focussed on a transparent liquid or solid, there is an emission of white light over a wide continuous spectral range. This process is known as self-phase modulation . We will not consider its physics. For our purpose it is important to note its photochemical implications. On the one hand, this pulse of white light can be used to provide a probe light in ps and fs flash photolysis (sections 8.1 and 8.2). On the other hand, it can be a source of stray light in some luminescence measurements. This comes as a surprise to many users of lasers for luminescence kinetics measurements, but it is an unavoidable problem. 

All of our natural experience with optics occurs in the linear domain. In order to apply nonlinear optics in practice, light must first interact with the NLO material. In our laboratories, free space interconnections are usually employed for this purpose. That is, a laser beam is aimed at the material under examination. In any practical use of NLO, such simplistic solutions will not be possible, for reasons both of safety and rugged construction of the device. Light will need to be moved around in space within the device. In many second order devices, whether they are color-specific lasers, such as doubled diode or YAG lasers, or EO modulators such as spatial light modulators (SLM s) waveguide or fiber optic connections will be used. Aspects of these materials will not be reviewed. 

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