Laser modulation

The most spectacular applications of ECLs are the possibiUty of direct overwrite (DOW) with laser modulation (79,80) and of magnetically iaduced superresolution (81,82). The stacks comprise at least a storage layer s and a bias layer b. For both appHcations, the storage layer s has the lower and the higher at room temperature when compared to the bias layer b. At room temperature, b is homogeneously magnetized (initialized) by an external permanent magnet is about 400 kA/m (5 kOe)). 

Laser communication systems based on free-space propagation through the atmosphere suffer drawbacks because of factors like atmospheric turbulence and attenuation by rain, snow, haze, or fog. Nevertheless, free-space laser communication systems were developed for many appHcations (89—91). They employ separate components, such as lasers, modulators, collimators, and detectors. Some of the most promising appHcations are for space communications, because the problems of turbulence and opacity in the atmosphere are absent. 

Major, A., Cisek, R., and Barzda, V. 2006. Femtosecond Yb KGd(W04)(2) laser oscillator pumped by a high power fiber-coupled diode laser module. Opt. Exp. 14 12163-68. 

Figure4.110 Principle of laser structuring and photograph of the laser module showing the two axes-driven laser head [109],...

Figure 4.111 Principle of continuously working laser module and folding module [109].

Sometimes the mirror velocity must be calculated from what the instrument manufacturer specifies as the He-Ne laser modulation frequency. 

Fig. 20. Schematic diagram of the Synchroscan streak camera system. A Spectra Physics model 164 acousto-optically mode-locked argon ion laser modulated at 69.44MHz pumps the Rhodamine 6G dye laser formed by mirrors Mi, M2, M3 and M4. This dye laser typically produces pulses of 2 ps duration with an energy content of 0.6 nJ. The second harmonic is generated intracavity in an ADP crystal. The UV radiation is then coupled out through mirror Ms and a filter F2 is used to eliminate any transmitted visible light before focusing into the sample cell with lens Lt. The fluorescence is detected at 90 to the incident beam. A lens L2 collects the fluorescence which passes through a polarizer and a bandpass filter and then onto the slit of the streak camera. (After ref. 69.)...

Figure 9 Magnetic-field dependence of the FM NMOR signals, showing quadrupole resonances at B = 143.0 fj,G, and the hexadecapole resonances at 71.5 /liG. Laser modulation frequency is 200 Hz, and modulation amplitudes is 40 MHz peak to peak the central frequency is tuned to the low-frequency slope of the F = 2 — F = 1 absorption line. Plots (a) and (b) show the in-phase component of the signal at two different light powers plot (c) shows the quadrature component. Note the increase in the relative size of the hexadecapole signals at the higher power. The insets show zooms on hexadecapole resonances.

For the results shown below, a Becker Hickl BHL-600 laser module was used, with a wavelength of 650 nm, 80 ps pulse duration, and 50 MHz repetition rate. The incident power density at the surface of the leaf was approximately 1 mW/mm. The measurement wavelength was selected by a 700 15 nm bandpass filter. The fluoreseenee deeay curves were recorded in one TCSPC channel of a Beeker Hickl SPC-134 system. One fluorescence decay curve was recorded eaeh 2 seconds, at a count rate of about 2-10 s Dead time compensation was used to avoid the influenee of counting loss on the recorded intensity. Typical results are shown in Fig. 5.32. 

There are two methods that have been used to determine fluorescence lifetimes in DNA sequencing. In the first method, known as the frequency-domain or phase-modulation method, the excitation beam is intensity modulated. The a.c. portion of the resulting emission is phase-shifted relative to the laser modulation this phase-shift contains information about the fluorescence lifetime, or lifetimes if more than one fluor is present [140]. McGown and coworkers [144,145] used this method for four-color sequencing. In that work, 488 nm or 514 nm laser light was electronically modulated with a Pockels cell before being focused onto a capillary column. Detection, made normal to the laser direction, was optically filtered to reduce laser scatter and was focused onto the detector of a... 

The amplitude of the laser-cooled ion is enhanced resonantly near o)+ and 0) with maxima shifted from co+ and co by an amount that increases with y,. The resonance width is approximately y,. The in-phase amplitude has a dispersive shape, as for identical ions, and when only the laser-cooled ion is subject to a driving force (excitation by laser modulation) the amplitude has a zero-crossing at C0+ and co. For electrode excitation, where both ions are driven, the zero-crossing is offset from co+ or co by an amount that, for yi/co+ 1 is of the order of (yi/co+J. Intuitively, such an offset is present because, when both ions are driven, the driven motion of the non-cooled ion perturbs the phase of the laser-cooled ion. In contrast, when only one ion is driven, the other ion is pulled or pushed into phase with the driven ion. 

Experimental setup of the MOPA laser system is shown in Fig. 9.9 [98]. The master oscillator contained two laser modules, with a plano-plano symmetrical stmcture. One of the laser modules served as the amplifier stage. The internal time sequence was controlled by using a synchronous controller. In the setup, LI is the distance from the mirror Ml to the left end surface of the Nd YAG rod, L2 is the distance between the Nd YAG rods, and L3 is the distance from the mirror M2 to the right end surface of the Nd YAG rod. LI and L3 were 8 mm, which formed a symmetric resonator. L2 was 6 mm that was limited by the mechanical size of laser modules. The distance between the amplifier stage and the output mirror M2, i.e., L4, was 15 mm. Ml was coated to have 99.8 % high reflectance at 1064 nm. M2... 

Doppler-Limited Absorption and Fluorescence Spectroscopy with Lasers modulation carrier... 

Gulevich, A. V., etal. (1998). Fast Two-Core Pulse Reactor System with a Thermal Subcritical Laser Module Analysis of Startup Results, Trans. Am. Nucl. Soc. (USA) 78, 193. 

The direct modulation property of semiconductor injection lasers is one of their unique characteristics and this feature provides the potential for many scientific and commercial applications. Unlike other solid state and liquid lasers, modulating the injection current can directly control the optical output of the semiconductor laser. 

Schlleren and ombroscoplc cinematography using an argon laser modulated light (10 jjs duration, 900>1000 Hz frequency) and a drum camera. 

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