Electro-optic Phase Modulators

The electro-optic crystal changes its refractive index n(V) with the application of a voltage V = Vb(l + a sinf2r). The amplitude of the laser wave transmitted through the phase-modulator with optical length n L is... 

Simple demonstrations of electro-optic and nonlinear device functions such as phase modulation [146], optical limiting [148] and polarization... 

H. E., and Schilling, M. L., Electro-optic phase modulation and optical second-harmonic generation in corona-poling polymer films, Appl. Phys. Lett., 53, 1800, 1988. 

Circular dichroism employs standard dispersive or interferometric instmmentation, but uses a thermal source that is rapidly modulated between circular polari2ation states using a photoelastic or electro-optic modulator. Using phase-sensitive detection, a difference signal proportional to the absorption difference between left- and right-polari2ed light, AA is recorded as a function of wavenumber. Relative differential absorptions... 

Historically, the first instrument for the determination of lifetime was a phase fluorometer (designed by Gaviola in 1926) operating at a single frequency. Progress in instrumentation enabled variable modulation frequency by employing a cw laser (or a lamp) and an electro-optic modulator (0.1-250 MHz), or by using the harmonic content of a pulsed laser source (up to 2 GHz). These two techniques will now be described. 

Phase fluorometers using a continuous light source and an electro-optic modulator... 

However, unlike diode lasers, an external acousto-optic or electro-optic modulator is required for phase-modulation lifetime fluorometry to be performed with a HeNe laser. 

III. Electro-Optic Phase Modulators Using Organic Materials... 

Figure 5. Experimental setup for electro-optic phase modulation.

Fig. 1 Setup for transient holographic grating measurements. The electro-optic modulators (EOMs) are used for 180°-phase shifts of the holographic grating. The piezo mirror serves for phase matching between the diffracted beam and the coherent reference wave generated by the local oscillator. The setup is a modified version of the one described in [87]...

We have seen that a bulk transparent electro-optic crystal changes its index by a small amount, if an electric field is applied. Figure 4.9 shows a phase modulator for transverse geometry. Let us look at some numbers for LiNb03 d = 1 mm, L = 10 mm, r33 = 30.9 pm/V, ne = 2.2, U = 180 V, and A0 = 0.6 ptm. We find... 

Figure 4.9 Schematic of bulk electro-optic phase modulator in transverse geometry (a) standard electrode arrangement for static measurements, (b) travelling wave configuration...

Fig. 1. Set-up of the PTB laser system. The Nd YAG laser is frequency stabilized onto a selected iodine absorption line using the phase modulation method. The probe beam is modulated at 2.05 MHz by an electro-optic modulator (EOM), the pumb beam is frequency shifted by an acousto-optical modulator (AOM). The driving AOM rf power is chopped in order to cancel frequency offsets introduced by the Doppler background using a lock-in detection scheme. The transmitted probe beam signal is detected by a photodiode (PD) and mixed with the EOM rf in a double balanced mixer (DBM)...

Mode-locked laser A laser in which many resonant modes are coupled in phase, to yield a train of very short pulses (e.g. ps pulses). The coupling of the modes is obtained by modulation of the gain in the resonator, and can be active (electro-optic modulation of the losses or of the pump intensity), or passive (with a saturable absorber). 

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