Time multiplexing of high power laser diodes with single crystal photo-elastic modulators

Abstract

Time-multiplexing is a method to increase the brilliance of diode lasers, i.e. a sequence of laser pulses emitted from different laser diodes at different times is guided onto a common optical path via a cascade of polarizing cube beam splitters and polarization switches. The latter are made of piezo-electric crystals oscillating in resonance and making use of the photo-elastic effect to obtain the desired modulation of polarization. We realized a demonstrator for time multiplexing of four laser diodes with such self-excited photo-elastic modulators. The latter is a new alternative to conventional photo-elastic modulators used in ellipsometers.

Power scaling of AOM-switched lasers with SCPEM-based time-multiplexing

“…Its operation is based on polarization modulation utilizing the photo-elastic effect caused by an electrically induced mechanical oscillation of the crystal. The modulator retardation δ(t) [rad] is [14][15][16][17]…”

“…As an alternative we demonstrated a new approach based on the combination of two channels and two gain mediums and a type of time-multiplexing similar to that proposed in [14]. The basic idea is that the original single channel resonator is upgraded to two channels.…”

“…The Q-switching is carried out by one AOM in the common part of the resonator. Switching between the two channels is performed with a Single Crystal Photo-Elastic Modulator (SCPEM [14][15][16][17]) that is suitable for high frequency operation and requires just a few volts for driving.…”

New developments in the field of diode lasers

“…All lasers can have the same wavelength which opens the possibility to use additionally standard wavelength multiplexing for further increase of brilliance. In [11] a successful realization of this with four high power laser diodes is reported. 4W laser diodes emitting at 960 nm were used and pulsed with a repetition frequency of 1.1 MHz, a pulse duration of 300 ns and an average power of 3.6 W. The pulses were combined to one quasi-continuous laser beam with 10.5 W optical power (Fig.…”

A new material for single crystal modulators: BBO

“…The SCPEM offers a smaller, simpler and more costeffective solution than the conventional PEM, which is made of two pieces, namely one glass as the optical modulator and one piezo-electric actuator [1,2,3] . Applications of SCPEM's were already demonstrated for Q-switching [6,7,17] , timemulitplexing [4] , and ellipsometry [5] . A particularly advantageous configuration is offered by crystals from the symmetry class 3m, where a transversal excitation in y-direction is possible, while the light travel along the optical axis (the z-axis), such that no affect on polarization is found in the resting state.…”