FACILITY FOR CALIBRATION OF PHOTOMETERS FOR TEMPORAL LIGHT MODULATION

We developed a facility for calibration of TLM (temporal light modulation) photometers. The facility is based on a laser-fed reference source, of which the radiance can be modulated with an acousto-optic modulator (AOM). A system of photodiodes, amplifiers, and an analog-to-digital converter (ADC) is used to sample the temporally modulated radiance of the source. With the facility a TLM photometer was calibrated for display contrast ratio RMS (root mean square) with an absolute combined standard uncertainty of 0,037 %. In addition, the facility has been characterised with the aim of measuring flicker and stroboscopic effect, considering the Ecodesign ‘Single Lighting Regulation’. The frequency response of the facility shows to be sufficient to accommodate measurements of flicker and the stroboscopic effect.

Dependence of the energy efficiency of the acousto-optic modulator of terahertz radiation on the dimensions of the ultrasound transducer

The paper presents results of experimental investigation of an acousto-optic modulator of terahertz radiation based on liquefied sulfur hexafluoride. It was found that the intensity of diffracted radiation at a fixed ultrasound power depends on the dimensions of the ultrasound transducer. The optimal size of the ultrasound transducer in the direction orthogonal to the plane of the acousto-optic interaction was determined, at which the maximum energy efficiency of the acousto-optic modulator was achieved.

Double-Frequency-Shift Acousto-Optic Modulator with Controllable Pulse Pair Frequency Difference

A scheme for controlling the frequency difference of output pulse pair with double frequency shift loops is proposed. The frequency shift system includes two loop elements of 20 and 200 MHz. The first one carries out a single selective positive frequency shift of 1–20 MHz, and the second one can satisfy a single fixed positive frequency shift of 200 MHz. The reverse cascade technology of two acousto-optic crystals is introduced to solve the limitation of the small frequency shift of crystal size. A multichannel synchronization signal completes the time domain control of each acousto-optic modulator. Finally, the frequency shift difference of the output pulse pair ranges of 0–2 GHz, and the frequency shift accuracy is 5 MHz.

Mid IR Holmium, Praseodymium - doped Fluoride Fiber Laser Pulse Operation

Pulsed operation of a novel single-clad mid IR Ho3+, Pr3+ co-doped ZBLAN fiber laser ‎excited by a Nd:YAG laser at 1064 nm has been demonstrated using pulse-pumping. An acousto-optic modulator (AOM) has been used to modulate the CW input pump ‎laser and used in either zero-order or first-order operation. A regular output train of pulses was generated for modulation frequencies over 1 Hz - 100 kHz ‎with zero-order operation of the AOM. A maximum peak power of ~ 50 W and pulse ‎duration of ~200 ns have been obtained for a modulation frequency of 45 kHz and 9.3 ‎W pump power. Single-end and double-end pumping of the ‎first-order AOM operation for the fiber have also been demonstrated to avoid the overheating of the modulator which ‎reduces the modulation efficiency. The same results as the zero AOM operation were obtained when the fiber laser was pumped with a pumping power of about 5 watts. Keywords: Fiber lasers, Pump pulsed operation, Acousto-optic modulator (AOM), Single-end and double-end pumping. PACs: Fiber lasers, 42.55.Wd, Acousto-optical devices, 42.79.Jq.