D. T. Reid

Light-emitting diodes as measurement devices for femtosecond laser pulses

We present results showing that, when it is used as a photodetector, a light-emitting diode (LED) has a power-dependent response that can be used for sensitive detection and characterization of picosecond and femtosecond laser pulses. A characterization of a typical LED is presented at 800 nm, and we demonstrate how this effect can be used to construct an extremely compact novel autocorrelator based on a Wollaston prism.

Characteristics of a noncritically phasematched Ti: sapphire pumped femtosecond optical parametric oscillator

Abstract The operating characteristics of a singly-resonant famtosecond optical parametric oscillator (OPO) based on a noncritically phasematched geometry in KTP are described. The parametric oscillator is synchronously pumped by a self-modelocked Ti: sapphire laser and is operated in a standing-wave cavity configuration. With extracavity dispersion compensation, chirped pulses of 90 fs are generated, whilst shorter transform-limited pulses of 40 fs are generated with intracavity dispersion compensation. A numerical model of the effects of self-phase-modulation in the OPO has been developed and gives results which are in good qualitative agreement with experiment. Experimental results are presented relating to non-phasematched processes in the OPO, and the implications for the development of a tunable femtosecond source in the blue spectral region are discussed. A characterisation of the amplitude and phase noise of the OPO has also been performed, and provides insight into the important physical processes governing the stability of OPO operation.

Algorithm for complete and rapid retrieval of ultrashort pulse amplitude and phase from a sonogram

We describe an algorithm based on principal-component generalized projections that is capable of unambiguous retrieval of the amplitude and phase of an ultrashort pulse from a measurement of its sonogram. Running on a personal computer, the algorithm can complete more than 50 iterations per second which enables real-time display of an ultrashort pulse intensity and phase profile. Retrieval is demonstrated for a range of pulses with commonly encountered phase errors including linear chirp, self-phase modulation, and cubic spectral phase, and experimental results illustrate good agreement between the retrieved pulse characteristics and independent spectral measurements.

Amplitude and phase measurement of mid-infrared femtosecond pulses by using cross-correlation frequency-resolved optical gating

We describe a cross-correlation-based frequency-resolved optical gating (XFROG) technique for simultaneously measuring the amplitude and phase of two ultrashort pulses that have different wavelengths but are derived from a common mode-locked oscillator. A measurement is presented in which 4.0-mum mid-IR pulses from a synchronously pumped femtosecond optical parametric oscillator (OPO) are characterized by mixing with the 770-nm OPO pump pulses. Details of the pulse-retrieval algorithm are included, together with examples of pulse data retrieved from the experimentally measured XFROG trace.

HIGH-REPETITION-RATE ULTRASHORT-PULSE OPTICAL PARAMETRIC OSCILLATOR CONTINUOUSLY TUNABLE FROM 2.8 TO 6.8 MU M

We describe a synchronously pumped femtosecond optical parametric oscillator based on periodically poled LiNbO3 that is broadly tunable in the mid infrared. A transmission window of periodically poled lithium niobate beyond the conventionally accepted infrared absorption edge of 5.4xa0µm has been exploited to produce idler pulses that are tunable across a wavelength range of 4xa0µm, with milliwatt-level output powers at wavelengths as long as 6.8xa0µm. We also present experimental tuning results that are in good agreement with the theoretical phase matching predicted from published infrared-corrected Sellmeier equations for LiNbO3.

Femtosecond optical parametric oscillator based on periodically poled lithium niobate

We describe a femtosecond optical parametric oscillator based on periodically poled lithium niobate and pumped by a self-mode-locked Ti:sapphire laser. Signal and idler outputs almost continuously tunable from 975 nm to 4.55 μm were generated by a combination of grating tuning and cavity-length tuning, and an explanation of the tuning properties is given in terms of the gain bandwidth. A threshold of 45 mW was measured and, in the absence of optimized output coupling, signal powers of 90 mW and idler powers of 70 mW were obtained, with 140 mW of green light at 540 nm generated by phase-matched frequency doubling of the signal. Dispersion compensation produced near-transform-limited signal pulses of duration 140 fs. Observations regarding temperature tuning and pump depletion are also presented.

Broadly tunable infrared femtosecond optical parametric oscillator based on periodically poled RbTiOAsO 4

We present results from what we believe is the first reported example of an optical parametric oscillator based on periodically poled RbTiOAsO(4). The oscillator is pumped by a femtosecond self-mode-locked Ti:sapphire laser and, with a single-grating 2-mm-long crystal and one mirror set, a combination of pump and cavity-length tuning provided wavelength coverage from 1060 to 1225nm (signal) and 2.67 to 4.5 microm (idler). Average output powers were as much as 120mW in the signal and 105mW in the idler and interferometric autocorrelations recorded at signal and idler wavelengths of 1.1 and 3.26 microm, respectively, imply pulse durations of 125 and 115fs, respectively.

Noncritically phase-matched Ti:sapphire-pumped femtosecond optical parametric oscillator based on RbTiOAsO 4

The operation of a Ti:sapphire-laser-pumped femtosecond optical parametric oscillator based on the new nonlinear material RbTiOAsO(4) is described. Oscillation has been observed for pump powers as low as 50 mW, and output powers as high as 185 mW have been measured. With intracavity prisms for dispersion compensation, transformlimited pulses of less than 70-fs duration have been produced. Under noncritical phase matching, a signal (idler) tuning range over 110 nm (330 nm) is demonstrated with pump tuning.

Simultaneous femtosecond-pulse compression and second-harmonic generation in aperiodically poled KTiOPO 4

We report both extracavity and intracavity simultaneous second-harmonic generation and compression of pulses at 1.25 mum from a synchronously pumped RbTiOAsO(4) -based optical parametric oscillator, using an aperiodically poled crystal of KTiOPO(4) . The 290-fs input pulses were temporally compressed to 120 fs, with average output powers as great as 120 mW. The experimental results are compared with a numerical model that uses data obtained by characterization of the input pulses by use of the frequency-resolved optical gating technique.

Characterization and modeling of a noncollinearly phase-matched femtosecond optical parametric oscillator based on KTA and operating to beyond 4 /spl mu/m

We describe the design and operation of a critically phase-matched femtosecond optical parametric oscillator based on KTA. By employing a small pump-signal noncollinear angle, tuning of the idler to beyond 4 /spl mu/m is achieved using a Ti:sapphire pump laser. A Gaussian-beam model is described which can be used to identify the optimal noncollinear phase-matching geometry. Idler and signal pulses are characterized fully both temporally and spectrally and interferometric autocorrelation data at 3.5 /spl mu/m showing idler pulses of only eight optical cycles duration are presented.