Characterization of a High Efficiency, Ultrashort Pulse Shaper Incorporating a Reflective 4096-Element Spatial Light Modulator

Abstract

We demonstrate pulse shaping via arbitrary phase modulation with a reflective, 1×4096 element, liquid crystal spatial light modulator (SLM). The unique construction of this device provides a very high efficiency when the device is used for phase modulation only in a prism based pulse shaper, namely 85%. We also present a single shot characterization of the SLM in the spatial domain and a single shot characterization of the pulse shaper in the spectral domain. These characterization methods provide a detailed picture of how the SLM modifies the spectral phase of an ultrashort pulse.

Fig. 1

Schematic of the pulse shaping apparatus as seen (a) from above and (b) from the side. The LC SLM is placed in the Fourier plane of the pulse, where it is used to modify the spectral phase. In (b), note that the height of the pulse is changed using the spherical mirror and the LC SLM.

Fig. 2

Phase induced when applying constant voltages on the SLM for three given voltages. Note that we have taken advantage of the arbitrary DC phase shift inherent in the interferometric measurement to shift the center pixel of the SLM to a phase of zero radians.

Fig. 3

Setup for SEA TADPOLE imaging is simply a Michelson interferometer. One arm of the interferometer is the pulse shaping apparatus, and an imaging spectrometer is used to obtain the interference pattern. The image is created by overlapping the pulses in time, and imaging spatial interference of the pulses at the entrance slit of the interferometer.

Fig. 4

(a) Typical SI with the LC SLM o&. (b) Fourier transform of SI in spatial dimension only.

Fig. 5

Spectral phase and complex amplitude extracted from the SI shown in Fig. 4(a). The phase induced by the pulse shaping line can be clearly seen.

Fig. 6

(a) SI generated with a 63-pixel period sinusoidal phase written to the SLM and (b) the spatial Fourier transform of the SI.

Fig. 7

Spectral phase change due to the SLM and complex amplitude of output pulse from the SI shown in Fig. 6(a).

Fig. 8

Examples of amplitude modulation with the SLM. Both figures show the result of a rectangular phase variation 500 pixels in width written to the SLM. In (b) the spectrum is increased, and the input beam diameter is twice that in (a), resulting in twice the spectral resolution. The amplitude modulation occurs when the variation in phase happens quickly. This is the result of the spectral resolution being lower than the resolution of the SLM, thus the phase jump looks like a linear phase ramp for some of the frequencies in the pulse.

Fig. 9

This figure illustrates the progression from amplitude and phase modulation to phase-only modulation when the period of a sinusoidal phase written to the SLM is varied. The periods are measured in pixels, and for the figures shown are: (a) 63, (b) 157, (c) 314, (d) 471, (e) 628, and (f) 1256. Note that as the period is decreased, the features on the SLM become smaller than the spectral resolution, resulting in amplitude modulation.