Kevin T. Gahagan

Integrated electro-optic lens/scanner in a LiTaO3 single crystal.

We report what we believe to be the first stand-alone integrated electro-optic lens and scanner fabricated on a single crystal of Z-cut LiTaO(3). The independently controlled lens and scanner components consist of lithographically defined domain-inverted regions extending through the thickness of the crystal. A lens power of 0.233 cm(-1) kV(-1) and a deflection angle of 12.68 mrad kV(-1) were observed at the output of the device.

Large-angle electro-optic laser scanner on LiTaO 3 fabricated by in situ monitoring of ferroelectric-domain micropatterning

We report on a horn-shaped electro-optic scanner based on a ferroelectric LiTaO(3) wafer that is capable of scanning 632.8-nm light by an unprecedented 14.88 degrees angle for extraordinary polarized light and by 4.05 degrees for ordinary polarized light. The device concept is based on micropatterning ferroelectric domains in the shape of a series of optimized prisms whose refractive index is electric field tunable through the electro-optic effect. We demonstrate what we believe is a novel technique of using electro-optic imaging microscopy for in situ monitoring of the process of domain micropatterning during device fabrication, thus eliminating imperfect process control based on ex situ monitoring of transient currents.

Cascaded electro-optic scanning of laser light over large angles using domain microengineered ferroelectrics

We present a device concept based on cascaded electro-optic deflection in a domain microengineered ferroelectric chip. In our design, large deflection angles are achieved by cascading several smaller scanners in a single ferroelectric chip, such that each successive scanner stage builds upon the deflection of the previous stage. We demonstrate the basic concept using a two-stage device fabricated in a single crystal wafer of ferroelectric LiTaO3. By operating the device using a specially designed programmable multichannel driver that provides ±1.1 kV per stage, a total scan angle of 25.4° at 5 kHz was demonstrated. Even larger angles of deflection are possible with additional scanner stages.

Ultrafast interferometric microscopy for laser-driven shock wave characterization

We have applied ultrafast time-resolved two-dimensional interferometric microscopy to the measurement of shock wave breakout from thin metal films. This technique allows the construction of a two-dimensional breakout profile for laser generated impulsive shocks with temporal resolution of <300 fs and out-of-plane spatial resolution of 0.5 nm using 130 fs, 800 nm probe pulses. Constraints placed on the spatial extent of the probed region and on the spatial resolution of the technique by the short duration of the probe pulses are discussed. In combination with other techniques, such as spectral interferometry, this technique provides a powerful means of investigating shock dynamics in a variety of materials.

Ultrafast nonlinear optical method for generation of planar shocks

Planar shocks generated by short pulse lasers are useful in studies of shock compression phenomena and may have applications in materials science, biology, and medicine. We have found the fluence profiles of 120–400 fs duration Gaussian spatial mode incident laser pulses are reproducibly flattened via surface optical breakdown and Kerr focusing in thin dielectric substrates at fluences just above the ablation threshold. These flat laser profiles have been used to produce planar shocks that are flat to 0.7 nm root-mean-square over a 75–100 μm diameter.

Integrated high-power electro-optic lens and large-angle deflector

We present a theoretical discussion and experimental demonstration of what to our knowledge is a novel integrated electro-optic lens and beam deflector fabricated in lithium tantalate. The cylindrical lens collimates Gaussian beams as small as 4 mum in diameter, whereas the independently controlled deflector is capable of scanning the collimated beam through an angular range of nearly 20 degrees .

Electro-optic coefficients of lithium tantalate at near-infrared wavelengths

The unclamped linear electro-optic coefficients r13 and r33 for lithium tantalate are known at only one wavelength, 632.8 nm, whereas the clamped coefficients are also known at 3.39 μm. In the unclamped mode the effects of mechanical changes caused by piezoelectric and elasto-optic effects are accounted for in the electro-optic coefficient. We demonstrate a novel technique that uses a ferroelectric domain micropatterned electro-optic deflector to measure the unclamped linear electro-optic coefficients r13 and r33 at any wavelength. Using this method, we have determined these values for lithium tantalate at 980, 1330, and 1558 nm.

Fabrication and characterization of high-speed integrated electro-optic lens and scanner devices

We demonstrate two high-speed electro-optic devices: an integrated lens/scanner and a variable radius collimating lens stack fabricated on a single crystal of Z-cut LiTaO3. The lens and scanner components consist of lithographically defined domain-inverted regions extending through the thickness of the crystal. A lens power of 0.233 cm-1kV-1, a deflection angle of 12.68 mrad kV-1, and a scan rate of 225 kHz at 375 V were observed. The collimating lens stack is theoretically capable of collimating the output from 2 - 10 micron diameter channel waveguides.

Sub‐picosecond Laser‐Driven Shocks in Metals and Energetic Materials

A high‐energy sub‐picosecond laser was used both to drive a shock into thin film targets and to spectroscopically interrogate the shocked material. Targets were thin films of molecular materials coated or grown upon thin vapor‐plated metal films on thin glass substrates, or neat metal films on thin glass substrates. The non‐linear optical interaction of the shock‐driving laser with the thin glass substrate produced surprisingly flat shock waves. Sub‐picosecond time‐resolved frequency‐ and spatial‐domain interferometries were used to characterize the shock wave as it transited from the thin metal film into the thin molecular material layer. Overviews of the effect of the pressure‐dependent complex index of refraction of the shocked thin film metal layer, ultrafast interferometric interrogation of shocked molecular materials (examples: glycidyl azide polymer and nitrocellulose thin films), and progress in preparation of, as well as the need for, uniform, well oriented, thin energetic material layers appropr...

Ultrafast time-resolved 2D spatial interferometry for shock wave characterization in metal films

We discuss the application of ultrafast time‐resolved two‐dimensional interferometric microscopy to the measurement of shock wave breakout from thin metal films. This technique allows the construction of a two‐dimensional breakout profile for laser generated impulsive shocks with temporal resolution of < 300 fs and out‐of‐plane spatial resolution of 1.5 nm using 130 fs, 800 nm probe pulses. Constraints placed on the spatial extent of the probe region and on the spatial resolution of the technique by the short duration of the probe pulses will be discussed. In combination with other techniques, such as spectral interferometry, this technique provides a powerful means of investigating shock dynamics in a variety of materials.