We present a 10 W average power saturable Bragg reflector (SBR) cw modelocked laser operating at 1064 nm. The laser produces 35 ps pulses at repetition rates between 75 MHz and 250 MHz. The laser gain material used is Nd:vanadate (Nd:YVO₄), which is pumped with 30 W from a fiber coupled diode bar operating at 808 nm. SBR modelocking provides a reliable and robust method of modelocking solid state lasers. It behaves like a high damage threshold solid state saturable absorber. The modelocking process is self- starting and requires no active cavity stabilization thus enabling turn-key operation. We present results on power stability, damage thresholds and beam quality taken over many hours of operation. In addition we present our results on efficient single pass second and third harmonic generation of this laser system using LBO and KTP.

We present an overview of the single-box diode-pumped sub- picosecond ultrafast oscillators that are currently commercially available for industrial and scientific applications.

The temporal high-contrast structure of intense, ultrashort optical pulses is important for many laser-matter interactions. I propose to distinguish four different temporal structures of the ultrashort pulses: wings, pedestal, (ASE) background, and replica. I further propose to include this description into specifications of commercial and state-of-the-art scientific high-peak power ultrashort pulse systems and use them homogeneously throughout the literature.

The use of femtosecond lasers allows materials processing of practically any material with extremely high precision and minimal collateral damage. Advantages over conventional laser machining (using pulses longer than a few tens of picoseconds) are realized by depositing the laser energy into the electrons of the material on a time scale short compared to the transfer time of this energy to the bulk of the material, resulting in increased ablation efficiency and negligible shock or thermal stress. The improvement in the morphology by using femtosecond pulses rather than nanosecond pulses has been studied in numerous materials from biological materials to dielectrics to metals. During the drilling process, we have observed the onset of small channels which drill faster than the surrounding material.

We show material processing results obtained with a diode- pumped ultrafast regenerative amplifier that produces 5 μJ, 150 fs pulses at 100 kHz.

Terahertz imaging has been shown to be a powerful tool for analyzing a variety of materials. From the amount of water in a leaf over time to looking at the spectroscopic species in a flame, this technique shows great potential for commercial applications. However, in order to work in a commercial environment, the present free-space optical systems must be abandoned in favor of fiber-optic delivery. To this end, we have developed a compact, fiber-pigtailed terahertz imaging system that utilizes a hermetically sealed, photoconductive, transmitter and receiver. The receiver uses an integrated amplifier to obtain a 1000:1 S/N with only 1 mW of power on both the transmitter and receiver and with a one second integration time. This system has usable energy extending from 0.04 to 2 THz and has both a rapid (20 Hz) scanner for short, 40-ps, scans as well as a long rail for scans up to 1 ns. The system hardware is contained in a 1.5 cu. ft. box with fibers feeding both the transceiver units. These units can be configured into either a transmission or reflection mode depending on the user's application. An advanced software system controls the hardware, collects the data, and does image processing.

Non-cryogenic, high sensitivity infrared detection is one of the fundamental criteria for future sensor technology. To this end, we propose mimicking the natural infrared detection structures found in certain snake pit tissue. We hypothesize that the pit organ behaves like a photonic bandgap in that a regular arrangement of sub-micron micropits removes or traps visible radiation and enhances infrared radiation transmission. In order to simulate the 2- and 3-D pit surface morphology, we used holographic two- photon induced polymerization (H-TPIP), a new microfabrication technique previously reported by this group. Using the ultrafast H-TPIP procedure, we can write large area biomimetic structures into an optical resin. Due to the quadratic dependence of the absorption probability on the incident radiation intensity, molecular excitation via the simultaneous absorption of two photons has been shown to lead to improved 3-D control of photochemical or photophysical processes. Using spatial variations in the incident intensity within a photopolymerizable resin, these structures can be readily fabricated. We report our progress on duplicating the surface morphology of snake infrared pit tissue using H-TPIP.

Spatial separation of isotopes in ultrafast laser ablation plumes is observed for a variety of elements in the periodic table. Observations are made with a charge-state discriminating mass analyzer as a function of angle relative to the center of the ablation plume. Data is presented for femtosecond and picosecond laser pulses showing enrichments by factors of 2 to 20 depending on element, charge state, and laser pulse duration. Thin films are deposited from the plasma plumes, as a function of distance from the ablation source, and used to record the spatial distribution of isotopes. This information is utilized to construct a model for the isotopic separation process and to infer characteristics of the electromagnetic fields in the ablation plasmas.

The inversion of high-power ultra short pulse lasers has opened way to investigations aimed at creation of a new type of bright x-ray source for different applications including material science and time resolved x-ray diffraction for biology. The conversion efficiency of the laser energy incident onto a solid target into the x-ray emission depends on many factors, including the temporal profile of laser pulse. We report here the results of our theoretical and experimental investigations of the line x-ray emission from solid targets irradiated by ultra short laser pulses. The parameters of laser pre-pulse are optimized in order to get the maximum laser energy conversion into the emission in the selected x-ray line.

The eye is potentially an ideal target for high precision surgical procedures utilizing ultrafast lasers. We present progress on corneal applications now being tested in humans and proof of concept ex vivo demonstrations of new applications in the sclera and lens. Two corneal refractive procedures were tested in partially sighted human eyes: creation of corneal flaps prior to excimer ablation (Femto- LASIK) and creation of corneal channels and entry cuts for placement of intracorneal ring segments (Femto-ICRS). For both procedures, results were comparable to standard treatments, with the potential for improved safety, accuracy and reproducibility. For scleral applications, we evaluated the potential of femtosecond laser glaucoma surgery by demonstrating resections in ex vivo human sclera using dehydrating agents to induce tissue transparency. For lens applications, we demonstrate in an ex vivo model the use of photodisruptively-nucleated ultrasonic cavitation for local and non-invasive tissue interaction.

We present Terahertz Pulse Imaging (TPI) results of different human tissue types. Our results are part of an initial study to explore the potential of TPI for biomedical applications. A survey of different tissue types has demonstrated the various contrast mechanisms that are available in TPI, allowing different tissue types to be readily identified. This encourages the pursuit of further studies of TPI for a variety of biomedical applications.

We describe the development of a 3D, real-time environment that enables seamless interaction with the microscopic world.

The early detection and treatment of pathological change tissue has long been a medical priority. Optical coherence tomography (OCT) is a new kind of noninvasive cross- sectional imaging technique. In this paper, experimentally we set up the first OCT system in China that can be obtaining 2D image of biological samples. OCT performs optical ranging in tissue by use of a fiber-optic Michelson interferometer with a low illuminating source, a tunable mode-locked Ti:Sapphire femtosecond pulse laser source, with center wavelength of 830 nm. A matching length of single- mode optical fiber wrapped around a piezoelectric modulator is placed in the reference arm for phase modulation. The properties and experimental results of our OCT system are analyzed. We got cross-sectional images of animal tissue samples. The OCT image of a mouse nephridium cortex tissue is agreed with the histological images. On the other hand, mouse brain (animal model of cerebral embolism) pathological changes tissue and normal tissue can be discriminated. The blood rheology characteristic of brain blood vessel block is discussed. It shows that this technique holds promise as a potential tool for the tissue diagnosis.

Hollow optical wave-guides represent an alternative method for the delivery of short laser pulses to a target tissue or a target detector. In many applications, the delivery may require bending and winding through various openings and conduits. Hollow waveguides are made of teflon or silica tubes and allow flexibility and rigidity including the ability to operate in a liquid environment. Biomedical applications include diagnostics and surgery. This study evaluates the use of hollow waveguides for the delivery of short and ultra short laser pulses.