Nanosecond class lasers have been the mainstay of optical machining for decades, delivering pulses with high fluences (>1 J/cm2) that cause many material sets to undergo thermally-induced phase changes to cause removal of matter. While in many cases their delivery of sheer laser power has proved useful, nanosecond lasers have fallen short of addressing current micromachining requirements with respect to decreased feature sizes and more complex substrates. One main issue is the laser pulse width endures throughout the ablation process, depositing energy is deposited into plasma formation and local material heating. Plasma shielding takes place when the laser pulse energy contributes to plasma formation to a greater extent than direct material ablation processes. The result is a crude "plasma cutter" of the substrate, leaving a telltale trail of localized dross and droplet deposition. Nanosecond lasers of sufficient process speeds are typically Q-switched with repetition rates less than 200 kHz. As a result, the scribed lines are made of a sequence of "blast events" that result in a variety of undesired consequences and a limited process speed.
Noncritical temperature-tuned phase-matching and large nonlinear coefficients make potassium niobate an attractive material for frequency doubling tuneable near-infrared radiation. We have mounted a KNbO3 crystal intracavity in an argon ion pumped, continuous wave Ti:Sapphire ring laser to increase the power level of the second harmonic. Wavelength selection at the fundamental frequency is accomplished with a birefringent filter. By using the crystal orientation that defines the d32 coefficient of KNbO3 we have obtained a blue second harmonic output tuneable from 425-445 nm. The laser is also characterized by the narrow linewidth of the Ti:Sapphire ring oscillator and good temporal stability. A continuous wave, frequency doubled Ti:sapphire laser is well suited to excite the resonance Raman spectrum in heme proteins with strong absorption bands in the range of 400 to 450 nm. We demonstrate the feasibility of such a setup for Raman studies of ligand binding to myoglobin. The Raman bands yield information on the reaction dynamics and on conformational changes near the linkage between the heme and the protein. In particular, a shift of the stretch frequency of the iron- histidine bond with high pressure may be attributed to a protein conformational change.
The production of the laser host material YVO4 via high temperature solution growth (HTSG) is described as a facile alternative for producing optical quality crystals for research. The effects of dopant concentration on optical absorption properties in 0.7% and 3% Nd:YVO4 crystals are discussed. The rare earth ions Ho3+ and Er3+ have been doped into YVO4 with the HTSG method, and inaugural optical properties of Ho0.04Y0.96VO4 are presented.
Production refinements and pragmatic optical properties of the frequency converter crystal KNbO3 (KN) are highlighted regarding its commercialization. The growth, morphological orientation, and processing of KN crystals into devices are outlined. Passive absorption data are presented that define the effective window range for KN devices. An absorption band at 2.85 micrometers is attributed to the presence of OH groups in the crystal, and its vibrational strength varies with crystal growth conditions and incident polarized light orientation. Although blue light induced infrared absorption (BLIIRA) can reduce second harmonic generation (SHG) efficiency at high powers, single-pass conversion efficiencies of 1%/W(DOT)cm may be achieved with incident fundamental powers of 10 W. The ability of KN to noncritically phasematch by temperature tuning provides blue-green wavelengths; together with critical angle-tuned phasematching, the entire visible spectrum may be accessed with efficient SHG conversion.