T.A. King

Investigation of a 791-nm pulsed-pumped 2.7-µm Er-doped ZBLAN fibre laser

A pulsed Er3+-doped ZBLAN fibre laser with 1.9 mJ of output energy at 2.7 µm in near transverse-single-mode operation is reported. A maximum slope efficiency of 13.5% with respect to launched pump energy at 791 nm was determined. The laser line shifts to a longer wavelength at the end of the output pulse because of reabsorption losses from the lower laser level at shorter wavelengths. The temporal behaviour of the laser output cannot be explained by the common rate-equation models. Possible quenching processes of the pump level are discussed.

Erbium-YAG and holmium-YAG laser ablation of bone

Results are presented for the latent heat of ablation of bone using an erbium-YAG laser operating at 2.9Μm, and a holmium-YAG laser operating at 2.1Μm. The values are 8.2±1.0 kJ cm−3 and 18±2.0 kJ cm−3, respectively. Secondary damage to surrounding tissue is found to extend approximately 5Μm with the erbium laser and is greatly increased to 80Μm with significant charring in the case of holmium. These secondary damage zones are much smaller than those produced by the CO2 laser.

Characterisation of doped sol-gel derived silica hosts for use in tunable glass lasers

Measurements of laser-relevant properties of neodymium doped sol-gel derived silica hosts are described. Samples with Nd as the only dopant reveal anomalously short fluorescence lifetimes characteristic of concentration quenching TEM measurements revealing clumping of the neodymium. Co-doping with aluminium allows better dispersion of the neodymium throughout the gel-silica matrix, but fluorescence lifetimes and efficiencies are still lower than expected. Phonon quenching by residual OH- ions is suspected, absorption, FTIR and Raman spectroscopy being used to support this theory.

Soft and hard tissue ablation with short-pulse high peak power and continuous thulium-silica fibre lasers.

Thulium lasers operating near ∼2 μm are the subject of interest for various medical applications. The newly developed Tm3+ silica fibre laser in Q-switched and CW operation was investigated to determine its efficiency in the interaction with soft and hard tissues. The interaction was investigated using a free-running continuous (CW) Tm3+-doped fibre laser (wavelength 1.99 μm, with self-pulsation ranging over 1 to few tens of microseconds) and for novel Q-switched operation of the same fibre laser (pulse durations from 150 to 900 ns and pulse repetition rates from 100 Hz to 17 kHz). Residual damage and affected zones using the Q-switched laser were nearly six times smaller than using the CW fibre laser for about 50 s of exposure time, and increased with pulse repetition rate. The energy required to ablate tissue with the Q-switched fibre laser ranged from 0.2 to 0.6 kJ/cm3 and was significantly smaller than that for the CW fibre laser of 153 to 334 kJ/cm3. Under both high-resolution reflected optical microscopy and histological examination, tissue crater depths were observed as cleanly cut with smooth walls and minimal charring in the case of Q-switched operation of the fibre laser. This study is the first direct comparison of tissue interaction of short-pulse (Q-switched) and CW Tm3+-doped silica fibre lasers on crater depth, heat of ablation and collateral damage. The Q-switched Tm3+-doped silica fibre laser effectively ablates tissue with little secondary damage.

Modelling of high-power diode-pumped erbium 3-µm fibre lasers

Abstract We present theoretical calculations that relate to the cw operation of a high-power Er3+, Pr3+:ZBLAN double-clad fibre laser. Using the measured energy-transfer, energy-transfer-upconversion and cross-relaxation parameters relevant to Er3+-doped and Er3+, Pr3+-codoped ZBLAN, we compare the theoretical calculations from the model with recent experimental measurements. The model is then used to analyse the important pump and interionic processes occurring in Er3+, Pr3+:ZBLAN fibre lasers. The theoretical results indicate that energy transfer from Er3+ to Pr3+ leads to a fast depletion of the lower laser level and, due to the cw threshold condition, to low population densities in both laser levels. Thus, ground-state bleaching, pump excited-state absorption and energy-transfer upconversion amongst the Er3+ ions are avoided.

Remote Detection of Gases by Diode Laser Spectroscopy

A new method is demonstrated for the remote optical detection of gases based on the differential absorption of radiation from two longitudinal modes of a laser diode. The sensor is shown to be capa...

Er:YAG (λ=2.94 µm) Laser Etching of Dental Enamel as an Alternative to Acid Etching

Abstract.Acid etching is widely used in clinical dentistry to facilitate the mechanical retention of resin-based materials to teeth, in particular enamel surfaces. Several laser systems have been developed with the aim of modifying dental hard tissues and the Er:YAG (λ=2.94 µm) laser may offer a possible alternative to the acid etching technique.This study compares the shear bond strengths of composite beads attached to sound enamel surfaces prepared using either (a) no etching (negative control), (b) acid etching (positive control) or (c) Er:YAG laser etching, either with or without water, at one of three fluences: 15 J/cm2, 18 J/cm2 or 24 J/cm2. A histological appraisal was also conducted using environmental scanning electron microscopy (ESEM) techniques.The mean shear bond strength for acid-etched enamel was 16.6 MPa (SD 4.4, n=10), whereas the best laser-etched mean bond strength obtained was 11.5 MPa (SD 4.1, n=11) using a fluence of 24 J/cm2 with water. These values were significantly greater than those obtained for the negative control (no etching) of 4.4 MPa (SD 0.9, n=8). There was a significant positive correlation between the etching fluence and the shear bond strength, but pitting of the enamel surface at fluences above 25 J/cm2 limited the maximum fluence for etching purposes. Although Er:YAG laser etching enhanced the retention of a resin-based material to an enamel surface when compared to a negative control, the mean shear bond strengths were significantly lower than those obtained using conventional acid etching. The optimal laser etching parameters in this study were shown to be 24 J/cm2 in conjunction with water.

Diode-pumped Q-switched Yb:S-FAP laser

Abstract A diode-pumped, repetitively Q-switched 1% doped Yb 3+ :Sr 5 (PO 4 ) 3 F laser has been demonstrated for the first time, pumped with a strained InGaAs continuous-wave diode laser. The maximum output energy per pulse was 125 μJ at 1.047 μm, with a pulse duration of sub-30 ns. The Q-switched average power was identical to the steady-state CW power at repetition rates over 1 to 10 kHz, consistent with a 1.26 ms emission lifetime.

Efficient high power Yb3+-silica fibre laser cladding-pumped at 1064 nm

Abstract A Yb 3+ -silica fibre laser has been cladding pumped at 1064 nm by a Nd:YAG laser and operated with a slope efficiency of 72±5% with respect to the incident pump power, a total efficiency of 41% and at powers up to 3.7 W in a small scale device. The Yb 3+ -silica double-clad fibre had a quasi-polygonal sinusoidal inner cladding geometry giving high launch efficiency to the fibre and efficient transfer of pump light from the fibre cladding to the core.

Continuous-wave diode-pumped Yb3+:S-FAP laser

Abstract A continuous-wave InGaAs diode-pumped Yb 3+ :S-FAP laser has been demonstrated. We report an output power of 75 mW with a slope efficiency of 78%. Power improvements of up to 2.5 times are reported with crystal cooling.