High efficiency,high repetition-rate Nd:YVO<Subscript>4</Subscript> laser with TEM<Subscript>00</Subscript> end-pumped by 887 nm

Thermal effect of laser crystal is a very important factor for solid lasers. The most of heat is generated from the quantum loss between pump light and lasing light. If a longer wavelength of pump light is adopted, quantum loss and quantum loss efficiency can be reduced and improved, respectively. In this paper, a Nd:YVO₄ laser end-pumped by 887 nm LD is reported. Output power of 25 W is obtained from a single Nd:YVO₄, when the crystal absorbs pump light power of 38 W. The corresponding opto-optic conversion efficiency is up to 65.7%. When 30.7 W pump light is absorbed in the crystal, 19.4 W TEM₀₀ is obtained with M _x ² = 1.30, M _y ² = 1.26 and opto-optic conversion efficiency of 63.2%. The laser can work at the Q-switched mode. The uniform pulses are generated at high repetition of 100 kHz. And the conditions of pulse stability are analyzed in this paper.     

A novel prism beam-shaping laser diode bar end-pumped TEM<Subscript>00</Subscript> mode Nd:YVO<Subscript>4</Subscript> laser

A beam-shaping diode end-pumped TEM₀₀ mode CW Nd:YVO₄ laser is presented. A special beam-shaping element made up of isosceles right-angled prism pieces is adopted to realize beam symmetric. Two cylinder lenses are used to couple the shaped beam into a 3 × 3 × 9 mm Nd:YVO₄ crystal with 0.3 at % neodymium doping. By using this laser system, we have achieved 6.1 W CW laser operated in single transverse mode at 1064 nm with 95.2% reshaping efficiency and 25.6% optical-optical conversion efficiency.     

Ultrahigh-efficiency TEM<Subscript>00</Subscript> diode-side-pumped Nd:YVO<Subscript>4</Subscript> laser

Ultrahigh-efficiency TEM₀₀ operation is demonstrated in a diode-pumped Nd:YVO₄ laser in a bounce amplifier geometry using a specially designed astigmatically optimised cavity configuration. Optical efficiency >68% is demonstrated and up to 27.1 W of output power for multimode operation. For single-mode TEM₀₀ operation, an output power of 23.1 W for 39.5 W of diode pumping was produced with beam propagation parameters of M_x ²=1.3 and M_y ²=1.1. Received: 10 October 2002 / Revised version: 9 December 2002 / Published online: 19 March 2003 RID="*" ID="*"Corresponding author. Fax: +44-20/7594-7744, E-mail: a.minassian@ic.ac.uk     

A 20.1 W solid-state laser pumped by 887 nm with high efficiency and TEM<Subscript>00</Subscript> mode

High efficiency, TEM₀₀ mode, high repetition rate laser pumped by 887 nm is reported. 20.1 W output laser emitting at 1064 nm is achieved in a 0.3 at % Nd-doped Nd:YVO₄, which absorbs pumping light of 30.7 W at 887 nm. The opto-optic efficiency and the slope efficiency are 65.5 and 88.5%, respectively. The stable Q-switching operation worked well at 100 kHz and the beam quality is near diffraction-limit with M² factor measured as M² ≈ 1.2. And the pulse waveform is analyzed in this paper.     

Compact TEM<Subscript>00</Subscript> grazing-incidence Nd:GdVO<Subscript>4</Subscript> laser using a folded cavity

A compact diode-side-pumped Nd:GdVO₄ laser system using a folded cavity and grazing-incidence configuration is presented. The highest multimode output power obtained was 21.8 W at 36 W of effective diode pump power. Highest optical-to-optical conversion efficiency of 61.5% was achieved at 33 W of effective diode pump power with 20.3 W of multimode output power. For single-mode TEM₀₀ operation, an intracavity telescope was adopted for mode matching in the horizontal direction. Because of the folded cavity and the intracavity telescope, this laser head was the most compact to our knowledge of the TEM₀₀ grazing-incidence laser geometry. At last, an output power of 15 W was produced at 36 W of effective diode pump power. The stable Q-switching operation was also obtained. PACS 42.55.-f; 42.55.Xi; 42.60.Gd     

High power Q-switched TEM<Subscript>00</Subscript> Nd:YVO<Subscript>4</Subscript> laser with self-adaptive compensation of thermal lensing effect

a high power dual-end-pumped Nd:YVO₄ laser with adaptive compensation of thermal lensing effect by adjusting HR mirror along the optical axis was proposed. In Q-switching operation at 70 kHz, the laser worked at different pump power (from 90 W to 70 W) with stable beam quality (M ² ∼ 1.15) and high output power (from 39 to 28.4 W), corresponding to the absorbed-output conversion efficiency of 55%. In the meantime, the pulse duration was increased from 24 to 31.7 ns. At various repetition rate from 60 to 100 kHz, the beam quality factors were all measured less than 1.2.     

High-efficiency 17 W, 80 MHz repetition rate,passively mode-locked TEM<Subscript>00</Subscript> Nd:YAG oscillator pumped at 885 nm

We report on a passively mode-locked TEM₀₀ Nd:YAG oscillator with the beam quality at M ² = 1.1 by a semiconductor saturable absorber mirror under 885 nm laser diode direct pumping for the first time. A maximum average output power of 17 W at a repetition rate of 80 MHz with 39 ps pulse width was obtained under the absorbed pump power of 38 W, corresponding to an optical-optical efficiency of 44% and the slope efficiency of 69%, respectively.     

Performance improvement of high repetition rate electro-optical cavity-dumped Nd:GdVO<Subscript>4</Subscript> laser

We improved the electro-optical cavity-dumped Nd:GdVO₄ laser performance at high repetition rates by employing continuous-grown GdVO₄/Nd:GdVO₄ composite crystal under 879 nm diode-laser pumping. A constant 3.8 ns duration pulsed laser was obtained and the repetition rate could reach up to 100 kHz with a maximum average output power of 13.1 W and a slope efficiency of 56.4%, corresponding to a peak power of 34.4 kW.     

A high beam quality laser-diode end-pumped Nd:GdVO<Subscript>4</Subscript> slab laser

An 83 W, near-diffraction-limited LD end-pumped Nd:GdVO₄ slab laser with hybrid resonator was presented with the pumping power of 238 W, the slope efficiency and optical-to-optical conversion efficiency were 39.4 and 34.9%, respectively. At the output power of 70 W, beam quality M² factors were 1.2 in stable direction and 1.3 in unstable direction.     

Influence of LD temperature fluctuation on the performance of corner-pumped TEM<Subscript>00</Subscript> CW composite Nd:YAG laser

The influence of LD temperature fluctuation on the performance of corner pumped TEM₀₀ CW composite Nd:YAG laser was investigated by numerical ray tracing method and experiment. Both the theoretical analysis and experimental results show that the corner-pumped TEM₀₀ laser has a good tolerance to temperature fluctuation. At a drive current of 40 A, when the LD temperature varies from 15 to 25°C the fluctuation of output power as less than 5% and the beam quality remains almost invariable.     

Compact diode-directly-pumped passively mode-locked TEM<Subscript>00</Subscript> Nd:GdVO<Subscript>4</Subscript> laser at 1341 nm using a semiconductor saturable absorber mirror

We report on a compact 880-nm diode-directly-pumped passively mode-locked TEM₀₀ Nd:GdVO₄ laser at 1341 nm with a semiconductor saturable absorber mirror (SESAM) for the first time. Under the absorbed pump power of 14.6 W, the maximum output power of 1.27 W was obtained at the repetition rate of 85.3 MHz with the pulse width of 45.3 ps, corresponding to an optical-optical efficiency of 8.8% and the slope efficiency of 33.3%, respectively. The beam quality factor was measured to be M ² = 1.18, indicating a TEM₀₀ mode.     

Comparison of electro-optical and acousto-optical Q-switched,high repetition rate Nd:GdVO<Subscript>4</Subscript> laser

The differences between the performances of electro-optical (EO) and acousto-optical (AO) Q-switched, diode pumped Nd:GdVO₄ laser at high repetition rates were detailed in this paper. The results revealed that EO Q-switch was more favorable to obtain short pulse width and high peak power laser than AO Q-switch under high repetition rate operation. The minimum pulse widths at 100 kHz were 20.2 ns under EO operation and 28.7 ns under AO operation, corresponding to peak powers of 3.1 kW and 2.2 kW, respectively. The corresponding values at 10 kHz were 5.3 ns, 9.0 ns and 77.4 kW, 45.6 kW, respectively.     

Simultaneous self-mode-locking of TEM<Subscript>0,0</Subscript> and TEM<Subscript>1,0</Subscript> modes in a Nd:YVO<Subscript>4</Subscript> laser: Application for measuring the thermal focal length

We demonstrate that the simultaneous self-mode-locking of TEM_0,0 and TEM_1,0 modes can be achieved in a standard end-pumped Nd:YVO₄ laser. With this simultaneous self-mode-locking, the transverse beat frequency can be accurately measured as a function of the absorbed power. We employ the measured beat frequency and the cavity theory to precisely determine the effective focal length of the thermal lens in the gain medium.     

Cavity-dumped mode-locked Nd:GdVO<Subscript>4</Subscript> laser at low repetition rate

We report a cavity-dumped mode-locked Nd:GdVO₄ laser with semiconductor saturable absorber mirrors at low repetition rate. In this laser system, a single mode-locked laser pulse is generated, amplified and cavity-dumped by means of electro-optic modulator at 1 to 10 Hz repetition rate. The energy of the pulse is about 150 nJ and the pulse duration is determined to be 10 ps.     

Diode-pumped short pulse passively Q-switched 912 nm Nd:GdVO<Subscript>4</Subscript>/Cr:YAG laser at high repetition rate operation

A diode-end-pumped passively Q-switched 912 nm Nd:GdVO₄/Cr:YAG laser is demonstrated for the first time. In a concave-piano cavity, pulsed 912 nm laser performance is investigated using two kinds of Cr:YAG crystal with different unsaturated transmission (T _U) of 95% and 90% at 912 nm as the saturable absorbers. When the T _U = 90% Cr:YAG is used, as much as 2.6 W average output power for short pulsed 912 nm laser is achieved at an absorbed pump power of 34.0 W, corresponding to an optical efficiency of 7.6% and a slope efficiency of 20.3%. Moreover, 10.5 ns duration pulses and up to 2.3 kW peak power is obtained at the repetition rate around 81.6 kHz.     

High-pulse-stability double-end continuous-grown YVO<Subscript>4</Subscript>/Nd:YVO<Subscript>4</Subscript>/YVO<Subscript>4</Subscript> acousto-optically Q-switched laser at high repetition rates

High pulse amplitude stability of 0.62% (rms) is achieved at 60 kHz repetition rate in fundamental mode with double-end continuous-grown YVO₄/Nd:YVO₄/YVO₄ composite crystal. The average output power and pulse peak power are 32.9 W and 27.7 kW, respectively, with 19.8 ns pulse width and 548 μJ pulse energy. The pulse amplitude stability is investigated experimentally. The stability gets improved with the decrease of repetition rate and output transmission. From theoretical analysis, the reason of pulse instability at high repetition rates is that the initial population inversion doesn’t saturate and the final population inversion doesn’t approach zero. With the decrease of repetition rate and output transmission, the final population inversion decreases and the interaction between two adjacent pulse periods is weakened. Therefore, pulse stability improves.     

LD end-pumped passively mode-locked Nd:YVO<Subscript>4</Subscript> laser with single-walled carbon nanotubes

We demonstrate a LD end-pumped passively mode-locked Nd:YVO₄ laser using a single-walled carbon nanotubes saturable absorber (SWCNT-SA). The SWCNT wafer was fabricated by electric arc discharge method on quartz substrate with absorption wavelength of 1064 nm. At the absorbed pump of 15.8 W, an output power of 750 mW CW (continuous wave) mode-locked laser pulse was achieved with the repetition of 79.7 MHz, corresponding to optical-optical efficiency of 4.75%.     

Irradiation of amorphous Ta<Subscript>42</Subscript>Si<Subscript>13</Subscript>N<Subscript>45</Subscript> film with a femtosecond laser pulse

Films of 260 nm thickness, with atomic composition Ta₄₂Si₁₃N₄₅, on 4″ silicon wafers, have been irradiated in air with single laser pulses of 200 femtoseconds duration and 800 nm wave length. As sputter-deposited, the films are structurally amorphous. A laterally truncated Gaussian beam with a near-uniform fluence of ∼0.6 J/cm² incident normally on such a film ablates 23 nm of the film. Cross-sectional transmission electron micrographs show that the surface of the remaining film is smooth and flat on a long-range scale, but contains densely distributed sharp nanoprotrusions that sometimes surpass the height of the original surface. Dark field micrographs of the remaining material show no nanograins. Neither does glancing angle X-ray diffraction with a beam illuminating many diffraction spots. By all evidence, the remaining film remains amorphous after the pulsed femtosecond irradiation.     

High efficient double end-pumped <Emphasis Type="Italic">b</Emphasis>-cut Tm,Ho:YAlO<Subscript>3</Subscript> laser

High efficient continuous wave (CW) and acousto-optical (AO) Q-switched operation of a b-cut Tm,Ho:YAlO₃ (Tm,Ho:YAP) laser are reported in the paper. The Tm,Ho:YAP crystal was cooled by liquid nitrogen and pumped by a fiber-coupled laser diode (LD). Different pump wavelengths were tried in the experiment. An 8.36-W output power was acquired at 2.12 μm in the CW operation with an optical-optical conversion efficiency of 33.3%, and an 8.14-W average power was obtained at the pulse repetition frequency (PRF) of 10 kHz with an optical-optical conversion efficiency of 32.4%.     

High-peak-power,high-repetition-rate LD end-pumped Nd:YVO<Subscript>4</Subscript> burst mode laser

A compact high-peak-power, high-repetition-rate burst mode laser is achieved by an acousto-optical Q-switched Nd:YVO₄ 1064 nm laser directly pumped at 878.6 nm. Pulse trains with 10–100 pulses are obtained using acousto-optical Q-switch at repetition rates of 10–100 kHz under a pulsed pumping with a 1 ms duration. At the maximum pump energy of 108.5 mJ, the pulse energy of 10 kHz burst mode laser reaches 44 mJ corresponding to a single pulse energy of 4.4 mJ and an optical-to-optical efficiency of 40.5 %.The maximum peak power of ~468.1 kW at 10 kHz is obtained with a pulse width of 9.4 ns. The beam quality factor is measured to be M ² ~1.5 and the pulse jitter is estimated to be less than 1 % in both amplitude and time region.