A 200 W diode-side-pumped CW 2 μm Tm:YAG laser with water cooling at 8°C

A water-cooled 785 nm diode-side-pumped high-power CW Tm:YAG laser system at 2 μm is reported. 200 W output power is achieved with cooling water running at 8°C. As far as we know, this is the highest output power for a diode-pumped all solid-state 2 μm Tm:YAG laser. The output corresponds to optical-to-optical conversion efficiency of 11.2%, with a slope efficiency of about 22.8%. To make the system structure simple, only deionized water is used as the coolant instead of alcohol- or glycol-water mixture or the liquid nitrogen in the reported high-power Tm rod laser experiments, which were performed at low temperature near the freezing point of water, or even below.     

Passively Q-switched 1.32-μm Nd:YAG laser with a V:YAG saturable absorber

By using a new saturable absorber V³⁺:YAG, a flash-lamp-pumped passively Q-switched Nd:YAG laser at 1.32 μm has been realized. The single-pulse energy and the pulse width of the output laser versus the pump energy are measured. With a cavity length of 440 mm and a pump energy of 43.4 J, the obtained single-pulse output energy and pulse width are 10 mJ and 86.9 ns, respectively, corresponding to a peak power of 115 kW.     

1. 32μm Nd~(3 ): YAG Pulse Laser

Using specially coated mirrors, an output energy of 0.97 J at 1.32 μm from a Nd3 : YAG pulse laser is obtained with pumping energy of 66 J. The repetition rate is 1 pulse/sec and the slope efficiency is 1.7%. The repetition rate can be changed from 1 pulse/sec to 10 pulses/sec.     

Low-cost low-threshold diode end-pumped Tm:YAG laser at 2.016?μm

We report a low-threshold continuous-wave Tm:YAG laser that can be excited near 785?nm with low-cost, single-mode AlGaAs laser diodes. Low-threshold operation was achieved using a tightly focused, astigmatically compensated x-cavity containing a 2-mm-thick Tm:YAG crystal with 5?% Tm³⁺ concentration. Two linearly polarized single-mode diodes operating at 785.8?nm were polarization coupled to end pump the resonator. With a 6?% output coupler, as high as 32?mW of output power could be obtained at 2016?nm with 184?mW of incident pump power. The output could be further tuned in the 1935?C2035?nm range. Slope efficiency measurements indicated that cross-relaxation was very effective at this doping level. With a 2?% output coupler, lasing could be obtained with as low as 32.3?mW of pump power. In the limit of vanishing output coupling, the incident threshold pump power could be reduced to as low as 25?mW. To our knowledge, this is among the lowest lasing thresholds reported to date for continuous-wave, room-temperature thulium lasers.     

Gallium-nitride-based plasmonic multilayer operating at 1.55 μm

In this Letter, we have designed and fabricated a III-V semiconductor multilayer based on surface plasmon resonance (SPR) operating at the telecom wavelength. Optimization of the optogeometrical parameters and the metal/semiconductor layers required for this novel structure was conducted accurately by theoretical tools using the Maxwell equations. Technological fabrication of the device and its experimental characterizations using an evanescent coupling configuration was performed: the results have confirmed the existence of SPR associated to a sharp width response. This study could be a first step in the design of new plasmonic-semiconductor-based optical devices such as modulators and switches.     

Synchronously pumped femtosecond optical parametric oscillator based on AgGaSe2 tunable from 2 μm to 8 μm

The operation of a continuous-wave mode-locked silver gallium selenide (AgGaSe₂) optical parametric oscillator (OPO) is reported. The OPO was synchronously excited by 120-fs-long pulses of 1.55-μm radiation at a repetition rate of 82 MHz. The 1.55-μm radiation is generated by a noncritically phasematched cesium-titanyl-arsenate (CTA)-OPO pumped by a mode-locked Ti:sapphire laser. The AgGaSe₂-OPO generates signal and idler radiation in the range from 1.93 μm to 2.49 μm and from 4.1 μm to 7.9 μm, respectively. Up to 67 mW of signal wave output power has been obtained. The experimentally determined pulse duration and chirp parameters are in reasonable agreement with results from a numerical model taking into account group velocity mismatch, group velocity dispersion, self phase modulation, and chirp enhancement. Received: 6 August 1999 / Revised version: 4 October 1999 / Published online: 3 November 1999     

Light scattering and 2-μm laser performance of Tm:YAG ceramic

The scattering effect of Tm:YAG ceramic has been investigated and the scattering coefficient at 1064 nm wavelength is measured to be 0.014 cm⁻¹. Furthermore, a high power Tm:YAG ceramic laser with a slope efficiency of 10.7% has been built, which is end-pumped at a central wavelength of 805 nm. The 2-μm maximum output power is 7.1 W with an optical-optical conversion efficiency of 7.2%.     

Detection of HCl on the first and second overtone using semiconductor diode lasers at 1.7 μm and 1.2 μm

Sensitivity studies are also performed, to evaluate the minimum detectable concentration of HCl in air. Received: 7 August 1998/Revised version: 5 October 1998     

Thermally tunable double-peak phase-conjugate reflectivity in InP:Fe at 1.32 μm

We report on double-peak thermally tuned reflectivity of optical phase conjugation in InP:Fe under dc fields. A single-pump four-wave mixing geometry generates a phase-conjugate reflectivity up to 6.7% for a pump intensity of 28 mW/cm² at 1.32 μm wavelength. The phase-conjugate reflectivity exhibits strong temperature dependence that is attributed to the phase-shift variations of the index grating due to optical power density of the intensity distribution. Two strong peaks in phase-conjugate reflectivity are observed near room temperature and are separated by 3 °C. Our theoretical predictions, which are based on the modified single-defect model, are in good agreement with the experimental findings. Received: 6 December 2000 / Revised version: 13 February 2001 / Published online: 27 April 2001     

Fe:ZnSe laser pumped by a 2.93-μm Cr,Er:YAG laser

We demonstrated an Fe:ZnSe laser pumped by a 2.93-μm Cr, Er:YAG laser at liquid nitrogen and room temperature in single-shot free-running operation for the first time. The xenon flash lamp pumped Cr, Er:YAG laser had a maximum single pulse energy of 1.414 J, and the threshold and slope efficiency were 141.70 J and 0.70% which were respectively reduced by 29.3% and increased by 52.2% compared with the Er:YAG laser. At liquid nitrogen temperature of 77 K, the maximum single pulse energy of the Fe:ZnSe laser was 197.6 m J, corresponding to a slope efficiency of 13.4%. The central wavelength and full width at half maximum(FWHM) linewidth were 4037.4 nm and 122.0 nm, respectively. At room temperature, the laser generated a maximum single pulse energy of 3.5 mJ at the central wavelength of 4509.6 nm with an FWHM linewidth of 171.5 nm.     

Pulsed quantum-cascade-laser spectroscopy with intermediate-size pulses: application to NH3 in the 10 μm region

Pulsed quantum-cascade-laser spectrometers are usually used to detect atmospheric gases with either the interpulse technique (short pulses, typically 5–20 ns) or the intrapulse technique (long pulses, typically 500–800 ns). Each of these techniques has its drawbacks. Particularly the gas absorption spectra are generally distorted. We have previously developed another technique called intermediate-size pulses (typically 50–100 ns) technique for gas detection using pulsed QCL spectrometers. In this paper, infrared spectra of ammonia recorded with this technique in the 10 μm region are presented. For the NH₃ spectra recorded at low pressure (i.e. in the mbar range), the spectra show typical oscillations after the absorption. The Beer–Lambert law cannot explain these oscillations, termed the rapid-passage effect. Comparisons between experimental and calculated spectra will be realized. This phenomenon is not satisfactory from a spectroscopic point of view and spectra must be recorded at higher pressures. For the NH₃ spectra recorded at higher pressure (i.e. in the 50 mbar range), the oscillations disappear and the Beer–Lambert law could be reused. This paper will demonstrate that the intermediate-size technique gives reliable measurements for NH₃ detection. Moreover the typical apparatus function (0.003 cm⁻¹ HWHM) is far lower from the typical apparatus function of the interpulse QCL spectrometers (0.015 cm⁻¹ HWHM).     

High peak power 16 μm InP-related quantum cascade laser

In this paper ～16 μm-emitting multimode InP-related quantum cascade lasers are presented with the maximum operating temperature 373 K, peak and average optical power equal to 720 mW and 4.8 mW at 303 K, respectively, and the characteristic temperature (T₀) 272 K. Two types of the lasers were fabricated and characterized: the lasers with a SiO₂ layer left untouched in the area of the metal-free window on top of the ridge, and the lasers with the SiO₂ layer removed from the metal-free window area. Dual-wavelength operation was obtained, at λ ～ 15.6 μm (641 cm^?1) and at λ ～ 16.6 μm (602 cm^?1) for lasers with SiO₂ removed, while within the emission spectrum of the lasers with SiO₂ left untouched only the former lasing peak was present. The parameters of these devices like threshold current, optical power and emission wavelength are compared. Lasers without the SiO₂ layer showed ～15% lower threshold current than these ones with the SiO₂ layer. The optical powers for lasers without SiO₂ layer were almost twice higher than for the lasers with the SiO₂ layer on the top of the ridge.     

A cw room-temperature Ho,Tm:YLF laser pumped at 1.682 μm

We present the results obtained with a Ho,Tm:YLF crystal grown at a new crystal growth facility in Pisa. The optical quality of the sample has been tested by studying its performance as the active medium of a laser operating at 2.06 μm. We employed three different pump laser sources: a Ti:sapphire, a diode (both tuned at 793 nm) and, for the first time, a continuous-wave Co:MgF₂ laser, tuned at 1.682 μm. At room temperature the best slope efficiency was 30 % in the case of “red” pumping, and 59 % in the case of “infrared” excitation. The typical lasing threshold is about 100 mW. Received: 14 March 2001 / Revised version: 15 June 2001 / Published online: 19 September 2001     

Diode-pumped passively Q-switched Nd:GdVO4 lasers operating at 1.06 μm wavelength

With a 10-W diode laser to pump Nd:GdVO₄ crystal in a folded cavity, we demonstrated Cr⁴⁺:YAG passively Q-switched Nd:GdVO₄ lasers at 1.06 μm. The maximum average output power of 2.1 W and the highest peak power of 625 W were, respectively, obtained when the initial transmissions of the Cr⁴⁺:YAG crystals were 90% and 80%. Received: 8 September 1999 / Revised version: 30 December 1999 / Published online: 8 March 2000     

A 7-W diode-pumped Nd:YVO4 cw laser at 1.34 μm

A Nd:YVO₄ laser, end-pumped by a fiber-coupled diode-laser array, generates 7.3 W of output power at 1342 nm, the highest so far reported for this host crystal. The slope efficiency is 40% and the output-beam divergence is close to the diffraction limit. An important point in attaining such results is the choice of crystals with low Nd concentration. Received: 16 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +39-050/844333, E-mail: dilieto@df.unipi.it RID="**" ID="**"Permanent address: Scuola Normale Superiore, Piazza dei Cavalieri 7, Pisa, Italy     

Spectroscopic properties of 1.8 μm emission of thulium ions in germanate glass

A new type host of germanate glass (GeO₂− BaO−BaF₂−Ga₂O₃−La₂O₃) codoped with Tm₂O₃ has been investigated for application as laser material. It possesses a large emission cross section with the value of 9.3×10⁻²¹ cm² at 1.8 μm. Judd-Ofelt intensity parameters and radiative transition probability are calculated and analyzed by Judd-Ofelt theory and absorption spectra. The infrared emission spectra at 1.8 μm have been obtained by using a 794 nm laser diode as excitation resource. The emission intensity ratio of 1.8 (³F₄→³H₆) to 1.47 μm (³H₄→³F₄) increases, while the experimental lifetime of the Tm³⁺:³H₄ level decreases by increasing Tm₂O₃ concentration, which is attributed to the presence of a cross relaxation process. The most intensive emission at 1.8 μm is achieved from the germanate glass with the concentration of Tm₂O₃ reaches 1.0 wt%. The extended overlap integral method is used to calculate the microparameter of the energy transfer and the critical distance, which are derived to better understand the energy transfer process of thulium ions in the germanate glass responsible for emission at 1.8 μm.     

Er∶YAG晶体1.6μm波长激光输出特性理论分析

由跃迁速率方程推出了三能级系统的激光阈值和斜率效率解析式.根据测试的吸收谱，计算了YAG晶体中Er³⁺离子的吸收截面.分析了1.6μm波长的激光特征.