High peak power 1.0 μm and tri-wavelength 1.3 μm Nd:ScYSiO_5 crystal lasers

With a Nd:ScYSiO_5 crystal, a high peak power electro-optically Q-switched 1.0 μm laser and tri-wavelength laser operations at the 1.3 μm band are both investigated. With a rubidium titanyle phosphate(RTP) electro-optical switcher and a polarization beam splitter, a high signal-to-noise ratio 1.0 μm laser is obtained, generating a shortest pulse width of 30 ns, a highest pulse energy of 0.765 mJ, and a maximum peak power of 25.5 kW,respectively. The laser mode at the highest laser energy level is the TEM200 mode with the Mvalue in the X and Y directions to be M_x~2= 1.52 and M_y~2= 1.54. A tri-wavelength Nd:ScYSiO_5 crystal laser at 1.3 μm is also investigated. A maximum tri-wavelength output power is 1.03 W under the absorbed pump power of7 W, corresponding to a slope efficiency of 14.8%. The properties of the output wavelength are fully studied under different absorbed pump power.     

Diode-pumped cw and Q-switched Nd:GdVO4 laser operating at 1.34 μm

A diode-pumped 1.34 m Nd:GdVO₄ laser operating in cw and active Q-switching modes has been demonstrated. 4.15 W of cw output power was obtained at the highest attainable pump power of 12.3 W, resulting in an optical conversion efficiency of 33.7%, the slope efficiency was determined to be 37.6%. In Q-switching operation, a maximum average output power of 2.7 W was generated at pulse repetition frequency (PRF) of 50 kHz, with an optical conversion efficiency of 22% and a slope efficiency of 29.2%. The laser pulses with shortest duration, highest energy and peak power were achieved at PRF of 10 kHz, the parameters being 15 ns, 160 J, and 10.7 kW, respectively. By intracavity frequency-doubling with a type II phased-matched KTP crystal, 0.62 W average power at 0.67 m was produced at a PRF of 15 kHz, the resulting pulse energy, peak power, and pulse width being 41.3 J, 2.2 kW, and 19 ns, respectively. A group of analytical formulae, based on rate equations, are presented to evaluate the operational parameters of an actively Q-switched laser. Calculated results were found to be in close consistency with the experimental data.     

High efficiency beam combination of 4.6-μm quantum cascade lasers

The quantum cascade laser （QCL）, a potential laser source for mid-infrared applications, has all of the advantages of a semiconductor laser, such as small volume and light weight, and is driven by electric power. However, the optical power of a single QCL is limited by serious self-heating effects. Therefore, beam combination technology is essential to achieve higher laser powers. In this letter, we demonstrate a simple beam combination scheme using two QCLs to extend the output peak power of the lasers to 2.3 W. A high beam combination efficiency of 89% and beam quality factor of less than 5 are also achieved.     

High performance complex-coupled 1.55 μm distributed feedback lasers for digital transmission

We report low threshold and high speed 1.55 m complex-coupled distributed feedback (CCDFB) lasers with gain coupling induced by a current blocking grating. Excellent device performance has been demonstrated with a record-low threshold of 5.6 mA, a large modulation bandwidth of 11 GHz and useful high temperature operation up to 95°C.     

Current and frequency modulation characteristics for continuous-wave quantum cascade lasers at 9.06 μm

We report the characteristics of current induced frequency modulation (FM) for two continuous-wave quantum cascade lasers (QCLs) at 9.06 μm. Both the frequency tuning rate and the phase shift between intensity modulation and FM are measured at different modulation frequencies from 10 Hz to 200 kHz. The frequency tuning rate of the QCLs depends on both the modulation frequency and amplitude. The tested QCL has been used to detect ambient water vapor with wavelength modulation spectroscopy for validation with a numerical model.     

Fabrication and characterization of Ge-Ga-Sb-S glass microsphere lasers operating at ～1.9 μm

We report the fabrication and characterization of germanium gallium antimony sulfide(Ge–Ga–Sb–S or 2 S2 G, doped with Tm~(3+)ions) microsphere lasers operating at ～1.9-μm spectral band. Compared to the chalcogenide glasses that are used in previous microsphere lasers, this 2 S2 G glass has a lower transition temperature and a higher characteristic temperature. This implies that 2 S2 G microspheres can be fabricated at lower temperatures and the crystallization problem in the sphere-forming process can be alleviated. We show that hundreds of high-quality microspheres(quality factors higher than 105) of various diameters can be produced simultaneously via a droplet sphere-forming method. Microspheres are coupled with silica fiber tapers for optical characterizations. We demonstrate that Whispering Gallery mode(WGM)patterns in the 1.7–2.0 μm band can be conveniently obtained and that once the pump power exceeds a threshold, single-and multi-mode microsphere lasers can be generated. For a typical microsphere whose diameter is 258.64 μm, we demonstrate its laser threshold is 0.383 mW, the laser wavelength is 1907.38 nm, and the thermal sensitivity of the microsphere laser is29.56 pm/?C.     

1.56 μm and 2.86 μm Raman lasers based on gas-filled anti-resonance hollow-core fiber

We report here a single-pass 1.56 μm fiber gas Raman laser in a deuterium-filled hollow-core fiber and a 2.86 μm cascade fiber gas Raman laser with methane in the second stage. The maximum output powers at 1.56 and 2.86 μm are 27 and 8.5 m W with Raman conversion efficiency of 30% and 42%, respectively. The results offer a new method to produce a 1.5 μm fiber source and prove the potential of the cascade fiber gas Raman laser in extending the available wavelength.     

Actively mode-locked 1.3 and 1.55 μm InGaAsP diode lasers

Active mode-locking of uncoated InGaAsP diode lasers having an external diffraction grating cavity was investigated experimentally. A high frequency r.f. signal and short-duration electrical pulses were used to drive the lasers. The pulse duration was measured by an ultrafast streak camera. Pulses as short as 13 ps at 1.3m and 29 ps at 1.55m were generated at a repetition rate of 1 GHz. The reason for obtaining broader pulses from the 1.55m laser which had the same structure as the 1.3m diode laser is explained.Formerly with GEC Hirst Research Centre, Wembley, Middlesex, UK.     

Frequency of lamb-dip-stabilized 1.52 μm He-Ne lasers

A ³He-²⁰Ne and a ³He-²²Ne 1.52 m laser were frequency stabilized to the Lamb-dip of their respective gain curve and provided a resettability of 2 MHz. Using these lasers, absolute frequencies for the ²⁰Ne and ²²Ne laser transitions were measured by interferometric frequency comparison with an I₂-stabilized He-Ne laser at 0.633 m. A least-square analysis which accounts for the linear frequency dependence of the laser gas pressure yielded two parameters which can reproduce the measured frequencies within an accuracy of ±1.0·10^–8 at 1.52 m.     

Thermal effects in quantum cascade lasers at λ～4.6 μm under pulsed and continuous-wave modes

The thermal effects in InGaAs/InAlAs quantum cascade lasers (QCLs) emitting at λ∼4.6 μm under pulsed and continuous-wave (CW) modes using a three-dimensional (3D) heat dissipation model were investigated. Based on the experimentally measured results, the thermal characteristics were theoretically analyzed for various device and heatsinking structures. Also, the heat accumulation effects and dissipation processes were studied in detail under pulsed operation. High cooling efficiencies were achieved by a relatively fast heat diffusion rate from the active core region for the epilayer-down bonded single ridge waveguide buried heterostructure (BH) with a thick electroplated Au around the laser ridge. A further improvement was made by the use of InP embedding layer. In CW mode, the thermal conductance (G _th) value of 445 W/(K cm²) at 298 K was obtained for the epilayer-down bonded double-channel ridge waveguide QCL with AlN submount, which indicates a reasonable consistency with the available experimental data. By optimizing the device and heatsinking structures, the G _th was improved to a high value of 673 W/(K cm²) at 298 K for the epilayer-down bonded single ridge waveguide BH QCL with InP embedding layer on diamond submount in CW mode.     

Noise conversion from pump to the passively mode-locked fiber lasers at 1.5 μm

We characterize the noise conversion from the pump relative intensity noise (RIN) to the RIN and phase noise of passively mode-locked lasers at 1.5 μm. Two mode locking mechanisms, nonlinear polarization rotation (NPR) and semiconductor saturable absorber mirror (SESAM), are compared for noise conversion for the first time. It is found that the RIN and the phase noise of both types of lasers are dominated by the noise converted from the pump RIN and thus, can be predicted with the measured pump RIN and noise conversion ratios. The SESAM laser is found to show an excess noise conversion from the laser RIN to the laser phase noise due to the slow saturable absorber effect.     

A comparative study of laser tissue interaction at 2.94 μm and 10.6 μm

Laser cutting of gelatin and tissue with Er and CO₂ lasers is explained by combined action of evaporation, ejection of liquid and elastic deformation of the region of radiation impact. It is shown that the ejection mechanism is more pronounced at 2.94 m than at 10.6 m. The use of high speed photography has revealed the influence of the temporal pulse shape. The experimental results are explained by a thermo-mechanical model.     

Ablation of polyimide (Kapton™) films by pulsed (ns) ultraviolet and infrared (9.17 μm) lasers

Ablation of the surface of a polyimide (Kapton) film by single pulses of 248 nm or 308 nm radiation (20 ns) or 9.17 m laser radiation (170 ns) was studied by photographing the emergence of the blast wave and the plume by a pulse (<1 ns; 596 nm) of visible laser light. The dynamics of the blast wave was similar in the ultraviolet and in the infrared but the composition of the plume was obviously different. A mass of opaque solid material was ejected for as long as 2.6 s following the IR pulse in contrast to the minute amount of solids that are seen in the ablation by UV laser pulses of ns duration. UV laser pulses of 50–400 s duration interact with polyimide surfaces in a manner that is similar to IR laser pulses of ns duration or longer. Chemical analysis of the ablation products that are obtained under various conditions of ablation when compared to the known modes of thermal degradation of polyimide show that the reaction is a thermal process when IR laser pulses or UV laser pulses of long (>10 s) duration are employed. Ablation by ns UV laser pulses differs fundamentally in the chemistry of the products from all of the cases mentioned above.     

High efficiency double-pass-pumped 2 μm periodically poled MgO:LiNbO3 optical parametric oscillator

A high efficiency near-degenerate periodically poled MgO:LiNbO₃ optical parametric oscillator pumped by a nanosecond Nd:YVO₄ laser is demonstrated. Under a 1.064 ??m pump power of 7.2 W, an output power of 5.3 W with an optical-to-optical conversion efficiency of 74% and a slope efficiency of 82% in the 2 ??m region is obtained in a double-pass-pumped doubly resonant geometry at 20 kHz repetition rate.     

Efficient graphene Q switching and mode locking of 1.34 μm neodymium lasers

We demonstrate that few-layered graphene sheets used as a saturable absorber can provide efficient Q-switching and mode-locking modulation in 1.34 μm Nd:GdVO(4) bulk lasers. The minimum Q-switched pulses were 450 ns for 260 mW average power, 43 kHz repetition rate, and 2.5 μJ pulse energy. For the mode-locked laser, an average power of 1.29 W was achieved with 11 ps pulse duration and 13 nJ pulse energy. To our knowledge, this average power is the highest yet obtained from a graphene mode-locked laser, and the corresponding optical-optical efficiency of 23% is the best result among 1.3 μm neodymium mode-locked lasers. The quality factor M(2) of the Q-switched beam was 1.4 and 1.6 in the horizontal and longitudinal planes, respectively, and the M(2) of the mode-locked beam reached 1.1 and 1.0. These results clearly indicate the advantages of few-layered graphene as a saturable absorber.     

High sensitivity Faraday rotation spectrometer for hydroxyl radical detection at 2.8 μm

A distributed feedback diode laser based Faraday rotation spectroscopy (FRS) instrument was developed for detection of hydroxyl free radical (OH) at 2.8???m. Fast wavelength sweeping method was implemented and the instrument performances were compared with point-by-point wavelength tuning method. The fast sweeping operation mode showed the same short-term minimum detection limit and improved immunity to baseline drift. The effects of strong diamagnetic H₂O vapor absorption on FRS detection of paramagnetic OH were investigated. We demonstrated that in the case of strong H₂O vapor absorption, the magnitude of the FRS signal for OH might be affected due to changes in the received optical power. The effects of higher laser intensity on the FRS detection sensitivity were also studied experimentally.     

High Resolution and High Sensitivity Measurement of Methane at 1.51μm

The high-resolution absorption spectrum of CH4 at 1.51μm is observed by direct absorption spectroscopy technique with a White absorption cell. Multi-peak fitting technique is adopted to reveal line positions and line intensities of CH4 from 6608cm^-1 to 6625 cm^-1. Special attention is paid on the determination of the line positions, and the accuracy is better than ±0.002cm^-1. A minimum measurable absorption of 2.1×10^-8 （3σ） has been achieved based on the measured direct absorption spectroscopy.     

The infrared spectrum of HCCF around 17 μm

The absorption spectrum of HCCF in the region of the CH bending fundamental ν₄ has been studied at a resolution of about 0.03 cm^?1. In addition to the fundamental, the rotational analysis has been performed for six “hot” bands. Several molecular parameters have been derived. The effects of l-type resonances have been discussed. In particular, the influence of the resonance between the sublevels of ν₄ + ν₅ on the effective centrifugal distortion constants has been investigated.     

A comparison of algainas and InGaAsP-based 1.3 μm semiconductor lasers using high pressure

Abstract

We have compared the effect of hydrostatic pressure on the threshold current, I_th, and lasing energy, E_lase, of 1.3 pm quantum-well devices based upon AlGaInAs and InGaAsP. Whilst we observe a very similar dependence of E_lase on pressure for the two materials, we measure strikingly different variations of I_th. By applying pressure to 1.3 μm InGaAsP lasers, I_th typically decreases by ～ 10% over 1 GPa consistent with the reduction of Auger recombination, which forms ～ 50% of I_th at room temperature. However, for the 1.3 μm AlGaInAs-based lasers, we observe an increase in I_th by ～ 8% over the same pressure range. From these results we conclude that non-radiative recombination accounts for only ～ 20% of I_th in AlGaInAs-based devices. This is in good agreement with previous temperature dependence measurements and shows why AlGaInAs-based devices exhibit a reduced temperature sensitivity of I_th which is very important for telecommunications applications.     

Numerical study of strained InGaAs quantum well lasers emitting at 2.33 μm using the eight-band model

We investigate the band structure of a compressively strained In(Ga)As/In 0.53 Ga 0.47 As quantum well (QW) on an InP substrate using the eight-band k · p theory.Aiming at the emission wavelength around 2.33 μm,we discuss the influences of temperature,strain and well width on the band structure and on the emission wavelength of the QW.The wavelength increases with the increase of temperature,strain and well width.Furthermore,we design an InAs /In 0.53 Ga 0.47 As QW with a well width of 4.1 nm emitting at 2.33 μm by optimizing the strain and the well width.