New efficient laser dye for pulsed and CW operation in the UV

A new laser dye for pulsed and cw operation has been synthesized which can be tuned from 362 nm up to 412 nm. For pulsed excitation with a XeCl excimer laser an energy conversion of 18.5% has been measured at the tuning maximum of the dye; this is the highest efficiency for any known dye in the UV. For cw operation a low laser threshold and a goof efficiency have been observed. The range of tuned cw dye lasers is extended by 30 nm to shorter wavelengths. The dye shows high photochemical stability even at high pump laser power.     

Singly resonant continuous-wave optical parametric oscillator pumped by a diode laser

We report on what is believed to be the first singly resonant cw optical parametric oscillator (SRO) that is directly pumped by a diode laser. The SRO consists of a 38-mm-long periodically poled LiNbO(3) crystal in a four-mirror signal-resonant ring cavity. Pumped by 2.5 W of 925-nm diode-laser radiation, the SRO generates 480 mW of single-frequency idler radiation at 2.1mum . The wavelengths of the signal and the idler output are tuned in the ranges of 1.55 to 1.70mum and 2.03 to 2.29mum, respectively, by tuning the wavelength of the diode laser from 924.0 to 925.4 nm.     

Continuous-wave 4.3-mum intracavity difference frequency generation in an optical parametric oscillator

We have achieved 150 mW of cw output at 4.3mum, using difference frequency mixing in a singly resonant optical parametric oscillator (OPO). We pumped the OPO cavity, which contains periodically poled LiNbO(3) (PPLN), with a 14-W 1.06-mum Nd:YAG laser to generate a signal at 1.7 mum and an idler at 2.8 mum. Mixing of the two waves at the same crystal temperature and grating spacing yielded emission in the mid IR. This technique avoids the mid-IR absorption-high-threshold problem, which has limited the cw performance of PPLN OPO's at wavelengths beyond 4 mum. Provided that tunability is not required, this method is a simple alternative to multiple-crystal configurations.     

Low-temperature performance of InP-based long-wavelength VCSELs

We have studied, for the first time, the parameters of long-wavelength InP-based buried tunnel junction (BTJ) VCSELs with substrate temperature varied in the range between 150 and 330 K. The BTJ-VCSELs with threshold currents <1 mA were designed by VERTILAS (Germany) to operate near 1512 nm and 1577 nm at room temperature (models VL-1512 and VL-1577, respectively). Reducing the substrate temperature of the lasers from room temperature to 150 K resulted in more than a fourfold increase of the threshold injection current accompanied with threefold and twofold increases in output power and slope efficiency, respectively. We have observed continuous single-mode tuning over intervals up to ∼20 nm (VL-1512) and ∼22 nm (VL-1577) at constant injection currents and substrate temperatures varied in a 180 K range. The emission wavelength was found to shift linearly with temperature with rates of 0.11 nm/K and 0.12 nm/K for lasers VL-1512 and VL-1577, respectively. The single-mode laser output reached ∼3 mW for both lasers cooled down to 173 K. Gas sensors based on BTJ-VCSELs can be temperature tuned over wide spectral intervals using either a cooler or a low ambient temperature to control laser substrate temperature. Ultra-sensitive gas concentration measurements under low ambient temperatures may include chemical analysis of the lower earth stratosphere and of the martian atmosphere. PACS 42.55.Px; 42.62.Fi; 39.30.+w     

Continuous-wave rotational Raman laser in H(2)

A diode-pumped, far-off-resonance cw Raman laser in H(2) with rotational Stokes emission is reported for the first time to our knowledge. The Raman laser can produce single-wavelength emission at either 830 nm (rotational Stokes) or 1180 nm (vibrational Stokes) depending on the frequency tuning of the pump laser. The mirrors for the rotational cw Raman laser are easier to produce; the laser also exhibits a wider continuous tuning range and is less sensitive to thermal effects than the previously studied vibrational Raman laser [Opt. Lett. 26, 426 (2001) and references therein].     

A cw AgGaS2 difference frequency spectrometer with diode lasers as pump sources

2 and two diode lasers as pump sources and experiments with this setup are presented. In contrast to the majority of known applications of the difference frequency mixing with solid state or gas lasers, we apply two single mode diode lasers with emission wavelengths of 690 nm and 805 nm, respectively. By fixing the emission wavelength of one diode laser and tuning the wavelength of the second laser, by changing temperature or excitation current, we can cover typically 0.87 cm^-1 (FWHM) in good agreement with recently published data and theory. With an input power of 20 mW and 6 mW we achieved an output power in the nW-range. To demonstrate the capabilities of the spectrometer we scanned CO and OCS absorption lines near 2107 cm^-1. From these experiments we deduce an overall signal-to-noise ratio of 1000:1 and a spectral resolution better than 30 MHz. With such parameters a trace gas detection of CO at sub-ppm level will be possible. Received: 19 August 1996/Revised version: 5 November 1996     

Single-frequency continuous-wave radiation from 0.77 to 1.73 microm generated by a green-pumped optical parametric oscillator with periodically poled LiTaO3

We describe a cw optical parametric oscillator (OPO) with multigrating periodically poled LiTaO(3) . Pumped by a single-frequency 532-nm laser, the OPO emits single-frequency radiation at wavelengths from 0.77 to 1.73mum with as much as 60 mW of output power. Mode-hop-free operation for as long as 50 min, a low frequency drift (<70MHz/h), and as much as 700-MHz continuous frequency tuning of signal and idler are demonstrated.     

Sub-5-pm linewidth, 130-nm-tuning of a coupled-cavity Ti:sapphire oscillator via volume Bragg grating-based feedback

A novel coupled-cavity Ti:sapphire oscillator architecture featuring a volume Bragg grating as a feedback element is presented. The oscillator provides continuous wave lasing within a spectral linewidth as narrow as 5 pm. The output can be wavelength-tuned over an ultrabroad spectral range of 130 nm, extending from 714 to 842 nm. This unique combination of narrow spectral linewidth and wide tuning range makes the laser suitable for applications such as sensing and Raman and absorption spectroscopy. The laser also displays ideal TEM₀₀ mode operation throughout its tuning range with output powers beyond 300 mW. Detailed studies of the cw lasing dynamics across the wide tuning range are described. The general architecture of this design can be implemented for high resolution tuning across the broad spectral emission bands of other solid state lasers with single mode operation.     

Recent progress in the development of type II interband cascade lasers

Type-II interband cascade lasers combine the advantage of an interband optical transition with interband tunneling to enable the cascading of type-II quantum well active regions as is done in type-I quantum cascade laser. The relatively high radiative efficiency resulting from interband optical transitions translates into very low-threshold current densities, and when combined with the high quantum efficiency of cascade lasers, this diode laser design has the potential to operate under cw conditions at room temperature with high output power. Experimental results have already demonstrated some of this potential including high differential external quantum efficiency (>600%), high peak output power (6 W/facet at 80 K), high cw power conversion efficiency (>17% at 80 K), and operation at 300 K under pulsed conditions. Recent work aimed at reducing device thermal resistance and increasing cw operating temperature is reviewed including the demonstration of significant reductions in thermal resistance (averaging 25 K/W or 40% for 1-mm-long devices), 80 K cw operation at 3.4 μm with high-power conversion efficiency (23%) and high differential external quantum efficiency (532%), and cw operation up to 214 K.     

Optically pumped,indirect-gap Al_{\rm x}Ga_{1-{\rm x}}As lasers

We demonstrate optically pumped lasers with active layers of indirect-gap AlGaAs operating up to room temperature. The emission wavelength is 609 nm at 20 K and 639 nm at 300 K, respectively. The laser threshold shows a weak sensitivity on the lattice temperature. The relevant parameters of the lectron-hole plasma close to threshold are determined from gain spectroscopy using the variable stripe-length method. Received: 20 June 1996 / Accepted: 14 August 1996     

GaInAsP/InP double-heterostructure lasers for fiber odtic communications

This paper reviews the performance of GaInAsP/InP double-heterostructure diode lasers prepared by liquid-phase epitaxy. These lasers have the advantage that exact lattice-matching between the GaIn-ASP active region and the InP substrate is possible for quaternary alloy compositions giving emission wavelengths over a range that includes 1.1-1.3 μm, the optimum region for optical communication systems utilizing fused silica fibers. Continuous operation at room temperature has been achieved in this region for proton-defined stripe (PDS), oxide-defined stripe (ODs), and junction-defined, buried-stripe (JDBS) lasers. The first three PDS devices to be life-tested have already logged over 6,000, 5,700, and 4,000 h, respectively, of cw operation at room temperature without any degradation.     

4.0-4.5-mum lasing of Fe:ZnSe below 180 K, a new mid-infrared laser material

Lasing of Fe:ZnSe is demonstrated, for the first time to the authors' knowledge, for temperatures ranging from 15 to 180 K. The output wavelength of the Fe:ZnSe laser was observed to tune with temperature from 3.98mum at 15 K to 4.54mum at 180 K. With an Er:YAG laser operating at 2.698mum as the pump source, a maximum energy per pulse of 12muJ at 130 K was produced. Laser slope efficiencies of 3.2% at 19 K and 8.2% at 150 K were determined for an output coupling of 0.6%. A laser emission linewidth of 0.007mum at 3.98mum was measured at 15 K. Absorption and emission spectra and emission lifetimes for Fe:ZnSe are also discussed.     

Widely tunable, narrow-linewidth, subnanosecond pulse generation in an electronically tuned Ti:sapphire laser

Widely tunable subnanosecond Ti:sapphire laser radiation pumped with a cw Q -switched laser-diode-pumped Nd:YAG laser has been demonstrated in a simple laser system with a configuration of variable cavity length. Laser wavelengths can be continuously tuned by adjustment of the rf of an intracavity acousto-optic tunable filter with a computer through the whole range of the laser gain. During tuning of the whole spectral range, there is no need to realign any optics in the laser, except for moving the mirror to track the change of the rf. The peak powers of the output pulses at a pump level of 300 mW are comparable with those of conventional tunable picosecond Ti:sapphire lasers at a cw pump level of almost 10 W.     

GaInAsP/InP double-heterostructure lasers for fiber odtic communications

Abstract

This paper reviews the performance of GaInAsP/InP double-heterostructure diode lasers prepared by liquid-phase epitaxy. These lasers have the advantage that exact lattice-matching between the GaIn-ASP active region and the InP substrate is possible for quaternary alloy compositions giving emission wavelengths over a range that includes 1.1–1.3 μm, the optimum region for optical communication systems utilizing fused silica fibers. Continuous operation at room temperature has been achieved in this region for proton-defined stripe (PDS), oxide-defined stripe (ODs), and junction-defined, buried-stripe (JDBS) lasers. The first three PDS devices to be life-tested have already logged over 6,000, 5,700, and 4,000 h, respectively, of cw operation at room temperature without any degradation.     

Long wavelength vertical transition quantum cascade lasers operating CW at 110 K

The continuous wave (cw) operation of a quantum cascade laser at wavelengths ∼8 μm is reported. The structures, grown by molecular beam epitaxy in the AlInAs/GaInAs material system, are based on a vertical intersubband transition scheme and use a plasmon-enhanced waveguide geometry to reduce the losses and increase the confinement factor. The single mode optical power from one facet is 2 mW at a maximum operating temperature of 110 K. In pulsed operation the highest temperature is 210 K and the threshold shows a weak temperature dependence typical of this class of lasers, with aT_o=110 K.     

Tunable,dual-wavelength interferometrically coupled continuous-wave parametric source

Generation of dual-wavelength continuous-wave (cw) radiation with independent and arbitrarily tuning, and indefinitely close spacing, using two cw optical parametric oscillators (OPOs) coupled with an anti-resonant ring interferometer is reported. The singly resonant OPOs, based on identical 30-mm-long MgO:sPPLT crystals, are pumped by a single cw laser at 532 nm. Two pairs of signal and idler wavelengths can be independently and arbitrarily tuned, with each signal (idler) pair tuned through degeneracy and beyond. Frequency separation between two distinct resonant signal waves from 7 down to 0.8 THz is demonstrated, and their overlap at 951 nm providing a frequency difference as small as ~220 MHz is shown. The OPOs independently provide a signal (idler) wavelength coverage across 870–1,000 nm (1,040–1,370 nm) and simultaneously generate idler powers of >1 W.     

A novel structure of visible semiconductor lasers

Terraced substrate inner current stripe lasers emitting in the range of 750–780 nm are developed with very simple fabrication processes. The lasers have good performance of cw room temperature, linear light-current output over 30 mW per facet and maintain stable fundamental transverse and longitudinal mode of 2–4 times current threshold. The current threshold of 25 mA under cw room temperature operation has been achieved.     

A continuous wave SrMoO4 Raman laser

We demonstrate a cw, laser diode-pumped Nd:GdVO4/SrMoO4 crystalline Raman laser. First Stokes laser output at 1173.5?nm of 2.18?W was achieved with a diode-to-first Stokes efficiency of 8.7%. With intracavity frequency doubling in LiB3O5, 3.1?W of cw yellow emission at 586.8?nm was obtained with a 12.4% diode-to-yellow efficiency. The experimental results show that SrMoO4 is an excellent stimulated Raman scattering gain material for high-power cw near-IR Stokes and yellow lasers.     

Long-wavelength (lambda approximately 8-11.5 microm) semiconductor lasers with waveguides based on surface plasmons

Laser waveguides based on surface plasmons at a metal-semiconductor interface have been demonstrated by use of quantum cascade (QC) lasers emitting in the 8-11.5-microm wavelength range. The guided modes are transverse magnetic polarized surface waves that propagate at the metal (Pd or Ti-Au)-semiconductor interface between the laser top contact and the active region without the necessity for waveguide cladding layers. The resultant structure has the advantages of a strong decrease in the total layer thickness and a higher confinement factor of the laser-active region compared with those of a conventional layered semiconductor waveguide, and strong coupling to the active material, which could be used in devices such as distributed-feedback lasers. These advantages have to be traded against the disadvantage of increased absorption losses. A peak output power exceeding 25 mW at 90 K and a maximum operating temperature of 150 K were measured for a QC laser with an emission wavelength lambda approximately 8 microm . At lambda approximately 11.5 microm the peak power levels are several milliwatts and the maximum operating temperature is 110 K.     

Single-mode and tunable VCSELs in the near- to mid-infraredInvited Paper

Single-mode, long-wavelength vertical-cavity surface-emitting lasers (VCSELs) in the near- to mid-infrared covering the wavelength range from 1.3 to 2.3μm are presented. This wide spectral emission range opens applications in gas sensing and optical interconnects. All these lasers are monolithically grown in the InGaA1As-InP material system utilizing a buried tunnel junction (BTJ) as current aperture. Fabricated with a novel high-speed design with reduced parasitics, bandwidths in excess of 10 GHz at 1.3 and 1.55 μm have been achieved. Therefore, the coarse wavelength division multiplexing (CWDM) wavelength range of 1.3 to 1.6 μm at 10 Gb/s can be accomplished with one technology. Error-free data-transmission at 10 Gb/s over a fiber link of 20 km is demonstrated. One-dimensional arrays have been fabricated with emission wavelengths addressable by current tuning. Micro-electro-mechanical system (MEMS) tunable devices provide an extended tuning range in excess of 50 nm with high spectral purity. All these devices feature continuous-wave (CW) operation with typical single-mode output powers exceeding 1 mW. The operation voltage is around 1 - 1.5 V and power consumption is as low as 10 - 20 mW. Furthermore, we have also developed VCSELs based on GaSb, targeting at the wavelength range from 2.3 to 3.0 μm. The functionality of tunable diode laser spectroscopy (TDLS) systems is shown by presenting a laser hygrometer applying a 1.84-μm VCSEL.