Frequency noise of free-running 4.6 μm distributed feedback quantum cascade lasers near room temperature

The frequency noise properties of commercial distributed feedback quantum cascade lasers emitting in the 4.6 μm range and operated in cw mode near room temperature (277 K) are presented. The measured frequency noise power spectral density reveals a flicker noise dropping down to the very low level of <100 Hz(2)/Hz at 10 MHz Fourier frequency and is globally a factor of 100 lower than data recently reported for a similar laser operated at cryogenic temperature. This makes our laser a good candidate for the realization of a mid-IR ultranarrow linewidth reference.     

High efficiency cw far infrared lasers at 119 μm and 127 μm

The optically pumped FIR laser lines at 119 m from CH₃OH and at 127 m from¹³CD₃OH are known to be the most powerful in the far infrared spectral region. We report on efficiency measurements for our waveguide laser system. The effect of various parameters was investigated, resulting in the highest efficiency ever reported for the 119 m line. The Stark effect and others parameters of the 127 m were measured, and a new¹³CD₃OH laser line at 175 m discovered, with the same pump transition. These measurements are helpful for completing the assignment already proposed for the 127 m line.     

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.     

Frequency measurements in the 10 μm spectrum of 11BCl3

This paper presents a study of the spectroscopy of ¹¹BCl₃ using the Doppler-free saturated absorption technique. Many lines in the degenerate ν₃ fundamental of this molecule have been recorded using the 10P branch of a carbon dioxide laser. The absolute frequencies of the linecentres of these absorptions have been measured to an accuracy of better than 10 kHz, using frequencies calibrated against transitions in SF₆ and OsO₄. Hyperfine structure due to the Cl nuclei was easily resolved, and more detailed structure, which may be attributed to the ¹¹B quadrupole interaction, was also seen. The splittings between individual quadrupole components were measured to an accuracy of better than 2 kHz where SF₆ references were used, and to about 8 kHz in the case of OsO₄. Peak-to-peak linewidths as low as 22 kHz have been recorded, representing the highest resolution data yet obtained for this molecule.     

Experimental investigation of pulse diodes side-pumped 2 μm Tm:YAG lasers

The free running and Q-switched operation of 2 μm Tm:YAG lasers side-pumped by pulse laser diodes were reported. In the free running mode the maximum output energies were 102.5 mJ at 1 Hz and 94.6 mJ at 10 Hz, respectively. With an acousto-optic modulator in the laser resonator, 21 mJ 2 μm Q-switched pulse was obtained, with a pulse width of about 330 ns. The dependences of the output energy and the efficiency on the laser resonator parameters were investigated.     

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.     

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.     

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.     

Investigation of the mode crossing resonance shape of the 1.52 μm and 633 nm neon transitions

The shape of zero field mode crossing resonances has been investigated both theoretically and experimentally. Taking into account the effect of collisions, the resonance shape is given generally by superposition of four Lorenzians. Two of them are caused by the aligned laser levels (ifJ≧1), the other two are produced by phase destroying collisions. Investigations of the zero field mode crossing resonances of the 2s ₂→2p ₁(λ=1.52μm) and 3s ₂→2p ₄ (λ=633nm) Ne laser transition revealed deviations of the measured data from a Lorentz profile. By computer fitting both the alignment relaxation rate \(\gamma _{2s_2 } \) (2) and the relaxation rate of the optical coherence \(\gamma _{2s_2 ,2p_1 } \) was obtained from one resonance curve. An investigation of the relaxation rate of the optical coherence as a function of the Ne pressure yields the pressure broadening constant (7±3) MHz/Torr and the natural linewidth 1/2 \(\tfrac{1}{2}(\gamma _{2s_2 } + \gamma _{2p_1 } ) = (18.8 \pm 1.7)\) MHz which are in agreement with inverted Lamb dip measurements.     

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.     

Threshold conditions for 800 nm pumping of 2 μm Tm : Ho lasers

Pumping requirements of pulsed and continuous wave (CW) 2 m Tm : Ho lasers are investigated experimentally and theoretically for excitation at 800 nm. The influence of the pulse duration on threshold is measured using a chopped Ti : Al₂O₃ laser. Based on the experimental and simulated results the spatial and temporal pump requirements in future quasi-CW high-power diode-pumped 2 m Tm : Ho lasers are determined. The experiments and the model allow the evaluation of different loss mechanisms and indicate significant 540 nm emitting loss mechanisms.     

Reduction of the threshold temperature sensitivity of 1.55 μm InGaAsP lasers by subnanosecond optical excitation

In GaAsP lasers operating at 1.5 to 1.6 m were pumped optically with a pulsed 1.06 m source. The temperature dependence of the pump energy at laser threshold has been measured for temperatures from 170 to 330 K. Pump pulse widths of 300 ns and 150–300 ps were employed, long and short compared to the carrier life-time in the laser material. Over the high-temperature range of 260 to 330 K short pulse excitation gives a considerable reduction of the threshold temperature sensitivity with a characteristic temperatureT ₀ =85 K compared to T ₀ ^h =45 K for long-pulse excitation. This is in qualitative agreement with previous results on electrically excited lasers although the temperature sensitivity of the optically excited lasers is larger. At temperatures between 170 to 260 K no reduction of the temperature sensitivity was observed.     

Saturable absorbers for passive Q-switching of erbium lasers emitting in the region of 3 μm

The phototropic properties of Fe:ZnSe, Co:ZnSe, and Co:ZnS single crystals have been investigated. It is shown that these crystals can be used to advantage as the saturable absorbers in solid-state erbium lasers emitting in the region of the 3-μm range. The absorption cross sections of the ground states of the Co²⁺ ion in the ZnSe (σ_GSA = 11·10⁻²⁰ cm²) and ZnS (σ_GSA = 5.6·10⁻²⁰ cm²) crystals and of the Fe²⁺ ion in the ZnSe (σ_GSA = 50·10⁻²⁰ cm²) crystal at λ = 2.79 μm were determined experimentally. It has been established that the above-indicated crystals in the excited state absorb light weakly. The use of these crystals as passive Q switches made it possible to realize, for the first time, the regime of Q-switching of a Cr,Er:YSGG laser emitting at a wavelength of 2.79 μm. Single pulses with an energy of 60 mJ and a duration of 170 nsec were obtained in the regime of passive Q-switching. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 747–751, November–December, 2005.     

Bifurcations and observation of strange attractor in He-Ne lasers

We report the experimental observation of deterministic chaos in an He-Ne laserat 0.6328μm by varying the discharge current.Strange attractor of laser system in the recon-structed phase-space picture has been obtained.The mechanism of the phenomena was dis-cussed.     

Injection lasers in the 1.3–1.8 μm wavelength range

Conclusion There are developed techniques for the preparation of diode lasers in the 1.3 to 1.8 m range on the basis of quaternary epitaxial heterostructure. Devices for a particular wavelength of 1.3 m are now commercially available. The state of art in the laser studies with connection to lower room-temperature threshold and to higher operation temperature is illustrated in fig. 9. We feel that the laser system of InGaAsP, which is known since 1974 [1, 2], may be elaborated further for higher laser characteristics in spite of the fact that present state is quite acceptable for different applications. There are many fibre-optics projects based on the conception of laser optical communication with the use of diodes in the range of 1.3–1.8 m.Invited talk at the International Conference on Radiative Recombination and Related Phenomena in III–V Compound Semiconductors, Prague, 4–7 October, 1983.The author is indebted to Dr. L. M. Dolginov, B. N. Sverdlov, A. E. Drakin, P. A. Louk, E. G. Shevchenko for the help in this work.     

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.     

Frequency stabilization of diode laser to 1.637 μm based on the methane absorption line

The frequency of an external-cavity diode laser has been stabilized to 1.637 μm by using the reference of absorption lines of methane. The method can be applied to wavelength division multiplexed optical communication, fiber-optic sensing systems, as well as the high-sensitivity detection of methane. The derivative-like error signal yielded by frequency modulation and phase sensitivity detection technology is inputted into the PI feedback loop circuit in order to stabilize the frequency to the line center. After stabilization, the frequency fluctuation of diode laser is held within 5.6 MHz, and the root of Allan variance of error signal reaches a minimum of 1.66×10-10 for an average time of 10 s.     

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.