Frequency stabilization of 1.55 μm DFB laser diode usingvibrational-rotational absorption of 13C2H2 molecules

The vibrational-rotational absorption of ¹³C₂H₂ molecules (VRAMs) in the 1.52-1.55 μm region was investigated in detail. On the basis of this investigation, frequency stabilization of 1.55-μm distributed-feedback (DFB) laser diodes was demonstrated. Frequency stability to within 2 MHz peak/peak fluctuation was achieved at the 1.54949-μm wavelength. In addition, frequency stabilizations in the wavelength regions of 1.53 μm and 1.54 μm were also carried out by using the strong absorption lines of ¹³C₂H₂ VRAM in these wavelength regions. The spectral width of the frequency-stabilized DFB laser diode was found to be 25 MHz. The absolute frequency was found to be stabilized at least to within 25 MHz by the measurement of beat spectrum     

Frequency stabilization of laser diodes using 1.51-1.55 μmabsorption lines of 12C2H2 and 13C2

Frequency stabilization of a 1.55 μm DFB laser diode is demonstrated using vibrational-rotational absorption of ¹²C ₂H₂ and ¹³C₂H₂ molecules (named VRAM). Frequency stability within 2 MHz peak to peak fluctuation can be achieved in the wavelength region of 1.51-1.55 μm. Frequency-stabilized DFB laser compact modules have been constructed. Frequency stabilities are evaluated by measuring the beat spectrum of the two lasers. In addition, the temperature and pressure dependences of the acetylene absorption lines are characterized     

High-power, tunable, high-repetition rate TEA-13C18O2 laser

The authors report the power enhancement of a high-repetition-rate TEA-¹³C¹⁸O₂ laser by substitution of rare ¹⁵N₂ isotope instead of ¹⁴N₂ and its tunable single-mode operation. Efficient, high-power operation with a maximum average power of 25 W (100 Hz) at a slope efficiency of 5.6%, which is improved by a factor of 2 by substitution of ¹⁵N₂ instead of ¹⁴N₂, has been successfully achieved from a discharge volume of 57.5 cm³ with an active length of 26 cm. In addition, high-power, tunable, single-mode operation has been achieved with a three-mirror cavity consisting of two mirrors and a Littrow grating     

Frequency stabilization of the sequence-band CO2 laserusing the 4.3-μm fluorescence method

The saturated 1.3-μm fluorescence stabilization method is applied to the 00⁰2-[10⁰1, 02⁰1]_I,II sequence band CO₂ laser transitions. For this purpose, the 4.3-μm fluorescence is observed using an external longitudinal CO₂ absorption cell heated to 300°C. The dependence of the frequency stability upon the gas temperature and pressure in the cell as well as laser parameters have been carried out in absolute frequency scale with the help of a two-channel heterodyne system. Under optimal conditions, the standard deviation of the beat note frequency between sequence band and regular band lasers for 30 s averaging time is less than 20 kHz, and the long-term stability and reproducibility is achieved at about 10 kHz     

New CO2 laser lines in the 11-μm wavelength region:new hot bands

Nineteen new laser lines in the 11-μm wavelength region have been observed in CW oscillation from a CO₂ laser with a high-Q, high-resolution cavity at a higher than usual current density. The frequency of each line has been measured using heterodyne frequency measurement techniques. Analysis of the frequencies shows that 15 lines are rotation-vibration transitions of the 01¹2-[11¹1,03¹1]_I band (the first sequence hot band) of the CO₂ molecule and four lines belong to the rotation-vibration transitions of the 02²1-[12 ²0, 04²0]_I band of CO₂     

LaNiO3: a promising material for contact with YBa2Cu3O7-x thin films

Epitaxial LaNiO₃ metallic oxide thin films have been grown on c-axis oriented YBa₂Cu₃O_7-δ thin films on LaAlO₃ substrates by pulsed laser deposition technique and the interface formed between the two films has been examined by measuring the contact conductance of the same. The specific contact conductance of the interface measured using a modified four probe method was found to be 1.4 to 6×10⁴ ohm^-1 cm^-2 at 77 K. There are indications that contact conductance can be brought closer to that obtained for noble metal-YBCO interface     

Subnanosecond multi-gigawatt CO2 laser

A semiconductor switching technique has been utilized to produce 30-300 ps variable duration CO₂ laser pulses of 0.5-MW peak power. Eight passes through a 1.2-m long, UV-preionized, 3-atm TE CO₂ amplifier raise the output laser peak power to the 10¹⁰ W level. Sampling the amplifier gain in linear and saturated regimes using CO₂ laser radiation ranging from CW to 30 ps pulse length permits comparison with computer modeling of picosecond CO₂ pulse amplification. The potential for further peak power scaling of picosecond molecular lasers is discussed     

New CW CO2 laser lines: the 9-μm hot band

We have made what we think is the first observation of the oscillation of the 9-μm hot-band lines 01¹1→[11¹ 0,03¹0]_II of CO₂. We have observed 40 lines with a maximum power of 8 W. They will provide a new source of laser radiation for spectroscopy. The set of lines has been positively identified by directly measuring the frequencies of two of the lines with a heterodyne technique using a CO₂ laser standard     

Fabrication of Microcavity Light-Emitting Diodes Using Highly Reflective AlN–GaN and Ta2O 5–SiO2 Distributed Bragg Mirrors

We report the fabrication of microcavity light-emitting diodes (MCLEDs) with high reflectivity and crack-free AlN-GaN distributed Bragg reflector (DBR). The 5lambda microcavity structure consists of an n-type GaN, ten pairs InGaN-GaN multiple quantum wells and p-type GaN sandwiched between the hybrid cavity mode of an AlN-GaN and a Ta₂O₅-SiO₂ DBR. The AlN-GaN DBR has 29 periods with insertion of six AlN-GaN superlattice layers showing a crack-free surface morphology and a high peak reflectivity of 99.4% with a stopband of 21 nm. The output power of MCLED is about 11 W at an injection current of 7 mA. The electroluminescence has a polarization property with a degree of polarization of about 51%.     

Electrical Characterization of ZrO2/Si Interface Properties in MOSFETs With ZrO2 Gate Dielectrics

MOSFETs incorporating ZrO₂ gate dielectrics were fabricated. The I_DS-V_DS, I_DS-V_GS , and gated diode characteristics were analyzed to investigate the ZrO₂/Si interface properties. The interface trap density (D _it) was determined to be about 7.4times10¹² cm ^-2middoteV^-1 using subthreshold swing measurement. The surface-recombination velocity (s₀) and the minority carrier lifetime in the field-induced depletion region (tau _0,FIJ) measured from the gated diodes were about 3.5times10 ³ cm/s and 2.6times10^-6 s, respectively. The effective capture cross section of surface state (sigma_s) was determined to be about 5.8times10^-16 cm² using the gated diode technique and the subthreshold swing measurement. A comparison with conventional MOSFETs using SiO₂ gate oxides was also made     

Observation and assignment of D218O FIR laserlines optically pumped by a waveguide CO2 laser

By means of a detailed analysis of the v₂ infrared band of D₂¹⁸O, it has been possible to assign most of the FIR emissions reported in the literature. Moreover, two FIR laser lines which fall in the range of tunability of the CW waveguide CO₂ laser have been predicted and observed. The frequency of the stronger line was measured and found to be 2611.4185(10) GHz, thus filling a gap in the presently available comb of FIR laser lines whose frequencies have been measured. The wavelength precision of the assigned lines was improved by about two orders of magnitude     

Thermal shifts of the spectral lines in the 4F3/2 to 4I11/2 manifold of anNd:YAG Laser

A report is presented of the thermal shifts of eleven of the twelve lines from the ⁴F_3/2 Stark energy levels to the ⁴I_11/2 energy levels in an Nd:YAG laser for a temperature change from 20-200°C. The thermal shift difference between the Stark sublevels R₁, R₂ in ⁴F_3/2 is found to be about -0.6±0.6 cm^-1/100°C. Within experimental uncertainty, all of the lasing lines either moved to longer wavelength or remained unchanged with increasing temperature     

Emission cross sections and spectroscopy of Ho3+ laserchannels in KGd(WO4)2 single crystal

The spectroscopic properties of Ho³⁺ laser channels in KGd(WO₄)₂ crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho³⁺ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were Ω₂=15.35×10^-20 cm², Ω ₄=3.79×10^-20 cm², Ω₆ =1.69×10^-20 cm². The 7-300-K lifetimes obtained in diluted (8·10¹⁸ cm^-3) KGW:0.1% Ho samples are: τ(⁵F₃)≈0.9 μs, τ( ⁵S₂)=19-3.6 μs, and τ(⁵F₅ )≈1.1 μs. For Ho concentrations below 1.5×10²⁰ cm^-3, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law τ_ph ^-1(0)=βexp(-αΔE), where β=1.4×10^-7 s^-1, and α=1.4×10³ cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho³⁺ emission cross section σ_EM for several laser channels are calculated in σ- and π-polarized configurations. The peak a σ_EM values achieved for transitions to the ⁵I₈ level are ≈2×10^-20 cm² in the σ-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 μm are envisaged inside the ⁵I₇→⁵I₈ channel     

CO2 laser stabilization to 0.1-Hz level using externalelectrooptic modulation

We have developed a frequency stabilization scheme for CO₂ lasers using only external modulation via an electrooptic modulator (EOM). One of the two laser sidebands which are generated by the EOM and frequency-modulated is set in resonance with a Fabry-Perot cavity, itself filled with OsO₄ as an absorber. The saturation signal of an OsO₄ line detected in transmission of the Fabry-Perot cavity is used for stabilization. We obtained a stability of 0.1 Hz (Δν/ν=3.5 10^-15) on a 100-s time scale, and a reproducibility up to 10 Hz with the strongest OsO₄ reference lines. These results largely improve the performance of our previous setup for which modulation was applied through piezoelectric transducers. Further, the stabilized laser is not frequency-modulated and is easily tunable     

Raman Scattering and Nd3+ Laser Operation in NaLa(WO 4)2

The continuous-wave laser operation of Nd-doped tetragonal NaLa(WO ₄)₂ crystal is studied at room temperature by optical pumping in the spectral region overlapping AlGaAs diode laser emission. This crystal has inhomogeneously broadened optical bands. From the room-temperature spectroscopic parameters determined it is found that the optimum Nd concentration for the ⁴F_3/2rarr⁴I_J laser channels must be in the 3-5 at.% range. For J=11/2 and 13/2 channels (lambdaap1.06 and 1.3 mum) the most favourable polarization configuration is parallel to the crystallographic c axis, while for J=9/2 little polarization dependence of the laser efficiency is predicted. Laser operation was achieved with a 3.35 at.% Nd-doped sample grown by the Czochralski method. The laser operation was tested in an hemispherical optical cavity pumped by a Ti:sapphire laser. Stimulated emission at lambda=1056 nm was achieved for a wide spectral pumping range, lambda=790-820 nm. Stimulated Raman scattering was achieved in the picosecond regime with an efficiency similar to that of monoclinic KY(WO₄)₂ reference compound     

Further investigations of a 2-μm Tm:YVO4 laser

The performance of a Tm:YVO₄ laser has been optimized by varying the thickness of the laser crystal and the reflectivity of the output coupler. This has led to the measurement of a slope efficiency of 48% for the laser output. Formulas describing the saturation of the pump and the upper laser level in the presence of up-conversion loss have been developed. Fitting of the experimental data to the saturation curves calculated using these formulas has yielded an up-conversion rate constant from ³F₄ to ³ H₅ of 2·10^-18 cm³ s^-1      

Fast axial flow CO2 laser excited by silent discharge

A fast axial flow CO₂ laser excited by silent discharge has been developed. With a new electrode system applied to the laser, homogeneous discharge of power density of up to 80 W/cm³ is obtained without applying any stabilization techniques on the discharge. An output laser power of 920 W in stable TEM₀₀ mode operation is attained with an efficiency of over 14%. Beam fluctuation common to fast axial flow lasers is suppressed by the combination of smooth gas flow and low CO₂ molar fraction     

Frequency chirp in a 10 ATM RF-excited CO2 waveguidelaser

Various mechanisms causing frequency chirping in multiatmospheric-pressure CO₂ lasers are discussed. The frequency chirp has been measured in a pulsed 10 atm CO₂ waveguide laser. It has been found that the dominating cause of the frequency chirp in this laser is heating of the gas by the RF discharge. The chirp increases with increasing RF input power. The chirp levels off at about 100-150 MHz/μs for 25 kW of input power. This leveling off the chirp is believed to be due to the negative lensing effect of the gas density perturbation. The effect of the anomalous dispersion on the chirp is observed when the laser is operated at the flanks of the CO₂ gain branches     

Anomalous gain in an isotopically mixed CO2 laser andapplication to absolute wavelength calibration

Measurements are reported on a grating-tuned CO₂ laser, containing an isotopic mixture of ¹⁶O¹²C¹⁶ O, ¹⁶O¹²C¹⁸O, and ¹⁸O ¹²C¹⁸O. The P₆ and R ₁₄ lines of ¹⁶O¹²C¹⁶O were found to have anomalously high intensities. These anomalies are produced by the near coincidence of the transition frequencies in two distinct isotopes, permitting them to act as a single indistinguishable population. These two lines can be used to identify the rotational quantum numbers in the P and R branch spectra, thereby permitting absolute wavelength calibration to be achieved     

Frequency measurements of 9- and 10-μm N2O lasertransitions

We have measured frequencies of N₂O transitions by heterodyning sub-Doppler fluorescence-stabilized N₂O laser radiation with that from a reference CO₂ laser. A high-resolution cavity incorporates a ribbed tube and a highly reflective grating, permitting the CW oscillation of both the 10⁰ 0-02⁰0 9-μm and the 10⁰0-00⁰1 10-μm regular bands. This is the first sub-Doppler frequency measurement of the 9-μm band. The accuracy in the determination of the rotational constants for both bands has been improved by an order of magnitude, and calculated transition frequencies are presented