Small Signal Gain Measurements Research Articles

Two-dimensional small-signal gain measurements in a laser diode-pumped flowing Nd3+:POCl3:SnCl4 liquid medium

Two-dimensional (2-D) small-signal gain is measured using amplification method in a laser diode-pumped flowing inorganic aprotic liquid laser medium which is prepared by dissolving 0.3 mol/l neodymium ions (Nd3+) in a mixture of phosphorous oxychloride (POCl3) host solvent and Lewis acid tin tetrachloride (SnCl4). An experimental setup is developed for the small-signal gain measurement which helps in investigating the liquid medium response under high power laser diode pumping. The liquid medium is circulated transversely through the laser cavity under laminar flow regime at flow rates of 15–20 l/min to mitigate the thermal induced effects. The spatial (2-D) profile of the small-signal gain is plotted and uniform gain of 0.01 cm−1 is measured along the optic axis at diode pump power of 1497 W. The 2-D distribution of small-signal gain in the liquid medium is also calculated theoretically. The measured and calculated values of small-signal gain are observed to be in close agreement with each other. Hence, the results are promising towards laser power scale up.

Detailed investigation of absorption, emission and gain in Yb:YLF in the 78–300 K range

We present spectroscopic measurements focusing on a detailed investigation of temperature dependence of absorption, emission and gain in the uniaxial Yb:YLF laser gain medium. Measurements are carried out in the 78–300 K range, but we especially targeted our attention to the 78–150 K interval, which is the desired working range of liquid nitrogen cooled cryogenic Yb:YLF lasers/amplifiers. A tunable (770–1110 nm) Cr:LiSAF laser with around 100 mW continuous-wave output power and sub-0.2 nm bandwidth is used as an excitation source. The average power of the Cr:LiSAF laser is low enough to prevent heating of the sample, and its spectral flux (W/nm) is high enough to enable large signal-to-noise ratio measurements. Measured absorption data is used to cross-check the validity of the emission measurements, while the measured temperature dependent small-signal gain profile provided a second independent confirmation. The acquired absorption cross section curves match the previous literature quite well, whereas the measured strength of c-axis emission is stronger than some of the earlier reports. Direct measurements of small signal gain confirmed the emission cross section data, where single pass gain values above 50 have been measured for the 995 nm transition of E//c axis at 78 K. We further provide simple analytic formulas for the measured temperature dependence of absorption and emission cross section. We hope the presented results to be useful for the development of next generation of cryogenic Yb:YLF laser and amplifier systems.

Ho:YAG single crystal fiber: fabrication and optical characterization.

0.5% Holmium (Ho) doped YAG single crystal fiber (SCF) was fabricated using Laser Heated Pedestal Growth (LHPG) method and characterized for its optical absorption and emission properties involving transitions between the 5I8 and 5I7 energy levels. The results verified the absorption peaks suitable for in-band direct pumping at 1908 nm and 1932 nm with the emission occurring between 2050 and 2150 nm. Small signal gain measurements were also performed for demonstrating the fiber like characteristics of the SCF.

Amplification characteristics of a cryogenic Yb3+:YAG total-reflection active-mirror laser

We have studied the amplification characteristics of a cryogenically cooled Yb³⁺:YAG total-reflection active-mirror (TRAM) ceramic laser including wavefront distortion, birefringence loss, small signal gain (SSG), and temperature rise for developing high-performance master oscillator power amplifier (MOPA) systems. A 0.6 mm thick Yb³⁺:YAG ceramic sample was used, and maximum pump intensity ~10 kW/cm² was reached. The transmitted wavefront was measured by using a Shack-Hartmann wavefront sensor, and we evaluated the thermal lens focal length and Strehl ratio for different pump conditions. We have also observed a butterfly-like leakage profile of thermally induced birefringence loss at the maximum pump intensity. From SSG measurements, we obtained moderate laser gain of G=3 for one bounce with a near aberration-free wavefront. Gain calculations, which included also temperature dependence of the emission cross section and reabsorption of Yb³⁺:YAG, were in good agreement with the experiments. These experimental results will be useful as benchmark data for numerical simulations of temperature distribution in TRAM and for designing multikilowatt-class high-performance MOPA systems.

Saturation pulse width effect for small signal gain measurement: theoretical model and experiment

We report a new method to measure amplitude small signal gain of a chopper base Q-switched Nd:YAG laser using saturation pulse width effect of nanosecond relaxation oscillation (RO) spikes. Formation of such RO pulses is theoretically modeled and simulated by attributing a loss function to the internal Q-switch chopper and solving the standard rate equations using real practical values associated with a laboratory Q-switched cw Nd:YAG high-power laser. It is found that at a certain chopper frequency, pulse width of the simulated RO spikes is saturated and tends to a minimum value. The performance of the represented model is verified by experimental measurements through generating nanosecond RO spiked using a frequency-variable chopper inside the cavity of the laboratory Nd:YAG laser. We observed that at a certain input pump power of 180 and 290 W, when the frequency of Q-switch chopper is respectively raised up to 5.8 and 12 kHz, oscillation of single RO pulse is established. We also found that by further increasing of the chopper frequency up to 18 kHz, FWHM pulse width of the RO fundamental pulse is saturated toward \(\sim \)163 ns. Moreover, at this frequency of chopper and input pump powers of 270 and 180 W, saturated FWHM RO pulse widths of 170 and 330 ns are measured, respectively. Obtained results show good consistency between theoretical model and experimental measurements. This saturation effect, is used to obtain amplitude small signal gain of the utilized Q-switched Nd:YAG laser as 3 and 0.8 at the above input pumping levels, respectively. At the same time by using Findlay–Clay approach the small signal gain is measured to provide a quantitative comparison with the above results. From the final results we found excellent agreement between the presented method and Findlay–Clay approach.

液氧的小信号增益测试

液氧的小信号增益测试

Small-signal gain measurements for highly doped and co-doped Er3+:YAG at

Abstract Direct small-signal gain measurements have been made for a 50% doped Er3+:YAG rods for the 2.936 μ m wavelength. We also provide gain measurements for 55% Er3+:YAG and co-doped 55% Er3+:YAG rods. Erbium doped solid-state lasers are typically used in a flash-pumped configuration, where the gain dynamics is highly dependent on the pump–pulse length. In this paper we have reported the small-signal gain over the pulse duration, along with average small-signal gain, so as to provide the laser-engineer with data to efficiently design the mid-IR laser system.

Small signal gain measurement by amplified spontaneous emission content of an inverted medium: simplified treatment

A method is introduced for small signal gain measurement in a low-saturation regime using an amplified spontaneous emission (ASE) footprint of a gain media. By this method, the ratio of intensities, with and without a reflector, is measured beside the bandwidth of the ASE, hence two equations are formed. An iterative solution of these equations will simultaneously determine both the small signal gain and the loss.

Small signal gain and loss measurement of a CW Nd:YAG laser using an antiresonant ring interferometer

An antiresonant ring (ARR) interferometer configuration is introduced for the characterization of a continuous wave (CW) Nd:YAG laser output. The output of the ARR device is precisely characterized to determine the gain and loss of a laboratory CW Nd:YAG laser by using the Findlay-Clay approach. The ARR arm is then experimentally arranged inside the cavity of an arranged high power side-pumped CW Nd:YAG laser. A coated beam splitter with 50-50% reflectivity at normal incidence is placed inside the cavity to provide a wide range of reflectivity from 0 to 100%. This is performed by a rotatable stage and tilting the beam splitter by 10o with the steps of 0.05. By changing the input electrical power of the laser pump the variation of the output laser power is monitored for 20 individual reflectivity of ARR arm. Average pump threshold power of about 180 W is obtained. With the help of the derived equations and obtained threshold power, small signal gain and loss associated with the emerging beam is estimated. It is verified that the former is very dependent to the input parameters. Laser efficiency is also measures 5.6% which is quite comparable with the reported values.

Temperature dependence of the emission cross section of Nd:YVO_4 around 1064 nm and consequences on laser operation

We propose an accurate measurement of the evolution of the emission cross section of Nd:YVO4 versus temperature around 1064 nm. This was done by using two complementary methods involving spectrum acquisition and laser oscillator small signal gain measurement. We observed a 44% decrease of the peak emission cross section for a 64 °C temperature increase but also a shift of the peak emission cross section wavelength at a rate of 3 pm/°C. The influence of the crystal temperature on the performance of a laser oscillator in continuous wave was also investigated.

超音速氮稀释连续波HF化学激光器小信号增益测量

超音速氮稀释连续波HF化学激光器小信号增益测量

Measurement of Small-Signal Gain on COIL With Chemically Generated Molecular Iodine

A chemical gas-phase reaction between <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Cl}_{2}$</tex></formula> and HI was used in the generation of molecular iodine for the chemical oxygen-iodine laser (COIL) operation. A yield of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm I}_{2}$</tex></formula> in the generation reaction up to 85% was achieved in a reasonable volume of the reactor. A small-signal gain up to 0.75%/cm at a temperature of 150 K in the center of supersonic cavity was measured. A comparison with the established evaporation way of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm I}_{2}$</tex></formula> delivery confirmed that the chemical method has little or no impact on the COIL pumping kinetics. This chemical method is easily scalable and can simplify the COIL operation by providing better control of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm I}_{2}$</tex></formula> flow rate.

变耦合率法测量化学激光器小信号增益

变耦合率法测量化学激光器小信号增益

Terahertz gain on shallow donor transitions in silicon

Small signal gain measurements of optically excited terahertz silicon lasers are reported. Two types of lasers, Si:P and Si:Bi, were investigated. They were optically excited with radiation from a free electron laser or a CO2 laser. The experiments were performed with an oscillator-amplifier scheme where one sample serves as a laser while the other one is an amplifier. In case of the free electron laser the pump frequency corresponds to intracenter excitation of the 2p0 or 2p± states of the P and Bi Coulomb centers, and the gain was determined for the 2p0→1s(E), 2p0→1s(T2) transitions in Si:P and the 2p±→1s(E) transition in Si:Bi. Pumping with a CO2 laser leads to photoexcitation of the Coulomb centers. In this case the gain was determined for the 2p0→1s(T2) of Si:P transition. The gain for intracenter pumping is in the range 5−10 cm−1 while for photoexcitation the gain is considerably less, namely ∼0.5 cm−1. The experimental results are analyzed and found to be in good agreement with theoretical calculations based on balance equations.

Measurements of the small-signal gain and saturation intensity for a cw CO2 laser using an intracavity loss element

A new scheme with an intra-cavity loss element for small-signal gain measurement at two main wavelengths of a tunable gas flow longitudinally excited CO2 laser is presented. By inserting a ZnSe stack polariser into the cavity, the critical condition for the laser is obtained. The small-signal gain and saturation intensity are calculated using the Rigrod formula. The small-signal gain measurement was performed for different gas pressures and different input electric powers. Under the same experimental conditions, the values of the saturation intensities were calculated from the output power and the measured small-signal gains. The advantage of this method is that no probe laser system is required. The results agree with experimental data obtained earlier by the conventional oscillator—amplifier method.

RF Excited High Efficiency CO2 Slab Waveguide Laser Array with Multiple-Slot Optical Coupling

In this paper we report a high-efficiency phase-locked CO2 slab waveguide laser array with compact multisegment RF excitation. Composed of two 3×8×400 mm3 waveguide slabs, the laser array delivered a maximum output power of 115 W with efficiency up to 19.5%. Small signal gain and saturation power measurements indicated that the laser configuration is well suited for RF driving of a CO2 slab laser array. Multiple-slot optical coupling devised in the two-slab laser array also resulted in low insertion loss and high-field coupling between the slabs.

Small signal gain measurements in a small scale HF overtone laser

The overtone gain medium of a small-scale HF overtone laser was probed using a sub-Doppler tunable diode laser. Two-dimensional spatially resolved small signal gain and temperature maps were generated for several ro-vibrational transitions in the HF (v=2→v=0) overtone band. Our results compare well with previous measurements of the overtone gain in a similar HF laser device.

Direct measurements of fluorine atom concentration, gain length and small signal gain in an hydrogen fluoride overtone laser

Experimental techniques have been developed to directly measure the concentration of fluorine atoms, the gain length and the small signal gain in a hydrogen fluoride 5 cm slit nozzle laser. A gas phase titration technique was utilized to measure the fluorine atom concentration using HCl as the titrant. The gain length was measured using a pitot probe to locate the interface of the primary flow with the high Mach number shroud flows. A tunable diode laser was utilized to perform small signal gain measurements on HF overtone ( ν=2→0) transitions.

Results of small-signal gain measurements on a supersonic chemical oxygen iodine laser with an advanced nozzle bank

High-resolution diode laser spectroscopy has been used to probe the gain in the active medium formed by an advanced supersonic chemical oxygen iodine laser (COIL), ejector nozzle bank. The probe beam was directed through the medium at 90/spl deg/ (normal) to the flow velocity and at an angle of 27.5/spl deg/ away from normal incidence. Analysis of the small-signal gain spectrum allowed for the determination of the gain, average gas velocity, static pressure, and temperature. The dependence of gain, temperature, and gas velocity on the primary nitrogen molar flow rate and basic hydrogen peroxide temperature was obtained. A maximum small-signal gain of 7 /spl times/ 10/sup -3/ cm/sup -1/, average gas velocity of 575 m/s, static temperature of 172 K were measured for flow rates of 270 mmole/s of primary nitrogen, 39.2 mmole/s of chlorine, 11 mmole/s of secondary nitrogen, and 0.8 mmole/s of iodine. Estimation of the static pressure in the flow core from spectroscopic data is very close to the static sidewall pressure. The role of transverse velocity components in the gas flow and their effect on the interpretation of gain profiles is discussed.

Temporal and 2-D small-signal gain measurements in a supersonic COIL

A dedicated CW chemical oxygen iodine mini-laser is constructed and used to probe the two-dimensional (2-D) distribution of small-signal gains in a supersonic CW chemical oxygen iodine laser (CW COIL). The uneven lateral gain distribution may possibly be explained by boundary layer effects.