11,397 research outputs found
A High Power Frequency-Stabilized Tunable Two-Frequency Diode Laser System for the Generation of Coherent THz-Waves by Photomixing
A tunable two-frequency high-power diode laser system at 850 nm for terahertz (Thz)-wave generation by photomixing in low-temperature-grown GaAs photo-conductors has been developed. The difference frequency is obtained through a three laser system, where two lasers are locked to different orders of a Fabry-Perot cavity and a third is offset-locked to the first, The difference-frequency signal is generated by the offset laser and the other cavity-locked laser. The spectral purity of the beat note is better than 1 MHz. The maximum output power of -500 mW was obtained by using the master oscillator power amplifier (MOPA) technique, simultaneous injection of two seed frequencies with a single semiconductor optical amplifier. Here we report the generation of THz waves and spectroscopy of acetonitrile as proof of concept
A tunable cavity-locked diode laser source for terahertz photomixing
An all solid-state approach to the precise frequency synthesis and control of widely tunable terahertz radiation by differencing continuous-wave diode lasers at 850 nm is reported in this paper. The difference frequency is synthesized by three fiber-coupled external-cavity laser diodes. Two of the lasers are Pound-Drever-Hall locked to different orders of a Fabry-Perot (FP) cavity, and the third is offset-frequency locked to the second of the cavity-locked lasers using a tunable microwave oscillator. The first cavity-locked laser and the offset-locked laser produce the difference frequency, whose value is accurately determined by the sum of an integer multiple of the free spectral range of the FP cavity and the offset frequency. The dual-frequency 850-nm output of the three laser system is amplified to 500 mW through two-frequency injection seeding of a single semiconductor tapered optical amplifier. As proof of precision frequency synthesis and control of tunability, the difference frequency is converted into a terahertz wave by optical-heterodyne photomixing in low-temperature-grown GaAs and used for the spectroscopy of simple molecules. The 3-dB spectral power bandwidth of the terahertz radiation is routinely observed to be ≾1 MHz. A simple, but highly accurate, method of obtaining an absolute frequency calibration is proposed and an absolute calibration of 10^(-7) demonstrated using the known frequencies of carbon monoxide lines between 0.23-1.27 THz
Robust, frequency-stable and accurate mid-IR laser spectrometer based on frequency comb metrology of quantum cascade lasers up-converted in orientation-patterned GaAs
We demonstrate a robust and simple method for measurement, stabilization and
tuning of the frequency of cw mid-infrared (MIR) lasers, in particular of
quantum cascade lasers. The proof of principle is performed with a quantum
cascade laser at 5.4 \mu m, which is upconverted to 1.2 \mu m by sum-frequency
generation in orientation-patterned GaAs with the output of a standard
high-power cw 1.5 \mu m fiber laser. Both the 1.2 \mu m and the 1.5 \mu m waves
are measured by a standard Er:fiber frequency comb. Frequency measurement at
the 100 kHz-level, stabilization to sub-10 kHz level, controlled frequency
tuning and long-term stability are demonstrated
High-resolution THz gain measurements in optically pumped ammonia
This study is aimed at the evaluation of THz gain properties in an optically pumped NH3 gas. NH3 molecules undergo rotational-vibrational excitation by mid-infrared (MIR) optical pumping provided by a MIR quantum cascade laser (QCL) which enables precise tuning to the NH3 infrared transition around 10.3 mu m. Pure inversion transitions, (J = 3, K = 3) at 1.073 THz and (J = 4, K = 4) at 1.083 THz were selected. The THz measurements were performed using a THz frequency multiplier chain. The results show line profiles with and without optical pumping at different NH3 pressures, and with different MIR tuning. The highest gain at room temperature under the best conditions obtained during single pass on the (3,3) line was 10.1 dBxm(-1) at 26 mu bar with a pumping power of 40 mW. The (4,4) line showed lower gain of 6.4 dBxm(-1) at 34 mu bar with a pumping power of 62 mW. To our knowledge these THz gains are the highest measured in a continuous-wave MIR pumped gas.Web of Science2616212482124
Active Faraday optical frequency standards
We propose the mechanism of active Faraday optical clock, and experimentally
demonstrate active Faraday optical frequency standards based on 852 nm narrow
bandwidth Faraday atomic filter by the method of velocity-selective optical
pumping of cesium vapor. The center frequency of the active Faraday optical
frequency standards is determined by the cesium 6 = 4 to 6
= 4 and 5 crossover transition line. The optical heterodyne
beat between two similar independent setups shows that the frequency linewidth
reaches 996(26) Hz, which is 5.3 10 times smaller than the
natural linewidth of the cesium 852 nm transition line. The maximum emitted
light power reaches 75 \upmuW. The active Faraday optical frequency standards
reported here have advantages of narrow linewidth and reduced cavity pulling,
which can readily be extended to other atomic transition lines of alkali and
alkaline-earth metal atoms trapped in optical lattices at magic wavelengths,
making it useful for new generation of optical atomic clocks.Comment: 4 pages, 4 figure
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