Polarization modulation in an optically-pumped far-infrared laser

Measurements performed on intracavity polarization modulation in an optically-pumped far-infrared laser are presented. The experimental work is a preparatory first step towards the development of a polarimeter diagnostic system for plasma physics applications. The present system utilizes a CO₂ laser whose output polarization state is modulated using a CdTe crystal placed within a sinusoidal magnetic field. The corresponding polarization modulated amplitude of the far-infrared output is determined, and the results obtained are in good agreement with the Verdet coefficient of CdTe previously reported.     

Optically-Pumped Far-Infrared Laser Lines in Hydrazine, Methanol, Heavy Water, and Ammonia: New Laser Lines and Frequency Measurements

A far-infrared laser cavity designed to favor short-wavelength laser lines was used to generate optically-pumped far-infrared laser radiation. New far-infrared laser lines were discovered in hydrazine, heavy water, ammonia, and several short-wavelength lines previously discovered in methanol were observed. Wavelength, frequency, and relative intensity measurements were performed on laser lines in the wavelength range 42.4 to 253.7 m. Each far-infrared frequency measurement was obtained by mixing the far-infrared radiation with radiation from two reference CO₂ lasers and from a microwave synthesizer in a metal-insulator-metal diode. The pump laser was a high-Q Fabry Perot resonator oscillating on 275 grating-selected laser lines including regular, sequence, and hot band lines.     

远红外激光等离子体散射系统的校准方法

本文依据多普勒效应,提出了利用转动细针对远红外激光的散射来模拟等离子体源对远红外激光的散射,从而对远红外激光等离子体散射系统进行校准,为完成等离子体散射实验作好准备。     

Effects of Buffer Gas on the Output of Optically Pumped NH3 Far-Infrared Cavity Laser

By solving the semi-classical density matrix equations and developing a buffer gas mechanism model, the effects of buffer gas on the output power of optically pumped NH₃ far-infrared cavity laser were calculated and verified by experiment. Our results showed that: the output power of NH₃ far-infrared laser could be increased when certain buffer gas was added into the laser medium, and there existed an optimum ratio of gases mixture and an optimum operating gas pressure which could make the output power of far-infrared laser reach maximum.     

Far-Infrared Laser Assignments for Methylamine

Reported far-infrared laser lines for five different transition systems of CH₃NH₂ optically pumped by a CO₂ laser have been identified spectroscopically through a high-resolution Fourier transform infrared study of the C-N stretching band together with CO₂-laser/microwave-sideband broad-scan and Lamb-dip measurements. From the infrared analysis plus previous far-infrared (FIR) results for the ground vibrational state, quantum numbers have been assigned for seven methylamine FIR laser transitions and their C-N stretching pump absorptions coincident with the CO₂ laser lines. The assignments are confirmed through the use of closed frequency combination loops that also provide improved FIR laser frequencies to spectroscopic accuracy.     

Self pulsing properties of optically pumped FIR NH3 lasers

We report on measurements of periodic and chaotic self-pulsing beyond the second threshold of far-infrared NH₃ lasers. While the instabilities of the 81 m¹⁴NH₃ laser follow a simple pattern, for the 374 m¹⁵NH₃ laser different pulsing properties are found in different parameter ranges.Pulses under conditions of high pumping power are measured in detail, in view of possible applications of these coherent, high-repetition rate far-infrared pulsed lasers.     

Investigation for long wavelength fir laser lines for EPR studies: New lines from CH2=CF2

The results described in this work are part of a systematic search for long wavelength laser lines to be used in high magnetic field EPR applications and in plasma diagnostic. Four new far-infrared laser lines of CH₂ = CF₂ (1,1 difluoroethylene), optically pumped by a waveguide CO₂ laser, have been discovered and characterized in wavelength, polarization relative to the pumping radiation and offset relative to the CO₂ center frequency. New measurements of polarization and offset of 5 already known laser lines are also reported. A table of all of the known CO₂ pumped FIR laser lines from this molecule is given.     

远红外固体激光器研究进展

8～12μm波段是大气的一个窗口,被定义为长波红外波段。该波段激光对雾、烟尘等具有较强的穿透力,在激光光电对抗、激光遥感、医疗、环境监测及光通讯领域具有重要的应用前景。本文调研了常用的8～12μm非线性频率变换晶体,以及基于非线性频率变换晶体的远红外光参量振荡器的研究进展,对国内外能实现8～12μm波段激光输出的非线性晶体及激光系统进行了系统地归纳和总结,通过分析比较得出在8～12μm波段获得的最大输出能量为毫焦量级,最大功率为瓦量级。国内该技术与国外有着不小的差距,主要受制于高重频、高功率脉冲1～3μm泵浦源技术不成熟及高性能非线性晶体材料研制基础薄弱,我国在长波远红外固体激光器领域研究进展缓慢,因此研制大尺寸、高质量远红外激光晶体及输出波长更长的远红外高功率激光器已经成为激光器未来发展方向之一。     

Far-infrared fountain laser on intraband transitions in semiconductor nanoheterostructures

A scheme for a far-infrared fountain laser on transitions between subbands of dimensional quantization in the conduction band in a AlGaAs heterostructure with quantum wells, generating an electromagnetic field in the far-infrared range, is proposed. It is shown that such a device can operate at room temperature using radiation of a CO₂ laser or several mid-infrared quantum cascade lasers as pump radiation.     

New far-infrared emissions and frequency measurements in hydrazine

By means of a new CO₂ laser we performed a new investigation of the far-infrared laser emission spectrum of hydrazine excited by the 10P(32) and 10R(8) CO₂ laser lines. We found seven new lines and measured the frequency of four of them; moreover we measured the frequencies of two more lines previously reported in the literature with only wavelength measurements. The frequencies of the far-infrared laser emissions have been measured by means of a frequency-synthesis chain based on new InP Schottky diodes. The detected signal was beat-note generated in a Schottky diode between the far-infrared radiation, the harmonics of a 72 GHz frequency reference and a rf signal. We also characterized all of the observed lines by their polarization relative to the pumping CO₂ laser, the optimum pressure and the offset relative to the CO₂ center frequency. PACS 42.55.Lt; 42.62.Fi     

New Far-Infrared Laser Lines and Frequency Measurements of Acetaldehyde and Vinyl Fluoride

Eight far-infrared laser lines have been obtained by optically pumping acetaldehyde (CH₃CHO) and nine by pumping vinyl fluoride (CH₂CHF) with a cw CO₂ laser. The far-infrared laser structure used a metal-dielectric waveguide cavity. This is the first reported observation of four of the laser lines in acetaldehyde. In this work, we measure the frequency, optimum pressure of operation, relative intensity, relative polarization, and pump offset from CO₂ laser-line center.     

New strong CW FIR laser actions and assignments in COF2

Thirty one new cw far-infrared laser lines have been discovered in COF₂ optically pumped by a CO₂ laser and a N₂O laser, in a metallic waveguide resonator. This number appreciably increases the number of eighteen lines appearing in the literature. Moreover, some of the new lines show that intense far-infrared laser action might be obtained with an optimized cavity, as it was the case for some of the previously reported lines. Twenty-seven, amongst the thirty one new lines, have been fully identified.     

12CH3OH and 13CH3OH optically pumped by the 10P and 10HP bands of a pulsed CO2 laser: New far-infrared laser emissions and assignments

We have re-investigated the ¹²CH₃OH and the ¹³CH₃OH molecules as optically pumped far-infrared laser sources. We have used our new waveguide pulsed-high-peak-power CO₂ laser for pumping, finding 20 new far-infrared laser lines emitted by ¹²CH₃OH and seven emitted by ¹³CH₃OH. For each line we report wavelength, pump offset from the center of the exciting CO₂ line, relative polarization, optimum operating pressure and intensity. The LaseRitz program was able to assign one of the new laser systems of ¹²CH₃OH, involving two new far-infrared laser lines.PACS 42.55.Lt; 42.62.Fi     

Measurement of far-infrared optical constants by ATR

Using an optically-pumped far-infrared laser as a light source, the far-infrared optical constants of liquid acetonitrile, methanol, dichloromethane, and chlorobenzene were obtained by measuring the attenuated total reflections of light for two mutually perpendicular polarizations. The ATR prism of hyper-pure silicon was made asymmetric to avoid the effect of the multiple reflection inside the prism.     

Optically Pumped Far-Infrared Laser Lines of Methanol Isotopomers: 12CD3OH, 12CH3OD, and 12CH2DOH

Twenty-seven new FIR, far-infrared, laser lines from the isotopomers of methanol: ¹²CD₃OH, ¹²CH₃OD, and ¹²CH₂DOH, were obtained by optically pumping the molecules with an efficient cw CO₂ laser. The CO₂ laser provided pumping from regular, sequence, and hot-band CO₂ laser transitions. The 2 m long far-infrared cavity was a metal-dielectric waveguide closed by two, flat end mirrors. Several short-wavelength (below 100 m) lines were observed. The frequencies of 28 laser lines observed in this cavity (including new lines and already known lines) were measured with a fractional uncertainty limited by the fractional resetability of the far-infrared laser cavity, of 2 parts in 10⁷.     

100 ps far-infrared laser pulses from optically pumped D2O

In this paper we report the generation of ultrashort far-infrared laser pulses with durations less than 100 ps, powers exceeding 200 kW and intensities of more than 1.5 MW/cm². Far-infrared radiation was produced via stimulated resonance Raman scattering using a high-pressure CO₂-laser as pump source and the heavy water isotopes D₂¹⁶O and D₂¹⁸O as far-infrared laser media. Pulses achieved from this laser system were detected by a novel type of detector, sensitive over a broad spectral range from the far-infrared to the visible, basing on quasiparticle heating in a strip-line structured YBa₂Cu₃O_7−δ thin film.     

Optically-Pumped Far-Infrared Laser Lines of Methanol Isotopomers: 12CH3OH, 12CH3OD, and 12CH2DOH

Twenty-seven new far-infrared laser lines from the isotopomers of methanol: ¹²CD₃OH, ¹²CH₃OD, and ¹²CH₂DOH, were obtained by optically-pumping the molecules with an efficient cw CO₂ laser. The CO₂ laser provided pumping from regular, sequence, and hot-band CO₂ laser transitions. The 2-m long far-infrared cavity was a metal-dielectric waveguide closed by two, flat end mirrors. Several short-wavelength (below 100 m) lines were observed. The frequencies of 28 laser lines observed in this cavity (including new lines and already known lines) were measured with a fractional uncertainty limited by the fractional resetability of the far-infrared laser cavity, of 2 parts in 10⁷.     

Frequencies of cw FIR laser lines for use in laser magnetic resonance spectroscopy

A transversely pumped far-infrared laser cavity has been used to discover two optically pumped laser lines: the 357.7 μm line from H₂C=CF₂ and the 242.3 μm line from CH₃OH. Using heterodyne techniques, the frequencies of fourteen far-infrared laser emissions have been measured, six for the first time. PACS  07.57.Hm; 42.55.Lt; 42.62.Eh     

The rotation-vibration constants of the 12CH3F ν3 band

Accurate rotational and vibrational constants for the ground and the ν₃ states of ¹²CH₃F are derived from a simultaneous least-squares fit of all the previous microwave, laser Stark and far-infrared laser data related to the ν₃ ← 0 band. Spectroscopic data, concerning the far-infrared laser emission in ¹²CH₃F, are discussed.     

The Umbella high-frequency EPR facility

The Umbella high-frequency electron paramagnetic resonance (EPR) facility is a part of the Nijmegen High Field Magnet Laboratory with special emphasis on multifrequency EPR for chemical and biological applications. At present the facility has various solid-state sources available for the frequency range between 95 and 400 GHz, combined with magnetic fields up to 30 T. For frequencies above 400 GHz a far-infrared laser is used. With superheterodyne detection techniques a typical dynamical range of 130 dB is obtained, with single-mode resonators, oversized cylindrical and Fabry-Perot resonators. Some examples will be shown to demonstrate the power of multifrequency EPR in high-spin systems.