Tomizo Kurosawa

dc bias dependence of W‐Ni and W‐Co point‐contact diodes as harmonic generators and mixers at 9.4 μm

The S/N ratios of the rf beat notes between harmonics of an x‐band microwave source and the mixed output of two CO2 lasers at different frequencies are studied by means of the W‐Ni and W‐Co point‐contact diodes at various mixing orders and various conditions of dc bias voltage. By applying the appropriate dc bias voltage to the W‐Co diode in the even mixing orders, improvements on the S/N ratios by 5–10 dB are obtained.

Frequency Chain to 3.39 µ mCH4-Stabilized He–Ne Laser Using Josephson Point Contact as Harmonic Mixer

A frequency-multiplication chain to the 3.39 µ m CH4-stabilized He–Ne laser has been constructed using the Josephson point contact as a harmonic mixer. The Josephson harmonic mixer simplifies the chain because it can directly connect the 90 GHz microwave and the 4.25 THz far-infrared frequencies. Tracking oscillators, which track the beat notes by phase locking and regenerate clean signals, also have been developed to correctly count the beat frequencies. The frequency fluctuations of free-running lasers are canceled by counting the beat frequencies with coincident gate timing. The absolute frequency measurement of the He–Ne laser is reported with a standard deviation of about 5 kHz (τ=8 s).

Properties of the S/N Ratio of the Beat Note in Frequency-Mixing Using the W-Ni Point Contact Diode at 32 THz

By mixing the radiation from two CO2 lasers (about 10 MHz apart, oscillating at R(24) of the 9.4 µm band in a W-Ni diode) the S/N ratio of the beat note was measured as a function of the incident laser power, the distance from the focal point of a lens, the incident angle onto the diode, the detected dc voltage, and the diode resistance. Furthermore, for frequency-mixing between R(24) and R(26) of the 9.4 µm band, the dependence of the S/N ratio on the diode resistance, the incident power of the CO2 laser and the microwave radiation on the diode is described. The detector performance is evaluated regarding the responsivity, effective coupling efficiency and noise equivalent power.

A SYSTEM FOR MEASURING ABSOLUTE FREQUENCIES OF UP TO 4.25 THZ USING A JOSEPHSON POINT CONTACT

A system for measuring the absolute frequency of a far-infrared (FIR) laser is described. Josephson point contacts have been utilized in the system as a frequency harmonic mixer connecting microwaves and optically pumped CH3OH laser lines. The Josephson point contacts are capable of generating beat signals of 90 GHz microwaves and FIR waves of up to 4.25 THz. To measure the frequency of the beat signals from the Josephson junction with a frequency counter, tracking oscillators have been developed, which tracks the beat signals by phase locking and regenerate clean signals for frequency counting. It is shown that the absolute frequency can be measured to an accuracy of about 100 Hz by using the tracking oscillators.

Harmonic Generation and Mixing with the W-Ni Point Contact Diode in the Far-Infrared

The S/N ratio of the beat note obtained from frequency mixing between a 469-µm CH3OH laser and a 71-GHz klystron was measured as a function of the incident power of the CH3OH laser and the klystron on a W–Ni point contact diode. A beat note with a S/N ratio of 35 dB was obtained during frequency mixing for simultaneous oscillations of the 469- and 251-µm lines.

Estimation of small signal gain and saturation intensity in a waveguide CO2 laser by a curve-fitting technique

Output power curves as a function of the frequency have been measured by heterodying between a gas flowing waveguide and a conventional sealed-off CO2 laser with a W–Ni point contact diode. The small signal gain, saturation intensity, collision-broadened linewidth and frequency tunability are simultaneously estimated by fitting a theoretical equation to output power curves according to a least-squares technique.

Millimeter‐wave harmonic mixing with high Tc superconducting materials at room temperature

Harmonic generation and mixing in the 8∼80 GHz region has been studied in point‐contact junctions made with sharply tipped tungsten whisker and sintered polycrystalline YBa2Cu3O7−y or single‐crystal Bi2Sr2CaCu2Ox at room temperature. The signal‐to‐noise ratio (SNR) of beat notes as a function of harmonic number n is observed up to the tenth order and decreases with a slope of n−5.6 for even harmonic numbers. The dependence of the SNR of the beat note on a dc bias voltage and the current‐voltage characteristics have been measured simultaneously and theoretically analyzed using the current‐dependent mixing characteristics. The potential barrier and the insulating thickness for YBa2Cu3O7−y are estimated.

W-YBa2Cu3O7-y point-contact junction at millimeter-wave

Experiments of up to the 8th harmonic mixing of 10 GHz have been carried out using point-contact junctions made with sharply tipped tungsten whiskers and sintered polycrystalline YBa2Cu3O7-y at room temperature and in liquid nitrogen. Some features of the W-YBa2Cu3O7-y point-contact junctions are described. The characteristics of the static current-voltage curve fitting to the 9th-order polynomial expression are discussed and the noise equivalent power is roughly estimated.

Stabilization Of CO2 Laser By Using Lamb Dip From A Photo-Acoustic Cell

A CO2 laser for an optically pumped CH OHlaser is stabilized on the center of the CH3OH absorption line y using a photo-acoustic spectroscopy. The frequency stability is measured by referring to a CO2 laser which is stabilized by Freed-Javan method. The stability of the pump laser is obtained to be Jy(t) = 3.0 x 10-9 x t-1 /2 ( is , 1:c100s ) in the terms of the square root of Allan variance. The offset frequency between the CO2 laser line center and the CH3OH absorption line center is also obtained from the beat frequency to be 24.8± 0.1 MHz.

Output Characteristics of a Waveguide CO2 Laser

A gas flow type waveguide CO2 laser has been made of Pyrex glass. The output power, frequency tunability and relative change in refractive index of the amplifying medium have been measured as a function of inlet pressure and discharge current. The small signal gain and saturation intensity are determined by fitting a theoretical equation to output power curves measured as a function of the frequency for two gas-mixingra tios.