Koichi Shimoda

Proposal for an Electron Accelerator Using an Optical Maser

Among many possible applications of the extremely high brightness temperature and the radiation density obtainable with the optical maser, a high energy electron accelerator is proposed and discussed in this paper. It consists of a cylindrical tube of maser material excited by a pumping radiation through an interference filter coated on its outer surface and, it generates an oscillation in a TM0NM type mode. An optical peak power of 10 kw/cm2 was calculated to accelerate electrons by 109 ev/meter. A gas-filled cavity is proposed for velocity matching. Selection of the particular mode might be made by placing a periodically printed absorption layer on the inner surface of the maser cylinder. However, mode separation would be extremely difficult because of thermal expansion of the maser material.

Microwave Spectrum of Formaldehyde I. K -type Doubling Spectra

Microwave spectral lines for the direct transitions between the K -type doublets were measured from 3 kMc to 40 kMc for H 2 CO and for its isotopically substituted molecules HDCO, H 2 C 13 O and H 2 CO 18 . The observed spectra and the previously reported data for H 2 CO were analyzed by a digital computer by the use of Kivelson and Wilsons method for the centrifugal distortion correction. The asymmetry parameter b and B – C were obtained for each isotopic species as follows:

Stark Effect of the Absorption Line of Methane Observed by the 3.391 µm He-Ne Maser

The Stark effect in CH 4 which has no permanent dipole moment in the ground vibrational state is observed on one component line at 2947.802 cm -1 of the P (7) line in the ν 3 band by a magnetically tuned infrared maser. The effect is interpreted on the basis of the second-order induced dipole moment in the degenerate vibrational state which has the F 2 symmetry. The magnitude of the induced dipole moment of CH 4 in the ν 3 vibrational mode is evaluated from the observed Stark effect.

Limits of sensitivity of laser spectrometers

Theoretical considerations are given on the sensitivity of laser spectrometers in which the molecular transition is observed by a photoelectric detector, a photoconductive detector, or a diode. It is shown that the single-pass absorption spectrometer has extremely high sensitivity at a relatively high gas pressure and with optimum laser power. The holeburning spectrometer is less sensitive, though in offers much higher resolution of the homogeneous width at a low gas pressure. The nonlinear fluorescence method is characterized by both high resolution and high sensitivity, provided the fluorescence from the laser-excited level can be observed.The minimum detectable number of absorbing molecules is calculated to be 102 to 106 depending on the parameters of the spectrometer. Thus a concentration of absorbing molecules lower than 10−12 is expected to be detectable in some cases.

Infrared-Microwave Double Resonance in H2CO with a Zeeman-Tuned 3.5µm He-Xe Laser

Infrared-microwave double resonance effects in formaldehyde are observed by using a method of microwave pumping and infrared detection. The pressure dependence of the double resonance signal is observed with the gas cell either inside or outside of the laser cavity. The signal is observed to change its sign at a low pressure of formaldehyde. A rate-equation approach is used to calculate the pressure dependence of the double resonance signal. The observed change in sign is explained by higher-order effects of double resonance. A good agreement between the theoretical and the observed results is obtained. The double resonance effects on the inverted Lamb dip of the infrared absorption of formaldehyde are also observed. The dip splits into a doublet when the strong resonant microwave is applied.

High-resolution Stark spectroscopy of molecules by infrared and far-infrared masers

Some of the He-Ne and He-Xe laser lines in the infrared can be tuned within several gigahertz by applying an axial magnetic field. Stark patterns of vibration-rotation lines of organic molecules were observed at 3.36-, 3.39-, 3.50-, and 5.57-μm wavelengths. With applied Stark fields up to 50 kV/cm, many Stark components were resolved and some of the transitions of H 2 CO, HDCO, and CH 4 were definitely assigned. Molecular masers in the far infrared cannot be tuned over any appreciable range, but the Stark effects of the rotation lines of NH 3 at two fixed far-infrared frequencies of the D 2 O maser were observed. The observations of a Stark component of the J = 3 \leftarrow 2 line at 171.6 μm and the forbidden Stark components of the J = 6 \leftarrow 5 line at 84.1 μm are reported.

Stark Effect of Vibration-Rotation Lines of Formaldehyde Observed by a 3.5 µm Laser

A high resolution infrared spectroscopy of the Stark effect of H 2 CO and HDCO by using a magnetically tunable infrared-maser (laser) is reported. The output frequency of the He-Xe laser centered at 2850.6 cm -1 is tuned within ±6GHz to observe Stark patterns of vibration-rotation lines of formaldehyde in the electric field up to 44 kV/cm. Some of the lines have been assigned from their Stark effects. The observed Stark shift, K -type doubling, intensity change of the forbidden transition with the Stark field, and the assignment of lines are discussed in connection with the molecular constants of H 2 CO and HDCO.

A prism anamorphic system for Gaussian beam expander

Basic properties are given of the prism anamorphic expander of a Gaussian beam composed of a couple of prisms in tandem. Its shorter overall length for a given expansion, relative ease of optical adjustment, a sharp selection of polarization component, and rather small inclusive dispersion make it an excellent beam expander in a specific laser cavity. The design principle is presented of the prism system with a grating for an anastigmatic optical resonator for a dye laser of narrow linewidth and of short pulse duration.

Beam-Type Masers for Radiofrequency Spectroscopy

Beam-type masers for radiofrequency spectroscopy of molecules are considered. The theoretical estimate of sensitivity is discussed and a table of minimum detectable beam intensity and estimate of available beam intensity for some of the low frequency transitions is given. A K -type doubling transition, 4 31 →4 32 , of formaldehyde was observed as an emission line at 4.5769±0.0023 Mc, and compared with theories. The observed saturation in focusing is probably due to the non-adiabatic change of rotational states in the focuser. The saturation broadening of the line with increasing rf field shows agreement with theory.

Magnetic Hyperfine Spectrum of H2CO by a Maser

The magnetic hyperfine structure in J =3, K -1 =1, Δ J =0 transition of formaldehyde at 29 Gc/sec was studied by a beam type maser spectrometer. The hyperfine components corresponding to Δ F =0 transitions were observed with good signal-to-noise ratio. The splittings are measured as 23.0 kc/sec and 10.4 kc/sec which are compared with theory. As well as the I · J coupling, spin-spin interaction term I 1 · I 2 between the two protons is fairly large and cannot be neglected. Coupling constants were determined as µ N 2 g H 2 r -3 =19.9 kc/sec and \(\sum\limits_{g}\langle{J_{g}}^{2}\rangle(A_{1g}+A_{2g}){=}54.6\) kc/sec.