Internal-mirror He-Ne Laser Research Articles

Frequency stabilization of an internal mirror He–Ne laser with a high frequency reproducibility

A method has been developed for the stabilization of an internal mirror He-Ne laser to achieve a high frequency reproducibility that is mainly influenced by the temperature of the stabilized laser. However, it is difficult to achieve a reproducible temperature in a short time under different ambient temperatures. In this paper, the He-Ne laser is stabilized based on the relationship between the laser mode number and the laser cavity temperature where a reproducible temperature can be rapidly achieved under different ambient temperatures, resulting in a high frequency reproducibility. Experiments have demonstrated that the He-Ne laser used can be stabilized in approximately 10 min, typically 6 min; the frequency stability is less than 2×10(-10); the frequency reproducibility is less than 1×10(-9).

Experimental study on frequency stabilization method of internal-mirror He-Ne laser

Frequency of an internal-mirror He-Ne laser is stabilized by using a micro cooling fan, instead of traditional heating method. Both the relationship between driving voltage and rotating speed and the thermal expansion of the intermal-mirror laser are discussed. The cavity length of the laser is controlled and adjusted by air cooling. The frequency stabilization is based on a theory of power balance between two longitudinal modes. The average temperature of the laser tube is less than 50 ℃ when the frequency is stabilized. A frequency fluctuation of less than 1.4 MHz in 20 h and a frequency relative standard uncertainty of U=4.710-9 in 4 months are evaluated by measuring the beat signal with a high-precision laser stabilized by iodine.

Frequency stabilization of internal-mirror He–Ne lasers by air cooling

Instead of the traditional heating method, the cavity length of an internal-mirror He-Ne laser is controlled by air cooling which is implemented by a mini cooling fan. The responsive property of the cooling fan and the thermal expansion of the internal-mirror laser tube are investigated. According to these investigations, a controlling system is designed to drive the cooling fan controlling the cavity length of the laser. Then the frequency is stabilized by comparing the light intensities of two operating longitudinal modes. The results of beating with an iodine stabilized He-Ne laser show that a relative uncertainty (Δf/f-) of 4.3×10(-9) in 5 months, a frequency fluctuation of <1.4 MHz, and an Allan deviation of 6×10(-11) (τ=10,000 s) in 20 h are obtained.

Laser output power stabilization for direct laser writing system by using an acousto-optic modulator

We present experimental results on the output power stabilization of an Ar(+) laser for a direct laser writing system (LWS). Instability of the laser output power in the LWS cause resolution fluctuations of being fabricated diffractive optical elements or computer-generated holograms. For the purpose of reducing the power fluctuations, we have constituted a feedback loop with an acousto-optic modulator, a photodetector, and a servo controller. In this system, we have achieved the stability of +/-0.20% for 12 min and the relative intensity noise level of 2.1 x 10(-7) Hz(-12) at 100 Hz. In addition, we applied our system to a 2 mW internal mirror He-Ne laser. As a consequence, we achieved the output power stability of +/-0.12% for 25 min.

Accurate frequency control of an internal-mirror He–Ne laser by means of a radiation-heating system

Radiation heating enables fast temperature control. I applied radiation heating to the oscillation frequency control of an internal-mirror He-Ne laser. The laser system has a fast frequency response, and its oscillation frequency is offset-locked in an iodine-stabilized He-Ne laser by a phase-lock loop circuit. The frequency discrepancy σ between the master and the slave lasers is less than 10(-13) with a 100-s gate time.

Frequency and power stabilization of a three longitudinal mode He-Ne laser using secondary beat frequency

A method of frequency and power stabilization for an internal-mirror He-Ne laser using the secondary beat frequency between the three longitudinal modes is presented. Frequency and power fluctuation was ±1 MHz (2 parts in 109) and ±0.10% over 10 000 s, respectively. The square-root Allan variance between the laser stabilized in this study and the iodine stabilized He-Ne laser was 5×10−11 at average time of τ=1 s. Furthermore, we could obtain the output power of 2 mW in a single longitudinal mode.

Frequency stabilization of a HeNe laser at 543.5 nm wavelength using frequency-modulation spectroscopy

Two internal mirror HeNe lasers emitting at 543.5 nm wavelength were frequency stabilized to hyperfine components of the iodine R(12)26-0 and R(106)28-0 transitions utilizing frequency-modulation spectroscopy. Beat frequency measurements yielded difference frequencies which differ in a range of +1.8 kHz to -0.8 kHz. Realizing nearly shot noise limited detection, the minimum two probe standard deviation of 2.7x10 -13 was reached at a sampling time of 10000 s using an iodine pressure of 1.44 Pa. From the measured hyperfine line splitting hyperfine structure coupling have been calculated. The wavelength of the reference HFS-component α 9 has been measured.

Frequency Stabilization of an Internal-Mirror He-Ne Laser using an Axial Mode Beat.

The frequency of a commercially available internal-mirror He-Ne laser (λ=633nm) was stabilized by using an axial-mode beat frequency. The beat-frequency conversion technique between the axial-beat frequency and the output signal of a frequency synthesizer was used for the laser frequency stabilization. The frequency stability of 4.5×10-10 was estimated by means of the Allan variance analysis. The amplitude stability of this stabilized laser was estimated to be 0.21 %.

A technique for frequency stabilization of an internal mirror He-Ne laser

A technique for frequency stabilization of an internal mirror He-Ne laser using phase sensitive detection without cavity length modulation is suggested. The orthogonally plane polarized modes are separated and then convered into two photoelectric signals using two photodetectors. The photoelectric signals are switched alternately so as to generate a square wave, whose amplitude is proportional to the intensity difference between the two orthogonal polarizations. A lock-in amplifier is used to detect this square wave, with the switching frequency as reference. The phase detected signal is used for thermal stabilization of the laser. The frequency stability of 5 × 10−9 was obtained with an integration time of 1 s.

Frequency stabilization of an internal-mirror He-Ne laser using axial-mode beat

A frequency stabilization of a 633-nm internal-mirror He-Ne laser using the axial-mode beat frequency has been reported. The frequency stability achieved is 2.2 MHz (4.6×10−9) for an averaging time 1 s. The amplitude stability of this stabilized laser is 0.21%.

Frequency Stabilization of an Internal-Mirror He-Ne Laser by Means of a Microprocessor Controller (II).

Simultaneous stabilization of the amplitude and frequency of a two-mode internal-mirror He-Ne laser (λ=633 nm) using a microprocessor controller is reported. The intensity difference between two orthgonally-polarized axial modes normalized by the total intensity is caluculated as a controlled signal. The cavity length is controlled by manipulating the current of a heater wound around the laser tube according to digital PID or I-PD algorithms so that the controlled signal coincides with a reference signal. By adjusting the reference signal, stabilized laser frequency can be tuned within ±300 MHz around the mean frequency of the atomic resonance frequencies of 20Ne and 22Ne. Frequency stability estimated by the error between the controlled and reference signals is better than 3×10-8 over a period of 30 minutes. Beat frequency fluctuations between two stabiliezed lasers over a 8 minutes are in the range 1×10-8 to 2×10-8 depending on the selected direction of polarization.

Self-optogalvanic effect of internal-mirror He-Ne lasers.

A self-optogalvanic effect in the laser positive column of internal-mirror He-Ne lasers is investigated both experimentally and theoretically. The effect of laser power fluctuation on the voltage across a laser discharge tube and its dependence on laser currents (3-7 mA) are observed. A general model based on the steady-state solution of rate equations is developed to interpret the measurements. Good agreement between experimental and calculated results is obtained.

Performance of internal-mirror frequency-stabilized He-Ne lasers emitting green, yellow or orange light

A comprehensive control system has been developed for the stabilization of internalmirror He-Ne lasers to their power envelopes. It is designed particularly for use with lasers emitting at 552, 505, or 490 THz (543, 594, 612 nm). The aim has been to combine convenience in routine operation with good day-to-day resettability and minimal frequency drift during a day. The lasers are observed to emit in up to four modes simultaneously and their tuning behaviour is highly alignment-sensitive. They also tend to flip between modes having orthogonal linear planes of polarization. Reliable control of polarization and mode frequency are possible using permanent magnets and active length control through thermal expansion. The stabilized single-frequency outputs have frequency drifts of about 2×10−8 per year, and powers of between 150 μW and 850 μW.

Frequency stabilization of an internal mirror HeNe laser at 543.5 nm to I2-Saturated absorptions

An internal mirror green HeNe (GRENE) laser at 543.5 nm has been frequency stabilized to I2-Doppler free absorption signals with a frequency stability of few parts in 1010. The saturated absorption signals were detected using doubly-differential saturated absorption which eliminates the Doppler background and allows first-derivative locking methods. Two absorption lines R(12)26-0 and R(106)28-0 of 127I2 were investigated and the hyperfine structure was resolved. Random polarization flips of the GRENE were suppressed by applying a transverse magnetic field to the laser tube near the anode.

Frequency stabilization of an internal-mirror He-Ne laser by means of a microprocessor controller.

Frequency stabilization of an internal-mirror He-Ne laser by means of a microprocessor controller.

Stabilization of single frequency internal mirror He–Ne lasers

A relative amplitude stability of +/-0.013% and a relative frequency stability of +/-3.5 x 10(-10) are achieved over a period of 10 min or longer for a commercial single frequency, internal mirror He-Ne laser.

Polarization properties and frequency stabilization of an internal mirror He-Ne laser emitting at 543.5 nm wavelength

Frequency stabilization to the gain profile of an internal mirror He−Ne laser emitting at 543.5 nm wavelength is described. The dependence of the power and polarization on frequency was investigated for multi-mode and two-mode operation. The emitted laser modes are linearly polarized. Two orthogonal eigenpolarizations fixed to the laser tube were observed. Spontaneous switching between these polarizations occurred when the laser frequency was scanning through the gain profile. In two-mode operation, these polarization flips have been suppressed by applying a weak magnetic field transversal to the gas discharge. Under such operation conditions the frequencies of the laser could be stabilized to the gain profile by controlling the power difference of the two modes to zero. The fractional frequency reproducibility is in the region of Δf/f≃3×10−8.

Temperature distribution and cavity length properties of internal-mirror He-Ne laser tubes.

The thermal properties of internal-mirror He-Ne (λ = 633 nm) laser tubes are reported. Inside and outside temperatures of the laser tube are measured with a PbS photodetector and thermo-couples, and also the thermal expansion properties of the laser tube are measured. The outside temperature at the fore part of the laser tube is higher than that at other parts of the laser tube. The heat that generated inside the fore part of the laser capillary tube is conducted in the radial direction and mainly elevates the temperature of other parts of the laser tube by heat conduction. The high temperature at the fore part would affect the laser thermal stability. The optimum laser tube structures are discussed.

Effect of the cooling fan position for a stabilized He-Ne laser.

Simultaneous amplitude and frequency stabilization of an internal-mirror He-Ne laser (λ=633nm) by a fan cooling method was studied at different laser-tube positions. The total back beam intensity is fed back to control the cavity length of the laser tube. Since the temperatures of the laser tube vary according to the position, its stabilization properties also vary. At the fore part of the laser tube, the relative amplitude stability was found to be ±0.08 % and the relative frequency stability to be ±5×10-9 over a period of 10 minutes or longer. At the hinder part of the laser tube, the relative amplitude stability was ±0.05 % and the rela tive frequency stability was ±3×10-9 over a period of 10 minutes or longer.

Principles of optical phase-locking: Application to internal mirror He-Ne lasers phase-locked via fast control of the discharge current

While phase-locking techniques have long been in routine use in the microwave frequency domain, the ten-thousand-fold increase of the carrier frequency in the visible domain brings new problems for effective optical phase control. Particularly robust locks can be based on combining phase-locking under quiescent conditions with an outer frequency-control loop which takes control when phase lock is lost. Electronic strategies for implementing this process are discussed. Diagnostic techniques to allow characterization of phase-lock performance of optical oscillators are presented and discussed using as an example the phase-locking of a low-cost internal mirror He-Ne laser tube. Effectively complete phase lock was possible using small variations of the discharge current to provide fast frequency control.