JPS6035837B2 - Pockels cell drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulsed laser device that performs gigantic pulse oscillation, and uses a transistor that utilizes an avalanche phenomenon as a switching element in a Pockels cell drive circuit to expand the switch operating voltage range. The feature is that the temperature range in which it can be used has been expanded.

FIG. 1 shows the configuration of the pulse laser device.

In the figure, 1 is a laser active material, 2 is a polarizer, 3 is a Pockels cell, 4 is a Pockels cell driving circuit, and 5 is a first
prism, 6 is the second prism, 7 is the low reflectance mirror, 8
This is an arrow indicating the emission direction of laser light.

The Pockels cell 3, which uses a crystal having an electro-optic effect as a Q-switch element essential for generating giant pulses, is often used in practical devices because of its high switching speed.

In this case, the Pockels cell 3 must be driven by high-voltage and high-speed pulses, and a high-voltage and high-speed Pockels cell driving circuit 4 is also essential.

Conventionally, one of the high-voltage and high-speed Pockels cell drive circuits 4 uses a transistor that utilizes the avalanche phenomenon as a switching element. Figure 2 shows its configuration. In the figure, QI is the trigger from terminal A. The first transistor, Q2, becomes conductive due to the signal, and the second transistor, Q2, becomes conductive due to an avalanche phenomenon.
N is the Nth transistor that becomes conductive due to the occurrence of an avalanche phenomenon, and RI is the first transistor that biases the transistor QI.
R2 is the second resistor that biases transistor Q2, RN is the Nth resistor that biases transistor QN, Ra is the resistor that connects the base and emitter of transistor QI, Rb is the current limiting resistor, Rc is a resistor that applies voltage to the Pockels cell connected to terminal b, CI is a coupling capacitor, and C2 is an energy charging/discharging capacitor.

In Figure 2, when voltage is applied to terminal C and a trigger signal is applied to terminal A, transistor QI
becomes conductive in response to a trigger signal, and an avalanche phenomenon occurs from transistor Q2 to transistor QN, making them conductive.

Therefore, the charge stored in capacitor C2 is discharged from transistor QNT through transistor Q2, transistor QI, and resistor Rc.

At this time, a high-speed negative pulse voltage is obtained between terminal D and terminal E. The relationship between the range of the voltage V applied to the terminal C and the ambient temperature T is shown in FIG.

In the figure, 9 indicates that an avalanche phenomenon occurs even when no trigger signal is input from terminal A in the slave circuit configuration shown in FIG.
A line representing the lower limit of voltage V that conducts all the way up to N, 1
0 is a line indicating the maximum voltage V that is conducted from transistor QI to transistor QN when a trigger signal is applied from terminal A, and 11 is a drive voltage of Pockels cell 3 that provides the highest output at each temperature. and
It is approximately equal to the quarter wavelength voltage of Pockels cell 3.

Note that lines 9 and 10 in FIG. 3 are obtained when two (N=20) transistors having a collector-emitter breakdown voltage of 140 V are connected in series in the configuration shown in FIG. 2.

According to the characteristics shown in FIG. 3, the range of the operating voltage V of the drive circuit for the Pockels cell 3 is from 4 KV to Iso V, and the Pockels cell 3 can be driven when the ambient temperature T is from 0° C. to 40 qo. For example, it can be seen that the Pockels cell 3 cannot be driven at temperatures below 0°C.

In order to eliminate these drawbacks, the present invention expands the operating voltage range of the Pockels cell drive circuit 4 by increasing the number of transistors that can be activated by a trigger signal applied to the base of the transistor. do.

FIG. 4 shows an embodiment of this invention.

In the figure, 12 is a transformer. According to the configuration shown, the transformer 12 has five secondary windings, and a trigger signal applied from terminal A can cause transistors QI to Q5 to conduct. The remaining transistors up to QN will cause an avalanche phenomenon and become conductive. However, in the circuit configuration shown in FIG. 4, unlike the circuit configuration shown in FIG. Even if the applied voltage V is low, the switching operation can be performed. Fourth
FIG. 5 shows the relationship between voltage V and ambient temperature T when the number of transistors driven by the trigger signal applied from terminal A is five as shown in the figure. In the figure, 13 indicates the lower limit of the voltage V at which all transistors from QI to QN become conductive even when there is no trigger signal from terminal A in Figure 4, and 14 indicates a line from QI to This line indicates the minimum voltage at which all transistors up to QN are conductive. According to the improved circuit configuration shown in FIG. 5, the Pockels cell 3 can be driven at ambient temperatures T ranging from -2 to 14 degrees. In addition, in the above, all the transistors are driven by the trigger signal by the transformer 12,
Although the description has been made using one transformer 12, it goes without saying that the same effect can be obtained even if one transformer is used for each transistor. Furthermore, it goes without saying that the number of transistors driven by the trigger signal can be appropriately selected depending on the operating temperature range of the pulse laser device.

As described above, in the Pockels cell drive circuit 4 according to the present invention, a transistor that utilizes an avalanche phenomenon is used as a switch element, and the number of transistors that are activated by an external trigger signal is set to two or more, so that the operating voltage V of the Pockels cell drive circuit 4 is By expanding the range, there is an advantage that the operating temperature range of the pulsed laser device can be expanded.

[Brief explanation of drawings]

Figure 1 is a block diagram of a pulse laser device, Figure 2 is a circuit diagram of a conventional Pockels cell drive circuit, Figure 3 is a diagram showing the relationship between the operating voltage range and ambient temperature of a conventional Pockels cell drive circuit, and Figure 4 is a diagram showing the relationship between the operating voltage range and ambient temperature of a conventional Pockels cell drive circuit. The figure is a circuit diagram of an embodiment of the invention, and FIG. 5 is a diagram showing the relationship between the operating voltage range and ambient temperature of the embodiment of the invention. In the figure, 1 is a laser active material, 2 is a polarizer, 3 is a Pockels cell, 4 is a Pockels cell driving circuit, 5 is a first prism, 6 is a second prism, 7 is a low reflectance mirror, and 12 is a Pockels cell drive circuit. transformer, QI is the first transistor, Q2 is the second transistor, Q3 is the third transistor, Q4 is the fourth transistor, Q5 is the fifth transistor, QN is the Nth transistor, RI is the first resistor , R2 is the second resistor,
R3 is the third resistor, R4 is the fourth resistor, R5 is the fifth resistor, RN' is the Nth resistor, Ra is the resistor connecting the base and emitter of the transistor QI, Rb is the current limiting resistor, Rc is a resistor that applies voltage to the Pockels cell, CI is a coupling capacitor, and C2 is a charging/discharging capacitor. In the figures, the same or corresponding parts are denoted by the same reference numerals. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. In a Pockels cell drive circuit used in a pulsed laser device, two or more transistors that utilize the avalanche phenomenon are connected in series as switch elements, and two or more of the transistors are made conductive at the same time by an external trigger. A Pockels cell drive circuit characterized in that it is configured to expand the range of switchable operating voltages.